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Staying Fit and Staying Well: Physical Fitness as a Moderator of Life Stress

Jonathon D. BrownUnivers i ty of Wa shington

Previous research suggests that ph ysical fitness moderates the adverse effects o f stressful life events.

However, a reliance on self-reports of fitness and health may limit the validity of prior investiga-

tions. Th e present research tested the stress-buffering effect of fitness with subjective and objectiveindicators o f exercise, fitness, and physical well-being. For self-reports of health, bot h self-reports of

exercise and objective measures of fitness showed the buffeting effect; however, only objective

fitness levels buffered stress when visits to a health facility were considered. Additional evidenceindicated that this effect was largely independent of measures o f psychological distress. Implica-tions for unders tandi ng the link between fitness, stress, and health status are discussed.

Physical fi tness plays an im por ta nt role in heal th prom otion

and maintenan ce. For example, fi tness reduces cardiovascular

morbidi ty and mor tal i ty (Oberman, 1985) , lowers blood pres-

sure (Blair, Good year , Gib bons , & Cooper , 1984) , and aids in

the m etabolism of carbohydrates (Lenn on et a l ., 1983) and fats

( Rosentha l, Haske ll , So lomo n, W id s t r om, & Reavan , 1983) .

Fitness also has been l inked to numerous psychological bene-

f i t s . These inc lude impr ovements in s e l f - concept ( Hughes ,

1984), mo od state s (Folkins & Sime, 1981), an d cognitive lunG3

tioning (Tomporowski & Ellis, 1986). In short, physical f itness

i s an imp or tan t genera l comp onen t o f wel l -be ing .

One benef i t of fi tness that is receiving increased at tention is

its ability to m ode rate the negative effects of stress. In recen t

years, several laborato ry s tudies have found that high-fi t peopleevidence less physiological react ivi ty to s tress than do those

who are less fi t. For ins tance, H olme s and Roth (1985) exposed

high-f i t and low-f i t wo men to a s tressful psychological tes t.

Com pare d with low-f it subjects , high-f it subjects evinced lower

elevations in hea r t ra te . Other researchers have obtained s imilar

evidence that f itness reduces physiological reactivity to experi-

menta l ly induced s t r es s ( Ke l le r & Ser aganian , 1984; L ight ,

Obrist, James, & Strogatz, 1987; Sinyor, Golden, Steinert, &

Seragania n, 1986).

Complementing these laboratory s tudies are invest igat ions

of f itness and na tur a l ly occu r r ing s t r e ss . Br o wn a nd S iege l

(1988) cond uct ed a pro spective stu dy o f stressful life events,

exe r ci se hab it s , and hea l th s ta tus amo ng adolescents . They

found th at s tress and exercise interacted to p redict changes in

The preparation of this article was supported by National ScienceFoundation G rant BNS-8958211.

I thank M ike Best and D avid Watson for their help in the planningand execution of this research.

Correspondence conc erning this article should be addressed to Jon-athon D. Brown, D epartm ent of Psychology (NI-25), University ofWashington, Seattle, Washington 98195.

self - repor ted health over t ime: Although s tressful l i fe events

were l inked to deter iorat ing health s ta tus am on g subjects who

exercised infrequently, they had little negative effect am on g sub-

jects who exercised on a regular bas is. W ith the results of other

s tudies (Brown & Lawton, 1986; Roth & Holmes, 1985) , these

findings suggest that f itness mitigates the deleterious effects of

life stress (but see also Roth , W iebe, Fillingim, & Shay, 1989).

Before this conclus ion ca n b e prof fered with any conf idence,

however , several issues need to be addressed. T he f irs t concerns

the use o f self- repor t . With o ne exception (Roth & H olmes,

1985), pr ior researc h te sting th e stress-buffering role of f itness

has use d subject ive repor ts o f exercise an d f i tness rather than

more object ive measures . I l lness a lso has been assessed with

self- repor t . Alth ough research sup por ts the val idi ty of self -re-

ports of f itness (Roth & Fillingim, 1988 [cited in Roth et al.

1989]) and health (Davies & Ware, 1981; Kapla n & Cam acho,

1983), i t is impo r tant to determin e w hether the apparen t s tress-

mod erat ing role of fi tness can be replicated w ith more object ive

measures .

Toward th at end, the present research used relat ively direct

me tho ds o f assessing fitness and h ealth status. Expressly, physi-

cal f itness was assessed by per forma nce on a su bmax imal bicy-

cle ergometer tes t (cf . Roth & Ho lmes, 1985) ; heal th s ta tus was

indexed by exam ining subjects ' vis its to a med ical faci l i ty for

physical il lness. Altho ugh neither o f these measures provides a

per fect index o f their respective under lying c onstructs , th ey are

less subject to response biases and other potentia l confounds(e.g. , forgetting) tha n are self-report measures.

A second, and related, issue concerns how to interpret the

stress-buffering effect of f itness on hea lth status. Peopl e who

are physical ly fi t dif fer f rom those w ho are no t on a n umb er o f

dimensions . Only som e of these dif ferences are a direct conse-

quence of f i tness, p er se . Because cor relat ional des igns are be-

ing used to tes t th e s tress-buffering hypothesis, one can not be

cer tain whether f i tness or some th ird var iable is responsible for

the stress-buffering effect.

Journ al o f Personali ty and Social Psychology, 1991, Vol. 60, No. 4, 555-561Copyr ight 1991 by the Ame ric an Psychological Association, Inc. 0022-3514/91/$3.(30

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556 J O N A T H O N D . B R O W N

I n t h e o ry , t h e n u m b e r o f p o t e n t i a l t h i r d v a r i a b l e s i s in f i n it e .

H o w e v e r , o n e v a r i a b l e s t a n d s o u t a s a u s e f u l p o i n t o f d e p a r t u r e

f o r e x a m i n i n g t h i s i s su e . T h i s v a r i a b l e i s a b r o a d p e r s o n a l i t y

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

a n d m o o d s t a te s . S o m e p e o p l e v i e w t h e m s e l v e s n e g at i v e ly a n d

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

v i e w t h e m s e l v e s p o s i ti v e ly a n d t y p i c a l l y d o n o t e x p e r i e n c e a f -

f e ct iv e d is t r es s . T h i s c o n s t r u c t h a s b e e n g i v e n v a r i o u s n a m e s ,

i n c l u d i n g n e u r o t i c i s m ( C o s t a & M c C r a e , 1 9 8 7 ), e m o t i o n a l i t y

( E y s e n c k & E y s e n c k , 1 9 7 5 ) , a n d n e g a t i v e a f f e c t i v i t y ( W a t s o n &

C l a r k , 1 9 8 4 ). F o l l o w i n g T e s sl e r a n d M e c h a n i c ( 1 9 7 8 ), a m o r e

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

p o r t t o d e s c r i b e t h i s c o n s t e l l a t i o n o f f a c to r s.

I n a d d i t i o n t o b e i n g c h a r a c t e r iz e d b y l o w s e l f- e s t e e m a n d

n e g a t i v e m o o d s t at e s , d i s tr e s s e d p e o p l e a l s o t e n d t o p e r c e i v e

t h e c i r c u m s t a n c e s i n t h e i r l i fe as s tr e s s f ul a n d t o r e p o r t a v a r i e t y

o f h e a l t h p r o b l e m s ( C o s t a & M c C r a e , 1 9 8 7 ; W a t s o n , 1 9 89 ; W a t -

s o n & P e n n e b a k e r , 1 9 8 9 ). A s a c o n s e q u e n c e , t h e r e l a t i o n b e -

t w e e n s e l f -r e p o r te d s t re s s a n d s u b j e c ti v e i n d i c a t o r s o f h e a l t h

c a n b e s p u r i o u s l y i n f l a t e d i f o n e f a il s to t a k e t h i s f a c to r i n t o

a c c o u n t . F o r t h i s r e a s o n , i t i s i m p o r t a n t t o e x a m i n e t h e r o l e o fp s y c h o l o g i ca l d i s tr e s s a s a p o s s i b l e c o n f o u n d o r c o n t a m i n a t i n g

v a r i a b l e w h e n i n v e s t i g a t i n g t h e r e l a t i o n b e t w e e n t h e s e v a r i -

a b l e s (C o s t a & M c C r a e , 1 9 8 7 ; W a t s o n & P e n n e b a k e r , 1 9 89 ) .

T h e r e l a t i o n b e t w e e n f i tn e s s a n d p s y c h o l o g i c a l d i s t r e ss a l s o

n e e d s t o b e e x p l o r e d . P h y s i c a l f i t n es s h a s b e e n l i n k e d t o e l e v a -

t i o n s i n m o o d s t a te s a n d a f a v o r a b le s e lf - vi e w ( F o l k i n s & S i m e ,

1 9 81 ) . A l t h o u g h t h e s e a s s o c i a t i o n s a r e n o t a l w a y s o b s e r v e d

( W a t s o n , 1 9 8 9 ), t h e y a d m i t t h e p o s s i b i l i t y t h a t p h y s i c a l l y f i t

p e o p l e m a y b e l e s s d i s t r e s s e d t h a n l o w - f i t p e o p l e . I f so , t h e

a p p a r e n t s t r e s s - b u f f e ri n g p o w e r o f f it n e ss d e m o n s t r a t e d i n

p r e v i o u s s t u d i e s m a y b e a r t i f a c t u a l . S p e c i f i c al l y , t h e s t r e s s - b u f -

f e r i n g e ff e ct m a y b e d u e t o t h e s h a r e d v a r i a n c e b e t w e e n f i t n e s s

a n d p s y c h o l o g i c a l d i s t re s s o n t h e o n e h a n d a n d b e t w e e n p s y c h o -

l o g i c al d is t r e s s a n d s t r e ss a n d h e a l t h p e r c e p t i o n s o n t h e o t h e r

h a n d . I n a n a t t e m p t t o e x a m i n e t h i s p o s s ib i li t y, s u b j e c ts i n t h e

p r e s e n t s t u d y c o m p l e t e d t h r e e p e r s o n a l i t y s ca l e s as s e s s in g p s y -

c h o l o g i c a l d i s t r e s s .

T o s u m m a r i z e , t h e p r e s e n t s t u d y h a d t w o a i m s . T h e f i r s t w a s

t o d e t e r m i n e w h e t h e r t h e s t r e s s - b u f f e ri n g ro l e o f p h y s i c a l f it -

n e s s w o u l d b e f o u n d w i t h r e la t iv e l y o b j e c t iv e m e a s u r e s o f f i t-

n e s s a n d h e a l t h s t at u s ; t h e s e c o n d w a s t o d e t e r m i n e w h e t h e r t h e

b u f f e r i n g ef fe c t o f f it n e s s w a s i n d e p e n d e n t o f m e a s u r e s o f p s y -

c h o l o g i c a l d i s t r e s s .

M e t h o d

S u b j e c t s

T h e s u b j e c t s w e re 3 7 m a l e a n d 7 3 f e m a l e u n d e r g r a d u a t e s a t t e n d i n g a

pr iva te un iversi ty . They par t ic ip a ted in in d iv id ua l es t ing sess ions dur-

ing the fa l l academ ic sem es te r in exchange fo r ex t ra c red i t in the i r

i n t r o d u c t o r y p s y c h o lo g y c o u rs e s . T h e e x p e r i m e n t w a s c o n d u c t e d b y

o n e o f t h r e e f e m a l e e x p e r i m e n t e r s .

P r o c e d u r e

At the s ta r t o f the exper im enta l sess ion , sub jec ts were to ld abou t the

n a t u r e o f t h e e x p e r i m e n t a n d w e r e a s k e d t o s i g n a n i n f o r m e d c o n s e n t

fo rm . T hey were a lso asked to s ign a re lease g iv ing the inves t iga to rs

access to the i r u n ivers i ty hea l th cen te r records . For bo th the fa l l and

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

e a c h s u b j e c t m a d e t o t h e h e a l t h c e n t e r a n d i n d i c a t e d w h e t h e r t h e v i s i t

was fo r i l lness , in ju ry , o r o ther m at te rs re la ted to phys ica l hea l th (e .g .,

checkup). V is i t s fo r phys ica l i llnesses se rved as the m ain de pen den t

var iab le in th is research .

D u r i n g t h e n e x t p a r t o f t h e s t ud y , s ub j e c ts c o m p l e t e d a n u m b e r o f

se l f - repor t m easures (descr ibed la te r ) a t the i r own pace . A base l ine

m e a s u r e o f h e a r t r a t e w a s t h e n o b t a i n e d . A M a r s h a l l 89 O s c i l l o m e t r i c

S p h y g m o m a n o m e t e r c u ff w a s a t t ac h e d t o t h e s u b j e c t' s n o n d o m i n a n t

a r m , a n d t w o p u l s e r e a d i n g s w e re t a k e n 3 0 s a p a r tf l T h e t w o r e a d i n g s

were averaged to c rea te a m ea sure o f res t ing he ar t ra te.

A t th is po in t , sub jec ts were asked to doff the i r shoes in p repara t io n

for r id ing an exerc ise b ike . Af te r be ing weighed , sub jec ts m ou nted a

Bodygua rd 955 Ergocycle . Fo l lowing a b r ie f war m -u p per iod a t n o

r e s is t a n c e , s u b j ec t s b e g a n p e d a l i n g a t 5 0 r p m w i t h t h e w o r k l o a d s e t a t

3 0 0 K i l o p o n d m e t e r s / m i n u t e . H e a r t r a t e w as c o n t i n u o u s l y e c o r d e d b y

an Am erec 130 pu lsem ete r a t tached to the sub jec ts ' le f t ea r lobe . I f

neede d , the work loa d was increased to ach ieve a ta rge t hear t ra te be-

t w e e n 1 2 0 a n d 1 6 0 b p m . A f t e r t h e t a r g e t h e a r t r a t e h a d b e e n r e a c h ed

for a 2 -m in per iod , sub jec ts con t inue d to r ide the e rgom eter fo r 2 m ore

m i n u t e s . A t t h e e n d o f t h e f i n a l p e r i o d , f i n a l h e a r t r a t e a n d w o r k l o a d

were used to es t im ate ae rob ic capaci ty .

M e a s u r e s

E x e rc i s e . Self-reports of phy sical exercise were assessed w ith the

Phys ica l Act iv i ty Que s t ionn a i re (PAQ; Brown, 1989). The PAQ con-

sists of 14 exercise activities. I tem s inclu de both aerob ic (e.g. , jogg ing,

s w i m m i n g , b i k i n g ) a n d a n a e r o b i c ( e .g ., w e ig h t l i f t i n g , y o g a, b a l l et )

fo rm s o f exercise. 2 Addi t ion a l space i s p ro v ided fo r sub jec ts to e n te r

a n y o t h e r t y p e s o f e xe rc is e t h e y e n g a ge i n t h a t a r e n o t i n c l u d e d o n t h e

l i st . F o r e a c h i t e m , s u b j e c ts i n d i c a t e h o w m u c h t i m e t h e y s p e n d d o i n g

the ac t iv i ty each week . A to ta l exerc ise score i s found by s um m in g

these va lues . A s l igh t ly m odif ied vers io n o f the p re sen t sca le has been

s h o w n t o b e r e l ia b l e o v e r a 3 - m o n t h p e r i o d ( r = . 61 ) a n d h a s b e e n u s e d

in p r io r research on exerc ise and phys ica l wel l -be ing (Brown & S iege l ,

1988).• Li fe s t ress . Life s tress was m ea sured w i th the L i fe Exper iences Sur-

vey (LES; Sam son , Joh nson , & S iege l , 1978) . The LES is a wel l -es tab-

l i s he d m e a s u r e o f l i f e e v en t s t h a t h a s b e e n u s e d i n n u m e r o u s i n v e s ti g a -

t ions o f s t ress and i l lness . I t was chosen fo r use in th e p rese n t research

b e c a u s e i t h a s a n u m b e r o f i t e m s o f p a r t i c u l a r r e l ev a n c e t o c ol le g e

s tuden ts (e.g. , m o ving away f rom h om e fo r the f i r s t t im e) . For each o f

t h e 6 0 e v e n t s o n t h e L E S , s u b j e c t s in d i c a t e d w h e t h e r t h e y h a d e x p e r i -

e n c e d t h e e v e n t i n t h e p r e c e d i n g 1 2 - m o n t h p e r i o d a n d , i f so, whether i ts

i m p a c t w a s p r e d o m i n a n t l y n eg a t i v e o r p o s it i v e ( - 3 = e x t r e m e l y n e g a -

t ive; 3 = ex t rem ely posi t ive) . Add i t iona l space was p rov ided fo r sub jec ts

t o r e c o r d a n y o t h e r s i g n i f i c a n t e v e n t s t h e y h a d e x p e r i e n c e d i n t h e

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

o f n e g a t iv e l i f e e v e n t s )

B lood p ressure rea d ings were a lso taken to iden t i fy h igh-r i sk sub-

j e c t s p r i o r t o t h e e r g o m e t e r t e s t. A l l o f t h e s u b j ec t s h a d n o r m a l b l o o d

pressure read ings .

2 Scores fo r the Aerob ic and A naero b ic subsca les o f the PAQ were

h igh ly re la ted in the p res en t sam ple (p < .0009) , m akin g i t d i f f icu lt to

em pir ica l ly d is t ingu ish be twe en sub jec ts on th is bas is . So th is d is t inc-

t i o n i s n o t c o n s i d e r e d f u r t h e r i n t h i s r e p o r t.

3 F o u r i t e m s f r o m t h e L E S w e r e e l i m i n a t e d b e f o r e a n a l y z i n g t h e

da ta . Two i tem s ("changes in ea t ing hab i ts" and "changes in s leep ing

hab i ts" ) were exc luded because o f the i r p robab le re la t ion w i th psycho-

log ica l d is t ress ; one i tem ("m a jor phys ica l i l lness" ) was e l im ina ted to

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



PHYSICAL FITNESS, STRESS, AND HEALTH STATUS 557

Illness. Self-reports ofil lness were assessed with an illness checklist

used by Brown and Siegel (1988). This measure is based on the Serious-

ness of Illness Rating Scale, which was developed and validated by

Wyler, Masuda, and Holmes (1968). The present scale was composed

of 36 medical conditions and physical illnesses that range in severity

from a cold or sore throat to diabetes and cancer. Subjects indicated

which of the illnesses they had experienced during the previous 6-

month period; a total illness score was found by summing he number

of items checked.

Psychologicaldistress. As used in this report, psychological distress

is a rubric for describing a complex of factors perta ining o low self-es-

teem and depressed affect (of. Costa & McCrae, 1987; Watson & Penne-

baker, 1989). Three scales were used to measure this construct in the

present investigation.

The Rosenberg Self-Esteem Scale (1965) was used to assess percep-

tions o f self-worth. This scale is a widely used measure of self-esteem;

many investigations support its validity. The affective consti tuent of

psychological distress was assessed with the Center for Epidemiologic

Studies Depression Scale (CES-D; Radloff, 1977). The CES-D is a

20-item, self-report inventory that was developed to assess the pres-

ence of depressive symptomatology in the general population. The

measure places particular emphasis on the affective component of de-

pression. The third measure of psychological distress used in this re-search was a mood measure developed by Watson, Clark, and Tellegen

(1988). This measure asks subjects to indicate how often they typically

feel each of 10 emotions (e.g., distressed, scared, upset). Subjects com-

pleted this measure 3-10 weeks prior to the experimental session in a

mass-testing session.

Results

P r e l i m i n a r y A n a l y s e s

Missing cases . Complete health center records were avail-

able for only 90 of the 110 subjects. The percentag e of incom-

plete cases did not vary as a func tio n of subject sex, x 2 (1, N =

110) = 1.91, ns . Incomplete records were prima rily due to ad-

ministrative error, the stude nts' refusal to grant us access totheir health center records, or students' dr opping out of school

before the end of the aca demic year. Analyses compar ing the

scores of subjects with missing data with those who had com-

plete data revealed no significant effects for any of the st udy

variables. Rather than using listwise deletion, analyses were

performed using all subjects who had available data relevant to

that analysis. Degrees of freedom therefore vary somewhat

from analysis to analysis.

Es t ima ted m axim a l oxygen up take. Aerobic fitness was esti-

mated using the procedure outlined by Astrand and Rodahl

(1977). Heart rate and work load for the final 2 rain on the

ergometer were entered into a standardized nomogram. The

resulting estimate of ma ximal oxygen uptake provides a reli-

variable; another item ("major changes in recreational activities") was

discarded to avoid a possible confound between the stress measure and

the measure of aerobic fitness. Only negative life events were consid-

ered, because prior research on stress and fitness (Brown & Lawton,

1986; Brown & Siegel, 1988; Roth & Holmes, 1985) has focused only on

undesirable events. (Consistent with this emphasis, preliminaryanaly-

ses showed that positive life events did not interact with fitness or exer-

cise to affect health status.) Finally, although the data reported in the

text are based on a unit weighting of negative events, analyses using

subject's 7-point impact ratings yielded a comparable set of results.

able an d va lid, albeit approximat e, in dex of aerobic fitness (As-

trand & Rodahl, 1977). The mean in the present sample for

men was 34.2 (S D = 5.69); for women , the me an was 26.9 (SD =

4.76). These values are comp arabl e to, thoug h somewhat lower

than, those found in other research with young adults (Astrand

& Rodahl, 1977).

Psychological distre ss. The a ssumption underly ing the use

of three personality scales to assess psychological distress isthat all tap a co mmon theoretical construct. Two sets of analy-

ses were performed to e xami ne this issue. First, the zero-o rder

correlations amon g the three scales were examine d. Self-es-

teem was negatively correlated with C ES -D scores (r = - .5 0,

p < .001) and with scores on the mood measure of negative

affect (r = - .30 , p < .005); the CES-D and mo od measure were

positively correlated ( r= .25, p < .025). In a second analysis, the

three variables were subjected to a princi pal-compo nents naly-

sis. A single factor emerged, acc ount ing for 59% of the ex-

plained variance. The moo d measure and CE S-D loaded posi-

tively on this factor (.60 and .83, respectively); the Rosenberg

Self-Esteem Scale loaded negatively (-.85). In sum, though not

identical, the three scales showed a good dealofov erlap. Accord-ingly, after reversing the scoring for t he Rosenberg Self-Esteem

Scale, the three measures were standardi zed and su mmed to

create a single index of psychological distress. (Analyses using

each scale separately showed a pa tter n of results nearly identical

to those to be reported in the text.)

D e s c r i p t i v e D a t a

Table I shows the means, stand ard deviations, and zero-order

correlat ions among t he s tudy variables. Self-reports of exercise

were reliably related to physical fitness levels. Moreover, both

exercise an d fitness were significantly related to restin g heart

rate. These findings are meaningful as they provide some im-

porta nt validity for the measures of fitness used in this re-search. Table 1 also reveals that self-reports of neit her exercise

nor fitness were related to life stress. However, fitness but not

self-reports of exercise tended to be related to psychological

distress. Finally, neit her of these variables was associated with

self-reports of health o r healt h cent er visits.4

As concerns stress and well-being, consistent with a good

deal of prior research (Dohrenwen d & Dohrenwend, 1974),

stressful life events were lin ked to psychological distress. Life

stress also predicted self-reports of health and visits to the

health facility. Finally, higher levels of psychological distress

were also linked to more health complaints and more frequent

visits to the health center. Although the relation between dis-

tress and self-reported health is well documented, a l ink be-

tween distress and visits to a medical facility has bee n observed

less frequen tly (see Watson & Pen nebake r, 1989, for a review).

M a i n A n a l y se s

Hierarchical regression analyses (Cohen & Cohen, 1983)

were used t o ex amin e whether exercise/fitness an d stressful life

events interact in the prediction of physical health status.

4 Preliminary analyses revealed that students' health center visits

were not normally distributed. A log transformation was therefore ap-

plied before analyzing these data.



P H Y S I C A L F I T N E S S , S TR E SS , A N D H E A L T H S T A T US 559

Tab le 2

Hierarchical Multiple Regression An alyses

Before controlling After controlling forfor psychological psychological

distress distressDependent

variable /~ R 2 • ~ R 2 •

Self-report illnessStress .3351"** .3193***Exercise .0669 .12"** .0767 .11"**Stress × Exe rcise - .1777"* .03** - .143 4 .02

Stress .3477*** .3393***Fitness - .04 10 .12"** -.07 33 .11"**Stress × Fitness - .20 71 "* .04** -.19 41" * .04**

Health center visitsStress .2181"* .1681Exercise - .05 67 .05 .0105 .03Stress x Exe rcise - .126 7 .02 - .1283 .02

Stress .2136** .1639Fitness .0384 .05 .0543 .03Stress × Fitness - .21 40 "* .04** -.1 99 6" .04*

Note. AU analyses w ere conducted after controlling for sex o fsubject.• Chang e in R 2 for step .* p < . 0 6 . * * p < . 0 5 . * * * p < . 0 1 .

c o n t r a s t , c o n t r o l l in g f o r p s y c h o l o g i c a l d i st r e s s h a d v i r t u a ll y n o

e f fe c t o n t h e m a g n i t u d e o f t h e S t r e ss × F i t n e s s i n t e ra c t i o n . S u b -

s t an t iv e ly , t h e s e f i n d i n g s s u g g e s t t h a t p s y c h o l o g i c a l d i s tr e s s

p l ays an im po r t an t r o l e i n t he s t r e s s -bu f f e r i ng e f f ect o f s e lf - r e-

p o r t e d e x e r c i s e, b u t d o e s n o t u n d e r l i e t h e s t r e s s - b u f f e r i n g 3

pow er o f phys i ca l f i tne ss .

T h e r e s u l ts p r e s e n t e d i n t h e b o t t o m r i g h t si d e o f T a b l e 2

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

S t r e ss x F i t n e s s i n t e r a c t io n w a s v ir t u a l ly u n c h a n g e d w h e n p s y -

cho log i ca l d i s tr e s s w as s t a t is t i c a l l y con t ro l l ed . A l tho ugh t he i n -

t e r a c t i o n t e r m n o w fa ll s j u s t s h o r t o f s t a ti s t ic a l s i g n if i c a n ce I

(p = . 057 ) , a s a p r ac t i ca l m a t t e r con t ro l l i ng fo r p sych o log i ca l L

d i s t r e s s had ve ry l i t t l e e f f ec t on t he s t r e s s -bu f f e r i ng pow er o f

ph ysi cal fi tness. L

Prospective analyses. Seve ra l add i t i ona l ana lyse s w ere pe r -

f o r m e d t o e x a m i n e f u r t h e r t h e s t r es s - b u ff e r in g e f fe c t o f p h y s i - l ~ 2

ca l f i tne s s on hea l t h cen t e r v i si ts . F i r s t , a p rospec t i ve h i e r a r ch i - E

c a l r e g r e s si o n a n a l y s is w a s c o n d u c t e d t o d e t e r m i n e w h e t h e r t h e S

S t r e s s × F i t nes s i n t e r ac t i on p r ed i c t ed changes i n hea l t h s t a t u s

o v e r t i m e . T h e d e p e n d e n t v a r i a b l e f o r t h is a n a l y s is w a s s u b j e c t s 'v i si ts t o t h e h e a l t h f a c i li t y d u r i n g t h e s p r i n g a c a d e m i c s e m e s t e r

(M = . 74 ) . A f t e r con t ro l l i ng fo r hea l t h cen t e r v i s it s du r in g t he

f a l l s em es t e r (M = . 76 ) , s t anda rd i ze d s t r e s s an d f i t ne s s s co re s

w e r e e n t e r e d i n t o t h e p r e d i c t i v e e q u a t i o n . T h e c r o s s p r o d u c t

t e r m o f t h e s e l a t t e r f a c t o r s f ol l ow e d .

Th e on ly e f fec t t o ach i eve s i gn i f i cance w as t he S t r e s s × F i t -

nes s i n t e r ac t i on (~ - - - . 2 43 5 , p < . 05 , R 2 chan ge = . 06 ) . A s i n

t h e e a r l i e r a n a l y s e s , s t r e s s f u l l i f e e v e n t s w e r e m o r e s t r o n g l y

l i n k e d t o p o o r h e a l t h s t a tu s a m o n g l o w -f it s u b j e c ts t h a n a m o n g

h igh - f i t sub j ec t s . M oreove r , t he i n t e r ac t i on con t i nued t o be a

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

t r e s s w a s s t a t i s t i c a l l y c o n t r o l l e d ( /~ = - . 2 4 4 6 , p < . 0 5 , R 2

c h a n g e = . 0 6 ). B e c a u s e t h e s e a n a l y s e s e x a m i n e c h a n g e s i n

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

phys i ca l f i t ne s s bu f f e r s t he adve r se e f f ec t s o f l i f e st r e ss . H ow -

eve r , t he abso lu t e n um ber o f v i s it s i n t h i s ana lys i s w as l ow , i nd i -

c a t i n g t h e n e e d f o r c a u t i o n w h e n i n t e r p r e ti n g t h e s e f i n d i n g s.

Gen eral utilization o f health services. A f ina l s e t o f ana lyse s

w a s c o n d u c t e d t o d e t e r m i n e w h e t h e r s t r e s s a n d f i t n e s s i n t e r -a c t e d t o p r e d i c t v i s it s t o t h e h e a l t h c e n t e r f o r r e a s o n s o t h e r t h a n

phy sical i l lness (e .g . , che cku p, pre scr i pt io n ref il l; M = .99). N o

s ign i f i can t e f f ec t s w e re found . A s i n t he p r eced ing ana lys i s ,

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

the abso lu t e nu m b er o f v is i ts i n t h i s ana lys i s w as l ow . Th i s ca -

v e a t n o t w i t h s t a n d i n g , t h e s e r e s u lt s a r e o f i n te r e s t b e c a u s e t h e y

ind i ca t e t ha t s t r e s s and f i t ne s s w ere un ique ly r e l a t ed t o hea l t h

cen t e r v i s i t s f o r phys i ca l i l lne s s r a the r t han t o a t en den cy t o v i s i t

t he u n ive r s i t y hea l t h f ac i l i t y i n gene ra l .

D i s cu s s i o n

P r i o r r e s e a r c h s u g g e s t e d t h a t p h y s i c a l f it n es s m a y s e r v e t o

p r o t e c t p e o p l e f r o m i l l n es s u n d e r p e r i o d s o f h i g h s t re s s ( B r o w n

& Law ton , 1986 ; B row n & S iegel , 1988 ; R o th & H o lm es , 1985).

H ow eve r , p r i o r r e sea rch w as po t en t i a l l y l im i t ed by ( a ) r e l y ing on

e i t he r s e l f - r epo r t s o f f i tne s s o r s e l f - r epo r t s o f hea l t h an d (b ) by

f a il i n g t o c o n s i d e r t h e i n f lu e n c e o f p o s s i b l e t h i r d v a r i a b l es . T h e

p u r p o s e o f th e p r e s e n t s t u d y w a s t o a d d r e s s t h e s e p o s s ib l e l im i -

t a t i o n s a n d t h e r e b y p r o v i d e a s t r ic t e r t e s t o f th e s t re s s - b u ff e r in g

hypo thes i s .

L O W

F I T

H I GH

F I T

1 I I

L o w H i g h

STRE SS

Figure 1. Schematic representation of the Stress x Fitness interactionin the prediction o f illness (health center visits).



56 0 JO N A TH O N D . B R O W N

The r e su l t s w e re cons i s t en t w i th t he c l a im tha t phys i ca l f i t -

ne s s c ush ion s t he de l e t e r i ous e f f ec ts o f l if e s tr e s s . L i f e s t r e s s w as

s t rong ly r e l a t ed t o i l l ne s s (hea l t h cen t e r v i si ts ) am o ng sub j ec t s

w h o s e p e r f o r m a n c e o n t h e b i c y c l e t e s t i n d i c a t e d a r e l at iv e ly l o w

leve l o f phys i ca l f i tne ss , bu t l i fe s t r e s s ha d l i tt l e i ll e f f ec t am on g

sub j ec t s w h ose f i t ne s s l eve l w as r e l a t i ve ly h igh . M oreove r , t he se

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

d i s t r e s s w e re s t a t i s t i c a l l y con t ro l l ed . These da t a t hus sugges tt ha t f i tne s s m ay m i t i ga t e t he adv e r se im p ac t o f li f e s t r e ss .

O n e ' s c o n f i d e n c e i n t h i s c o n c l u s i o n i s b o l s te r e d f u r t h e r b y

t h e f i n d in g s f r o m t h e p r o s p e c t i v e a n al y s es . T h e s e a n a l y s es e x -

a m i n e d w h e t h e r f it n es s m o d e r a t e s t h e e f fe c ts o f s tr e s s o v e r a

6 - m o n t h p e r i o d . B y p a r t i a l i n g o u t i n i t ia l h e a l t h s t a t u s, t h e y a l s o

t e s t e d w h e t h e r t h e S t r e s s × F i t n e s s i n t e r a c t i o n p r e d i c t e d

c h a n g e s i n h e a l t h s t a t u s o v e r t im e . F i t n e s s c o n t i n u e d t o b u f f e r

t he nega t i ve e f fec t s o f l i fe s t r e s s i n t he se ana lyse s . B ecau se t he se

a n a l y s e s e x a m i n e d c h a n g e s i n h e a l t h s t a t u s o v e r ti m e , t h e y p r o -

v ide pa r t i cu l a r l y sug ges t i ve ev iden ce t ha t s t r e s s and f i tne s s a f -

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

w h e n m a k i n g t h i s c l a im b e c a u s e e v e n p r o s p e c t i v e a n a l y s e s c a n -

no t un equ ivo ca l l y e s t ab l ish cau sa l r e l a ti ons .

O t h e r a s p e c t s o f t h e c u r r e n t r e s e a r c h a l s o i n d i c a t e a n e e d f o r

c a u t i o n w h e n i n t e r p r e t i n g t h e f i n d in g s . T h e m e a s u r e s o f fi tn e s s

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

o v e r s e lf - r e p o rt m e a s u r e s . N o n e t h e l e s s, t h e y p r o v i d e o n l y a n

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

T h i s c a v e a t is p a r ti c u l a r ly p e r t i n e n t r e g a r d i n g t h e h e a l t h m e a -

s u re . A l t h o u g h m a n y p e o p l e v i s i t a d o c t o r w h e n i ll , o t h e r s d o

n o t ; t h u s , h e a l t h c e n t e r v i si ts r e p r e s e n t o n l y a r o u g h m e a s u r e o f

phys i ca l w e l l -be ing . Fo r t h i s r ea son , a r ep l i ca t i on o f t he f i nd -

i n g s u s in g m o r e p r e c i s e m e a s u r e s o f i U n e s s i s n e e d e d . R e s e a r c h

u s i n g a m o r e o b j e c ti v e m e a s u r e o f li fe s tr e s s t h a n t h e r e t r o s p e c -

t i ve s e l f - r epo r t m easu re u sed he re i s a l so des i rab l e . M ore d i r ec t

m e a s u r e s o f f i tn e s s (e .g ., a c t u a l a s o p p o s e d t o e s t i m a t e d m a x i -

m u m o x y g e n u p t a k e ) a r e a l s o d e s ir a b l e f o r f u t u r e r e s e a rc h .A n o t h e r p o s s i b le l i m i t a t io n o f t h e p r e s e n t r e s e a r c h c o n c e r n s

the age o f t he sub j ec t s. Th e s t r e s s fu l even t s t ha t co l l ege s t uden t s

expe r i ence , t h ou gh sub j ec t i ve ly t r oub l i ng , m ay be l e s s s eve re o r

c h r o n i c t h a n t h e e v e n t s o l d e r a d u l t s e n c o u n t e r . C o l le g e s t u d e n t s

a l s o t e n d t o b e i n b e t t e r h e a l t h t h a n o l d e r ad u l ts . T h u s , a l t h o u g h

t h e i l l ne s s e s e x a m i n e d i n t h e p r e s e n t r e s e a r c h w e r e s e ri o u s

e n o u g h t o w a r r a n t m e d i c a l a t t e n t i o n , t h e y w e r e r e l a t i v e l y

m ino r i n s eve ri ty . Fo r t he se r ea sons , r e se a rch i s needed t o de t e r -

m i n e w h e t h e r f it n es s m o d e r a t e s t h e e f fe c ts o f s tr e s s i n o l d e r

p o p u l a t i o n s .

T h e r e la t iv e h e a l t h o f su b j e c ts i n t h i s s t u d y m a y e x p l a i n w h y

f i tne s s d id no t have a d i r ec t e f f ec t on hea l t h s t a t u s . E f f ec t s o f

f it n es s a m o n g y o u n g a d u l t s m a y e m e r g e o n l y w h e n h e a l t h i st h r ea t ene d . I n t h i s s ense , po o r f i tne s s w o u ld func t i on a s a d i a th -

e s i s i n t h i s popu l a t i on ; l i f e even t s f unc t i on a s t he s t r e s s t ha t

ac t i va t e s the vu lne rab i l i t y f ac to r .

A n i m p o r t a n t a s p e c t o f t h e p r e s e n t r e s e a r c h w a s a n a s s e ss -

m e n t o f t h e p o t e n t i a l m e d i a t i n g r o l e o f p s y c h o l o g i c a l di s tr e ss .

A s n o t e d e a rl ie r , a n u m b e r o f p a p e r s h a v e r e c e n tl y a p p e a r e d

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

s u b j ec t iv e i n d i c a t o r s o f h e a l t h m a y b e s p u r i o u s i n s o f a r a s p s y -

c h o l o g i c a l d i s t re s s m a y u n d e r l i e b o t h o f t h e s e v a r i a b l e s ( C o s ta

& M cC rae , 1987 ; W a t son & Penne bake r , 1989) . I n t heo ry , t h i s

c r i t iq u e a p p l i e s t o v a r i a b le s t h a t h a v e b e e n i d e n ti f ie d a s m o d e r a -

t o r s o f t he s t r e s s - i l l ne s s r e l a t ion , su ch a s phys i ca l f it ne s s and

soc i a l suppor t (C ohen , She r rod , & C la rk , 1986) .

A s p e c t s o f t h e p r e s e n t f i n d i n g s p r o v i d e s u p p o r t f o r t h e c o n -

t i n u e d e x a m i n a t i o n o f t h i s i s su e . A l t h o u g h s e l f- r e p o rt s o f e x e r-

c i s e and s t r e s s i n t e r ac t ed t o p r ed i c t s e l f - r epo r t s o f hea l t h , t hey

d id n o t i n t e r ac t t o p r e d i c t hea l t h ce n t e r v is it s. M oreove r , t he se

v a r i a b le s d i d n o t i n t e r a c t t o p r e d i c t s e l f -r e p o r ts o f h e a l t h a f t e r

psych o log i ca l d i s t r e s s w as s t a t i s ti c a l l y con t ro l l ed .O n e w a y t o a c c o u n t f o r t h e s e f i n d in g s i s t o a s s u m e t h a t s e lf -

r epo r t s o f s t r es s , exe rci s e , and hea l t h hav e bo th va l i d and i n -

v a l i d s o u r c e s o f v a r ia n c e ( W a t s o n & P e n n e b a k e r , 1 9 8 9) . T h e

i n v a li d s o u r c e o f v a r i a n c e d e r iv e s f r o m t h e i n f lu e n c e o f p s y c h o -

log i ca l d i s t r es s . W he n sub j ec t i ve pe rce p t i ons o f t he se va r i ab l e s

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

t h e p o s s i b le c o n t a m i n a t i n g e f fe c ts o f p s y c h o l o g i c a l d i s tr e s s

( W a t s o n & P e n n e b a k e r , 1 9 8 9) . T h e n e e d t o c o n t r o l f o r d i s t re s s

a p p e a r s l e ss c r i t ic a l w h e n m o r e o b j e c t i v e i n d i c a t o r s o f s t re s s,

f it nes s , an d h ea l t h a r e u sed .

C o n c l u d i n g R e m a r k s

T o s u m m a r i z e , t h e p r e s e n t r e s e a r c h p r o v i d e d a c o n s e r v a t i v et e s t o f t he h ypo th es i s t ha t phy s i ca l f it ne s s bu f f e r s t he nega t i ve

e f f ec t s o f l i f e s t r es s . I n a cco rdan ce w i th t h i s hypo thes i s , t he

f i nd ings show ed t ha t p eop l e w h o a r e phy s i ca l ly fi t a r e l e s s vu l -

ne rab l e t o t he ad ve r se e ff ec ts o f l i fe s t re s s t han a r e t hose w ho a r e

l e ss fi t. A l t h o u g h i n t h e a b s e n c e o f r a n d o m a s s i g n m e n t t o c o n -

d i t i ons , one can neve r be ce r t a in t ha t f i t ne s s , pe r s e , i s t he

ope ra t i ve va r i ab l e , t he r e su l t s a r e ce r t a in ly sugges t i ve o f t ha t

c o n c l u s i o n . A t t h e v e r y l e as t , t h e y p r o v i d e t h e m o s t c o n v i n c i n g

ev idence t o da t e t ha t phys i ca l f i t ne s s s e rves t o p ro t ec t peop l e

f rom the de l e t e r i ous e f f ect s o f l i f e s tr e s s .

A s ev ide nce fo r t he s t r e s s -bu f f e r i ng ro l e o f fi t ne ss con t i nu es

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

unde r l i e t he e f fec t. B o th phys io log i ca l and psycho log i ca l va r i -ab l e s a r e ve ry l i ke ly i nvo lved (B row n & S i ege l, 1988) . A s co n -

c e r n s p s y c h o l o g i c a l v a r ia b l e s, t w o m e d i a t i n g m e c h a n i s m s

s e e m p a r t i c u l a r ly p r o m i s i n g . O n e c o n c e r n s f e e li n g s o f p e r -

c e i v ed c o n t r o l a n d m a s t e r y . S i m o n s , M c G o w a n , E p s t e i n ,

K u p f e r , a n d R o b e r t s o n 0 9 8 5 ) r e c e n t l y r e v i e w e d t h e r e l e v a n t

l i t e ra tu r e a nd con c lud ed t ha t f ee l i ngs o f m a s t e ry and s e lf -e ff i-

cacy i nc r ea se a f t e r r egu l a r ph ys i ca l exe rc is e . Th i s f i nd ing i s

i m p o r t a n t b e c a u s e t h e b e l i e f t h a t o n e c a n c o n t r o l e v e n ts h a s

b e e n s h o w n t o r e d u c e s t r e s s r e s p o n s i v i t y ( R o d i n , 1 9 8 6 ) .

W h e t h e r f e e li n g s o f m a s t e r y a n d s e lf -e f fi c ac y u n d e r l ie t h e b e n -

e f i t s t ha t f i t ne s s p rov ides unde r s t r e s s r ep re sen t s a p rom is ing

top i c fo r f u tu r e r e sea rch .

A n o t h e r v a r i a b le t h a t d e s e r v e s c o n s i d e r a t i o n i s a tt e n t i o n a l

focus . Phys i ca l f i t ne s s t r a i n ing t yp i ca l l y t u rns peop l e ' s a t t en -t i o n a w a y f r o m t h e s t r e s sf u l c i r c u m s t a n c e s i n t h e i r l if e ( B a h r k e

& M o r g a n , 1 9 7 8) . B y p r o v i d i n g a t e m p o r a r y r e s p it e f r o m l if e

s t re s s , exe rc i se m ay se rve a bene f i c i a l r e s to r a t i ve func t i on t ha t

a l lo w s p e o p l e t o d e a l w i t h s t re s s fu l c i r c u m s t a n c e s m o r e e f f e c-

t iv el y. I n t h i s m a n n e r , a t t e n t io n a l f o c u s m a y p r o v i d e a n o t h e r

rou t e t h rou gh w h ich s t a y ing f it is l i nked t o s t ay ing w e ll .

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