Specificity and Reversibility of InspiratoryMuscle TrainingLEE M. ROMER' and ALISON K MCCONNELL 2

'Sports Medicine (rid Human Performarnce UnIit, School of Sport andz1 Exercise Sciences, The UniversitY of Birmingham,Edgbaston, Birmingham, UNITED KINGDOM; and 2 Departmeat of Sport Sciences, Brunel University, Uxbridge,Middlesex, UNITED KINGDOM

ABSTRACT

ROMER, L. M., and A. K. MCCONNELL. Specificity and Reversibility of Inspiratory Muscle Training. Med. Sci. Sports Exerc., Vol.35, No. 2, pp. 237-244, 20)3. Purpose: The purpose. of this study was to evaluate the pressure-flow specificity of adaptations toinspiratory muscle training (IMT), in addition to the temporal effects of detraining and reduced freqluency of training upon theseadaptatiois. Methods: Twenity-four healthy subjects were assigned randomly to one of four groups (A: low-flow- high-pressure IMT;B: high-flow-low-pressurre IMT; C: intermediate flow-pressure IMT: and D: no IMT). Subjects performed MIT 6 d.wk ' for 9 wk,and inspiratory muscle fiunction was evaluated at baseline and every 3i wk. Groups A, B, and C were then assigned randomly to eitheera maintenance group (M) (IMT 2 d-wk- i) or a detraining group (DT) (no IMT). Inspiratory muscle lunction was reassessed at 9 and18 wk post-IMT. Resullts: At 9 wk, group A exhibited the largest iricrease in pressure. B a large increase in flow, C more uniformincreases in pressure and flow, and D no changes in pressure or flow. Maximuim inspiratory muscle power increased in groups A, B,and C by 48 + 3%, 25 t 3%, anid 64 - 3%, respectively (tnean ± SEiM, P c 0.01). Maximurn rate of pressure development increasedin groups A, B, and C by 59 + I %, 10 t I %, and 29 ±- I %, respectively (P - (101). A decrease in inspiratory muscle function wasobserved at 9 wk post-IMT in DT. Inspiratory muscle function plateaued between 9 and 18 wk but remained above pre-IMT values.(Group M retained the improvements in inspiratory muscle functior. Conclusion: These data support the notion of pressure-flowspecificity of IMT. Detraining resulted in small but significant reductions in inspiratory muscle fLunction. Reducing training frequencyby two thirds allowed for the mnaintenance of inspiratory muscle finction tlip to 18 wk post-IMT. Key Words: RESPIRA'TORYMUSCLE TRAINING, BREATHING EXERCISES, DETRAINING, MAINTENANCE

T he training principles of specificity and reversibilityare well established for peripheral skeletal miuscles.Specificity implies that the nature of the change in

muscle structure and function is determined by the nature ofthe applied stimulus (21). The reversibility principle holdsthat when physical training is stopped (detraining), the bodyreadjusts in accordance with the diminished physiologicaldemand, and the beneficial adaptations may be lost (22).Few studies have been conducted to deternmine whetherinspiratory muscles also respond to the aforementionedtrainiing principles, but it is reasonable to suppose that theydo.

The force-velocity specificity of training proposes thattraining with high-force-low-velocity contractions specifi-cally increases maximal force but not maximal shorteningvelocity, whereas training with high-velocity-low-force

Address for corresponidence: Lee M. Romer, John Rankin Laboratory ofPulmonary Medicine, Department of Population Ilealth Sciences, Ulliver-sity of Wisconsin, 504 Walnut Street, Madison, WI 53726; E-mail:romerlin @ hotmail.com.Submitted for publication May 2002.Accepted for pttblication September 2002.

0195-91 31103/3502-0237/$3.0010)MEDICINE & SCIENCE IN SPORTS & EXERCISE,Copyright C) 2003 by the American College of Sports Medicine

DOI: 10.1249/01 .MSS.0000048642.58419. tE

contractions specifically increases maximal rate of shorteningbut not maximal force (7). Inspiratory airflow is proportional tovelocity of muscle shortening, and inspiratory pressure is pro-portional to force generation. Therefore, increases in maximalinspiratory flow mnight be expected with high-velocity trainingand increases in maximal inspiratory pressure with high-forcetraining. Indeed, training with resistive loads and high-flowloads appear to increase maximal static pressures (17,27,28)and miaximal inspiratory flow rates (27,28), respectively. Therate of rise in peak tension may also be improved by specifictraining. For examnple, training with contractions of high-forceand high-velocity increases the maximum rate of force devel-opment in petipheral skeletal muscle (9,20). The influence ofinspiratory muscle trainiing (IMT) upon the maxinmum rate ofpressure development (MRPD) is less clear. There is evidencethat MRPD increases with both high-pressure and high-flowtraining (27). However, these findings await independent ver-ification, and the timze course of the adaptations is unknown.

Although nortmal whole-body endurance training pro-mlotes a variety of physiological adaptations. long periods ofinactivity (detraining) are associated with a reversal of manyof the adaptations (22). Unfortunately, the extent and timecourses of detraining are not well documented for inspira-tory muscle function. From a practical perspective, it wouldbe useful to know whether reducing the frequency of IMI'while maintaining the training intensity attenuates any de-crease in inspiratory muscle function associated withdetraining.

237

TABLE 1. Descriptive obaracteristics of ttie subjects (nmean t SE'-M).:: y :: _y) 5 fS.:: :f ? ::- f ;-2--=- +--0 --: -----:-----::- :- --- -- -- -t- ---S --D---

___Grouip A' fGroup SI Group C- firot:p DI-------- -- ----...... , . . . .. . _ _ . _ _ . ... . ... .. . . . . . . ..... ...... .

Gender (int) 4/2 3/3 3/3 3.'3Age (yr 24.2 2. 30.5 - 4.0 29.7 - 2.5 25. . 2.6 Stature (in) 1.74 :- 02 1.73 . 003 1.74 +0.02 1.73 0.05Body mass 'kg) 77,9 51 71.2 3.4 716 - 3.1 72.0 - 6.4RtO (L) 5.06 ± 0.08 4.85 0.25 5.04 7 0. 9 5.06 ± 0.27

(10011) (100 1) (10311 103 --itFEVy (L) 4.29 -0.06 4.04 -02Q 4.17 . On3 427 0.20

(100Q- 1 (99±1) (101 -1) (102± 1)PEF (1mi ) -5876 -5.4 5707 19.4 5840 16.1 587.7 181

(100 . 1) (99 1 (102 1) (102- 1)IV - 6; FVC, forced vita' capacity; FEVy forced exp ratory vorunme n one second; PEF, peak exoiratorv flov.w Values en parefltheses represent perc-ent of prediced values based on

age, stature, and gender (24).

Based on the aforemnentiioned considerations, the purposeof tlis sttudV was to determinite the pressure-flow specificityof adaptations to mIr, in addition to the teinporal effects ofdetraining and reduced frequency of trailrng upon: theseadaptations. We hypothesized that I) training with resistiveloa&s aned high-flow loads would increase mtaximatl staticpressures and nnaxinnal inspiratory flow :rates, respectivelv:2) detraining would result in a reversal of these adaptations:and 3) reducing the frequenticv of trainin,g while maintainingthe training intensity would atteniuate any decrease in in-

spiTatory mtuscle functiont associated Withl detrailinig.

METHODS

Subjects

After approval fronn the Human Sutbject Research EthicsCommittee of the University of Birmningharm anrid writteninformed conisent, 24 healthy individuals 1l3 onale) wereassigned riandoimly in equal nurnbers to onfle of four groups(Table I). Grotip A performed IMIT witsh low-flow, high-

pressure loads, group B performed IMT wxith high4flunvv,

low-pressure loads; groupr C performed IMT vvith (uterine-

diate flow and pressure loads; and group D received nio

traiining (i.e.. control). None of the subjects had experience

in perforining respiratory exercises.

Study Design

Pulmonary futnction antiaxiatuni dynamnic ienspiratorny

miuscle function were assessed. Subjects wvere familliar-

ized thorou,glnly with test procedures (visit 1) before tile

preintervention trial (visit 2). Visits I and 2 were sepa-

rated by at least 48 h and coimipletedt within 2 vwk. Sub-

jects' inspiratory rauscles Were trainled 6 dwl-vk for 9 wk,

and respiratory fLnctionr wvas reevaluated every 3 wk.

After the intervention, trained su-bjects (groups A, B, and

C) were assignedl randoml-Ly to) either a inainiteriance grou:p

(M) who redueced their trainin(g frequencv to 2 d-wk--' or

a detraining g-oup (DT) who refrahined freotn IMT. Sub-

jects' pulnionary and inispiratory nusciee fintetsion were

reassessed at 9 and S 1wk postintervention. Thus, the

overall duration of the studs was -29 wk.

Procedure

Pulmonary function. A pneumotachograph spirome-ter (Vitalegraph 2120, Buckingham., UK) was uIsed tomeasure resting flow-volutme profiles. The followingvariables vvere derived: forced vital capacity ilFVC').forced expiratory voiluie in i s (FEV)s, and peak expi-ratory flow (PEF). Pulmonary funiction rneasureniertswere tmade according to European Respiratory Societyre nniendration (24) (Table I).

Maximum dynamic inspiratory muscle function.Th' pressutre-flowx relatiiuship for i§nspirat1oVi musclesworking inn synergy was assessed using inaxirrmal inspiratoryefforts pertormtned agaitnst a presstre-threshold valve au'-rarngeinent (61) Inspiratory niouth pressure was miieasuredwith a pressure transducer (Mercury M14, Glasg-ow, UJK)connected by polyethylene tubinig to a 4-mmn ID1) vent locatedineur the moutlpipece of the breathing circuit. Inspiratoryairfiow was neasured -with an ultrasonic pase-shift flowrmieter (Birainingham Flowrnetrics ;td., Bintnttinghann, UK)located distal to the pressure-threshold valve. Pressure andflow signals were amplified, passed through a 12-bit analo,g-to-digital converter at a sanpiing irate of 200 Hz. recordedon a comiputer, and processed qsimg bespoke softvare (Lab-view 3, National Instrurnetits, Austin TX).

MaxiRmum- 1p:ressure at zer o flow (Po) was measured withcomplete closure (f the threshold valve. A I -imni orifice wasexposed t(o prevent the subject fiomr, producing artificiallyhighi inspiratory pressures with the miuscles of the buccalcavitv (4). To ensutre that inspirartorv efforts were performiedat the sanne lungy \vlunne (residual volutne), changes in vitalcapacity were mneasured with a pneumotachogr4ph spirom-eter (Vitalograph 2120) connected ihi series to ite expiratoryport of the pressure-threshold dLevice. After thie determlina-dion of P,1 individutls performiied inspiratory maneuverswvith mnaximial effort against six discrete load settings (-0,20, 25, 35. 50(, anid 65% fP). which were assigned randomlyusing a balatnced Latin square for an even nunber Of treat-meat conditions. The or(der of treatments was: retainedthroughout the reninainimng trials. Three twchnically correcttrials were performed at each of the loading intensities and30 s was permnitted between efforts. Maximal pressure andunloaded flow were reevaluated at the end of each mieasure-mtent session. No changes Were observed conuipared withinitial values, suggesting the absenice of pressure and flow

238 Official Journal of the American College of Sports Medicine httpi//vVvvvv.acsm-msse.org

150

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100

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0 I ,

o 1/' T FD

1 300

200 -1 I0

100 _ v /~~~~~~~~

__ A_7_ - __ -, 1 0

0 2 4 6 8 10

VI (L.s-')

FIGURE I-Schematic representation of inspiratory pressure-flow-power calculations. V1, inspiratory flow rate; Pi, inspiratory mouthpressure; WI, inspiratory muscle power. A, maximal flow (Vn,,); B,maximal pressure at zero) flow (P9); C, maximal power (Wl -J,a); D,optimal flow (VY,,); E, optimal pressure (P,,p1).

fatigue. All maneuvers were performed while seated andwere completed within -15 mimi. Subjects received visualfeedback of pressure and flow to miaximize respirator-y ef-forts, and were instructed to inhale maximally and as rapidlyas possible.

Pressure and flow measures were obtained from the sin-gle inspiratory effort at each level of %P0 that gave thelargest product of inspiratory pressure and flow (i.e., pow-er). Pressure-flow data for the diffe-rent %P,, trials werefitted by curves drawn accordini to a linear least squaresrepresentation [P = aV + b], where P is pressure (cm H20),V is flow (L-s-'), and a and b are constants. Maximal flow(V,,ax) was derived for each subject from the experimentaldata by extrapolation. Inspiratory muscle power (W1) wascalculated fromii the product of inspiratory pressure and flowrate. Maximal power of the inspiratory muscles (WI inax; cm

H,O-L-- l *s- l) was calculated by differentiation from a zeroslope tangent to the flow-power data. Optimal flow (VP,;L-s-' and YoV,,1ax) and optimal pressure (P Pt; cmn H,O and%P.) were defined as the flow and pressure values coiTe-sponding to WI on the power-flow curve, respectively(see Fig. 1). The MRPD occurring during the initial inclineof the maximal inspiratory pressure curve was assessed anddefined as the positive peak of the pressure derivative as afunction of time.

IMT. After completion of the baseline measurements,each training group performed IMT twice daily (6 d-wk 1)for 9 wk using a pressure-threshold device (POWER-breathe®'D. IMT Technologies Ltd., Birmingham, UK) iden-tical to that used to measure baseline dynamnic inspiratorymuscle function. The first training session was supervised,and subsequent sessions were performed in the subjects'own time away from the Iaboratory. Group A performed 10sets of three maximal static inspiratory mianleuvers withminirmal recovery between sets frorm RV daily. During thesemaneuvers, inspiratory airflow was negligible although a1-mm orifice was exposed to prevent contraction of theibuccal mnuscles. Subjects were instructed to contract their

inspiratoiy muscles maximally for -2 s. Group B performed

30 maximal inspiratory efforts with no added external re-sistance from RV daily. Group C performed 30 maximalinspiratory maneuvers from RV at 50% P,. Subjects inGroups B and C were instructed to continue the inspiratoryefforts up the lung volume where the inspiratory muscleforce output for the given load limiited further excursion ofthe thorax. Because of the increased tidal volume, a de-creased breathing fiequency was adopted to avoid hyper-ventilation and the consequent hypocapnia. Control subjectswere assigned to group D and received no training. After theintervention, three of the subjects from each of the threeIMT groups (A, B, and C) were assigned randomly to amaintenance group (M). These subjects continued with theiroriginal training but reduced their training frequency to 2d-wk-'. The remaining subjects were assigned to a detrain-ing group (DT) who refrained from IMT. It was impressedupon subjects that all inspiratory efforts should be maximaland rapid. The number of inspiratory efforts completed bysubjects during the nonsupervised sessions was monitoredusing a thermistor suspended within the main body of thetraining device that sensed acute drops in air temperatureassociated with changes in airflow. Subjects completed bothIMT and physical activity diaries throughout the interven-tion study.

Data Analyses

Mixed factorial ANOVA was used to test for betweengroup effects dVe to treatment (group A, B, C, D, M, or DT)and within-group effects due to time (week 0, 3, 6, 9, 18, and27) on each of the dependent variables. Planned pairwisecomparisons were made with repeated measures 1-tests andthe Bonferroni adjustment was used to modify the per fam-ily Type I error rate per comparison. Results are expressedas mean ± SEM. An alpha level of 0.05 was chosen a priorito represent statistical significance.

RESULTS

Habitual Physical Exercise and IMT Compliance

Physical activity did not vary between or within groups.Furthermore, no differences were observed between andwithin groups for the number of actual completed IMTsessions relative to the expected number of sessions. GroupA completed 98 ± 3 of the 108 IMT sessions (91 % adher-ence), group B completed 95 ± 2 of the 108 IMT sessions(88% adherence), whereas group C completed 96 ± 3 of the108 IMT sessions (89% adherence). For the 18-wk postint-ervention period, group M completed 32 ± 2 of the 36 IMTsessions (90% adherence).

Pulmonary Function

For all groups, pulmonary function remained unchangedfrom baseline values throughout the period of study.

Medicine & Science in Sports & Exercise,. 239SPECIFICITY AND REVERSIBILITY OF IMT

Maximum Dynamic Inspiratory Muscle Function

Pressure41owjpower rel"atonships. Fir group D)maximum dynamic ilnspiratory Imusle funl¢ction remiairnedunchanged from baseline values throughout the du:rationof stuLdy. For the training groups, the post-IMTf effctsupon inspiratory mlUuscle function were dependnt on thetraining protocol. After 9 wtk of training, ,roup A in-creased P 0 (41 + ± , p * (),)101) but n3ot 4max U _ liaroup B showed an increase in V. (I 8 t 1 %, P 0AI)but not Pl1 (9 ± 1% ), atid roup C showed an increase inP0 (34 4 1%, JP• 0.01) and Vmnx (26 z 1%. P 0.01).The slopes of the mtaximnum instpiratoy pressure-flowregression incs measured at basclinse were not diffierentbetween groups. After 9 wTk of training, the slopes ofthese lines were different frotm baseline. values for groupA (--15.3 ± 0.7 vs 1-1 II. 7 +0.t6 ct H[10 'ps ', P0.01) anid group B (-10.8 ± 0.3 vs -- I.7 .-4 0.3 cmiH970 W- J'S-1, P < 0.01 ) but not group CC- 12.8 t0 0.8 vs- 1.8 -- 0 7 [ 1n HP0,-' s-'p > t 0.05) (Figl 2). In linewith the changes in presssure and filo, mraximum powerof the inspiratory muscles (W Smjx) was, increased ingQrouips A, B4, and C by 48 _- 3%, 25 + 3%YeX and 64 + 3%,respectively (Fjig. 3). Most of the ibmprove6ltenis wereapparenit after 6 wk of'IMT and further traing resultedin mniinimal improvemenit. Pressure-flow-power dlata forall groups are summarized in Table 2. The percentagechanoes with training are summnarized in Fig. 4.

MRPD. Significant increases In N4RPD above baseline val-ues were. observed after 9 wIk of IMT for group A (59 ± I%)group B (10 ± 1%). antd gtup C (29 ± 1%), respectively (P• 0.01) (Table 2). The timi e course of imrtvemient in MRPDcotinitnued up) to 9 wkt for groups A and C (Fig. 4).

200 Group A

150is

100

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V, (L.s-')

200 . Group B

150 1

IE 100

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200 - Grup C

150

E 100

60

Maintenance of Inspiratory Muscle Function

A dece ase in inspiratory muscle funiction was observedat 9 wk post-IMT in the group abstaining from trainling.Between weeks 9 and IS. inspiratory muscle function pin-teaued but renmained atibove pre-IMT values. 'T'he rnainte-n3anlce group retainied the imipr:o-vemiienits in inspiratory Mus-cle function (Table 3).

DISCUSSION

Main Findings

T'he purpose of this study was to determine the pres-sure-flow speciicity of adaptations to TINT. irL acdition tothe termporal effects of detraining and reduced freqtuencyof training upon these adaptations. As hypothesized.high-pressure training produced the largest iiprovementin pressure. high-flow training prodtuced large imvprove-

mnciit in flow, and intermediale trainling resulted in a moreuniform increase in pressure and flow. Tlhe maximalpower of the inspiratory muscles was improved most bythle. intermediate trainitng and least bv the high-flow train-ing. The MRPD increased in all trailing groups wvith the

240 Official Journal of the American College of Sports Medicine

0

200 -,

I 1 .. -0: - }

2 4 6

VI (L.rS1)

8 10 12

Group D

150 -

0 2 4 6 a 10 12

V' (L.S-)

FIG(URE 2-4aspiratory mouith pressure (Pi) vs inspiratory tlowv rateW1) befoire (dosed circles) and after 9 wk of IMIT iopen cireles) for

grupsI A-ID. P1-V1 data are represented In both axes aspooled m ean± SEM.

high-pressure and intermediate pressure-flow training

eliciting the largest changes. Most of the pressure-flow-po-wer adaptations were expressed fully by the sixth weekof traiining. Detrainfiing resulted in small but significant

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a 10 12

10 12

500 Group A

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W - -- - ___ - - .- T

0 2 4 6 a 10 12

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Group C

2 4 6 8 10 12

V, (L.s-1)

Group D

-i --- - ---- __ 0 2 4 6

Vu (L.s')

8 I _ 1 28 10 12c

FIGULRE 3-Itspiratory muscle work rate (W1) vs inspiratory flowrate (V,) before (closed circles) and after 9 wk of IMT (open eircles) forgroups A-D. W,-_, data are represented in both axes as pooled mean+ SEM.

reductions in inspiratory muscle function toward pre-training values. Reducing the frequency of training by upto two-thirds resulted in the maintenance of inspiratorymuscle function.

SPECIFICiTY AND REVERSIBILITY OF IMT

Maximum Dynamic Inspiratory Muscle Function

Pressure-flow-power relationships. Our results sup-port evidence that the general principle of force-velocityspecificity of skeletal muscle training applies to the inspira-tory muscles. Specifically, training with high-pressure wasfound to increase maximal static pressures (17,27.28) andiraining with high-flow to increase maximal inspiratoryflow rates (27,28). The finding of an increase in both max-imum pressure and flow after training with a mixed proto-col, characterized by pressures and flows intermediate inmagnitude to their respective maximum, is in agreementwith the results from a previous study (28). The posttrainingincrease in Vrn 1 U8%) with flow training was appreciablysmaller than the increase in P0 with pressure training in thepresent study (41%) and in previous studies of IMT(I 7,27,28). This finding suggests that P0 is more responlsiveto trainiing stimuli than Vm-ax and is consistent with ourunderstanding of the factors that determine the force-veloc-ity characteristics of muscle (16).

Although our results provide further Support for a pressure-flow specificity of IMT, it is unknown whether these adapta-tions reflect changes in the contractile proteins or are related todifferences in inspiratory muscle activation induced by thedifferenit protocols. In general, the initial period of improvedperformance with strength training has been attributed primar-ily to neural adaptations that occur in the first 5-6 wk oftraining (20,25). Neural adaptations that may have occurred inresponse to IMT include an increased number of motor unitsrecruited (1), an increased motor unit firing rate (25), enhancedsynchrony of motor unit firing (19), decreased co-activation ofantagonist muscle groups (8). or a combination of these factors.Alternatively, the initial velocity-specific adaptation withinmuscle might reflect acquisition of skill, such that trainingimproves coordination and muscle activation at the trainingvelocity (2). Later in the training cycle, the myogenic phase oftraining tends to predominate where changes occur in thecontractile proteins (25). Muscle hypertrophy and a transfor-nmation of Type Tl muscle fiber subtypes (from Type lix to lla)have been reported responses to strength training (26). To whatextent, if any, these latter adaptations explain strength increasesis unclear, but there is substantial support for the involvementof muscle hypertrophy in the increased strength observed withtraining (26).

MRPD. The MRPD for the zero flow condition increasedin all training groups, with hiigh-pressure (group A) and inter-mediate pressure-flow (group C) training eliciting the largestchanges. This finding is in contrast with the widely held beliefthat training with static loads increases the maximal forceproduction of a muscle without changing the rate of forcedevelopment, whereas training with dynamic loads inducessmaller changes in force generation but increases the rate offorce development (9,12,13). All subjects in the present studyunclertook training that involved rapid, ballistic contractions,chalracterized by short times to peak tension development.Thus, the finding of an increase in MRPD in response to bothhigh-pressure and intermediate pressure-flow IMT is in agree-ment with recent evidence that the intent to make a high-speed

Medicine & Science in Sports & Exercise,, 241

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400 1

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TABLE 2. Summary of pressure-flow-Power data fcr groups A to D0 (mean m 9ENI4).

Pre-IMT

Week Ko. 0

P, (cm 920)AB

ma'L-s i')AB0

W, naar (cm H,0-L I sAB

DP0i,i lcm 120)

AB

9,,' (L's 1)AB

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105 10,05 1 0

101 ±997 * 10.

59 0.7,

5.6 + 05,53 + o.5,

289 52248 +F k4,

222 ± 35203 ± 286

56 5- 554 5.51 5,449 -59

4A 034.4- 0.3443 1 04,c4.2 4~ 0.3,

_MT

3

?38 4-12,110 1%,11 + t1097 + 10°

95 + 0.7,9.9 t0.7,9.6 .O0,V8.4 1 0.4,

337 50,279 41b296 + 45,212 + 29,

69 6,

59 - 5b51 + 5,

4.5 t V.4,4.g +0.3,4.9 -04,4.2 . 0.3,,

6

146 13,112 10,131 s 11,97 1 0v,

9.7 710.3 ±0.7,10.9 + 0.9,8.3 t 05,

364 - 54,297 + 44,355 + 55205 ' 26

73 6 956+ 565 ± 6,.49 5:,

49 _ 0452 - 0'4C53± 0.5,4.2 02,

9

151 t 13,113 + DQ136 + '3102 a 10.

C9S - 0.8610.5+ 08107 I 10

8.1 - a3

381 : 59,307 _ 47,372 60,206 24,

75 7,57 t557 + 5c51 -

4.9 0.4,5.3 + 045.3 t .5,4.0 + 01,

A .53 HQ5 01 +-0.627 0.007. 0.842 + 0.007,B 0.25 r 0 tOOS 575 0.0505., 0978 004, 0.578 f 05C 0517 t 0006, 0.639 - 0.002, 0.655 12 0.65 t .01 1,.D 0;521 H O.T07 0.530 0006, 0531 + 0007. 0.531 a 0.007,

N' - 6 in achr group. p,, maximuam inspiratery pressure at zero flow; V,ai, mrax,eIurm inspiralory flow: W ,. maximTum inspiratory muscle work rate; P,,,, optImal pressure; V,p,opt:mal flow; MRPD, max.murn rate of pressura developinment, Means in tUe same roSw that do not share subscripts ditfer at P - 0.05.

contraction m4ay be the mtosa crucial fator in determinfing thedegree of adaptation in the velocity of a Mechanical response(3). It is also in agreemeint with previous evidene iht theMRPD increases in respontse to boh high-esure mad high-flow n-aiming during these respeecive maxial" efforts (t7). Theprecise mechanism(s) responslible for the change in MRPDwith taining is uLinknown, 'The uniq*ue fing frequency associ-ated with dynamnic contractions suggests possible adapitationsin the freqency of mtiotor unit disehqre with this tvyp oftraining (3). This sLggestion is supported by more recent ex-pennuental data showing that the decrease in time to pektension after dynamic training is associated with increasedmaximal firing freqncies of motor units (29).

Time Course of Adaptations

Most of the adaptations in inspiratory muscle fuinctionwere apparent with 6 wk of IMT and ftuther training up to9 wk resulted in minirnal improvements. In the rajority ofreported studies in healthy individuals, the diuration of IMThas beeen 4-8 wk. In a few studies, the trainingz period h1aslasted for as little as ' 6 d lI) or as long as 1 Wk (30).Volianitis et at. (30) did not detect an imnprovenment irinspiratory muscle furnction between 4 and I I Wk of IMT. Inthe absence of an objective measure of IMT compliance.those authors concluded that differences in subject mofiva-tion mnight have accounted for the finding. Otr data suggestthat there is a physiological plateau in strenlgth and powerdevelopmlent in response to IMT at 6 Wk.

242 Official Journal of the Amnerican College of Sports Medicine

Maintenance of Inspiratory Muscle Function

To the authors' knowledge, this is the fi stud 'y to in 'es-tigate specifically the effect of detraining upon inspiratorymuscle function Nine weeks of detraining resulted in s:mall butsigniificant reductionl in moSt measures of inspiratory Imusclefunction. Betwveen weeks 9 and t-8, inspiratory miusele ftnctioniappeared o) plateau, although it rem-painietd above pre-INMT val-aes. In peiipherai skeletal miuscle, a limiited decay in strengthhas been olbserved during short periois of detraining of 2--44 wkin yolung adult subjects (15,23). in contrast loknger periods oftraining cessation are usuially accompanied by a mnore pro-nounced decline in strength, but this loss is still limited to8-12% duLrinig periods of inactivity rangingy fromr 8-31 wk(l4. 1 8). This is consistent with our findinig that P1 was reducedby 7% after 9 wk of deaining and remained unchangedthereafter uLp to 18 wk posuraining. Our subjects exhibited airiore prionounced decrease withi detraining in miiaximlumi in-spiratory mruscle power compared with strength (17 vs 7%).

'This findilng is consistent with a study that showed a significant14%.yo redtiction in the ability of collegiate swimmers to generatepower duri:n actual swimmning despite a nonsignificant changein mnuscular strength as measured on a swirn bench (23).

Aniother unique feature of the present stuidy was theassessmient of inspiratory nausele function during a periodof' reduced training. Sub jects who reduced the frequencyof training by up to two thirds while keeping trainingintensity constant mnaintai ned inspiratory miutssle functionfor up tol) 18 wvk post-IMT. Tbis is consistent with theresults of other studies that found training intensity to be

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50t o

40 t

.~30

2 20

10 _

A B C D

Group

Week 3 Week 6 U Week 9

30

F 2 0 . * . 20i

>- t , ,

'(D 10;

cm I ...,.... ,_C

-10A B

Group

* g Week 3 0 Week 6 a Week 9

80

E60) t *

4 0

200

A B C

Group

* Week 3 Week 6 gWeek 9

80

t t

4060 *

40

0 20 :.*

0: ' r - I- 1 \-1 I A B C

Group

D

a Week 3 a Week 6 * Week 9

FIG(URE 4-Relative changes in maximum dynamic inspiratory muscle function from baseline values for high-pressure (A), high-flow (B),intermediate pressuire and flow {C), and control groups (D) (mean :±- SEM). Pt, inspiratery pressure at zero flow; r maximum inspiratory flow;WmIx' maximtim inspiratory muscle work rate; MRPI), maximum rate of pressure development; * siginificantly different from baseline (P 5 0.05):; signiflicantly different from preceding time point (P s 0.05).

more important than training frequency for the inainte-nance of peripheral muscle strength (5,10).

Findings in the present study pertaining to the revers-ibility of inspiratory muscle function have importantpractical implications for individuals participating inIMT programs. When training frequency must be reduced

for short periods of time, inspiratory muscle functioni maybe maintained by training as little as 2 d.wk-- ' as longas the intensity of training is maintained. Completelyterminating training will result in significant reductionsin inspiratory muscle function, mostly within the first9 wk.

TABLE 3. Summary of post-IMT inspiratory muscle function data for maintenance (M) and cetraining (DT) groups (mean + SEM).Pre-IMT IMT Post-IMT

Week No. 0 9 18 27PO (cm H,20)

M 112 7a 142 ±1+ 0 142 t 0, 139 t l0DT 96t7, 124 ± 1, 115 t 8 115 + 7-

V,,. (L s )M 9.2 + 0.6a 10.17 -03c 106 ± 0.8b 10.4 0.8,,DT 8.6 0.5, 1f. 06 91 n05 91 _ 05

W, (cn H2O-L'*s 6)IV 267 32a 386 ±45, 381 - 46, 369 + 44,DT 225 32, 320 ±43b 267 31, 269 27,.

Pt, (cm H2 0)M 57± 4 71 b- Sb 71 5S 70 -5,CT 49+ 4 62 t5, 57+ 4 58- 3

M1 4.5 0.3 5.4 t0.4 5.3 t 0.4, 5.2s 0.4,DT 4.2 i- 0.2, 5.0 ±0.3, 4.5 +-0.3,, 4.6 +0.2,b

MRPD (cm H.0-ms ')M 0.517 s 0.005, 0686 +.041, 0.683 0 0.040, 0.680 t 0.041,DT 0 531 + 0.003a 0.704 UV+ 0.605 t: 0.034, 0.601 ± 0.036

N 9. See Table 2 for definitions. Means in the same row tnat do not share subscripts differ at P 0.05.05.

t

C Q

D

I ---

SPECIFIC[TY AND REVERSIBILITY OF IMT Medicine & Science in Sports & Exerclse,,, 243

CONCLUSIONS

Data frotn the present study support tihe pressure-flow

(force-velocity) specificity of IMT established previouslyfor other peripheral muscle trttning regillens. M/ost of thepressure-flow-power adaptations were expressed It ly by

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TITLE: Specificity and Reversibility of Inspiratory MuscleTraining

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