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BXOWEXXUWICAL CUMPARISOH OF BACESAHD TECH'NLQUES

USED BY IOVXCE: AND ADVAMCEb TE;NMIS PLAYERS:

fBaeLICATf0'NS FOR LATERAL EPICUHDYLITIS

J o b Patr ik Ingelman

B-Sc., Dalhous ie Un ive r s i t y , 1988

THESIS SUBMITTED I N PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

i n t h e School o f Kines io logy

( F a c u l t y of Appl ied S c i e n c e s )

O J. P a t r i k Ingelman 1991

SIMON FRASER UNIVERSITY

December 1991

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ISBN 8-315-83674-1

Y uan-ctrerrg Ftrng, Professor Bioengineering Department University of California, Sm Diego La folfa, Caliifcrrnia 92W3

November 20, 1991

Dear Professor Fung,

I am presently writing my Master of Science thesis at Simon Fraser liniversity in Vancouver, Canada. ]I would like to include in my thesis a phstwogy of a figure from your b k "Biomechanics: Mechmical Properties of Living Tissues", 1981, page 210 (a typical load-elongation curve for tendon). f understand that this book has been copyrighted by Springer-Verlag and, therefore, technically f require their permission to include it in my work. Unfortunatefy, the pubfisher's address was not given in the book. Perhaps i t would be equaI1y acceptibfe if you were to grant me ~[lemission since you are the author.

ff you have no objections to this request could you please sign below and mail this letter back to me as soon as possible. Otherwise, I would appreciate it if you coufd pass this on to Springer-Verlag. I am hoping to have my thesis published in the National Library of Canada earIy in f 992.

Thanking you in advance,

Patrik Ingelman 2495 West 13th Avenue Vancouver, KC. Canada V6A IS6

'=7 -

/7' /-- ".$& &La - I ---- I < of the above

permission to 3. Patrik

Techniques Used by Novice and Advanced Tennis Players: fmplications for L3~;erd Epi~~ndyf i t i s~

Dorling KindersIey Limited 9 Henrietta Street London, Hngland WC2E8PS

Dear Publisher,

I am presently writing my Master of Science thesis at Simon Fraser University in Vancouver, Canada. I would like to include in my thesis photocopies of a picture in "The Handbook of Tennis" by Paul Douglas, 1982 (upper left photo on page 64). I understand that this book has been copyrighted by your company and, therefore, I require your permission to include then in my work.

If you have no objections to &e above request, could you please sign below and mail this letter back to me as soon as possible. I am hoping to have my thesis published in the National Library of Canada early in 1992,

Thanking you in advance-

3. Patrik Ingelman 2495 West 13th Avenue Vancouver, B.C. Canada V6A IS6

I pLt& c: ~itu~ccy~r ., t r of Darling Kindersley Limited, give permission to J. Patrik Ingefman to use the above mentioned picture in his thesis entitled "Biomechanical

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BIOlE4ECHANICAL COMPARISON OF BACKHAEJD TECHNIQUES USED BY

NOVICE AND ADV-WCED TENNIS PLAYERS: IMPLICATIONS FOR

LATERAL EPLCONDYLITIS

(zigna cure)

John P a t r i k Irqelman

(dace )

Approval

Wame : John Batrik Ingelman

Degree : Master of Science (Kines iolagy)

T i t l e of thesis:

Biomechanical Comparison of Backhand Techniques Used by Novice and Advanced Tennis Players:

Impfieations fur Lateral Epicondylitis

Examining Co~szttee:

Chair: Dr. Igor Mekjavie

-

Dr. Arthur chapmad Senior Supervisor School of Kinesiology Simon Fraser University

4 . - -

Dr. Murray Allen School of- Kinesiowgy Simon Fraser University

--

Dr. ~ ~ c h a r d Loomer External ExarnineZ Royal Columbian Hospital

Date Approved :

Abstract

It has been predicted that the majority of novice tennis

players will show symptoms of lateral epicondylitis at some

time during their playing careers. The reasons behind their

predisposition for the injury are unclear. Various

hypotheses regarding lateral epicondylitis etiology have been

suggested, but quantitative support for these hypotheses is

negligible.

This study was designed to test quantitatively one of

the suggested hypotheses, A biomechanical analysis, using

techniques of electromyography and electrogoniometry, was

carried out to compare the backhand stroke techniques of

novice and advanced tennis players.

It was hypothesized that novice players generate greater

farces with their wrist extensor musculature than do advanced

players due to poor backhand techniques. Parameters

associated with muscle force were measured and subsequently

compared between the players with different skill levels.

Results indicate significant ECRB muscle force parameter

differences between novice and advanced players. Parameter

differences observed for the greater part of the stroke were

believed to cancel each other out in terms of muscle force

estimat ior:s. Specifically, the force-elevating effects of

higher levels of muscle activation of the advanced players

iii

were balanced Sy the farce-elevating effects of l o n g e r muscle

l e n g t h s of the novice players- Just a f t e r impact, h c w r ver,

when forces were considered maximal, the r e s u l t s s u g g e s t that

the novice p l a y e r s had g r e a t e r ECRB impulses than did t h e

advanced players. This was due to highly s i g n i f i c a n t

d i f f e r e n c e s between their e c c e n t r i c muscle veXocities i n the

wrist fkexion/extemsion plane. The leading elbow backhand

technique, as used by many novice tennis players, i s

implicated as a significant c o n t r i b u t o r to lateral

epicondylitis etiology.

First cf 1 , A r t h u r , t h a n k you for a l l of y o u r

patience, gu idance and s u p p o r t . 1 a p p r e c i a t e you g i v i n g m e

the chance t o prove my c a p a b i l i t i e s .

T h a n k s t o my s u b j e c t s a n d lab a s s i s t a n t s f o r

v n l t ~ n t e e r i n g so much t i m e and energy . Without a l l of you my

exper iments would n o t have been p o s s i b l e .

Thank you, Ger ry and M e L , f o r s h a r i n g y o u r t e c h n i c a l

knowledge w i t h m e .

To Helen, Mary Ann, S c o t t and T a k e j i : t h e Biomechanics

Lab j u s t wouldn't have been t h e same w i t h o u t you. Thanks f o r

a l l of your he lp! ! (Helen and Mary Ann, t h a n k s fo r p u t t i n g

up w i t h m e for so long . I o w e you guys a l o t . )

To a l l of the o t h e r p e o p l e who hung i n t h e r e t h rough my

" a l l work and no p lay" stage (about t h r e e y e a r s ) : t h a n k s for

unde r s t and ing .

F i n a l l y , t o Mom a n d Dad: t h a n k s fo r your encouragement

f r o m a f a r . (Mom, y o u r m o t i v a t i n g w o r d s , " J u s t g e t t h a t

d a r n e d t h e s i s done!", h e l p e d m e t o s t a y on t r a c k . f d i d

it!!)

Table of Contents

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + . . . . . . . . . . . v

List of Tables .............................................. x

List of Figulres ............................ '.-....-........xi

1. INTRODUCTION ........................................... 1

Purpose .............................-...............-.. !

11. LITERATURE REVIEW ...................................... 3

. . . . . . . . . A. Lateral Epicondylitis - General Information 13

1. Definition . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * 3

2. Functional Anatomy of ECRB . . . . . . . . . . . . . . . . . . . . . . . H

........................................ 3. Etiology 10

a. General - Tendon Damage . . . . . . . . . . . . . . . . . . . . . :lrJ

.................................... b. Specific

B. Novice Tennis Players With Lateral

...................................... Epicondylitis 18

I . Gem9xal C i f f e r e n c e s Between Novice azd

............................. Advanced P e c h n i ~ e s 19

.................. . 2 Quantification of Tendon Force 25

............ . . a Direct Methoa Force Transducer 25

B . Indirect Methods ............................ 26

............. i) . Inverse Dynamics Approach - 2 6

.................. . ii) Muscle Model Approach 29

3 . Measurement of Parameters Associated With ECRB Force ...................................... 32

........ . . a Wtscle Activation Electromyography 33

b. Muscle Length and Velocity .

Electrogoniometsy ........................... 36

4. Past Attempts at Measuring Parameters

Associated With ECRB Force During Backhand

Tennis Strokes ................................ 39

a. Muscle Activation ............................ 39

................... b . Hascfe Length and Velocity 41

< ' A. SubSects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . =i ,.4

P 3 . Experirrentaf SeZ-up and Task -1 i,i . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C . Analysis Pexiad :ti

,. -. ., ~ ...................... li) . ECRa A c t f vat ion - E f ect romyography

E. Wrist Joint Angular Kinematics - "5 Electrogoniometry-.....~................--...,.,..-..

F. Experimental Protoca l , . . . . . . . . . . . . . . . . . . , . . . . , . . , , . . t + t

4' C . N. E t h i c s Approval ..................................... ..

A. General Patterns Throughout t h e 5trok ci.....,........ C.l:

a, Flexion .......,...,..,.,.....~........,,t3

. . . . . . . . . . . . . . . . . . . . c_t . =':car C e - ~ i a t i a n V e l o c i t y 74

..... . 2 Specific Dkfderences Around the T h e of Impact 7 5

................. C. Summary of S i c p i f i e a n t D i f f e r e n c e s 7 6

A . Comparison of Results With Those in the

Literature ......................................... 79

............ 8 . fmplicatiorzs for ECRB Force Comparisons 81

.................................. 1. Movement Phase 82

2 . Just A f t e r Impact ............................... 85

C. ConcPusi~ns ........................................ 91

.................................... Futuhe Research 93

......................................... List of References 95

L i s t of Tables

Table I. Significant Group differences during the

iriovezent Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?7

Table 2. Positive ECRB force-elevating effects which

occurred just after impact. . . . . . . . . . . . . . . . . . . . . . . G

L i s t of Figures

. . . . . . . . . . . . . . . . . . . . . . . . . . . F i g u r e l a W r i s t e x t e n s o r muscles 5

F i g u r e lb . O r i g i n s and i n s e r t i o n s of t h e w r i s t e x t e n s o r

muscles ......................................... 6

F igu re 2 . A t y p i c a l s t r e s s - s t r a i n cu rve for human

tendon ......................................... 1 2

F i g u r e 3a . Novice p l a y e r u s i n g t h e l e a d i n g elbow

backhand t echn ique ............................. 22

F i g u r e 3b . Advanced p l a y e r u s i n g t h e classic advanced

. . . . . . . . . . . . . . . . . . . . p l a y e r s ' backhand t e c h n i q u e 22

. . . . . . . . . . . F i g u r e 4 T y p i c a l r e l a t i o n s h i p s of muscle f o r c e 30

. F i g u r e 5 Measurement of w r i s t e x t e n s o r s t r e n g t h . . . . . . . . . 4 6

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . F i g u r e 6 Exper imenta l se t -up 4 8

. . . . . . . . . . . . . . . F i g u r e 7 Set-up used f o r MVC and EMD tests 5 6

. . . . . . . . . . . . . . . . . . . F i g u r e 8 Elec t rogoniometer c a l i b r a t i o n 59

. F i g u r e 9 EMG v e r s u s t i m e g raph . . . . . . . . . . . . . . . . . . . . . . . . . . 69

. F i g u r e 10 Flexion v e r s u s t i m e graph ...................... 70

Figure I1 . Ulnar d e v i a t i o n v e r s u s t i m e g raph . ............. 72

. F i g u r e 12 Flexion v e l o c i t y v e r s u s t i m e g r aph . . . . . . . . . . . . . 73

. . . . . Figure 13 . Ulnar d e v i a t i o n v e l o c i t y ve r sus time graph 7 :I

. F i g u r e 1 4 Typ ica l r e l a t i o n s h i p s of m u s c l e force . . . . . . . . . . 8 2

F i g u r e 15 . Flex ion v e l o c i t y ve r sus t i m e graph (pos t -

impact t i m e p e r i o d ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

. . . . . . . . . . . F i g u r e 1 6 . Force-ve loc i ty r e l a t i o n s h i p f o r ECRB 139

F i g u r e 17 . ECRB f o r c e v e r s u s t i m e graph (post-impact

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . time period) 90

x i i

Tennis i s a popu la r s p o r t , y e t a l o n g w i t h i t s p o p u l a r i t y

t h e r e e x i s t s a h i g h i n c i d e n c e of t e n n i s e l b o w .

Epidemiolog ica l s t u d i e s have observed t h a t o v e r f i f t y p e r c e n t

o f all t e n n i s p l a y e r s a c q u i r e t e n n i s e lbow a t l eas t once

during t h e i r p l a y i n g careers ( N i r s c h l , 1975; Gruchow &

P e l l e t i e r , 2979; Priest, Braden & Gerbe r i ch , 1980; Carrol l ,

f 981; and K a m i e x , 1988) . Al though there a r e numerous

t r e a t m e n t s avai lable f o r t h e i n j u r y , i n c l u d i n g s u r g e r y f o r

s e v e r e cases, p r e v e n t i o n is obv ious ly p r e f e r r e d .

P r e v e n t i o n of t e n n i s elbow is a p rob lem b e c a u s e i t s

e t i o l o g y i s p o o r l y unders tood . Numerous hypo theses have been

made w i t h r e g a r d s t o t h e e t i o l o g y , b u t s u p p o r t fo r them i s

minimal. One such h y p o t h e s i s is t h a t p o o r backhand t e c h n i q u e

may induce o v e r l o a d i n g o f w r i s t e x t e n s o r musc les , which may

r e s u l t i n t e n n i s e l b o w (Bernhang, Dehner & F o g a r t y , 1974;

Cohen, 1980; M c L a ~ q h f i n t M i l l e r , 1980; N i r s c h l & S o b e l ,

1981; Legwold, 1984; Levisohn & Simon, 1984; Allman, Torg &

Welsh, 1987; and S t i t e s , 1988) .

Purpose

The main purpose of t h i s s t u d y w a s t o t e s t t h e

hypothesis that poor backnand t e c h n i q u e i s a s i g n i f i c a n t

cone r < h * * + ~ - J Y U L V t t- L V c L ~ = & E ~ X ; D -I- - elhaw i n n o v i c e t e n n i s p l a y e r s .

Comparison of parameters associated w i t h w r i s t e x t e n s o r

m u s c l e force, namely a c t i v a t i o n , l e n g t h a n d v e l o c i t y , between

n o v i c e and advanced backhand t e c h n i q u e s , provided the m e a n s

for t e s t i n g t h i s hypothesis.

XI. LITERATURE REVIEW

A. Lateral Epieondylitis - General Information

1, D e f i n i t i o n

The medical t e r m f o r classic t e n n i s elbow, t h e v a r i e t y

t h a t i n v o l v e s p a i n n e a r t h e l a t e r a l humeral e p i c o n d y l e , i s

l a t e r a l e p i c o n d y l i t i s (LE) (Pe t e r son & Renstrom, 1 9 8 6 ) . Th i s

i s c o n t r a s t e d w i t h a s i m i l a r a i l m e n t i n v o l v i n g t h e med ia l

ep icondyle , namely media l e p i c o n d y l i t i s . LE is a t least f i v e

t i m e s a s p r e v a l e n t as medial e p i c o n d y l i t i s ( p r i e s t e t a l . ,

1980 and Legwold, 1984) .

It i s i n t e r e s t i n g t o n o t e t h a t LE d o e s n o t o n l y a f f e c t

t e n n i s p l a y e r s . O t h e r a t h l e t e s , i n c l u d i n g squash , badminton,

t a b l e t e n n i s , baseball a n d f o o t b a l l p l a y e r s , g o l f e r s , and

j a v e l i n t h r o w e r s have a l l been documented w i t h t h e a i l m e n t

(Root & Kiernan, 1974 and P e t e r s o n & Renstrom, 1986) . Also,

w o s k e r s , s u c h a s c a r p e n t e r s , p l u m b e r s , p a i n t e r s ,

e l e c t r i c i a n s , b u t c h e r s , d e n t i s t s a n d s u r g e o n s , h a v e

e n c o u n t e r e d t h e i n j u r y f G o l d i e , 1964; McLaughlin, 1978;

Gruchow & P e l l e t i e r , 1979; and D i m b e r g , 1987) . Even p e o p l e

who s i m p l y p e r f o r m a c t i v i t i e s l i k e k n i t t i n g , long-hand

w r i t i n g a n d p l a y i n g t h e v i o l i n c a n a c q u i r e LE {Root &

K i e r n a n , 1 9 7 4 a n d McLaughl i n , 1978) . R e p e t i t i v e w r i s t

motion, w h i l e g r i p p i n g a n o b j e c t i n t h e hand, s e e m s t o be t h e

i m p o r t a n t l i n k be tween t e n n i s p l a y i n g a n d these o t h e r

a c t i v i t i e s , i n t e r m s of p o t e n t i a l mechanisms of t h e i n j u r y

(SniSders , Volkers , Mechef se & Vleerning, 1987) .

V i c t i m s o f LE e x p e r i e n c e p a i n i n t h e r e g i o n of t h e

l a t e r a l e p i c o n d y l e . The p a i n o f t e n s h o o t s down t h e

p o s t e r o l a t e r a l a s p e c t o f t h e forearm, and can be unbea rab le

even w i t h t h e s l i g h t e s t movement o f t h e hand. The pain c a n

last for s e v e r a l months, making t h e numerous hand movements

of everyday l i f e d i f f i c u l t (Pe t e r son & Renstrbm, 1 9 8 6 ) .

The m o s t common f i n d i n g d u r i n g s u r g i c a l i n v e s t i g a t i o n of

p a t i e n t s w i t h severe casts of LE has been t e a r i n g of t h e

e x t e n s o r c a r p i r a d i a l i s b r e v i s (ECRB) t endon where it i s p a r t

of t h e common extensor t endon n e a r t h e l a t e r a l epicondyle

(see F i g 7 l r e 1). G r a n u l a r t i s s u e , p roduced i n response to

s o f t - t i s s u e t e a r i n g , h a s also been obse rved i n t h e damaged

area (Go ld i e , 1964; Coonrad & Hooper, 1973; R y a n , 1 9 7 7 ;

N i r s c h l & P e t t r o n e , 1979; and S h i e l d s , 1987) .

Figure la. Wrist extensor muscles (ECRF3 is shaded) , (Copied with permission from Anderson, 1983: fig. 6-91A.)

-- Cozxmn Extensor tendon -- Cozxmn Extensor tendon

FI. Digit~rzm B::~fcaCils

Ex?. Poi:icis Lezjcs I'rcnatc-r Tcrer

.\LA Po!!lcIs Luxgus

- Ert. Ca1r.i Xad. J$:cvi;

Est. Crrgi lilrzris - Esr. C ~ r y i R2d. I ~ r . ~ . . : s

- - - ---- 1st I)orr;al Inlc~crz?w$

--- EZL Pul!ic;s Jlre-..is

Err. I'oliicis I.ondus

Dorsal cxpansfan (Extens~r cx~ansicin)

Figure Ib. Origins and insertions of the vrist c z t c n s o x muscles {ECRB's snaded) . (Copied with permission from Anderson, 2 3 8 3 : f i g . 6-90.1

S t u d i e s have p r o v i d e d e v i d e n c e t o s u p p o r t t h e s u r g i c a l

f i n d i n g t h a t ECRB is the m o s t a f f e c t e d s t r u c t u r e i n LE

v i c t i m s . F o r example, an u l t r a s o n o g r a p h i c s t u d y o f t e n n i s

p l a y e r s w i t h LE showed t h a t m u l t i p l e l e s i o n s , i n c l u d i n g

e n t h e s o p a t h y , p e r i t e n d i n i t i s , t e n d i n i t i s , b u r s i t i s a n d

i n t r a m u s c u l a r haematoma, w e r e a l l associated s p e c i f i c a l l y

w i t h ECRB damage ( M a f f u l l i , Regine , C a r r i l l o , Capasso &

M i n e l l i , 1990) , Also, a c l i n i c a l s t u d y i n v o l v i n g p a t i e n t s

wi th LE demons t ra ted t h a t f o r c e d f i n g e r e x t e n s i o n s , which are

per formed main ly by the e x t e n s o r d i g i t o r u m communis muscle ,

d i d not, i nduce a n y p a i n , whereas f o r c e d w r i s t e x t e n s i o n and

r a d i a l d e v i a t i o n , b o t h f u n c t i o n s o f ECRB, d i d i n d u c e p a i n

fGo ld i e , 1964) . T h i s s u g g e s t s t h a t even though t h e e x t e n s o r

d i g i t o r u m communis muscle is invo lved i n w r i s t e x t e n s i o n , t h e

fact that it does n o t produce p a i n d u r i n g i ts o t h e r f u n c t i o n s

i n d i c a t e s t h a t it is n o t damaged i n LE s u f f e r e r s .

P h y s i c i a n s t oday are c o n f i d e n t t h a t LE is a n i n j u r y t h a t

i s p r i m a r i l y associated w i t h damage t o t h e ECRB tendon where

it o r i g i n a t e s a t t h e lateral ep i condy le . P a t h o l o g i c a l l y , t h e

main damage i s b e l i e v e d t o b e i n t h e f o r m o f e i t h e r

t e n d i n i t i s f N i r s c h l & P e t t r o n e , 1979; S h i e l d s , 1987; H e s s ,

C a p p i e l l o , Poole & Hunter, 1989; and Harvey, Gl ick , S t a n i s h &

T e i t z , 1.990) o r a n e n t h e s o p a t h i c l e s i o n [Burry , 1987 a n d

2. Functional Anatomy of ECRB

S t r u c t u r a l l y , ECRB i s a t w o - j o i n t musc l e s i n c e i t

c r o s s e s b o t h t h e w r i s t a n d elbow j o i n t s . F u n c t i o n a l l y ,

however, t h e muscle i s n o t c o n s i d e r e d t o c o n t r i b u t e t o elbow

movements b e c a u s e i t s o r i g i n l i e s on t h e e l h o w

f l e x i o n / e x t e n s i o n a x i s . T h e r e f o r e , i t i s r e a s o n a b l e t o

a n a l y z e o n l y t h e a c t i o n s o f ECRB a b o u t t h e w r i s t w h e n

a s s e s s i n g t h e mechanisms b e h i n d LE (Goldie , 1 9 6 4 a n d

McLaughlin & M i l l e r , 1 9 8 0 ) . T h i s i s f u r t h e r j u s t i f i e d by t h e

fac t t h a t G o l d i e (1964) found t h a t LE p a t i e n t s o n l y had

problems w i t h hand /wr i s t f u n c t i o n s and n o t elbow f u n c t i o n s .

ECRB i s one of f o u r w r i s t e x t e n s o r muscles , a l t hough i t

is c o n s i d e r e d t o be the main one, e s p e c i a l l y when t h e hand i s

c l e n c h e d (McFarland, Krusen & Weathersby, 1 9 6 2 ) . I t i s

assisted, u n d e r d i f f e r e n t c i r c u m s t a n c e s , b y t h e e x t e n s o r

c a r p i r a d i a l i s l o n g u s , e x t e n s o r d i g i t o r u m communis and

e x t e n s o r c a r p i u l n a r i s musc l e s (Backdahl & Car lso i i , 1961;

McFarland et a1 . , 1962; and Basma j i a n & D e Luca, 1985) . FXRB

i s a l s o c o n s i d e r e d t o be a pr ime mover i n r a d i a l d e v i a t i o n of

t h e hand, a l o n g w i t h f l e x o r c a r p i r a d i a l i s and e x t e n s o r c a r p i

r a d i a l i s l o n g u s fMcFarland e t a l . , 1962 and Basmajian & D e

Luca, 1985). Although t h e p r e c i s e c o n t r i b u t i o n o f ECRB t o

w r i s t e x t e n s i o n and radial d e v i a t i o n h a s n o t been q u a n t i f i e d ,

t h e l i n e of a c t i o n o f i t s tendon of i n s e r t i o n with r e s p e c t t o

4 k e wris: j o i n t indicates t h a t i t must be a major c o n t r i b u t o r

4 c bsth of these movements (Dempster h F i n e r t y , 1947).

Another impor t an t f u n c t i o n o f EC3B is s t a b i l i z a t i o n of

t h e w r i s t j o i n t d u r i n g c o n t r a c t i o n of t h e f i n g e r / w r i s t

f l e x o r s ( F i d e l u s , 1 9 6 7 and S n i j d e r s e t a l . , 1987) . T h i s

means, for example, t h a t ECRB is a c t i v e whenever t h e f i n g e r s

are g r a s p i n g an o b j e c t , S i n c e t h i s a c t i o n , as w e l l as w r i s t

e x t e n s i o n and r a d i a l d e v i a t i o n , are i n v o l v e d i n t e n n i s , most

n o t a b l y i n t h e backhand s t r o k e , and t h e o t h e r a c t i v i t i e s t h a t

produce LE, t h e ECRB muscle is l i k e l y t o be h i g h l y a c t i v e i n

t h e s e c o n t e x t s .

The anatomy o f a m u s c u l o t e n d i n o u s s t r u c t u r e h a s a

s i g n i f i c a n t b e a r i n g on t h e forces that it e x p e r i e n c e s . A s

ment ioned ear l ier , ECRB, v ia t h e common e x t e n s o r t e n d o n ,

o r i g i n a t e s a t t h e l a t e r a l e p i c a n d y l e o f t h e humerus. The

tendon crosses over t h e head of t h e r a d i u s b e f o r e forming t h e

muscle b e l l y , The muscle crosses t h e s u p e r i o r h a l f o f t h e

forearm p o s t e r o l a t e r a l l y a n d t h e n becomes a long , s l e n d e r

t e n d o n of i n s e r t i o n . T h i s t endon p a s s e s u n d e r n e a t h t h r e e

thumb m u s c l e s , e x t e n s o r p o f l i c i s l o n g u s a n d b r e v i s a n d

a b d u c t o r p o l l i c i s longus, and t h e e x t e n s o r r e t i n a c u l u m b e f o r e

o b l i q u e l y i n s e r t i n g on t h e l a t e r a l edge of t h e b a s e of t h e

t h i r d metacarpal bone (O 'Rah i l l y , 1986: p. 126) ( s e e F i g u r e

1)

3. Etiology

a. General - Tendon Dantage

Bicrmechanics research c e n t r e d around t fie trrsderst artd t i ia

of s o f t - t i s s u e i n j u r y etiology, i n c l u d i n g tendon t i a m ~ g t l , I :,

i n its i n f a n c y (Viano, King, M e l v i n & Weber, f 9 8 9 ) . W < : ? t a f

the research being carried o u t today is based on q u d ; t b ~ r i v c u

hypo theses as opposed t o quantitative evidence. 1 r*:.: ,tmi*l*c,

Viano a n d Lau (1988) have suggested that t h e r e xs ,x dirci - t

. ;321 tb r e l a t i o n s h i p between t h e f o r c e a p p l i e d t o a biuloy icd t t 1 . .

iind the r i s k of injury, T h i s implies thar a tendui-r, &%:;

example of a biological. tissue, is damaged by thr* appi ic-it ! i , r t

o f great forces . . There c e r t a i n l y is a 1 i m i t tu t r w amwrr r t % I !

stress ( f o r c e per u n i t o g c r o s s - s e c t i o n a l a redl t f r - i t r l

t e n d o n r l i k e any other material, c a n n o r m a l l y w i r h s t i a n d

(Elliott, 1965 a n d Fung, l98l), b u t t h e role of this i n

t endon i n j u r y e t i o l o g y h a s not been firmZy estahlishcd.

A t endon comprises fibres of c o l l a g e n and erask in , wh j r h

are embedded i n a p ro t eog lycaa r -wa te r matrix, EJt2 1 I icqf :r~

a c c o u n t s f o r 101-75 p e r c e n t of t h e t e n d o n ' s dry ve iq tr t . "Pkig:

collagen fibres are held t o g e t h e r i n a loose-: pa rd l i@: l

a r rangement w i t h t h e aid of c r o s s - l i n k a g e s . This st r ~ ~ c t k~ r e

enables the t endon to perform i ts main f u n c t i o n ~f p u l l i n g of1

a bane w i t h a tensile donee d i c t a t e d by tsre carrtractiorr of-

its attached musehe (Crisp, 31972 and Eess et a1 . , 13883) , T h e

The mfir,t;afiica3_ prcperties of a tendon are t y p i c a l l y

rcprssofited by a stress-strain r e l a t i o n s h i p such a s t h e one

;n Fig- re 2. This illustrates t h e f a c t t h a t t h e amount of

t e n s i l e stress experienced by t h e tendon is in f luenced by t h e

amount of applied s t r a i n (change i n l e n g t h d i v i d e d by rest

fci-ngitb) - There i s an i n i t i a l range of s t r a i n s d u r i n g which

stress remains close to z e r o 40 t o A ) . This i s followed by a

near e l a s t i c range, d u r i n g which stress i n c r e a s e s a lmost

I b n e a r l y w i t h added strain ( A t o E). F i n a l l y , when t h e

t e n d m is nearing rupture, it e x i s t s i n a so -ca l l ed p l a s t i c

reg ion , d u r i n g which a minimal amount of a d d i t i o n a l stress

p r o d u c e s a l a r g e amaunt of a d d i t i o n a l s t r a i n (B t o C )

The maqnitude of stxess a t which rupture o c c u r s i s

l a b e l l e d t h e u l t i m a t e stress, corresponding to t h e u l t i m a t e

strength of the tendon, Values ranging from about 50 t o 200

Pacewtons/squrmre m i 1 1 i m e t r e have been measured on in vitro

human tendons. The s t r a i n s corresponding t o tendon r u p t u r e

range between fO and 15 p e r c e n t ( E l l i o t t , 1965; Yamada, 1970;

and Furzg, 19821, It is impor tan t t o p o i n t o u t t h a t s i n c e

these experiments involved very s low s t r a i n rates, t h e

ulc hate strengths are probably i n a p p l i c a b l e i n vivo (McCully

& Earrlknler, 2986 and Viano et al . , 1989). The st t -Ces by Van

Brotzkl in and E l l i s (1 3 6 5 ) and Abraharns (19671 demonst r a t e d

t h a t h i g h e r rates o f s t r a i n produce steeper s t r e s s - s t r a i n

r e l a t i o n s h i p s . In o t h e r words, t h e stress exper ienced hy a

tendon i s i n c r e a s e d n o t o n l y by added s t r a i n , b u t a l s o by

i n c r e a s e d r a t e of strain. This may have i m p l i c a t i o n s f a r t h e

magnitude of stress a t which tendon r u p t u r e occurs (Curwin &

Stanish, 1984) .

Deformation I X )

Figure 2. A typical s t r e s s - s t r a i n curve fo r human tendon (stress represented by "load"; s t r a i n r ep resen ted by "deformat ion") . (Copied with permission from Fung, 1981 : p, 210.)

A s whole structures t endons can withstand v e r y high

tensile farces, but it is s t i l l common for microtears (i . c . ,

r u p t u r i n g o f i n d i v i d u a l c o l l a g e n f i b r e s ) t o o c c u r w h i l e

tendoas are e x p e r i e n c i n g nr;rrna!. p h y s i o l o g i c a l f o r c e s . T h i s

i s pe rhaps because of t h e a d d i t i o n o f compress ive , s h e a r and

f r i c t i o n a l f o r c e s t o these t e n s i l e f o r c e s ( F r o s t , 1973: p .

1 6 7 ) . Tendons are c a p a b l e o f f u n c t i o n i n g normal ly even a f t e r

a number o f m i c r o t e a r s have o c c u r r e d . I n fact , n o r m a l l y

t h e s e m i c r o t e a r s are good f o r t h e i n t e g r i t y of t h e tendon a s

t h e y s t i m u l a t e ongoing t u r n o v e r o f c o l l a g e n f i b r e s , keep ing

t h e t i s s u e young and h e a l t h y . I t i s o n l y when t h i s t u r n o v e r

is ~ n s u f f i c i e n t l y r a p i d t o m e e t t h e demands p l a c e d on t h e

muscle a t t a c h e d t o t h e tendon, t h a t s e r i o u s macrotears can

o c c u r ( F r o s t , 1973 a n d H e s s e t a l . , 1 9 8 9 ) . A l s o , a

d i s c o n t i n u i t y i n a t endon b rough t on by an accumula t ion o f

m i c r o t e a r s can raise the stress c o n c e n t r a t i o n i n t h e damaged

a r e a a n d c o n t r i b u t e f u r t h e r t o t h e o n s e t of macrotears, i n

agreement w i t h mechan ica l e n g i n e e r i n g p r i n c i p l e s ( S h i g l e y ,

1986: p . 206) . T h i s ex t r eme f o r m o f t endon damage i s t h e n

l a b e l l e d t e n d i n i t i s ( F r o s t , 1973 and Curwin & S t a n i s h , 1 9 8 4 ) .

Breakage of a material caused by r e p e a t e d or f l u c t u a t i n g

stresses w i t h i n t h e s t a t i c stress d e s i g n l i m i t s o f t h e

material i s known as f a t i g u e (Sh ig l ey , 1986: p . 2 2 8 ) . I f a

tendon , as an example of a material, i s f a t i g u e d , it can be

daaaged by r e p e t i t i v e stresses b e l o w i t s u l t i m a t e stress

[Frost, 1973 and Hess et al . , f 989) . P r o g r e s s i v e weakening

of a tendon ( 2 - e . , l ower ing of i t s u l t i m a t e s t r e n g t h ) upon

r e p e t i t i v e l o a d i n g h a s been c l e a r l y demons t r a t ed i n s t u d i e s

i n v o l v i n g r a t t a i l t e n d o n s (Rigby, H i r a i , Spikes & E y r i r t y ,

1 9 5 9 ) . T h e r e f o r e , any a c t i v i t y which i n v o l v e s repet it i v e

l o a d i n g of a t endon , p a r t i c u l a r l y when muscula r cont tact i o n

i s com9ined w i t h e x t e r n a l s t r e t c h i n g forces, makes t h e t e n d o n

s u s c e p t i b l e t o f a t i g u e - l i k e f a i l u r e .

Tendon i n j u r i e s c a n b e d iv ided i n t o t w o distinct

categories. Those which r e s u l t from one violent stress ,

presumably g r e a t e r t h a n the u l t i m a t e stress o f t h e t e n d o n ,

are known as acute s t r a i n s . Those which a r i s e f rom

r e p e t i t i v e l o a d i n g of stresses presumed t o be below t h e

u l t i m a t e stress are known as c h r o n i c s t r a i n s (Keene, 1 9 8 5 ) .

The e t io logy of these i n j u r i e s may n o t be i d e n t i c a l .

Al though b o t h i n v o l v e t e a r i n g of c o l l a g e n f i b r e s , t h e causes

of t e a r i n g may be q u i t e d i f f e r e n t .

I n summary, a t e n d o n has l i m i t e d stress t o l e r a n c e t o

either a s i n g l e h i g h stress or r e p e a t e d l o w e r stresses. ff

t h e s e l i m i t s are exceeded , t h e n damage w i l l o c c u r . T h i s

darnage can be repaired, b u t o n l y i f g i v e n a d e q u a t e t ime and

n o r m a l , h e a l t h y c o n d i t i o n s . U n f o r t u n a t e l y , little i s

p r e s e n t l y known a b o u t t h e stress l i m i t s of human tendons i n

viva (Curwin & Stanish, 1984).

b. Specific

Even though LE has been s t u d i e d fo r over one hundred

years, its e t i o l o g y is poor ly unders tood (Bernhang e t al.,

1 9 7 4 a n d Burry, 1975). Curwin and S t a n i s h ( 1 9 8 4 ) have

p rov ided a r e a s o n a b l e summary o f t h e v a r i o u s e t i o l o g i c a l

contributors t h a t have been sugges ted by t h e numerous t e n n i s

elbow r e s e a r c h e r s o f the r e c e n t p a s t . The f o l l o w i n g a r e

mentioned as p o t e n t i a l c o n t r i b u t o r s t o LE: massive over load

of t h e w r i s t e x t e n s o r muscles i n e c c e n t r i c c o n t r a c t i o n s ;

m u l t i p l e r e p e t i t i o n of w r i s t movements; o l d age; inadequate

strength, endurance and/or compliance i n t h e w r i s t e x t e n s o r

musculotendinous u n i t ; hormonal imbalance ( i n females on ly ) ;

abnormal elbow j o i n t design; m e c h a n i c a l l y u n f a v o u r a b l e

equipment used fo r t h e movements; and l a c k of s k i l l , o r

i n e f f i c i e n c i e s , i n performing movements o f t h e hand. They

conclude t h a t some, p r e s e n t l y unknown, combinat ion of t h e s e

f a c t o r s is r e s p o n s i b l e f o r induc ing stresses i n the damaged

tendon which exceed i t s strength c a p a b i l i t i e s . It i s quite

possible t h a t d i f f e r e n t combinations of f a c t o r s are involved

i n d i f f e r e n t i n s t a x e s of LE. Unfor tuna te ly , t h e r e i s no

consensus on t h e importance o f any one of t h e s u g g e s t e d

f a c t o r s ,

Both acute and chrmic cases of LE have been r e p o r t e d i n

the l i t e r a t u r e . but chronic cases p r e d o a i n a t e . E l l i o t t

(1965) and Curwin and S t a n i s h (1984) state t h a t tendons have

u l t i f n a t e s t r e n g t h s f o u r t i m e s as g r e a t a s a n y l o a d t h e y

e x p e r i e n c e d u r i n g normal a c t i v i t i e s , If t e n n i s playing can

be c o n s i d e r e d one o f t h e s e normal a c t i v i t i e s ( p e r h a p s it

canno t be d u r i n g b a l l - r a c q u e t c o n t a c t ) , t h e n t h e l o a d s p l aced

on t h e ECRB t e n d o n must t y p i c a l l y be t o o low for a c u t e

r u p t u r e t o o c c u r .

LE h a s been labelled a n o v e r u s e syndrome by numerous

r e s e a r c h e r s (Gruchow & P e l l e t i e r , 2979; M l r s c h l & Pettsune,

1979; Curwin & S t a n i s h , 1984; Allman et a l . , 1987; and Hess

et a l . , 1989) . O v e r e x e r t i o n of the ECRB muscle , t h r o u g h

mass ive r e p e t i t i o n of g r e a t f o r c e s , i s t h e presumed general

e t i o l o g y of t h e i n j u r y (McLaughlin, 1978; N i r s c h l & P e l t r a n e ,

1979; and B r i g g s & E l l i o t t , 1985) . It is apparent t h a t t h e

act ivi t ies n o t e d t o i n d u c e LE a l l i n v o l v e massive r e p e t it ion

o f w r i s t e x t e n s i o n a n d rad ia l d e v i a t i o n . A r e a s o n a b l e

h y p o t h e s i s , t h e n , i s t h a t t h e forces g e n e r a t e d i n t h e ECRB

t e n d o n of o r i g i n d u r i n g t h e s e a c t i v i t i e s are g r e a t enough,

when r e p e a t e d numerous t i m e s , t o induce tendon damage.

It is i m p o r t a n t t o p a i n t o u t t h a t f o r c e s other t h a n t h e

t e n s i l e o n e s t h a t t h e ECRB t endon w a s de s igned t o w i t h s t a n d

may be i n v o l v e d i n damaging t h e t endon . When a t endon is

e x p e r i e n c i n g t e n s i l e f o r c e s and bending, f o r example around a

hazy pro;;;ir;ence, c o m p r e s s i v e and f r i c t i o n a l farces a re

induced, The co~pressive forces act normal to the bony

prominence and t h e f r i c t i o n a l f o r c e s act i n d i r e c t i o n s

opposing the t e n s i l e ones (Frost , 1973: p . 1 6 7 ) . These

add i t iona l forces a r e proport ional i n magnitude t o t h e

tensile forces. The in t r i ca t e winding course of ECRB i s an

example of t h i s type of s i tua t ion . The speci f ic bending that

occurs around t h e radial head produces additional compressive

and f r i c t i o n a l forces, which increase a s t e n s i l e forces

increase. Some researchers have suggested tha t t h i s may be a

s igni f icant contributor t o LE (Goldie, 1964 ; Nirschl, 1975;

McLaughlin, 1978; and Briggs & E l l i o t t , 1 9 8 5 ) . Briggs and

E l l i o t t ( 1 9 8 5 ) have a l so suggested t h a t addi t ional shear

forces are produced i n the ECRB tendon of or ig in because of

unequal tension applied t o other attached so f t t i s sues . They

s t a t e t h a t the tendon does not simply o r ig ina t e a t the

l a t e r a l epicondyle. Rather, it adheres by means of

filamentous attachments t o the adjacent members of the common

extensor tendon, t h e r a d i a l c o l l a t e r a l l igament, t h e

arbieular ligament, the capsule of the elbow joint and the

surrounding deep fasc ia . The shear forces produced by these

attachments a r e proportional i n magnitude t o t he t e n s i l e

fo rces . It i s reasonable t o hypothesize t h a t excessive

tensile force i n t h e ECRB tendon leads t o excessive shear as

well a s compressive and f r i c t i o n a l forces . The precise

combination of these forces involved i n the etiology of LE i s

a * e ,isknown.

B. Novice Tennis Players With Lateral Epicondylitis

P r e s e n t l y , t h e r e i s no c l e a r consensus regarding t h e

e t i o l o g y o f l a tera l e p i c o n d y l i t i s i n t e n n i s p l a y e r s . V a r i o u s

p o t e n t i a l factors c o n t r i b u t i n g t o t h e o n s e t of LE i n t e n n i s

p l a y e r s have been proposed i n t h e v a s t amount o f l i t e r a t u r e

w r i t t e n on t h e t o p i c . The most n o t a b l e o n e s , i n n o

p a r t i c u l a r o r d e r of rank , a r e h i t t i n g backhand s h o t s w i t h a

p o o r t e c h n i q u e a n d / o r u s i n g e x c e s s i v e g r i p p r e s s u r e ;

i n a d e q u a t e w r i s t e x t e n s o r m u s c u l o t e n d i n o u s s t r e n g t h ,

e n d u r a n c e a n d / o r c o m p l i a n c e ; e l b o w j o i n t a n a t o m i c a l

a b n o r m a l i t y ; o l d age; hormonal imbalance ( i n f ema le s on Ly) ;

p l a y i n g f r e q u e n t l y a n d w i t h h i g h i n t e n s i t y ; u s i n g a r acque t

w i t h force- or v i b r a t i o n - e n h a n c i n g c h a r a c t e r i s t i c s ; p l a y i n g

i n c o l d , w e t w e a t h e r o r w i t h o u t a d e q u a t e warm-up; and

c o n t a c t i n g t h e ba l l away from the c e n t r e o f t h e r acque t ( f o r

f u r t h e r d e t a i l s , t h e r e a d e r i s r e f e r r e d t o t h e f o l l o w i n g :

Sykes, S c o t t & K e l l e t t , 1971; Bernhang e t a l . , 1974; N i r sch l ,

1975; Brody, 1979; F i o t t , 1979; P lagenhoef , 1979; E l l i o t t &

Blanksby , 1980; P l a g e n h o e f , 1980; P r i e s t e t a l . , 1980;

Brannigan & A d a l i , 1981; Roy & f r v i n , 1983; Briggs & E l l i o t t ,

1985; GroppeL, 1986; Allman e t a l . , 1987 ; Kamien, 1 9 8 8 ;

Brcrdy, 1989; a n d Widing & Moeinzadeh, 1990) . A l l of these

p ~ t e n t i a l factors have i n common t h e fact t h a t forces a r e

produced which can exceed t h e s t r e n g t h capabilities of t h e

ECRB t i s s u e a t a p a r t i c u l a r i n s t a n t i n t i m e d u r i n g t e n n i s

play. I t i s p o s s i b l e t h a t any one, o r combination o f t h e s e

f a c t o r s can b r i n g about l a t e r a l e p i c o n d y l i t i s i n a p a r t i c u l a r

t e n n i s p l a y e r .

One d i s t i n c t group o f t e n n i s p l a y e r s which commonly

acquires LE comprises novice p l a y e r s . These a r e people who

play r e c r e a t i o n a l l y and who use poor s t r o k e t echn iques , most

obvious ly on t h e backhand. Ni r sch l (1975) found t h a t novice

p l a y e r s are abou t f o u r t i m e s more prone t o t h e i n j u r y t h a n

are advanced p l a y e r s . The q u e s t i o n as t o why novice p l a y e r s

are so s u s c e p t i b l e t o LE has not been adequa te ly answered.

C . The Significance of Poor Backhand Technique as a Factor in Lateral Epicondylitis Etiology

1, General Differences Between Novice and Advanced Techniques

Many r e s e a r c h e r s b e l i e v e t h a t poor backhand t e c h n i q u e

contributes somewhat ( i f n o t comple te ly) t o LE e t i o l o g y i n

novice t e n n i s p l a y e r s (Bernhang e t a l . , 1974; Cohen, 1980;

McLaughlin & M i l l e r , 1980; N i r s c h l & Sobel , 1981; Legwold,

1984; Levisohn & Simon, 1984; Allman e t a l . , 1987; and

Stites, 1988). The evidence suppor t ing t h i s b e l i e f , however,

is q u a l i t a t i v e , coming mostly from epidemiologica l s t u d i e s of

which t h a t by Kamien (2988) i s a r e p r e s e n t a t i v e example.

Kamien found the most common response o f t e n n i s players wi th

t e n n i s elbow, when asked w h a t t h e y t h o u g h t c a u s e d t h e i r

i n j u r y , t o be poor s t r o k e t e c h n i q u e s . These same t e n n i s

e lbow s u f f e r e r s a l s o c l a i m e d t h a t t h e y had a 100 p e r c e n t

s u c c e s s rate i f t h e y s o u g h t c o a c h i n g t o alleviate their

t e n n i s elbow symptoms. I n fact , a l t e r a t i o n of t e n r i s strokes

i s c o n s i d e r e d by s o m e t o be t h e m o s t s u c c e s s f u l form of

t r e a t m e n t o f LE ( P r i e s t e t a h . , 1980)- Al though many

r e s e a r c h e r s have s u g g e s t e d t h a t poo r t e c h n i q u e i s the most

s i g n i f i c a n t f a c t o r i n LE e t i o l o g y , they have n o t produced a n y

q u a n t i t a t i v e ev idence t o s u p p o r t t h i s .

The g r e a t e s t l o a d i n g of t h e w r i s t e x t e n s o r m u s c l e s

d u r i n g t e n n i s p l a y i s l i k e l y t o o c c u r d u r i n g backhand s h o t s

b e c a u s e of t h e need t o resist w r i s t f l e x i o n a f t e r ball-

r a c q u e t c o n t a c t . It f o l l o w s t h a t t h e o v e r l o a d i n g a s s o c i a t e d

with LE i n t e n n i s p l a y e r s may o c c u r d u r i n g backhand shots.

I n l o o k i n g a t t h e p o s s i b i l i t y o f p o o r backhand t e c h n i q u e

b e i n g a predisposer t o LE i n nov ice p l a y e r s , it i s no ted t h a t

many o f t h e s e players use t h e s o - c a l l e d " l e a d i n g elbow"

backhand t e c h n i q u e . T h i s h a s been s u g g e s t e d as b e i n g a

h i g h l y p o t e n t i a l source of t h e prob lem f o r n o v i c e p l a y e r s

(Bernhang et a l . , 1974 and E l l i o t t , 1989) .

The l e a d i n g e l b o w backhand t e c h n i q u e has b e e n described

as f o l l o w s : swinging t h e r a c q u e t w i th body weight back o n t h e

heels, w r i s t f l e x e d , forearm prona ted , and elbow flexed a n d

p o i n t i n g towards the n e t (see F i g u r e 3a). A l s o , many novice

p l a y e r s are known t o have poor u s e of t h e i r h i p , t r u n k a n d

shoulder muscles, t o use p o o r t i m i n g , and to s n a p t h e i r .

w r i s t s e x t r a n e o u s l y i n t o e x t e n s i o n a f t e r h i t t i n g t h e b a l l

(Bernhang e t a l . , 1974; N i r s c h l , 1975; Cohen, 1980; Roy &

X r v i n , 1983; Legwold, 1984; and Macken, 1 9 9 1 ) . T h i s i s

c o n t r a s t e d w i t h t h e f o l l o w i n g g e n e r a l a t t r i b u t e s o f t h e

c l a s s i c advanced p l a y e r s ' backhand t e c h n i q u e : weight forward,

wrist firm and n e u t r a l , and elbow ex tended a n d p o i n t i n g down

a t impac t (see F i g u r e 3 b ) ; good foo twork ; t r a n s f e r r i n g

momentum e f f i c i e n t l y by t a k i n g a s t e p t o w a r d s t h e b a l l ,

r o t a t i n g t h e h i p s and t r u n k , and t h e n u s i n g s h o u l d e r , elbow,

forearm and w r i s t muscles i n t h e prox imal t o d i s t a l sequence

t o g e n e r a t e h i g h r a c q u e t v e l o c i t i e s ; a n d good t i m i n g

(Groppel , 1978; Douglas, 1982; Roy & I r v i n , 1983; Groppel ,

1986; E l l i o t t , Marsh d Overheu, 1989; and Macken, 1991) .

F i g u r e 3 a . Novice p l a y e r u s i n g the leading elbow backhand technique. . (Copied w i t h permission f r o m Bernhang et a l . , 1 9 7 4 : p. 253 . )

F i g u s e 3b. Advanced p l a y e r using t he classic advanced players' backhand t e c h n i q u e . (Copied w i t h permission from Douglas, 1982 : p . 6 4 . )

The i m p o r t a n t q u a l i t a t i v e d i f f e r e n c e s between t h e s e

t e c h n i q u e s a re t h a t advanced p l a y e r s u t i l i z e t h e l a r g e

moments o f f o r c e prodccec! by t h e s t r o n g l e g , h i p , t r u n k and

s h o u l d e r muscles and well- t imed t r a n s f e r s o f momentum between

body segments, whereas n o v i c e p l a y e r s r e l y more on t h e w e a k

elbow and w r i s t musc l e s t o p e r f o r m t h e dynamic a c t i o n o f

r a c q u e t movement (Bernhang e t a l . , 1974; Groppe l , 1 9 7 8 ;

Legwold, 1984; a n d G r o p p e l , 1986) . Van Gheluwe a n d

H e b b e l i n c k ( 1 9 8 6 ) , i n p e r f o r m i n g a n e l e c t r o m y o g r a p h i c

a n a l y s i s o f t e n n i s s t r o k e s , d e m o n s t r a t e d t h a t advanced

p l a y e r s u t i l i z e s t r o n g c o n t r a c t i o n s of s h o u l d e r musc l e s t o

e x e c u t e even moderate s t r o k e s . I f n o v i c e p l a y e r s are n o t

c a p a b l e of u s i n g t h e i r s h o u l d e r , as w e l l as h i p and t r u n k ,

musc les a d e q u a t e l y , t h e n LE may be induced by t h e consequent

o v e r l o a d i n g of t h e i r elbow and w r i s t muscles .

N i r s c h l (1975: p . 309) s ta tes t h a t m o r e s k i l l f u l t e n n i s

p l a y e r s h a v e b e t t e r "economy o f m u s c l e u t i l i z a t i o n and

e f f i c i e n c y o f s t r o k e p a t t e r n s " . T h i s a g r e e s w i t h t h e t h e o r y

t h a t t r a i n i n g r e s u l t s i n d e c r e a s e d a n t a g o n i s t i c musc l e

a c t i v i t y (Basmajian 6 D e Luca, 1985) . Fur thermore , N i r s c h l

(1975) and Legwold (1984) c l a i m t h a t advanced t e n n i s p l a y e r s

a c t u a l l y p r o t e c t t h e i r r e l a t i v e l y weak w r i s t musc les by o n l y

r e i y i n g on them fo r r a c q u e t c o n t r o l r a t h e r t h a n for powering

the stroke as d o n o v i c e p l a y e r s . Tney a l s o s u g g e s t t h a t

n o v i c e p l a y e r s have t o r e l y h e a v i l y o n t h e i r weak w r i s t

muscles in order +,a compensate for t*he f ac t : ? ? : t * 1 ~

shoulder muscles are a l s o tao w e a k for rhe deaands ~f t e n r n s

play -

The l i t e r a t u r e p rov ides f itt 1e q u a n t i t a t i v e eviderrc-tt t ,-I

suppor t t h e t h e o r y that novice p l a y e r s produce greater fo rces

i n t h e i r w r i s t e x t e n s o r musculature than do advanced p;aye~-:;

during backhand s h o t s , ffoshizswa, f t a n i and Jonssort f ! 987 3

found t h a t novice players exaibited higher f c v ~ f s o f EZRif

muscle a c t i v i t y and Bernhang e t al. (1974) f o u n d t h d t nt>vic:th

p l a y e r s used maximal gr ip p r e s s u r e fox l onger durat lo r ) : ; , nf;

compared t o advanced p l a y e r s , i n t h e i r studie:;. ' T j ~ r * ? j t .

r e s u l t s s u g g e s t t h a t nov ice p l a y e r s may fatigue t he i r I",CFiD

muscles s o o n e r than advanced players, which may l e a d ti>

tendon damage.

The backhand t e c h n i q u e s used by nov ice term is playt: r:;,

i n c l u d i n g t h e l e a d i n g e lbow t e c h n i q u e , appeal- t i 2 i r e

m e c h a n i c a l 1 y u n f a v o u r a b l e i n t e r m s af excess i wr- t r ~ r c - * ~

p roduc t ion i n ECRB. Since novice players a r e prnd ir;far~:;c*lf t i s

LE, it is reasonable to h y p o t h e s i z e that pctcir k J a c k h ~ ~ r : ~ i

t e c h n i q u e may inbace forces which are great er i r , :bqf , i f r

magnitude, a n d l o r long enough i n d u r a t i o n , tc prrjff-:cr- t k r e

c h a r a c t e r i s t i c t e a r i n g of t h e ECRB tendon of ~ r i r f i r r . 31 i s

hqrpothesis Bas not yet been tested validly.

2. Quantification of Tendon Force

If a Foor backhand t echn ique , such as the l e a d i n g e l b o w

tecf;r:irfue, i s somewhat r e s p o n s i b l e f o r t e a r i n g t h e ECRB

rendon o f origin, t h e n t h i s t e c h n i q u e may i n d u c e g r e a t e r

farces i n t h e t endon t h a n other, more advanced t e c h n i q u e s .

T h i s , of cou r se , is based on the assumption t h a t t h e r e i s no

difference between t h e s t r e n g t h capabi l i t i es o f t h e ECRB

t e n d o n s of t h e p e o p l e u s i n g t h e d i f f e r e n t t e c h n i q u e s . To

d e t e r m i n e whe the r or n o t t h e l e a d i n g e lbow t e c h n i q u e is an

impor tan t f a c t o r i n LE for n o v i c e p l a y e r s , it would b e u s e f u l

t o q n a n t i f y t h e forces t r a n s m i t t e d t o t h e ECRB t endon d u r i n g

backhand s h o t s .

a. D i r e c t Method - Force Transducer

D i r e c t measurement of force i n a t e n d o n c a n only b e

accompl i shed by s u r g i c a l l y i m p l a n t i n g a m i n i a t u r e "bucklew-

t y p e force t r a n s d u c e r a round t h e t endon . T h i s method h a s

been used i n a few i n vivo s t u d i e s w i t h cats (Gregor, Hager &

Roy, 1981 and S h e r i f , Gregor, Liu, Roy & Eager, 19831, h o r s e s

(Barnes & P i n d e r , 19741, monkeys ( P e r e s , Maton, Lan jer i t &

Philigpe, 19831, and , r e c e n t l y , humans (Gregor, K o m i &

J a r v i n e n , 1987 and K o m i , Sa lonen , J a r v i n e n & Kokko, 1987).

The human s t u d i e s have o n l y invo lved measurement of a c h i l l e s

t endon forces,

Although this method may sound encourag ing , it i s n o t

appropriate for t h e measurement o f ECRB tendon forces d u r i n g

t e n n i s s t r o k e s . Tnvas ive t e c h n i q u e s such as t h i s a r e n o t

common i n human i n vivo r e s e a r c h mainly f o r e t h i c a l r e a s o n s .

Fur thermore , b u c k l e t r a n s d u c e r s a r e o n l y des igned f o r u s e on

w e l l - d e f i n e d e x t e r n a l t e n d o n s s u c h as t h e a c h i l l e s t e n d o n

(Zajac & Gordon, 1 9 8 9 ) . Even w i t h such a tendon t h e r e e x i s t s

t h e s e r i o u s p rob lem o f t e n d o n l e n g t h d i s t u r b a n c e due t o

bend ing of t he t e n d o n a round t h e t r a n s d u c e r ( A n , B e r g l u n d ,

Cooney, Chao & Kovacevic, 1990) U n t i l t e chno logy a l l o w s t h e

p r o d u c t i o n of m i n i a t u r e f o r c e - d e t e c t i n g d e v i c e s t h a t are more

s u i t a b l e f o r m e a s u r i n g forces i n t e n d o n s s u c h a s ECRB, a

d i r e c t method of force measurement canno t b e used on t e n n i s

p l a y e r s w h i l e h i t t i n g backhand s h o t s . Even t h e n the major

problem of c o n v i n c i n g s u b j e c t s t o p a r t i c i p a t e i n i n v a s i ve

t e s t i n g would s t i l l e x i s t .

b. Indirect Methods

i), Inverse Dynamics Approach

F o r s t u d i e s i n v o l v i n g l i v e human s u b j e c t s researchers

u s u a l l y have t o rely on i n d i r e c t methods o f t endon force

q u a n t i f i c a t i o f i . The m o s t e s t a b l i s h e d of these methods i s

based on t h e Inverse Dynamics Technique. McLaughl i n ( 1 9 7 8 )

and Winter (1990) provide good d e s c r i p t i o n s of t h e I n v e r s e

Dynamics T e c h n i q u e . The t h e s i s b y M c L a u g h l i n ( 1 9 7 5 )

describes the Inverse Dynamics Technique as applied to

backhand tennis strokes. Essentially, muscle moments are

caf culated from Newtonian equations of motion, using segment

kinematics i . , displacements and displacement-time

derivatives) and kinanthropometric quantities i e . masses,

centre of mass positions, lengths, and moments and products

of inertia) as inpcts.

A muscle moment determined in this manner is considered

to be a generalized moment about the joint axis, representing

the sum of moments produced by all muscles crossing the

joint. If the contribution a particular muscle makes to the

total moment and an estimation of the muscle's moment arm can

be determined, then an estimate of that muscle's force can be

calculated. It follows that the attached tendon is

experiencing an equivalent tensile force because tendons are

attached in series to their corresponding muscles.

Unfortunately, it is presently impossible to determine

the contribution a specific muscle makes to the generalized

joint moment (Andrews, 1982) . Attempts have been made at

solving this "general distribution problem" for simple planar

motion at specific joints (ankle: Hof & van den Berg, 1977

and elbow: Caldwell & Chapman, 1991), but the distribution of

farces amongst the synergistic extensors and radial deviators

of the wrist is much more complex. The main problem, besides

the fact that these muscles function in at least two planes,

l i e s i n t h e g r e a t number o f f u n c t i o n a l l y s i n g l e - j o i n t

muscles , e ach w i t h p o t e n t i a l l y d i f f e r e n t moment c o n t r i b u t i o n s

a t d i f f e r e n t j o i n t a n g l e s . S i n c e ECRB, f o r example, ac ts t o

e x t e n d and r a d i a l l y d e v i a t e t h e w r i s t , as w e 1 1 a s p rov ide

a n t a g o n i s t i c s t a b i l i z a t i o n f o r c e s when t h e hand i s g r a s p i n g

a n o b j e c t ( s u c h a s a t e n n i s r a c q u e t f , it i s p r e s e n t l y

i m p o s s i b l e t o d i s c e r n f rom g e n e r a l i z e d w r i s t moments t h e

c o n t r i b u t i o n o f ECRB t o t h e d i f f e r e n t a c t i o n s . It w i l l be

n e c e s s a r y t o make direct muscle / tendon f o r c e measurements t o

s o l v e t h i s problem i n the f u t u r e .

McLaughlin (1978) a n d McLaughlin a n d M i l l e r ( 1980)

d e s c r i b e a n a t t e m p t t h a t h a s been made a t q u a n t i f y i n g t h e

t e n s i l e f o r c e s i n t h e ECRB t endon d u r i n g t h e backhand t e n n i s

s t r o k e . Al though their i n t e n t i o n s w e r e good ( s u c c e s s might

h a v e s o l v e d t h e p rob lem of LE e t i o l o g y ) , t h e i r r e s u l t s

i n c l u d e d f o r c e v a l u e s t h a t w e r e p h y s i o l o g i c a l l y i m p o s s i b l e .

T h e i r approach w a s f a r t o o complex f o r o u r p r e s e n t knowledge

r e g a r d i n g musc l e f o r c e e s t i m a t i o n . It i n v o l v e d too many

unknowns a n d u n j u s t i f i e d a s s u m p t i o n s , i n c l u d i n g t h e

i m p l e m e n t a t i o n of o p t i m i z a t i o n t e c h n i q u e s a s a means of

ove rcoming t h e g e n e r a l d i s t r i b u t i o n prob lem, f o r t h e i r

r e s u l t s t o be meaningfu l . T h i s approach needs t o be r e f i n e d

i n v a r i o u s ways before it can be used t o e s t i m a t e ECRB t e n d o n

forces d u r i n g t h e backhand t e n n i s s t r o k e .

5.5) . Muscle Made1 Approach

A n ~ t h e r i n d i r e c t method o f f o r c e e s t i m a t i o n has been

p r o p o s e d by v a r i o u s r e s e a r c h e r s i n t h e f i e l d o f musc l e

mechanics. They sugges t t h e u s e o f a H i l l - t y p e muscle model,

c o m p r i s i n g a c o n t r a c t i l e component , a series e l a s t i c

component and a p a r a l l e l e las t ic component, i n a mathemat ica l

o r eiectr ical force p r o c e s s o r (see B o u i s s e t , 1973; H o f , 1984;

Chapman, 1985; Winte rs , 1985; and Zajac, 1 9 8 9 ) . B a s i c a l l y ,

t h r e e p a r a m e t e r s a s s o c i a t e d w i t h m u s c l e force, namely

a c t i v a t i o n , l e n g t h a n d c o n t r a c t i l e component v e l o c i t y , are

t h e r e q u i r e d i n p u t s t o t h e p r o c e s s o r and an estimate o f f o r c e

i s t h e o u t p u t . V a r i o u s a s s u m p t i o n s i n v o l v i n g t h e

r e l a t i o n s h i p s between EMG a n d muscle a c t i v a t i o n , j o i n t a n g l e

and muscle l e n g t h and j o i n t a n g u l a r v e l o c i t y and c o n t r a c t i l e

component v e l o c i t y are u t i l i z e d .

Chapman (1985) p r o v i d e s a t h o r o u g h r e v i e w o f t h e

l i t e r a t u r e r e g a r d i n g m u s c l e m e c h a n i c s , i n wh ich f o r c e -

a c t i v a t i o n , f o r c e - l e n g t h and f o r c e - v e l o c i t y r e l a t i o n s h i p s are

d i s c u s s e d . B a s i c a l l y , t h e greatest force t h a t a muscle can

produce o c c u r s when a c t i v a t i o n is maximal, l e n g t h i s o p t i m a l

( t y p i c a l l y n e a r t h e upper l i m i t of t h e p h y s i o l o g i c a l r a n g e )

and c o n t r a c t i l e component v e l o c i t y i s n e g a t i v e . An example

of s u c h a c o m b i n a t i o n i s i n a baseball p i t c h e r who

e x p e r i e n c e s ' s t r e t c h - s h o r t e n i n g c y c l e s " i n t h e m u s c l e s

c r o s s i n g the shoulder, e l b o w a n d w r i s t j o i n t s p r i o r t o

r e l e a s i n g a b a l l (Herr ing, 1 9 8 9 ) . S t r e t c h i n g a muscle p r i o r

t o c o n t r a c t i n g i t i n t h e d e s i r e d s h o r t e n i n g d i r e c t i o n

i n c r e a s e s the force i n t h e muscle. Figure 4 i l l u s t r a t e s the

zypes o f r e l a t i o n s h i p s required b y muscle model le rs f o r t h e

e s t i m a t i o n o f muscle f o r c e s .

b E M S -

f 0

Resting length Muscle length ---+.

Isometric Force Muscular j

force ' 1 \

I Maximum 0 Veiocity of shortening ---..

Figure 4 . Typica l r e l a t i o n s h i p s of muscle force t o a c t i v a t i o n (upper g raph) , length (middle graph) and c o n t r a c t i l e component v e l o c i t y flower graph) . (Graphs adapted E r ~ m Bouisset , 1973. )

Presently, muscle models are only capable of estimating

generalized muscle monents during s t a t i c contractions or slow

dynamic a c t i v i t i e s such as walking (Hof & van den Berg, 1978;

H o f & van den Berg, 1981a; Olney & Winter, 1985; and H o f ,

Pronk & van Best, 1987j. Results from the walking studies,

which demonstrated para l l e l s between estimated and calculated

(Inverse Dynamics Technique) moments, ind ica te t h a t t h i s

approach has promise fo r the future. However, H o f and van

den Berg (1981a), who have one of the most accepted of the

present muscle models, ind ica te t h a t t h e i r model i s not

su i table fo r determining muscle moments during f a s t dynamic

a c t i v i t i e s . This may be due t o problems i n determining

precise parameters associated with t he p roper t i es of the

con t r ac t i l e and s e r i e s e l a s t i c components (Hof & van den

Berg, 198la,b,c), It i s a l so possible t ha t the H i l l model i s

too simple, perhaps with an insuf f ic ien t representation of

muscle/tendon v i scos i ty , t o be used f o r f a s t dynamic

a c t i v i t i e s . The H i l l model, for example, i s insuff ic ient for

the determination of the "force-enhancement" caused by rapid

muscle s t re tch , which has been observed by Edman, Elzinga and

Noble (1978) i n stimulated i so la ted frog muscle f i b r e s and

Thomson and Chapman (1988) i n voluntarily maximally activated

human muscles.

The rapid effects of bal l -racquet forces on w r i s t

mus~ubiture occurring j u s t a f t e r impact i n tennis shots l i m i t

t h e u s e f u l n e s s o f p r e s e n t muscle models. F u r t h e r made1

deve lopment , as w e l l a s a s o l u t i o n t o t h e general

d i s t r i b u t i o n problem f o r t h e e x t e n s o r s and r a d i a l d e v i a t o r s

o f t h e w r i s t , i s r e q u i r e d b e f o r e such an approach can be

u t i l i z e d i n d e t e r m i n i n g t h e f o r c e s i n ECRB d u r i n g t h e

backhand t e n n i s s t r o k e . A r e c e n t a t t e m p t a t implementing

i n d i v i d u a l s y n e r g i s t i c and a n t a g o n i s t i c muscle models t o a

dynamic j o i n t a c t i o n i l l u s t r a t e s t h e g r e a t deal of

development t h a t i s r e q u i r e d (see Caldwell & Chapman, 1 9 8 9 ) .

3. Measurement of Parametexs Associated With ECRB Force

Even though an a c c u r a t e muscle model cannot p r e s e n t l y be

des igned for u s e i n t e n n i s elbow research , it would be u s e f u l

t o compare t h e pa ramete r s a s s o c i a t e d wi th ECRB muscle f o r c e

between n o v i c e and advanced t e n n i s p l a y e r s w h i l e h i t t i n g

backhand s h o t s . A g r o s s comparison o f muscle f o r c e s could be

m a d e between t h e d i f f e r e n t p l a y e r s based on t h e assumptions

t h a t i n c r e a s e d a c t i v a t i o n , l e n g t h and e c c e n t r i c v e l o c i t y a re

a s s o c i a t e d w i t h g r e a t e r f o r c e . T h i s in fo rmat ion cou ld be

u s e d as t h e basis of a p r e l i m i n a r y i n v e s t i g a t i o n of t h e

p o t e n t i a l force d i f f e r e n c e s between novice and advanced

t echn iques .

S i g n i f i c a n t force parameter d i f f e r e n c e s found i n t h i s

s t u d y could i n s p i r e future muscle rnodeiiers t o use improved

m o d e l s t o make m o r e p r e c i s e ECRB f o r c e compszisons. T h i s

would prove unnecessary i f either no significant force

parameter differences were found or a l l differences were

indicative of greater forces i n one of the groups of tennis

players. If , for example, novice players were found t o have

higher muscle ac t iv i t ies , greater muscle lengths m a greater

eccentric muscle velocities, then quantitative evidence would

f ina l ly ex i s t t o support the hypothesis tha t the leading

elbow backhand technique induces greater ECRB forces than the

classic advanced players' backhand technique.

a. Muscle Activation - Electromyography

Muscle activation can be observed by using techniques of

electromyography ( E M G ) . The e lec t r i ca l s ignal transmitted

along a muscle's f ibres when it is contracting ref lects the

neural excitation, or activation, of that muscle. Basically,

t h e more active a muscle is, the higher w i l l be the relat ive

amplitude and frequency of the muscle's e l e c t r i c a l signal

(Basm jian and De Luea, 1985) . This signal can be detected

by attaching surface electrodes t o the s k i n overlying the

muscle belly and, when processed i n an appropriate manner and

i f careful t o avoid cross-talk from neighbouring muscles, can

be correlated t o the relat ive level of act ivi ty of the muscle

(Winter, 1980 and Hof, 1984) .

Besides level of muscle activation, an EMG is dependant

on electrode s i ze and positioning. Basically, the smaller

t h e e l e c t r o d e s a r e and t h e c l o s e r t h e y a r e t o a c t i v e motor

u n i t s , t h e m o r e r e p r e s e n t a t i v e i s t h e EMG of a p a r t i c u l a r

m u s c l e ' s level o f a c t i v a t i o n . Also, s e l e c t i v i t y o f t h e

s i g n a l i s dependant on spac ing between b i p o l a r e l e c t r o d e s ,

wi th narrower spac ing i n c r e a s i n g s p e c i f i c i t y . Zipp (1982a,b)

and Basmajian and D e Luca (1985) provide g u i d e l i n e s regarding

t h e s i z e and p o s i t i o n i n g o f s u r f a c e e l e c t r o d e s on sma l l

muscles such a s ECRB. It i s recommended t h a t m i n i a t u r e

e l e c t r o d e s (less t h a n 5 mm i n d iameter ) should be placed on

t h e s k i n o v e r l y i n g t h e middle of t h e muscle b e l l y and t h e y

should be placed between 1 and 2 cen t ime t res a p a r t .

Var ious methods o f c o n v e r t i n g a raw EMG s i g n a l i n t o a

q u a n t i f i a b l e s i g n a l have been used by d i f f e r e n t r e s e a r c h e r s .

A p r a c t i c a l method commonly used i s t h e l i n e a r envelope .

T h i s i n v o l v e s smoothing of t h e r e c t i f i e d v e r s i o n of t h e raw

s i g n a l w i t h the u s e of a low-pass filter. E s s e n t i a l l y , a

s i g n a l i s produced which r e p r e s e n t s t h e ave rages of muscle

ac t iv i t i es o c c u r r i n g d u r i n g p a r t i c u l a r i n t e r v a l s o f t i m e .

The g r e a t e r i s t h e d e s i r e d s i g n a l smoothing, t h e greater i s

t h e t i m e i n t e r v a l used i n a v e r a g i n g t h e s i g n a l (Winter ,

1980).

Recen t ly , computer t echno logy h a s made it e a s i e r t o

p e r f o r m h i g h - s p e e d d i g i t a l f i l t e r i n g , i n v o l v i n g t h e

c a l c u l a t i o n of a t ime-varying n;oving ave rage wi th a window

s i z e o f approximately 25 mi l l i seconds , f o r t h e q u a n t i f i c a t i o n

r;f EMG s i g n a l s (Got t l ieb, Corcos & Agarwal, 1989) . A 25

mihlf isecond moving b v e r a g e l e a v e s t h e EMG s i g n a l f a i r l y

rough, b u t t h i s can he smoothed s u f f i c i e n t l y and i n a more

z e l i a b l e f a s h i o n by a v e r a g i n g a number o f t r i a l s , b e i n g

c a u t i o u s n o t t o i n d u c e f a t i g u e i n t h e s u b j e c t s ( C a l v e r t &

Chapman, 19771 . A sampling rate of 1000 Her t z i s a p p r o p r i a t e

fo r EMG d i g i t i z a t i o n because EMG s i g n a l s have t h e i r g r e a t e s t

power below 300 H e r t z (Shwedyk, Ba la sub raman ian & S c o t t ,

1977). T h i s ra te agrees w i t h t h e recommendation of Da in ty

and Norman (1987: p. 81) t h a t s i g n a l s s h o u l d be d i g i t i z e d a t

3 t o 4 t i m e s t h e h i g h e s t f requency o f i n t e r e s t .

I t s h o u l d be n o t e d t h a t t h e EMG s i g n a l r e c o r d e d from a

p e r s o n ' s muscle is unique t o t h a t muscle and t h a t p a r t i c u l a r

pe r son , so on its own it canno t b e u s e d f o r i n t e r - s u b j e c t

compar i son . T h i s p rob lem i s overcome b y q u a n t i f y i n g t h e

m u s c l e ' s EMG while the p e r s o n p e r f o r m s maximal v o l u n t a r y

c o n t r a c t i o n s (MVCs) u n d e r s p e c i f i c c o n t r a c t i o n c o n d i t i o n s

(Hof, 1984 and Basmajian & d e Luca, 19851. T h i s e n a b l e s t h e

q u a n t i f i c a t i o n o f d i f f e r e n t l e v e l s o f EMG as p e r c e n t a g e s o f

t h e p rede t e rmined MVC. Such p e r c e n t a g e s can t h e n be used f o r

i n t e r - s u b ject comparison.

I n a s s o c i a t i n g an EMG s i g n a l w i t h a muscle force i t i s

n e c e s s a r y t o i n c l u d e t h e t i m e d e l a y , known a s t h e

electromechanical delay (EMD) , b e t w e e n t h e m u s c l e ' s

a c t i v a t i o n a n d t h e ensuing produced f o r c e , T h i s c a n b e

e s t i m a t e d b y h a v i n g s u b j e c t s p e r f o r m f a s t i s o m e t r i c

c o n t r a c t i o n s a g a i n s t a f o r c e t r a n s d u c e r and measur ing t h o

t i m e d i f f e r e n c e between t h e o n s e t of EMG and t h e o n s e t of

f o r c e (Cor se r , 1974; R a l s t o n , Todd & Inman, 1 9 7 6 ; Norman &

Komi, 1979; and Winter , 1990) . The e s t i m a t e d EMD can then be

u s e d as a g u i d e f o r t h e s y n c h r o n i z a t i o n of EMG and muscle

force. A s l o n g as t h i s and o t h e r n e c e s s a r y steps a re t a k e n ,

EMG t e c h n i q u e s c a n j u s t i f i a b l y be u s e d t o q u a n t i f y ECRB

muscle a c t i v a t i o n and, t h u s , assist i n t h e e s t i m a t i o n of ECRR

f o r c e d u r i n g backhand t e n n i s s t r o k e s .

b. Muscle Length and Velocity - Electrugoniometry

The l e n g t h and v e l o c i t y o f a muscle , when a c t i v e , a r e

r e l a t e d r e s p e c t i v e l y t o t h e a n g u l a r d i sp l acemen t and v e l o c i t y

of t h e j o i n t t h a t it crosses. Youm, I r e l a n d , Spxague and

F l a t t (1976) showed t h a t t h e ECRB t endon of i n s e r t i o n does

n o t change s i g n i f i c a n t l y i t s p o s i t i o n w i t h r e s p e c t t o t h e

bones o f t h e hand i n d i f f e r e n t w r i s t p o s i t i o n s . T h i s implies

t h a t t h e t e n d o n s t r e t c h e s a round t h e w r i s t bones w i t h a

f a i r l y c o n s i s t e n t r a d i u s of c u r v a t u r e . Gr ieve , P h e a s m t a n d

Cavanagh (1978) s t u d i e d t h e r e l a t i o n s h i p between a n k l e joi .f t

a n g l e and t e n d o c a l c a n e o u s l e n g t h and found t h e re l a t i o n s h i.p

t o be l i n e & r - Armstrong and Cha f f in (1978) a l s o found a n e a r

l i n e a r r e l a t i o n s h i p between w r i s t j o i n t a n g l e and change i n

w r i s t f l e x o r tendon l e n g t h . S i n c e t h e w r i s t e x t e n s o r t endons

are s i m i l a r i n structure t o t h e w r i s t f l e x o r ter:c!.,ns, i t i s

assumed t h a t a n e a r l i n e a r r e l a t i o n s h i p e x i s t s between ECRB

m u s c l e l e n g t h and w r i s t acgie (i .e., t h e w r i s t bones f u n c t i o n

l i k e a p u l l e y fo r t h e ECRB t e n d o n o f i n s e r t i o n t o b e

s t r e t c h e d a r o u n d ) . The e x a c t r e l a t i o n s h i p i s n o t p r e s e n t l y

known, b u t it can be stated, a t least i n a basic sense , t h a t

ECRB l e n g t h e n s as t h e w r i s t f l e x e s and /o r u l n a r d e v i a t e s , i n

a n e a r l i n e a r f a s h i o n .

W r i s t a n g u l a r d i s p l a c e m e n t s i n t h e p l a n e s o f

f l e x i o n / e x t e n s i o n a n d u l n a r / r a d i a l d e v i a t i o n c a n most

d i r e c t l y and a c c u r a t e l y be measured w i t h a n e l e c t r o g o n i o m e t e r

(elgon) (Nico l , 198%) . T h i s is a n in s t rumen t which c o n v e r t s

a n g u l a r p o s i t i o n i n t o v o l t a g e . An e l g o n h a s r e c e n t l y been

des igned by N i c o l (1987) which i n c o r p o r a t e s a t h i n , f l e x i b l e

beam c o n t a i n i n g a number o f s t r a i n g a u g e s . A n g u l a r

d i sp l acemen t between t h e two ends o f t h e b e a m i s measured by

summing t h e s t r a i n s e x p e r i e n c e d b y t h e s t r a i n g a u g e s

t h r o u g h o u t t h e beam. T h i s l i g h t - w e i g h t e l g o n p r o v i d e s a

l i n e a r r e l a t i o n s h i p b e t w e e n v o l t a g e o u t p u t a n d a n g l e

sub tended a n d it a v o i d s many of t h e e r r o r s o u r c e s i n h e r e n t i n

e l g o n s o f t h e p a s t , such as s k i n movement and mala l ignment ,

which are i n c r e a s e d i n impac t s i t u a t i o n s , s u c h as h i t t i n g

t e n n i s b a l l s (Chao, 1978 and N i c o l , 1987, 1 9 8 9 a f b ) .

To o b t a i n wrist a n g u l a r v e l o c i t i e s , p r o p o r t i o n a l t o ECRB

v e l o c i t i e s , t h e a n g u l a r d i s p l a c e m e n t v e r s u s t i m e d a t a

p r o v i d e d b y the e l g o n c a n be d i f f e r e n t i a t e d u s i n g f i n i t e

differentiation. Smoothing, using t y p i c a l i y a f;.:lrt,h-oriicr ,

zero time lag Butterworth f i f t e r , is usuaily r e q ~ i r e d be t:>r t7

the bif ferentiation 5 s carried oat: (Elowling, 19B: s r t ~ 3 W i i i t c a r ,

1990). 1 is important to note that angular i - e i ~ z i t i t a ; :

determined in this manner are not always proportional to t kt\

velocities experienced by the contractile component %-*f g C K H ,

When rapid changes of muscle length occur in rcsp,irt:;t% r n

external. impact forces the initiel changes are but. rrc:;t Ly t

the series elasticity (i-e,, stretching af the s e r i e ~ rt ,r:;t i r .

component) of the muscle. There is a lag in time h e f o r e t . h t &

length of the contractile component is drast ica 1 ly a f f t ~ l - t ~ t - + i L i

due to its viscosity (Ford, Muxley h Simmons, 18'77) . T h i s

means that high angular velocities result in9 from v x t ~r n,t f

impact forces overestimate contract if e component vu t r r * c it is::>

initially.

The efectsrogoniometry approach can pxolvirje t hi=

information used in the estimaticn of ECRB l engt - t i d n d

velocity during backhand tennis strokes. Together wi r,h t.ht*

EMG data, this information can be used to make yxo:::;

estimates of ECRS muscle force. These estimates are l i m i t ~ p l

by the insufficient knowledge regarding the pr ec i c-

properties of ECRB, especially those r e l a t e d t n . r q u i c k

application of force. It is assumed, n o m t h e l e s z , t L a t t.hc.7

are a4eqiiate for gross comparison DeCween g r m ~ p s E i e n r r i s

players,

4 . B a s t A t t t m p t s at Measuring Parameters Associated W i t h ECRB Force During Backhand Tennis S t t o k e s

a. Muscle Activation

A few studies involving ENG have been performed which

kave pruvided3 qvalitative Indications about ECRB forces

d:srir;g the backhand tennis stroke CMcLaughlin & Miller, 1980;

' f ~ ~ s k i z a w a et af -, 1987; afid Morris, Jobe, Perry, Pink &

ffealjr, 1988) . Tne study by Morris et af. (1989) found t h a t

t,he ECRB musefes af advanced p laye r s were used t o over 60

iFK near impact during nornrzlk backhand strokes. It was also

f~ilrxd in this scudy chat ECRB was the only wrist extensor

muscle expressing high activity for a great proportion of the

stroke. Vnf~rtprnatefy, no camparison was made with novice

players , The study by Yoshisawa et af. (1987) did compare

navice and advanced players, and their results indicated

higher mirscufar activities in the ECRBs af novice players

than in those of advanced players. This finding, however,

should Itre considered with caution because over half of t h e

advanced subjects used the two-handed backhand technique, a

technique which undoubtedly reduces ECRB activity.

Although, t h e strrdy performed by McLaughlin and Miller

(1S;CPOf failed at its main objective of determining ECRB

tc~lccfion fasees, i t bib, at least, determine that the wrist

extensor mtzscfes ow the radial side, aamely ECREI and extensor

carpi radial is L O ~ Q P ~ S , exhibited near maxizal activities in

attempted t o determine differences bet ween n o ~ ~ i c e ,3nd

advanced t e c h n i q u e s , but to do this they on ly utilizied one

advanced p l a y e r , who hit backhand s h o t s w h i l e u s i n q h i s

normal, t e c h n i q u e its w e l l as a simulated l e a d i n g elbow

t e c h n i q u e . T h e validity of this approach is h i g h l y

q u e s t i o n a b l e because t h e accuracy of the s imula t ed technique

is u n c e r t a i n , I t is p o s s i b l e , f o r i n s t a n c e , that t h e

k i n e m a t i c s w e r e accurately s i m u l a t e d , but t h a t t h e muscle

a c t i v i t i e s used t o a c h i e v e the kinematics were very

inaccurate. A further problem w i t h t h i s study was t h a t post-

impact ba l l velocity was not contxolled, so the subject h i t

balls w i t h h i s normal s t r o k e with g r e a t e r v e l o c i t y t h a n h e

d i d w i t h t h e s i m u l a t e d s t r o k e . T h i s , a s McLaughlin and

HE11 er admi t t ed , i n v a l i d a t e d any cornpar ison between t h e t w o

types of strokes. HR sumi i ry , t h i s study had ctsrssiderable

p a t e n t i a l f o r leading t o a b e t t e r u n d e r s t a n d i n g of LE

etiology, but t h i s p o t e n t i a l cou ld no t be realized because o f

The need still exists t o compare EGRB m u s c l e ac t$vi t ie : j

during backhand s t r a k e s between novice and advanced p laye r s ,

More precisely, it uouhd be u s e f u l t o make this cr~rrty~arisori

bekwcen the leading eltow backhand technique used k2y m a s t

novice players an the c l a ~ s i c one-handed backhand technique

used by mast advanced players,

b. Muscle Length and Velocity

E e s i d e s d i f f e r e n c e s i n t h e a c t i v a t i o n o f ECRB, it i s

likely t h a t t h e r e are d i f f e r e n c e s i n w r i s t j o i n t k i n e m a t i c s

between nov ice and advanced t e n n i s p l a y e r s which af fect t h e

forces induced i n t h e ECRB t e n d o n . One s t u d y h a s l ooked

s p e c i f i c a l l y a t t h e k i n e m a t i c s o f a d v a n c e d b a c k h a n d

t e c h n i q u e s ( E l l i o t t e t a l . , 1989), b u t it a p p e a r s t h a t no

s t u d i e s have looked a t t h e k i n e m a t i c s of backhand t e c h n i q u e s

u sed by nov ice p l a y e r s . It i s e s s e n t i a l t h a t b o t h t y p e s o f

t e c h n i q u e s be ana lyzed , and t h e n compared, s o t h a t estimates

s f ECRB f o r c e d i f f e r e n c e s can be de te rmined .

Gene ra l d i f f e r e n c e s between t h e backhand t e c h n i q u e s o f

n o v i c e and advanced t e n n i s p l a y e r s have been n o t e d i n t h e

literaturet b u t the s p e c i f i c d i f f e r e n c e s associated w i t h ECRB

tendon f o r c e have not yet been a d e q u a t e l y q u a n t i f i e d . A more

complete a n a l y s i s of ECRB EMG a n d w r i s t j o i n t a n g u l a r

k i n e m a t i c s d u r i n g t h e backhand s t r o k e , s p e c i f i c a l l y comparing

t h e n o v i c e p l a y e r s e l e a d i n g e l b o w t e c h n i q u e w i t h t h e classic

a d v a n c e d p l a y e r s ' t e c h n i q u e , would p r o v i d e q u a n t i t a t i v e

e v i d e n c e t o implicate t h e r e l e v a n c e of p o o r backhand s t r o k e

t e c h n i q u e t o t h e e t i o l o g y o f LE,

Although the q u e s t i o n of p o o r backhand t e c h n i q u e b e i n g

an impor t an t f a c t o r i n LE e t i o l o g y for n o v i c e t e n n i s p l a y e r s

cannot be f u l l y answered until. a va l id estimate of ECRB

tendon force is made, the comparison of p a r a ~ + ~ r s associated

wi th t h i s f o r c e between novice and advanced techniques would

p r o v i d e some i n s i g h t i n t o t h e problem. I f s i g n i f i c a n t

d i f f e r e n c e s w e r e found between ECRB EMGs, w r i s t j o i n t a n g u l a r

d ispacements and /o r w r i s t j o i n t a n g u l a r v e l o c i t i e s , w h i c h

i n d i c a t e t h e p resence of g r e a t e r f o r c e s i n novice p l a y e r s ,

t h e n t h i s would suppor t t h e h y p o t h e s i s t h a t poor backhand

technique induces over loading of ECRB.

X I L , METNODS

A. Subjects

Twenty m a l e t e n n i s p l a y e r s , aged 1 8 t o 5 9 y e a r s ,

p a r t i c i p a t e d a s s u b j e c t s i n t h i s s t u d y . The Advanced Group

(mean a g e : 31 .1 y e a r s ) c o n s i s t e d of t e n p l a y e r s who

demons t ra ted c h a r a c t e r i s t i c s of t h e classic advanced p l a y e r s '

backhand t e c h n i q u e and the Novice Group (mean a g e : 2 8 . 5

y e a r s ) c o n s i s t e d o f t e n p l a y e r s who d e m o n s t r a t e d

c h a r a c t e r i s t i c s of t h e l e a d i n g e lbow backhand t e c h n i q u e .

D i s t i n c t k i n e m a t i c c h a r a c t e r i s t i c s w e r e u s e d b y a n

e x p e r i e n c e d p r o f e s s i o n a l t e n n i s i n s t r u c t o r , G e r r y Macken

( J e r i c h o T e n n i s Club, Vancouver , B r i t i s h C o l u m b i a ) , i n

d e t e r m i n i n g t h e s u i t a b i l i t y of t h e s u b j e c t s , Based on t h e

d e s c r i p t i o n i n t h e L i t e r a t u r e R e v i e w s e c t i o n of t h e c l a s s i c

advanced p l a y e r s ' t e chn ique , e a c h Advanced Group s u b j e c t was

r e q u i r e d t o d e m o n s t r a t e t h e f o l l o w i n g c h a r a c t e r i s t i c s :

c o m p l e t e w e i g h t t r a n s f e r , a d e q u a t e r o t a t i o n o f h i p s and

t r u n k , e lbow e x t e n d e d a n d p o i n t i n g t o w a r d s t h e g round a t

impac t , no e x t r a n e o l ~ s w r i s t motion, good t i m i n g , and complete

f a l l ow- th rough (Groppel , 1978; Douglas, 1982; Roy & I r v i n ,

1983; E l l i o t t e t ax-, 1989; and Macken, 1991) . Based on t h e

d e s c r i p t i o n i n t h e L i t e r a t u r e Review s e c t i o n o f t h e l e a d i n g

e l b o w t e c h n i q u e , each Novice Group s u b j e c t w a s r e q u i r e d t o

demonstrate the f o i l o w i n g : i n c o m p l e t e w e i g h t t r a n s f e r ,

i n s u f f i c i e n t h i p a n d t r u n k r o t a t i o n , e l b o w f l e x e d a n d

p o i n t i n g towards t h e n e t p r i o r t o impac t , e x c e s s i v e w r i s t

movement, p o o r t i m i n g , and l i m i t e d fo l low- through (Bernhang

e t a l . , 1974; N i r s c h l , 1975; Cohen, 1980; Roy & I r v i n , 1983;

Legwold , 1984 ; a n d Macken, 1 9 9 1 ) . A l t h o u g h t h e s e

c h a r a c t e r i s t i c s are q u a l i t a t i v e i n n a t u r e , t h e tennis

i n s t r u c t o r had no d i f f i c u l t y w i th s u b j e c t c l a s s i f i c a t i o n .

Most of t h e s u b j e c t s w e r e r e c r u i t e d from t e n n i s c l u b s i n

t h e Lower Mainland o f B r i t i s h Columbia. Not ices descr ib ing

t h e i n c l u s i o n a n d e x c l u s i o n c r i t e r i a of t h e s t u d y were p o s t e d

a t t h e s e l o c a t i o n s . P o t e n t i a l s u b j e c t s w e r e i n t e r v i e w e d

a b o u t t h e s e c r i t e r i a and, i f t h e y w e r e met, t h e i r backhand

t e c h n i q u e s w e r e r e c o r d e d on v i d e o . I f t h e i r t e c h n i q u e s were

deemed a p p r o p r i a t e b y t h e p r o f e s s i o n a l t e n n i s i n s t r u c t o r ,

t h e n e x p e r i m e n t a l s e s s i o n s w e r e a r r a n g e d . Informed consen t

w a s g i v e n i n w r i t i n g by a l l s u b j e c t s p r i o r t o p a r t i c i p a t i n g

i n t h e s t u d y .

Two o f t h e Novice s u b j e c t s had h i s t o r i e s of LE, b u t

tests w e r e carried o u t t o e n s u r e t h a t t h e y w e r e syaptom-free

a t the t i m e of e x p e r i m e n t a t i o n . The e x p e r i m e n t e r pushed

a g a i n s t t h e dorsum o f t h e i r dominant hands, which were made

i n t o f is ts , as t h e y a t t e m p t e d t o move f o r c e f u l l y i n t o

e x t e n s i o n , N o p a i n w a s expe r i enced e i t h e r d u r i n g t h e s e tests

sr upon palpation of the i r l a t e r a l e p i c o n d y l e s , so the

s u b j e c t s w e r e c o n s i d e r e d suitable fo r the s t u d y ( H o ~ p e n f e l d ,

1976 and S c h a f e r , 1987) . These s u b j e c t s a l s o indicated t h a t

t h e y had n o t improved t h e i r backhand t e c h n i q u e s s i n c e

a c q u i r i n g LE, so i t c o u l d b e assumed t h a t t h e n o v i c e

t e c h n i q u e s demons t r a t ed p r i o r t o p a r t i c i p a t i o n i n t h e s t u d y

were t h e same as t h o s e used when t h e y a c q u i r e d LE.

A c o n t r o l l e d v a r i a b l e i n t h i s s t u d y w a s w r i s t e x t e n s o r

s t r e n g t h . Isometric s t r e n g t h measurements w e r e made w i t h a

m o d i f i e d h a n d - g r i p dynamometer as shown i n F i g u r e 5 . A

v e l c r o s t r a p w a s a t t a c h e d t o t h e h a n d l e of t h e dynamometer

and p o s i t i o n e d around t h e s u b j e c t ' s c l enched dominant f i s t a

d i s t a n c e o f 8 c e n t i m e t r e s f rom t h e w r i s t j o i n t a x i s . The

s u b j e c t w a s r e q u i r e d t o push maximally a g a i n s t t h e s t r a p i n

w r i s t e x t e n s i o n . The forearm w a s h e l d down by t h e tes ter t o

p r e v e n t unwanted elbow and s h o u l d e r movements. The h i g h e s t

moment measurement from three t r i a l s w a s u sed as t h e measure

of s t r e n g t h . The r a n g e o f w r i s t e x t e n s o r s t r e n g t h s for t h e

s u b j e c t s w a s 1 6 . 5 t o 21 .2 Newton-metres, t h e Novice Group

w i t h a mean of 18.0 Newton-metres and t h e Advanced Group wi th

a mean o f 18.9 Newton-metres (no s i g n i f i c a n t d i f f e r e n c e : p =

0.250) . The s u b j e c t s w e r e r e q u i r e d t o have s t r e n g t h v a l u e s

w i t h i n the r a n g e of p l u s and minus one s t a n d a r d d e v i a t i o n

from t h e mean s t r e n g t h o f a g r o u p o f f o r t y h e a l t h y m a l e

t e n n i s p l a y e r s p r e v i o u s l y t e s t e d by he i n v e s t i g a t o r (mean :

19.4 Newton-metres; s t a n d a r d d e v i a t i o n : 3 . 2 Newton-metres) . The dynamometer w a s calibrated w i t h w e i g h t s s i m i l a r t o t h e

r e s i s t a n c e forces produced by t h e s u b j e c t s .

Figure 5. Measurement of wrist extensor strength using a modified hand-grip dynamometer.

B, Experimental Set-up and Task

The main experiment involved t h e s u b j e c t hitting flat

backhand tennis drives in a labora tory s e t t i n g (Biomechanics

L a b - Simon F r a s e r U n i v e r s i t y , School. o f K i n e s i o l o g y ) . F i g u r e 5 i l l u s t r a t e s a s u b j e c t pe r fo rming t h i s t a s k i n t h e

e x p e r i m e n t a l test c o n d i t i o n . A b a l l was fed t o t h e s u b j e c t

by b e i n g r o l l e d down a descend ing c h u t e . A f t e r l e a v i n g t h e

c h u t e , t h e b a l l bounced o f f t h e f l o o r and t r a v e l l e d l i k e a

p r o j e c t i l e t o w a r d s t h e s u b j e c t , who t h e n s t r u c k it back

towards a target on a l a r g e n e t . Al though t h i s s e t - u p w a s

c o n s i d e r a b l y d i f f e r e n t t h a n t h a t on a t e n n i s c o u r t i n a game

s i t u a t i o n , it w a s assumed t h a t t h e s u b j e c t ' s s t r o k e t e c h n i q u e

w a s n o t s i g n i f i c a n t l y d i f f e r e n t . T h i s a s s u m p t i o n was

q u a l i t a t i v e l y validated by h a v i n g t he p r o f e s s i o n a l t e n n i s

i n s t r u c t o r compare v i d e o s o f v a r i o u s s u b j e c t s h i t t i n g

backhands on a t e n n i s c o u r t w i t h t h o s e i n t h e e x p e r i m e n t a l

t e s t c o n d i t i o n . H e i n d i c a t e d t h a t b a s i c s t r o k e

p a t t e r n s w e r e s i m i l a r . Fur thermore, the s u b j e c t s w e r e g iven

ample p r a c t i c e t i m e i n t h e l ab s o t h a t t h e y c o u l d become

comfor t ab l e w i t h t h e expe r imen ta l se t -up .

Figure 6. Experimental set-up (photograph above and schematic diagram below).

S i n c e t h i s s t u d y was d e s i g n e d t o compare d i f f e r e n t

backhand t e c h n i q u e s u sed by d i f f e r e n t t e n n i s p l a y e r s , t h e

t a s k was i d e n t i c a l f o r a l l s u b j e c t s . T h e r e f o r e , b o t h

e x t e r n a l i n p u t and o u t p u t w e r e c o n t r o l l e d . I n t e r m s o f t h e

t e n n i s s h o t , b a l l s w e r e f e d t o t h e s u b j e c t s w i t h a c o n t r o l l e d

v e l o c i t y and p o s i t i o n a n d t h e b a l l s w e r e r e t u r n e d b y t h e

s u b j e c t s w i t h a c o n t r o l l e d v e l o c i t y and p o s i t i o n . Although

l i t e r a t u r e s u g g e s t s tha t b a l l p o s i t i o n i n g on the r a c q u e t a t

impact may p l a y a r o l e i n c r e a t i n g h i g h stresses i n t h e w r i s t

e x t e n s o r s (P lagenhoef , 1979), t h i s w a s n o t measured i n t h e

p r e s e n t s tudy . I t is assumed t h a t b a l l p o s i t i o n w a s s i m i l a r

fo r t h e d i f f e r e n t s u b j e c t s s i n c e b a l l i n p u t and o u t p u t w e r e

k e p t c o n s t a n t . Any d i f f e r e n c e s found i n the musc le f o r c e

p a r a m e t e r s are assumed t o b e r e f l e c t i v e of d i f f e r e n t ways i n

which t h e r a c q u e t w a s swung by t h e d i f f e r e n t s u b j e c t s .

The i n c o m i n g h o r i z o n t a l b a l l v e l o c i t y w a s 3

met res / second . T h i s w a s c o n t r o l l e d by r o l l i n g ba l l s down t h e

c h u t e from a f i x e d h e i g h t . S i n c e t h e c h u t e w a s i n a f i x e d

locat ion , b a l l p o s i t i o n i n g was also c o n t r o l l e d . The s u b j e c t

w a s n o t r e q u i r e d t o per form e x c e s s i v e amounts of footwork i n

t h i s e x p e r i m e n t d u e t o t h e c o n t r o l l e d b a l l p o s i t i o n i n g .

A l s o , t h e s u b j e c t was a l l o w e d t o c o n t a c t t h e b a l l s a t h i s

p r e f e r r e d impact h e i g h t . T h i s removed any v a r i a b i l i t y t h a t

may have been c a u s e d by t h e d i f f e r e n t h e i g h t s o f t h e

s u b j e c t s .

The subject was required t o h i t a t a r g e t w i t h the b a l l .

Only those t r i a l s i n which t h e b a l l h i t t he t a r g e t were

counted a s successful t r i a l s . Post-impact b a l l veloci ty was

ca lcula ted by measuring tire time between impact and contact

with t h e t a r g e t and dividing t h i s i n t o the dis tance between

t h e point of impact and t h e t a r g e t . The time period was

measured by taking t h e difference between the sound of ba l l -

racquet contact and t h e sound of b a l l - t a r g e t contac t , a s

detected by a microphone and displayed on an oscil loscope. A

t y p i c a l d is tance between racquet and t a r g e t a t t h e time of

impact was 3 . 5 metres and the corresponding time d i f f e r ence

between impact and t a r g e t contact was about 0 . I 4 seconds,

This would be equated t o a b a l l - r e t u r n v e l o c i t y of 2 5

metres/second. A success range fo r v e l o c i t i e s was chosen t o

be between 20 and 30 metres/second, based on p i l o t s tudies

involving both advanced and novice players . T h e two groups

of subjec ts had very s imi la r means, 24-75 metres/second f o r

t h e Advanced Group and 2 4 . 5 5 metres/second f o r t h e Novice

Group (no s i cp i f i can t dif ference: p = 0.823).

A l l s u b j e c t s used t h e same t e n n i s racquet for t h e

experimental t r i a l s . I t was a mid-sized, graphic composite

Fischer Vacuum Twintechnic racquet w i t h s t r i n g tension s e t a t

60 pounds. Grip s i z e was matched t o the sub jec t ' s hand s i z e

by changing the number of g r i p wraps applied t o t h e handle.

Two g r i p s izes , 4 1/2 inches and 4 5/8 inches, were s u i t a b l e

for small and la rge hands, respect ively . A l l subjects

indicated tha t they had no problems adjusting f r o m t h e i r own

racquets t o the experimental one.

Tennis b a l l s were a l so controlled by having a t l e a s t

twenty d i f f e r e n t b a l l s a v a i l a b l e f o r each s u b j e c t ' s

experimental session t h a t were t e s t e d f o r t h e i r bounce

character is t ics . Prior t o use, each b a l l was rol led down the

c h u t e and was only deemed usable i f it bounced in to a box (25

centimetres wide, 2 9 centimetres long and 2 3 centimetres

deep) positioned on the f loor just past the impact zone.

C . Analysis Period

Pi lo t s tudies performed by t h e invest igator showed tha t

racquet movement during a typica l backhand shot l a s t s between

0.5 and 1 . 0 seconds and ECRB EMG can l a s t up t o about 1 . 5

seconds. To be sure t o capture a l l of the :.ubjects8 ECRB

EMGs during the experiments, 2 . 0 seconds were analyzed, 1 . 0

seconds pr ior t o and 1 .0 seconds a f t e r impact. 3.0 seconds

of data were captured from which the relevant 2 . 0 seconds

were ex t rac ted . T h e t e s t e r was adequately t r a ined a+,

i n i t i a t i n g the data co l lec t ion approximately 1 . 5 seconds

pr ior t o impact for each t r i a l .

Impact time was determineb by looking f o r an abrupt

change in voltage of a microphone s ignal . A microphone was

placed a t a speci f ic distance away from the posit ion of bal l -

r a c q u e t c o n t a c t t o d e t e c t t h e sound of izpact. v2 * , EIP ~ i " t i : i i l

d e l a y w a s c a l c u l a t e d u s i n g the c o n s t a n t 340 n e t r e s h s e c n d fQr

t h e speed of sound i n a i r a t room t e m p e r a t u r e . 3 ; 1 Z: :st

EMG and e l g o n , w e r e s y n c h r o n i z e d t o t h e estimated 1 i n i t :

impact.

F o r a n a l y s i s pu rposes the t i m e o f impact was ccnsiiier-ci-3

t o o c c u r i n the m i d d l e of the s t r o k e , a t 1 . 0 scconln:;. The.

s t r o k e was divided into a P r e p a r a t i o n Phase ( t? . t : tu ~ t . 8

seconds ) , a Movement Phase c e n t r e d a round impact (f; . R t * ~ 1 . l '

s e conds ) and a R e c o v e r y Phase ( 1 . 2 t o 2 . 0 seconds) . Tfic.::rh

t i m e s co r r e sponded w i t h d i s t i n c t changes observed i n t h e EM;;

p a t t e r n s o f a l l s u b j e c t s (see Results section).

D. ECRB Activation - Electromyography

The s u b j e c t ' s ECRB musc le activity was quafit if ied by

using techniques of EMG. F i r s t l y , the invest i g a t o x 1ncat.ed

the ECRB muscle belly by hawing t h e subject perform w r i z t -

extensor c o n t r a c t i a n s a n d t h e n p a l p a t i n g dhc 3ppr.r

posterolateraf. region of the forearm. Then, h a i r t jverlyincj

the muscle was shaved and t h e u n d e r l y i n g skin was abraded a r ~ d

c l e a n e d w i t h a s c o u r i n g pad and e t h a n o l , respersL igrr.3 y - 'i"h i::

w a s performed in order to decrease the r e s i ~ t a r . 2 ~ nc;rf,sz:

w h i c h the muscle' s e l e c t r i c a l . signal travellei, f.:li:iXa*.. u r e

silver-sif verhrh4.0ride bipolar surface elect rr,df:s I i s eckman ,

2.5 millimetres in d i a m e t e r ) , w i t h electrode gel s p p l i e f ~ LC,

t ? ~ i r S ~ J Z ~ ~ G F L S , were attached above t h e muscle b e l l y with

d5;kfe-si3ed acResive calfars and zeffophane tape. A l s o , an

eLast-,ir: tensor bandage w a s wrapped loosely around the

elecErodes i n order t o prevent excessive s k i n movement ( F - e . ,

tfi keep then i n a fairly const n t position relative t o t h e

u n d e r l y i n g muscle fibres} , The electrodes were placed near

the middle of t h e ECRB muscle bel ly , 1.5 centimetres apart

(kept constant, kiy sricking the two adhesive collars together

and identically for each subject). A ground electrode was

placed a t t h e d i s t a l end of the anter ior aspect of the

farearm for the safety of the subject.

Testing was carried out t o ensure that the signal was

representative of ECRB acltivity i l . , electrode positioning

was corxect]. Gredkest EMG levels were obtained when the

subject performed centractions in the direct ions of w r i s t

extension a n d radial deviation. The signal was increased

further by clenching the f i s t ,

The r a w signal picked u p by the electrodes was amplified

by a TECA -6 MIXI A.C. amplifier (input impedance: > 100

megaohms r"J 15 picofarads; cornon mode rejection ratio: >

TG, Oill'G.-f at 60 H c e n z ) , before being converted t o a d i g i t a l

s i g n a l by a Labcard 12-bit analog-to-digital board

cant roEled Sy a-s; IEH-i=oihi~>at ibh AT 286 personal computer.

'The input range ~ b i f ~ the analog-to-digital board was sf- 2 .5

WJ~: '= .S , ~ s 3 amplification was s e t t o give values optimally

w i t h i n t h i s range. Frequencies between 27 and 535 Hertz were

passed through the azpfifier, as controlled by t h e hkqh- and

low-pass f ifters of the amp1 if ier, respectively . (Prec i se -3

decibel cut-offs were determined with a signal generatcw by

the investigator.) The r e s u l t i n g signal was digitized aL a

sampling rate of 1Q00 Hertz. Power spectral density

functions of raw EMG signals in experimental condit-ions were

calculated by the investigator prior to selecting the f i l t p r

cut-offs and sampling rate, No signal power above 300 H e r t z

existed in the experimental conditions, in accordance with

the results of Shwedyk et al. (1977), so the filter cut-offs

and sampling rate were deemed appropriate- The raw EMG d a t a

were stored on disk for later quantification a n d analysis,

Two steps were involved in the processing of the raw EMC

s ignal for quantification purposes. Firstly, it w a s f t l l l-

wave rectified by computing absolute values of the digitized

data points. Secondly, a moving average, using a twenty- f ' i vet

millisecond window, was calculated, This methad was c t ~ c ~ s c h n

an the basis of techniques used by Gottlieb- et aX. (Z989r4) arid

pifat studies perfos~ed by the i n v e s t i g a t s x . The size r;if the

moving average window was selected subjectively c r ~ the b a s i s

that it parawided the greatest amount of sigria P. s m m t h i n g

without causing serious dis tor t i cx . No tiee lag was prodbced

by this pxocedure,

".? ,fie subject had h i s maximal ECRB a c t i v i t y e s t i m a t e d so

t h a t fieasured EMGs d u r i n g t h e exper iments c o u l d be q u a n t i f i e d

~ i t h respect t o this maximal v a l u e . T h i s was c a r r i e d o u t b y

hav ing ehe subject per form maximal v o l u n t a r y w r i s t e x t e n s i o n s

i s o r n e t s i c a l l y a g a i n s t r e s i s t a n c e . A padded hand le , a l i g n e d

k o x i z c m t a l l y , w a s u sed as t h e means of p r o v i d i n g r e s i s t a n c e

a g a i n s t a n upward push w i t h t h e dorsum of t h e hand ( s e e

Figure 7 ) . The subject had h i s forearm s e c u r e d h o r i z o n t a l l y

i n the rnidprane p o s i t i o n a n d h i s w r i s t i n t h e n e u t r a l

p o s i t i o n . These forearm and w r i s t p o s i t i o n s w e r e c o n s i d e r e d

hest because they could be e a s i l y c o n t r o l l e d and t h e y a r e

similar t o those u s e d i n t e n n i s backhand s t r o k e s . The

s u b j e c t w a s also required t o c l e n c h h i s f i s t maximal ly t o

simulate t h e muscle a c t i v i t y i n v o l v e d i n t i g h t l y g r i p p i n g a

tennis r a c q u e t .

Each maximal voluntary c o n t r a c t i o n (kliCS trial i n v o l v e d

t h e subject clenching his fist and push ing upwards as h a r d as

possible for a b o u t 3 s e c o n d s . Verbal encouragement w a s

provided by t h e tester. The raximal q u a n t i f i e d v a l u e d u r i n g

the 3 seconds of data was r eco rded .

Figure 7. Set-up used for MVC and EPSD tests.

This procedure was carried out six rimes, leaving ample

periods of rest (approximately 1 minute) between trials in ari

effort to avoid fatigue. Three measurements were t a k e n

before the main experimental trials and three after to

account for any fatigue that might have resulted from t h e

experimental t r i a l s , The average of the three highest values

from these s i x measurements was considered zo te I W l S .

The: Iswest three values w e r e not cortsidc-red kx:r=au:-;e crf

potential problems in naat ivating the subject to con: r&rr hi s

muscles rnaxima1l.y every t i m e . An average ~f tk:r_i C i : ~ e c :

h i g h e s t values was c h ~ s e n as t h e f inal , s t ep , s o that

smmthing biases created during the ca lcula t ion of moving

averages c ~ u l d be limited.

For the experimental t r i a l s , the a c t i v i t y of ECRB a t

each sampled point i n time was measured and given as a

percentage of the MVC. T h i s provided the means for assessing

the quantity of ECRB muscle ac t iv i ty , as w e l l a s performing

intersubject comparisons.

An additional s tep i n quantifying ECRB a c t i v i t y was the

ca lcula t ion of electromechanical delay (EMD). This w a s

carr ied out w i t h a procedure s imilar t o t h a t used i n t h e MVC

t e s t . A strain-gauge at tached t o t h e res i s tance handle,

unpadded i n t h i s case, provided t h e needed measure of force

production ( s ee Figure 7 ) . Five r a p i d l y developed,

submaximal isometric cantract ions against t h e handle were

u s e d i n determining the Ef4D. Time difference between EMG

onset and force onset w a s measured on a d i g i t a l oscilloscope.

The average of the measured values f r o m the f i v e t r i a l s was

used as the E m , T h i s could then be used t o synchronize the

EHC data w i t h t h e elgon data, when estimating ZCRB forces, by

simply moving each EMG data point forward i n t i m e by an

amowt equal to the EMD. Ems for subjects i n t h i s study

ranged from 10-5 te 25.1 milliseconds, w i t h a mean uf 18.2

mi EPisecsnds ,

E. Wrist Joint Angular Kinematics - Electrogoniometry

W r i s t j o i n t a n g u l a r d i s p i a c e m e n t s i n the planes of

f l e x i o n / e x t e n s i o n a n d r a d i a l / u l n a r d e v i a t i o n were measured

d i r e c t l y w i t h a Penny & G i l e s MllO twin-ax is e l g o n . The t w o

end b l o c k s of the e l g o n were a t t a c h e d t o t h e posterior aspect

of t h e s u b j e c t ' s hand ( above t h e t h i r d metacarpal) and

forearm (between t h e r a d i u s and u l n a ) . S i n g l e - a n d d o u b l e -

s i d e d tape w e r e u s e d t o s e c u r e t h e endb locks t o t h e s k i n .

They w e r e p o s i t i o n e d i n l i n e w i t h t h e l o n g i t u d i n a l h a n d ana

forearm a x e s w h i l e t h e f o r e a r m was h e l d i n t h e midprane

p o s i t i o n . C a l i b r a t i o n of t h e n e u t r a l . w r i s t pos i . t ion ( 0

degrees i n b o t h t h e f l e x i o n / e x t e n s i o n and ulnar/radial

d e v i a t i o n p l a n e s ) was c a r r i e d o u t by r e c o r d i n g e l g o n d a t a

w h i l e t h e s u b j e c t h e l d h i s forearm, midprone, and hand, palm

down, i n a s p e c i f i c l o c a t i o n a n a t a b l e a t a h e i g h t l e v e l

w i t h h i s s h o u l d e r (see F i g u r e 8 ) . A l l a n g l e s w e r e r e f e r e n c e d

t o their r e s p e c t i v e z e r o - c a l i b r a t i o n v a l u e s .

The voltage o u t p u t s of t h e e l g o n w e r e d i g i t i z e d with a

Penny & G i l e s DL1001 "data logge r f* a t a ra te o f 1000 H e r t z

a n d stored on disk for l a t e r a n a l y s i s . T h i s sampling r a t e

w a s deewed appropriate b e c a u s e i t i s fast enough t o

fac i l i t a te the c a p t u r e o f an a d e q u a t e number of da ta p c i n t s

during t h e 4 t o 8 m i l l i s e c o n d impac t period of a t e n n i s

stroke (Bernhang et a l . , I974 and Hatze, 197€j. it was

desirable to determine, within 1 millisecond, when impact

occurred.

Figure 8 . Electrogoniometer calibration.

The accuracy and precision of the elgon was estimated by

attaching it to a manual goniometer and making repeated

measurements at known acgles within the range of +/- 60

degrees for each plane of motion. This range encompassed the

angular deviations observed in the experimental trials (see

Results section). E i v e randomly positioned measurements were

made a t each angle corresponding t o a multiple of 15 degrees.

The mean e r r o r i n the flexion/extension plane was 2 . 2 1

degrees w i t h a mean standard deviation of 0 . 1 0 degrees,

whereas the mean e r ro r in the u lnar / radia i deviation p l a n e

was 0.44 degrees w i t h a standard deviation of 0 . 2 2 degrees.

These respect ive accuracy and precis ion estimations wexe

considered acceptable fo r the purposes of t h i s study.

W r i s t angular v e l o c i t i e s were ca lcula ted by finite

d i f f e r e n t i a t i o n of angular displacements. Smoothing of

displacements was requ i red p r i o r t o performing these

ca lcu la t ions , so t h e 'separation" technique described by

Dowling (1987) was u ~ e d . The displacement data were first

reduced i n frequency from 1000 Hertz t o 200 H e r t z b y

s e l e c t i n g every f i f t h da ta point , inc luding t h e ones

occarring a t 0.0, 1.0 (impact) and 2.0 seconds. Then, a

d i g i t a l fourth order, zero time lag Butterworth filter (low-

pass frequency 10 Hertz) was implemented w i t h the computer.

This was followed by the reinsert ion of the raw data points

corresponding t o the time period between 50 milliseconds

before and 50 milliseconds a f t e r impact. Finally, a second

four th order, zero time lag Butterworth filter (low-pass

frequency 4 5 Hertz) was implemented. T h i s technique was

determined t o be most appropr ia te from pilot s t u d i e s

performed by the Inves t iga tor , f o r smoothing data which

includes sharp changes in angular displacement such as those

~ c c u z r r i n g just a f t e r impact (see Results sec t ion) . I t w a s

a l s o used by Knudson (1990) f o r smoothing angular

displacement data of forehand tennis strokes.

F. Experimeataf Protocol

After a brief explanation of the experiments and having

the subject sign the informed consent form, the subject was

required t o perform a few minutes of s tretching exercises

w i t h t h e w r i s t of the dominant hand. After the subject f e l t

ready approximately f i f t y ba l l s were fed t o h i s backhand so

that he could slowly warm up and get comfortable w i t h the

experimental task and set-up. When the subject indicated

that he was w a r m and comfortable, the measurement of wrist

extensor strength was carr ied out. After t h i s the EMG

electrodes were attached. The subject was then required t o

h i t approximately f i f t y more warm-up shots w i t h the

electrodes i n piace. The reason for t h i s was tha t it was

desirable t o have the ECRB muscle warm while performing the

EMD and MVC experiments, comparable t o i t s temperature during

the main experiment. The f i v e EMD t r i a l s , followed by the

f irst three MVC t r i a l s , were then carr ied out. Then the

efgan w a s mounted and calibrated.

After everything fo r measurement purposes was attached

to the subject 's a r m and calibrated, the main experimental

t r i a l s w e r e in i t ia ted , Each t r i a l , or backhand shot, lasted

approx ima te ly f o r t y - f i v e seconds due t o t h e l e n g t h of time it

t o o k f o r t h e computer t o d i g i t i z e t h e c o l l e c t e d EMG data.

The s u b j e c t c o n t i n u e d t o h i t backhand s h o t s u n t i l twenty

s u c c e s s f u l t r i a l s e . , b a l l h i t t i n g t a r g e t and output

v e l o c i t y w i t h i n t h e c o n t r o l l e d range) w e r e accomplished. The

f i r s t f i f t e e n of t h e s e t h a t p roved a d e q u a t e f o r a n a l y s i s

pu rposes w e r e u sed i n t h e expe r imen ta l a n a l y s i s . The reason

t h a t f i v e e x t r a t r i a l s w e r e r e q u i r e d i s t h a t s o m e t r i a l s

c o u l d b e deemed i n a p p r o p r i a t e because of e i t h e r microphone

s i g n a l a m b i g u i t i e s or human errors i n d a t a a c q u i s i t i o n . The

number o f t r i a l s w a s chosen on t h e b a s i s o f variability shown

i n p i l o t s t u d i e s , The a v e r a g e of t e n t r i a l s was

u n r e p r e s e n t a t i v e of a s u b j e c t ' s s t r o k e t echn ique , whereas t h e

a v e r a g e of t w e n t y t r i a l s w a s no more r e p r e s e n t a t i v e t han t h e

average of f i f t e e n t r ia l s , i n t e r m s o f b o t h EMG and e lgon

data. T h i s number w a s a l so s u i t a b l e f o r t h e avo idance of

f a t i g u e . To accompl i sh twen ty s u c c e s s f u l t r i a l s t h e s u b j e c t

t y p i c a l l y had t o per form between t h i r t y and f o r t y attempted

t r i a l s . A l s o , t h e s u b j e c t per formed t w o o r three p rac t i ce

s h o t s between e a c h t r i a l i n order t o m a i n t a i n stroke rhythm.

A f t e r t w e n t y s u c c e s s f u l t r i a l s w e r e completed t h e e lgvr i

w a s removed so tha t t h e f i n a l t h r e e MVC trials could he

c a r r i e d o u t , This b e i n g t h e las t s t e p , t h e EMG electrodes

w e r e then resoved azid the snbject w a s able to t iash t h e

e l e c t r o d e g e l from h i s fo rearm. Each s u b jectr s expe r imen ta l

s e s s i o n lasted between two and a h a l f and t h r e e h o u r s .

G . Data Analysis

F i v e main t i m e - v a r y i n g p a r a m e t e r s i n v o l v e d i n t h e

backhand t e n n i s s t r o k e w e r e a n a l y z e d i n t h i s s t u d y . They

w e r e ECRB EMG ( t i m e - l a g c o r r e c t e d w i t h t he E M D ) , w r i s t

f l e x i o n a n g u l a r d i s ~ l a c e m e n t , w r i s t u l n a r d e v i a t i o n a n g u l a r

d i sp l acemen t , w r i s t f l e x i o n a n g u l a r v e l o c i t y and w r i s t u l n a r

d e v i a t i o n a n g u l a r v e l o c i t y . The f l e x i o n a n d u l n a r d e v i a t i o n

d i r e c t i o n s w e r e chosen as p o s i t i v e because t h e y co r r e spond t o

i n c r e a s e d ECRB muscle l e n g t h and e c c e n t r i c ECRB c o n t r a c t i o n

v e l o c i t y , b o t h r e l a t e d t o i n c r e a s e d f o r c e . T h i s makes it

r e l a t i v e l y e a s y f o r t h e r e a d e r t o look a t g r a p h i c d i s p l a y s o f

t h e t ime-va ry ing d a t a and associate h i g h e r v a l u e s on any o f

t h e g raphs w i t h p o t e n t i a l l y g r e a t e r f o r c e s ,

F o r each p o i n t i n t i m e d u r i n g t h e t w o s econd a q a l y s i s

p e r i o d , t h e t ime-vary ing pa rame te r s w e r e averaged amongst t h e

f i f t e e n t r i a l s of e a c h s u b j e c t . These averages w e r e assumed

t o b e r e p r e s e n t a t i v e o f the s u b j e c t ' s s t r o k e , The s i g n a l s

were s u b s e q u e n t l y r educed f r o m 1000 H e r t z t o 200 H e r t z by

s e l e c t i n g e v e r y fifth data p o i n t , i n c l u d i n g t h e o n e s

o c c u r r i n g a t 0.0, 1 - 0 ( impac t ) and 2 .0 seconds .

M u l t i p l e t w o - w a y a n a l y s e s of v a r i a n c e w i t h r e p e a t e d

measures w e r e p e r f o r m e d on t h e t i m e - v a r y i n g g r o u p aa t a .

63

Group differences and group-time in terac t ion e f f ec t s were

t e s t e d f i r s t l y f o r t he Preparation Phase ( 0 . 0 t o 0 . 8

seconds), the Movement Phase ( 0 . 8 t o 1 . 2 seconds) a n d t h e

Recovery Phase ( 1 . 2 t o 2 . 0 seconds) . Further divisions w e r e

made when necessary i n order t o determine more speci f ica l ly

when s igni f icant group differences occurred. The 0 . 0 5 l e v e l

of s igni f icance was used i n the t e s t i n g process a n d the

Huynh-Feldt adjustment was made t o account for group variance

and covariance differences.

r t i s important t o note tha t the time-varying parameters

a r e a l l associated w i t h muscle force, so they cannot validly

be assessed separa te ly when making force est imates. F o r

example, markedly d i f f e r e n t angular displacements and

ve loc i t i es do not indicate a difference i n force i f E M G s a t

the same time are zero. For t h i s reason, the parameters were

only i n i t i a l l y compared separately. The ultimate comparison

i n t h i s study involved a more qua l i t a t ive assessment of a l l

of the parameters together.

Two add i t i ona l parameters compared between t h e two

subject groups were maximal ECRB EMG and t o t a l ECRB ENG-time

in t eg ra l . Averages of these parameters from each subject ' s

f i f t e e n t r i a l s were ca l cu l a t ed . These d i sc re te EMG

parameters were analyzed i n addition t o the t imevarying EMG

parameter i n order t o determine more speci f ica l ly differ- price^

between the EMGs of the two subject groups. If maximal EMGs

occurred a t d i f f e r e n t times fo r the d i f f e r e n t subjects i n a

grcup, then t he average maximal EMG determined f o r the group

(time-varying EMG parameter) would not be s u f f i c i e n t f o r

group comparison of EMG. This would only correspond t o the

average value a t a s p e c i f i c time when a l l s u b j e c t s had

r e l a t i v e l y high E M G s , not a t t h e times t h a t a l l subjects '

EMGs were maximal. Comparison of maximal E M G s ( i r r e spec t ive

of time) between groups was considered bes t f o r t h i s purpose.

O f n o t e i s the f a c t t h a t the average of the d i s c r e t e maximal

EMG values fo r subjects i n a spec i f i c group i s always higher

than t h e maximal value from the group's average time-varying

EMGs. Total ECRB EMG-time i n t e g r a l s were a l s o compared

between groups i n order t o achieve an overa l l representat ion

of EMG d i f f e r e n c e s during t h e backhand s t r o k e . I t was

suggested t h a t t h i s comparison might l ead t o implicat ions

regarding ECRB f a t igue caused by the backhand t e n n i s s t roke .

The means of t h e s e d i s c r e t e EMG parameters were compared

between groups using two-tailed t - t e s t s .

The analyses were c a r r i e d out f o r t h e most p a r t w i t h a

s i g n a l a n a l y s i s s o f t w a r e package (DSP Development

Corporat ion : DADiSP 1.05) i n combination with computer

programs w r i t t e n by t h e i n v e s t i g a t o r . Simon F r a s e r

Universi ty mainframe (UNIX: SAS 6 . 0 3 ) and personal computer

s t a t i s t i c a l software packages were a l s o u t i l i z e d .

H. E t h i c s Approval

The e x p e r i m e n t a l p r o t o c o l for t h i s s tu t - iy w a s e t h i e a l 1 ) -

approved by t h e U n i v e r s i t y Ethics R e v i e w C o r m i t t e e a~ S i ~ n o r r

F r a s e r U n i v e r s i t y . There w e r e minor risks in.cvoi.c-ed, mi:s t

notably w i t h t h e a d n i n i s t r a t i o n of EMG, bur t h e y w e r c i n o t

deemed s i g n i f i c a n t by t h e c o m m i t t e e . S u b j e c t s wf:rtx f ~ : i i y

i n f o r m e d of t h e s e risks p r i o r t o p a r t i c i p a t i o n irt t t i t s

expe r imen t s .

I ) , Higher E7FE Z ? G ;

2 ) , GreaEer % r i s k ffexics angle;

3 ) . Greater wrist u h a r d e v i a t i o n angle;

4 ) . Greater wrist f l e x i o n angular velocity

51 , CrcaLer ur isr c h ~ a r deviation angular velcci ty

6 ) - G r e a C e r saxim; ECZB EEG;

T f Greater e s t a l ECRB EXG-time integral.

I n agreement v i e h the I leerature , it was hypothesized

tT.af.;, overa l l , the results would i n d i c a t e the presence of

greater ECRB forces in the Novice Group dur ing c e r t a i n

reif ions of the backharid stroke. Higher levels of muscle

aztivity, longer muse2e l e n g t h s and g rea te r velocities in the

d i r e c t i o n s of eccentric ont traction were assumed to indicate

t tie presecce of greater forces.

V. RESULTS

Since t5cz-e w e r e rto s i c p i i z i c a n t differences bc3twt>e i l t h e

characteristics of the t w o groups of sub-jects ~ t h ~ r c!l;in i n

-,heir backhand s t r o k e techniques (see E.te'_hcds sc.:t i ~ n f , i t

w a s assumed that. any differences fatrrtd i n r h i n st.tl,.;y

reflected souly their s t r o k e t e c h n i q u e d i f Zerences. Xi> o t h e r

diff ereaces between subject groups w e r e considered r ~ : r - v a r ~ t

to t be i s s n e of EC,W muscle force cornparisan.

A . General Patterns Throughout the Stroke

Time (s)

F i g u r e 3. EEG versus time graph-

a. Flexion

The mean fle:iier. versus t i m e profiles w e r e nearly

' 1 - g . i r 3 ,~e - f e z zhe ruo grc;ups of subjects , with the Novice

; c i x p displaying angles m a r e towards Ehe flexion direction

c L . . r - l ~ r i ~ t . , ~ T ?-- the stroke (see Figxre TO). Bcth groups h3d CheFr

- ? r i s ~ s rrten3ed at t ke begi2nir.g of t h e s t r o k e , zaved tcxards

Flgure z 3 , Pfexicw versus t i r e g r a ~ ? ~ .

"re mean u h a ~ deviation versus time profiles were a l s o

. r i r t u a l i i r p a s a l l e l for the t w o groups of subjects, w F t b the

fic~-ri.=e Group displaying angles mare in t h e ulnar deviation

d i r e c t i o n throughout t h e stroke ( s e e Figure 11) . The Novice

Group was positioned in slight ulnar dev ia t ion for the f i r s t

0 . 9 seconds, whereas the Advanced Group was p o s i t i o n e d i n

siight radial deviation during this period. Both groups were

yositianed i n ulnar deviation for the remainder of tine

:t yoke. The: Kovice Group had u l n a r deviatian a n g l e s

2 i g n i f icantly greater than the Advanced Group throughout t h e

stroke [Preparation Phase: p = Cf.0021; Movement Phase: p =

5.0297; and Recovery Phase: p = 0 .036 '7 ) .

Figure 11, Uhnar deviation versus time graph.

c, IPletian Velocity

Mean flexion velocity was similar far t h e t w o qsr~ups o f

subjects during the Preparation and Recovery Phase:;, k,il t

markedly different during the Movement Phase (see F ~ ~ L : T f: 12) ,

- I

6 0.2 0.4 016 0% i 1.5 1.2 1 :6 1:8 2 Time (s)

F i g u r e 12. F l e x i o n v e l o c i t y versus t i m e graph.

T h e Preparat ion and Recovery P h a s e s w e r e n o t

significantly d i f f e r e n t for t h e two groups (p = 0.1965 for

both phases). Although t h e r e also w a s no t a s i g n i f i c a n t

g r o u p d i f f e r e n c e du r ing the Movement P h a s e (p = 0.1753),

there was a highly significant group-t ime interaction e f f e c t

d a r i n g this time per i sd (p = 0.0001). This was de te rmined t o

be more from the 3 . 0 t o 1.2 seconds t i m e p e r i o d ( s i g n i f i c a n t

~rzup-time k x t e r a c k i i o l ? a t p = O-OOGii t h a n t h e 0 .8 t o 1.0

s e e m b s time period f;n=;-m; t --=--7=-- f icaxt group-time interaction at

--% = f3.19131.

d. Ulnar Deviation Velocity

The mean ulnar d e v i a t i o n v e l o c i t y v e r s u s time p r a f i l c s

appeared very s i m i l a r between t h e two groups of subjects ( sec

F i g u r e 13) . They b o t h had minimal v e l o c i t i e s d u r i n g t t l p

P r e p a r a t i o n a n d Recovery Shases and f a i r l y h i s h a l n a r

d e v i a t i o n v e l o c i t i e s just p r i o r t o impact. J u s t a f t e r ~ m p a c t

both groups changed r a p i d l y t o r a d i a l d e v i a t i o n a n d t h e n

s h a r p l y back t o u l n a r dev ia t io r l velocities . The v e i o c i t ies

i n t h i s p l a n e w e r e g e n e r a l l y s m a l l r e l a t i v e t o those i n t h e

f l e x i o n / e x t e n s i o n p l a n e .

*- U) 600 al 2? 0)

d 400 V

> I= 8 200 J Lu > = 0 9 b a 5 UJ -200 0 Ot b: f -400 , . . . , . . . . . . , . . 3 0 0.2 0-4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Time (s)

Figure 1 3 , Ufnar d e v i a t i o n v e f o c i t y versus t i m e graph.

m~ i t L e Preparation a n d R e c o v e r y Phases were n o t

ei7nificanrPy d i f f e r e n t fo r t h e two s u b j e c t groups ( p =

(";i. i318 a n d G. 3847 , r e s p e c t i v e l y ) . There w a s a s i g n i f i c a n t

gr.;tlp d i f f e rence , however, d u r i n g t h e Pllovement Phase ( p =

0 . 0 3 6 6 ) , which was f u r t h e r a n a l y z e d b e c a u s e t h e Advanced

G r o u p had slightly g r e a t e r u l n a r d e v i a t i o n v e l o c i t i e s p r i o r

t o impact whereas t h e Novice Group had s l i g h t l y g r e a t e r u l n a r

d e v i a t i o n v e l o c i t i e s a f t e r impac t . The s i g n i f i c a n t g roup

difference w a s d e t e r m i n e d t o e x i s t d u r i n g t h e 0 . 8 t o 1 . 0

seconds t i m e period (p = 0.0040) , b u t n o t d u r i n g t h e 1.0 t o

1.2 seconds t i m e period ip = 0.4419) .

B. Specific Differeaces Around the Time of Impact

The g r e a t e s t d i f f e r e n c e s b e t w e e n s u b j e c t g r o u p s

typically o c c u r r e d jus t af ter impac t , a t 1 . 0 1 s e c o n d s . A t

t h i s t i m e t h e Advanced Group had a mean EMG v a l u e o f 53.68

$MVC, which was s i g n i f i c a n t l y h i g h e r t h a n the 3 3 . 3 5 %MVC

v a l u e of t h e Novice Group fp = 0.011 9) , The Advanced Group

also had a s i g n i f i c a n t l y h i g h e r a v e r a g e of t h e s u b j e c t s '

i n d i v i d u a l maximal EMG vaf ues f irrespective o f t i m e ) , 63.37

fMVC compared to 4 6 - 8 0 OMVC for t h e Novice Group (p = 0 . 0 3 9 ) .

These v a l u e s occurred close t o impac t , w i t h t h e Advanced

Group averaging 0.003 seconds and the Novice Group a v e r a g i n g

e.Q26 seconds prim t o impact (no s i g n i f i c a n t t i m e d i f f e r e n c e

3t p = 8.298).

Jus t a f t e r impact t h e Novice G r o u p had a m a n f l e x i o n

angle of 1 - 7 5 degrees, compared to 16.52 degrees of e s t u n s i \ > n

f o r t h e Advanced Group (significantly different at p =

0 . 0 0 6 8 ) , a s w e l l a s a mean ulnar d e v i a t i o n a n y l c of 33.2.1

degrees , compared t o 8 . 5 2 degrees for t h e Advanced G r o u p

(insignificantly d i f f e r e n t at p = 0.2924) - At tk.e same t ime ,

t h e Novice Group had a mean f l e x i o n v e l o c i t y of 57.1.8

degrees / second , compared t o 6 8 . 8 degreesiseconrt Cr:r t h e

Advanced Group ( s i g n i f i c a n t l y d i f f e r e n t a t p - 0.00112) , a s

w e l l a s a mean u l n a r d e v i a t i o n velocity of 5 3 . 8

degrees/second, compared t o a mean radial d e v i a t i o n v e t o c i t y

of 7 1 . 2 degrees/second f o r t h e Advanced G I - s u p

( i n s i g n i f i c a n t l y d i f f erent a t p = 0.0951).

C . Summazy of Significant Differences

There were various d i f f e r e n c e s between the ECRB EM(;:; and

wrist kinematics of t h e N o v i c e and Advanced G r o u p s ~ :h rc$uqho~l t

the stroke. However, s i n c e EMGs of both groups w e r e m i r f i u t i i l

( l e s s than 10 % W C ) , as w e l l a s similar, i j * - a - ' - c -& A3rLj t he

Preparation and Recovery Phases, t h e i n v e s t i g a t s r t j c - , : i c j e : d

t h a t further analysis need on1 y f acus on t 9 e !%v~~~:.r:i.f_ i4i:;.i :,fa ,

Table 1 d i sp lays the s i g n i f i c a n t grotjy; di f f rsrer:,r:rs:; that ,

occurred during the Movement Phase.

m.. b e 1 , Significant group differences during the Movement Phase (larger values in bold print) .

ADVABCEE) DIFFERENCE I P NOY i CE

Ulnar Dev ("1

EMG fOrU9vC)

Flexion 4 " )

Flex ion ire1 ( O / s )

Significant graup diffexences in EMG, Pkexisn and u lna r

deviat ion w e r e observed throughout t h e Movement Phase - On

average, &he Advaeced Group used 9.46 % W C more EMG than the

Wowice Group f 3 4 - 0 4 versus 24-58 % W C ) , whereas the Novice

cvatt ,ib7~p was positioned 2 5 . 6 6 degrees more towards the flexion

direction 4-1-84 ve r sus -17.54) degrees) and fn 9 - 4 2 degrees

more u l n a r de~riation (12.21 versus 2 .?9 degrees) t h a n t h e

Advanced Group. Also, the Advanced G r o u p had a n average

ulnar deviation velociky 50.51 degreesjsecond greater t.l;an

the sovice Group (85.62 versus 35.11 degrcesisecanci) &ring

the first half of the Movement Phase (0.8 to 1.0 seconds) .

Just after impact, at time 1.01 seconds, significant

group differences existed in EMG, flexion and f l e x i o n

velocity. The Advanced Group used 20.33 % W C more EMG t h a n

the Novice Group, whereas the Novice Group was positioned i n

18-57 degrees mare flexion and experienced 506.0

degrees/second m a r e flexion velocity than the Advanced G r o u p

(see Table 1) .

WZ. DISCUSSION

A. Comparison of Results With Those in the Literature

The EMG r e s u l t s for advanced p l a y e r s compare f a v o u r a b l y

with l i t e r a t u r e r e s u l t s . Advanced p l a y e r s i n t h i s s t u d y

averaged abotlt 55 %MVC n e a r i m p a c t , which i s s l i g h t l y less

than t h e o v e r 60 % W C r e p c r t e d b y M o r r i s e t a l . (1989) a n d

c o n s i d e r a b l y less t h a n t h e n e a r maximal v a l u e r e p o r t e d b y

McLaughlSn a n d M i l l e r (1980) . It i s u n d e r s t a n d a b l e t h a t t h e

p r e s e n t scuciy would h a v e l o w e r values t h a n the v a l u e s i n

these s t u d i e s b e c a u s e a lesser i n p u t b a l l v e l o c i t y w a s u s e d

i n t h . s s t u d y . B a l l s w e r e fed t o s u b j e c t s i n b o t h of t h e

c t h e r s t u d i e s w i t h a bal l machine, so t h e i r i n p u t veloci t ies

must h a v e been closer t o t h o s e e x p e r i e n c c c i i n a n o r m a l game

s i t u a t i o n . Subjecte i n t h e present s t u d y c s ~ m e n t e d that t h e

experimental t a s k invalved backhand s h o t s %bat w e r e less

intense t h a n those ,nvolved i n a normal ga,.izT z . i t ; ? a t i c ~ ~ .

The m o s t surprising r e s u l t i n t h i s study w a s t h a t t h e

advanced players , on average, %zsed h i g h e r ENGs t h a n the

novice players %cr t h e entire Movement Phase of t h e s t r o k e .

T h i s cmtradicts t h e findings of Yoshizawa e t sl. (1987). I t

w a s mentioned previausly (see L i t e r a t u r e Review s e c t i o n , t h a t

t h i s study had a serious ccntrol problem i n tha t over haif of

t h e advanced s~ISjects used t w o h a n d s t o perform t h e i r

backhand shots, so further c

and t h e results of t h e p r e s e n t s t u d y W O U ~ ~ be f u t i l e . T h e

p r e s e n t s t u d y appears t o be t h e f i r s t to m a k e a r raZid

comparison of ECRB EMGs of no-.rice and advanced t e n n i s p f ~ ~ ' c r t;

while h i t t i n g backhan~ s h o t s ,

The o n l y relevant kinematic comparison that can he made

j u s t p r io r t o impact fo r advanced players. E l l i p t t eC a t .

r e s u l t a n t v e l a c i t y (somewhere between e:rt.endinq and u l n a r

l i t e ra lu re to make comparisons with.

necessary for capruring impac",nforrnst icn, w a s not , ~ t t e x ~ p t c+ 1

in past tennis s t roke studies.

B, Implications for ECRB Force Comparisons

The r e s u l t s of t h i s study ind ica te t h a t there a r c

various differences, a s well a s s imi la r i t i e s , b e t w e e n n d v i cc

and advanced tennis players i n terms of parameters dssnc id t rd

w i t h ECRB muscleJtendon forces during backhand s h o t s . S i n u u

the principle objective of the study w a s ta determine whether

t h e novice p l a y e r s s leading elbow technique i n v o l v e s

parameters which suggest g rea te r forces than the c l a s s i c

advanced p l aye r s ' technique, the parameter differences,

rather t h a n the s i m i l a r i t i e s , are focused on here. O n l y

those differences which were determined to be s t a t i s t i c a l l y

s ignif icant are discussed.

Three parameters have been associated w i t h e l e v a t e d

muscle force: high l eve l of muscle act ivat ion, fcirtq muscle

lengf h and eccentr ic contrac t i le component velocity (Chapman,

1985) (see Figure 2 4 ) . In t h i s study muscle act ivat ion was

estimated by ENG, muscle length was estimated by a n g u l a r

displacement and muscle v e l o c i t y (not i d e n t i c a l t o

c o n t r a c t i l e component ve loci ty) was est: h a t e d by a n g ~ ~ l a r

velocity. Differences i n these parameters were assumed to be

indicative of differences i n ECRB muscle forces.

1 0

Resting length Muscle length --+-

9 lsornetric force b

Muscufar I fwce "

t 1

Maximum 0 Velocity of shortening ---9

Figure 14. Typical relationships of muscle force t o activation (upper graph), length (middle graph) and contract i le component velocity (lower graph) . (Graphs adapted from Boulsset, 1973.)

1. Movement Phase

On average, during the Movement Phase of the stroke, the

Advanced Group had almost 1 . 4 times a s high a l eve l of ECRB

EMG a s compared with tke Novice Group ( 3 4 . 0 4 %MVC vs 24.58

T Without regards to kinematic differezzes, this W P - C I J

imply t h a t the Advanced G r o u p experienzed ECRF Eor;lPs

approximatefy 1.4 times as great, on average, as those :f t h e

Novice Group. Wrist kinematics, of course, c a n n o t L-re

disregarded. The Novice Group was positioned in qreatcr -

flexion and ulnar deviation during the Movement. P h a s e ,

meaning they were probably at a higher point on the fsrce-

length relationship. Unfortunately, the precise ECRB force-

length relationship is not 2resently known, s o it is

impossible to predict accurately how much of an effect thcse

angular deviation differences had on ECRE forces.

A final difference to mention during anly the first half

of the Movement Phase was that the Advanced Croup had

approximately 2.4 times as great of an ulnar deuiatjon

velocity as compared with the Nmice Group. Since this is i n

the eccentric direction for ECRB, this means that force was

probably elevated more, due to this effect, in the Advariced

Group than in the Novice Group. It should be emphasized t h a t

this difference was only in the overall velocities oi the

subjects' ECRB muscles and not in their contractile ccrnponent

velocities. Separation of the overall velocities i n t o

contractile and series elastic component velocities was not

possible, Furthermore, the precise force-velocity

relationship of the ECRB contractile component is not known.

Therefore, the effect of velocity differences on muecle

While there i s no way of d e t e r m i n i n g t h e e x a c t muscle

f~srcre magnitudes of t h e t w o subject g r o u p s d u r i n g t h e

M a w e m e f i t Phase, due t o v a r i o u s i n s u f f i c i e n c i e s i n p r e s e n t

rnusqle models, it can a t l eas t be s ta ted t h a t p a r a m e t e r

differences were obse rved d u r i n g t h i s t i m e p e r i o d t h a t w e r e

indicative of force differences. M o s t s i g n i f i c a n t l y , muscle

activation was h i g h e r i n t he Advanced Group, whereas muscle

length w a s greater i n t h e Novice Group. ( T h e s e w e r e

c ~ n s k d e t e d t o be m o r e r e l e v a n t c o n t r i b u t o r s t o f o r c e

d i f f e r e n c e s t h a n t h e g r e a t e r e c c e n t r i c muscle v e l o c i t y of t h e

Advanced Group d u r i n g t h e first h a l f of t h e Movement Phase . )

It i s p o s t u l a t e d by the i n v e s t i g a t o r that t h e s e d i f f e r e n c e s

e f f e c t i v e l y cancel e a c h o t h e r o u t , i n t e r m s of t h e i r e f f e c t s

on muscle forces, but c o n s i d e r a b l e muscle model improvements

a r e r e q u i r e d before t h i s can be c o n f i r m e d . The Movement

Phase results, along w i t h the s i m i l a r i t i e s found d u r i n g t h e

P r e p a r a t o r y a n d Recovery Phases, s u g g e s t t h a t t h e ECRB f o r c e s

of n o v i c e a n d advanced p l a y e r s are s i m i l a r , on a v e r a g e ,

d u r i n g t h e backhand s t r o k e . T h i s c o n t r a d i c t s t h e h y p o t h e s i s

that p o o r backhand t e c h n i q u e i n d u c e s e x c e s s i v e l o a d i n g of

ECRB .

2, Just A f t e r Impact

Even though t h e Movement Phase resu l t s suggest t h a t

a v e r z g e ECRB forces d u r i n g t h e s t r o k e are similar for nov i ce

and advanced p f a y e r s , t h e i r maximal forces m a y be q u i t e

d i f f e r e n t . The maximal ECRB f o r c e s of the subjects i n t h i s

s t u d y o c c u r r e d j u s t a f t e r impact , a t approximately 1 . 0 1

This is t h e time at which muscle activation was

near maximal, muscle l e n g t h was long and muscle velocity was

m o s t e c c e n t r i c . A t no other t i m e d u r i n g t h e 2 . 0 seconds of

t h e s t r o k e w e r e t h e s e t h r e e pa ramete r s i n s u c h a n o b v i o u s

f o r c e - e l e v a t i n g c o m b i n a t i o n ( r e v i e w F i g u r e s 9 t o 1 4 ) . F u r t h e r m o r e , a d d i t i o n a l " fo rce -enhancemen t" m u s t have

o c c u r r e d a t a n d just af ter t h i s p o i n t i n t i m e due t o t h e

r a p i d musc le s t r e t c h e s (Edrnafi e t aZ., 1978 and Thomson &

Chapman, 19881,

The Advanced Group had about 1.6 t i m e s as much ECHB EMG

( h i g h e r l e v e l of muscle a c t i v a t i o n ) as d i d tke Novice G r o u p

( 5 3 . 6 8 v s 33.35 % W C ) j u s t af ter impact. The Novice Croup,

however, w a s p o s i t i o n e d i n 1 8 . 5 7 d e g r e e s greater wrist

f E e ~ - i ~ n ( fonge r muscle length) (1.75 vs -16.82) and had about

8 . 4 times as g r e a t of a w r i s t f l e x i o n velocity (g rea te r

e c c e n t r i c muscle v e l o c i t y ) (574.8 vs 66.8 degrr?es/seccjnd) a s

compared t o the Advanced Group. As was the ease d u r i n g the

XawernenC Phase , t he Advanced Group had a positive muscle

a c t i v a t i o n f o r c e - e l e v a t i n g effect, whereas the file- ice Group

* - a

r .,, , a r,ce:~,:-~e zuscke l e n g t h force-elevating effect . A clear

.-tiffe_rer;ce a% t.3:~ p i n t i n t i m e , however, was w i t h the

- . ~ ~ 5 s rc lve ~ u s c l e velac iEy f o r c e - e l e v a t i n g effect of the Novice

Group. Additionally, t h e Movice Group h a d a positive "foree-

enhancement" f o r c e - e l e v a t i n g effect as a consequence of i t s

greater velocity of muscle stretch, i n a g r e e m e n t w i t h t h e

f i n d i n g s srf Thornson a n d Chapman 11988) . The f o r c e - e l e v a t i n g

effects which occurred j u s t a f t e r i m p a c t zre summarized i n

Table 2.

Table 2. P o s i t i v e ECRB f c r c e - e l e v a t i n g effects which o c c u r r e d just after i m p a c t .

SIGNIFICANT MUSCLE PAlRAMETER D IFFEREMCE

GROUP DISPLAYING POSITIVE FORCE-ELEVATING EFFECT

Higher L e v e l of Muscle A c t i v a t i o n

I

Advanced Group

Longer Muscle Length Novice Group

Greater E c c e n t r i c Muscle Novice Group V e l o c i t y

More "Force-enhancement" Novice Group

F i g u r e 15 i z l u s ' s r a t e s t h e pus:-impact. meal: f ?ex i i s* :

v e l o c i t y versus t i m e pxofiles of the Novice a n d Advancpi i

Groups. It is obvious f r o m t h i s y a p h t h a t t h e Novice G r c u p

had a s i g n i f i c a n t l y greater e c c c m t r i c ECRB velscit y d u r i n q

t h i s 20 m i l l i s e c o n d p e r i o d o k t i m e . I f it can be assurnrci

t h a t t h e muscle a c t i v a t i o n and muscle l e n g t h fo rce -e leva t ing

effects approximately cancel each o t h e r out b e t w e e n t h e t w ~

groups of s u b j e c t s (as was suggested for t h e Movement P h a s e ) ,

t h e n t h i s d i f f e r e n c e i n muscle vef o c i t ies indicates that t h e

Movice Group e x p e r i e n c e d somewhat g r e a t e r maximal ECRB forces

j u s t af ter i m p a c t . I t should once a g a i n be emphasized t h a t

t h i s d i f f e r e n c e was o n l y i n t h e o v e r a l l velocities of t h e

s u b j e c t s ' ECRB musc les and not i n t h e i r contractile component

velocities. Because of t h i s it i s no t p o s s i b l e a t present t o

make a c c u r a t e force comparisons.

1.01 Time (s)

Figure 15. Flexion velocity versus time graph (post-impact time period) .

Nonetheless, to give the reader an idea of the magnitude

of the positive muscle velocity force-elevating effect of the

Novice Group, the ECRB force (normalized) - velocity

(contractile component) relationship utilized in a recent

muscle model by Winters and Stark (1985) is displayed in

Figure 16. Similar to the general force-velocity

relationship In Figure 14 (lower graph), forces are greater

in the negative (eccentric) velocity direction than in the

positive (concentric) velocity direction, with appropriate

c i m e constants incorporated. While the exact relationship is

-1 000 -500 0 500 1 000 ECRB SHORTENING VELOCITY (degrees&)

Figure 16. Force-velocity re lat ionship for ECRB. (Based o n the relationship u t i l i z e d by Winters & Stark, 3985.)

The v e l o c i t i e s from Figure 15 w e r e u s e d as inputs t o t h e

equa t ions involved i n t h e force-ve loc i ty relationship of

F igu re 1 6 (see Winters & Stark, 1 9 8 5 ) . ( F l e x i o n ve toc i t i e s

had to be multiplied by -1 i n order for them to be c o n * ~ e z t c d

to ECRB shortening v e l o c i t i e s . ) This enabled the calcula t r i f in

clif normalized ECRB forces , which are shuwa in F i g u z e 1 7 .

2 ; r, * - .,. ,, f i g a r e t-Luz~zates the esti~ated force differences

b e t w e e 3 the two sabject groups. To quantify this difference

; the 20 millisecond time period, impulses (force-time

i n t e g r a l s ) were calculated. The Novice Group had an impulse

c>f C .0229 normalized(force unit) -seconds, compared to 0.0180

r , . i rnal ized(force unit)-seconds for the Advanced Group. This

earresponds tc a ratio of 1.27 of Novice Group impulse to

A4-zanced Group impulse,

0.4 A ADVANCED

0.2 - -E.- NOVICE I

0 , 1 1

1 1.01 1.02 Time (s)

Figure 17. EGRB force versus time graph (post-impact time period) .

If the force-velocity relat ionship i 2 1 i d i x t.h4 8

estimation can be considered to be a reasonable appr>x ina t io~- i

of the true relationship and the assumption t h a t the ~ e s i t i v e

muscle activation and muscle length force-elevating e f fec t s

of the two subject groups cancel each other cot, t h e n i: can

be s ta ted tha t the Novice Group had a t leas t a 1 . 2 7 t ! r ~ s

greater ECRB impulse than t h e Advanced Group ju s t - a f t e r n

impact. Inclusion of the adbi2ional "fcrce-enhancerr;er.,f_" c t t

the Novice Group would increase t h i s value f o r t h e r ,

The elevating effects of greater eccentric ve f ocit- i ts:; o n

khe ECRB forces of the Novice Group subjects, a s conparcci t 4 o

those of t h e Advanced Group subjects , may well h a v e

outweighed the e f fec ts of activation and length d i f fcrcrice~.

j u s t a f t e r impact. Unfortunately, this can only be conf j rmcd

by future muscle rnodellers. I f t h i s did prove t:t> h e t t ~ ~

case, then it could be stated that tennis players who ~ ~ s e thc

leading elbow backhand technique experience greater maximal

ECRB forces just a f t e r impact than do those who u s e t h e

c l a s s i c advanced players* backhand technique. T h i s woulrl

support the hypothesis tha t poor backhand technique i n r i u c c s

excessive loading of ECRB.

C , Conclusions

Various s i g n i f i c a n t ECRB muscle force parameter

differences, as w e l l as s imilar i t ies , were ohser-/cd in E h i s

~:t47 b e n o v i c e a n d advanced t e n n i s p l a y e r s w h i l e

m i Lackk-ar:d shots. Average differences observed

<1-- . w t h e I ? o - ~ e r ~ i r Phase, i n comkiination with t h e i r

similarly low levels of musc le a c t i v a t i o n d x r i n g t h e

P repa ra t i cm and Recovery Phases , lead t o t h e conclusion t h a t

r i5 t r ice a n d advanced t e n n i s p l a y e r s p r o b a b l y e x p e r i e n c e

s i ~ i l a a r ECRB forces, on a v e r a g e , d u r i n g backhand t e n n i s

s h s t C ,

During t h e s h o r t (20 m i l l i s e c o n d ) t i m e p e r i o d j u s t a f t e r

impact, when ECRB forces w e r e m o s t l i k e l y maximal, the nov ice

players d e r n o n ~ t r a t e d musc l e v e l o c i t i e s i r , t h e e c c e n t r i c

f l e x i o n d i r e c t i o n which w e r e c o n s i d e r a b l y g r e a t e r t h a n t h o s e

of t h e advanced p l a y e r s . T h i s d i f f e r e n c e p r o b a b l y outweighed

a l l o t h e r observed d i f f e r e n c e s i n t h i s s tudy , i n t e r m s o f i t s

e f f e c t on t h e compar i son o f ECRB m u s c l e forces. I t i s

c o n c l u d e d , based o n t h i s d i f f e r e n c e a n d t h e presumed

c a n c e l l i n g e f f ec t s of m u s c l e a c t i v a t i o n a n d l e n g t h

d i f f e r e n c e s , that n o v i c e t e n n i s p l a y e r s who u s e t h e l e a d i n g

e l b o w backhand t e c h n i q u e p r o b a b l y e x p e r i e n c e greater maximal

ECRB i m p u l s e s (and forces) j u s t a f t e r impact i n backhand

shots. S i n c e ECRB force overload i s t h e s u g g e s t e d mechanism

b e h i n d LE, the main i m p l i c a t i o n f r o m t h i s c o n c l u s i o n w i t h

regards t o LE etiology is t h a t poor backhand t e c h n i q u e i s

psczbably a significant contrihtor t o the i n j u r y for novice

players . The o b j e c t i v e of d e t e r m i n i n g whe the r o r not t h e

f eadf ng elbow teck2ique indzces forces grea? enot:gh to c~L;::c\

LE was not f=rfly met, b u t s o m e of the neztlssarq7 ~ $ t _ e ~ s rk-1 f hi;:

er.d w e r e t a k e n i n performing this s t u d y . C o n s idcrdtr l P

f c r t h e r r e s e a r c h is s u g g e s t e d b y t h e i n v e s t i g a t o r i n iIjr~itir

for t h e u l t i m a t e e t i o l o g i c a l objective to be f u l l y n1t.t .

Future Reseaxch

It i s hoped t h a t f u t u r e musc le mcrdellers x i ! 'n r r ~ c i r :

i n c e n t i ~e f r o m t h e present s t u d y t o q u a n t i f y t h e FXIifi t . i r t S c * : :

of nov ice and advanced t e n n i s p l a y e r s d u r i n g backhand shist :;.

Two m a j o r musc l e m o d e l l i n g prob lems m u s t f irst be s ~ l vcad.

F i r s t l y , a s o l u t i o n t o t h e g e n e r a l d i s t r ~ h u t i c m ptoh:t*ni f ~ r r

all muscles c r o s s i n g t h e w r i s t j o i n t m u s t be f o u n d . R c ~ e ~ ~ r c h

on t h i s p rob lem will h a v e to r e l y on improved m e t t x r ) c i s o f

direct muscle / tendon force measurement (Caldwei f & C h a p m r l n ,

1391) . Secondly , a n d e q u a l l y c h a l l e n g i n g , t h e prec i:,e ECRR

muscle properties corresponding t o conditions rrf r i Ip i A

s t z e t c h (up t o t h e e q u i v a l e n t o f about 600 degreec/:;r;-cor~rf

wrist flexion v e l o c i t y ) must be determined (Hof F; v a n d e n

Berg, l98Ta) . I t is s u g g e s t e d t h a t a m e a n s of ificlucii mg

"force-enhancement" i n a H i l l - b a s e d ~ s d e l i s neccszdry.

Improved methods of direct force rneast_tremer*t w i i i prc,ve

u s e f u l for t h i s task as well,

Once these p m M e m s are solved, it will be ; t ~ ~ ~ s i t ; J e t - , ~

quantify ECWB forces d u r i n g t e n n i s shots. T h e n t h e

hycsthesis regardiag p o o r b a c k h a n d t e c h n i q u e i n d u c i n g

t i then, u n f o r t u n a t e l y , LE e t i o l o g y for n o v i c e t e n n i s

~ f a y e r s will n o t be completely undexs tood . H o p e f u l l y t h e

popularity sf t e n n i s does not decline w h i l e the i n c i d e n c e of

LE remains high.

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