Effect of Creatine Loading on Neuromuscular Fatigue Threshold

8/12/2019 Effect of Creatine Loading on Neuromuscular Fatigue Threshold

1/4

Effect of creatine loading on

neuromuscular fa tigue t hreshold

J EF FR EY STOU T,1 J OAN ECK ERS ON ,1 K Y L E E B E R S O L E ,2 G E R I M O O R E ,1 SHARON PERRY,2

T ERRY HOUS H,2 ANTHONY BULL,2 J OEL CRAMER, 2 AND ASH B ATHE J A3

1Exercise Science Department, Creighton University, Omaha 68178; 2Cent er for Yout h

Fi tn ess a n d Sp ort s R esea rch , U n i versi ty of N eb ra ska , L i n col n 6 8 58 8 ; a n d 3Department

of Ph ysi ca l Th era p y, U n i versi ty of N eb ra ska M ed i ca l C en ter, Oma h a , N eb ra ska 6 8 1 9 8

Stout, J effrey, J oan Eckerson, Kyle E bersole, GeriMoore, Sharon Perry, Terry Housh, Anthony Bull, J oelCramer, and Ash Batheja. Effect of crea t ine loa ding onneuromuscular fatigue threshold. J . A p p l . P h y si o l . 88: 109112, 2000.The purpose of this investigat ion w as to d eter-m i n e t h e e ff ect of cr e a t i n e ( C r ) l oa d i n g on t h e on s et ofneuromuscular fatigue by monitoring electromyographic fa-t i g u e c ur v es f r om t h e v a s t u s l a t e r a l i s m u s c le u s in g t h ephys ica l w orking ca pa cit y a t t he fa t igue t hres hold (P WC

FT)

test . U sing a double-blind ra ndom design, 15 women a thletes[mean age 19.0 2.0 (SD ) yr] from the university crew tea mreceived a placebo (n 8; 20 g glucose) or Cr (n 7; 5 g Crmonohydra t e 20 g g lu cos e) f ou r t i m es p er d a y f or 5consecutive days. Ana lysis of covaria nce was u sed to ana lyzet he da t a (cova ried for presupplement a t ion P WCFT values).The ad justed mean postsupplementat ion PWCFT value for theCr gr oup (mean 186 W) was sign ifi cantly (P 0.05) hig hert h a n t h a t of t h e p la c eb o g r ou p ( m ea n 155 W). Thesefi n d i n gs s ug g es t t h a t C r l oa d i ng m a y d el a y t h e o n se t ofneuromuscular fatigue.

ergogenic a id; elect romyogra phy; cycle ergomet ry; mus clefa t igue

A NUMBER OF INVESTIGATIONS ha ve used surfa ce electro-m yo grap h ic (EM G ) p ro ce d ure s to id en ti fy th e p owe rou tp u t asso ciate d with th e on se t of n e u rom u scu larfatigue (NMF) during cycle ergometry (3, 4, 79, 14,21). NMF is typically characterized by an increase overtim e in the electrica l act ivity of the w orking muscles (2,4, 14, 15). M or i t a n i e t a l . (15) s u g g es t e d t h a t t h efat igue-induced increase in E MG a mplitude is a resultof p rog re ssive re cru itm e n t of ad d it ion al m oto r u n its(MU ) a nd/or an increa se in the fi ring freq uency of MUsthat have already been recruited. Theoretically, workbouts a t power outputs a t or below the NMF t hreshold

can be ma inta ined continuously with out EMG evidenceof fa t ig u e (i .e ., n o sign ifi can t in cre ase in EM G am p li-tu de over t ime).

DeVries et al. (3, 4) developed an incremental cycleergometer t est called the physical w orking capa city a tthe fatigue threshold (PWC FT) , wh ich u ti l iz e s EM Gfatigue curves to identify the power output that corre-

sponds to the onset of the NMF threshold. The PWC FTre pre sen ts th e h ig h e st p owe r ou tp u t t h at re su lts in an on sig n ifi can t (P 0 .05) in cre ase in th e e le ctricalactivi ty o f th e th ig h m u scle s o ve r t im e . Wh e re as th eP WCFT test ha s been shown to be reliable (2, 4), va lid(2) , an d se n si t ive to ch an g e s in fi tn e ss le ve l (2) , th ephysiological mechanism responsible for the increasein EMG a mplitude over time during a fa tiguing ta sk is

unknow n. Tw o potent ia l mechanis ms, however, includethe accumulation of metabolic by-products (lactate, H,P i, a nd a mmonia ) a nd/or the depletion of st ored energysubstrates [ATP, phosphocreatine (PCr), and glycogen](13). Housh et al . (8, 9) have reported that manipula-tion of blood a cid-base ba lance w ith a mmonia chloridea nd sodium bica rbonat e, as well a s glycogen depletionan d su p ercom p en sat ion , d id n ot af fect th e on se t ofNMF as mea sured by the P WC FT test. However, McCart-ney et al . (12) have suggested that alterations in theb lood acid -b ase sta te h ave l it t le in flu e n ce on m u sclep H . I n a d d i t ion , t h e r e i s ev id en ce t o s u gg es t t h a tsk e le tal m u scle PCr m ay se rve as a te m p o ral e n e rg ybuffer as well as a modulator of glycolysis and, there-

fore, ma y infl uence NMF (22). The effect of P Cr m a nipu-lat io n o n EM G fat ig u e cu rves, h o we ver, is u n k n own .Th e refore , th e p u rpose o f th e p rese n t s tu d y wa s todeterm ine th e effect of Cr loading on t he onset of NMF,as mea sured by the P WC FT test in women a thletes.

METHODS

Subjects. Fif t een fema le members of t h e univers it y crew team [age 19.0 2.0 (SD ) yr] volunteered a s subjects for thisinvestigation. All procedures were approved by the Institu-t iona l R eview B oa rd before t he init ia t ion of t he s t udy, a ndeach subject w as advised of a ny possible risks before provid-ing informed consent.

Suppl ementat ion protocol. N o n e o f t h e s u b j e c t s h a d i n -

gested Cr, or any other dietary supplements, for a minimumof 12 wk before the initia tion of the study. During the courseof t h e s t u d y, t h e s u bje ct s w e r e a s k ed t o m a i n t a i n t h e ircurrent diet a ry pa t t erns a nd a bs t a in from ot her nut rit iona lsupplements, nonprescription drug s, a nd caffeine. After pre-t es t ing, t he s ubject s w ere ra ndomly a s s igned t o one of t w otreatment conditions using a double-blind design: 1) 20 g offla vored dextrose powder a s a pla cebo (P l, n 8); or 2) 5.0 g ofCr monohydra t e plus 20 g of dext ros e in a fla vored pow derblend (Cr, n 7) (Crea t ine Edge Effervescent , Fort res sSys t ems , Oma ha , NE). The pow ders , ident ica l in t a s t e a nda ppea ra nce, w ere dis s olved in 16 oz of w a t er a nd inges t edfour times per day for 5 consecutive days before posttesting.

The costs of publication of this article were defrayed in part by thep a y m e n t of p a g e c h a r g es . Th e a r t ic le m u s t t h e r ef or e b e h e r e b ymarked advertisement in a ccordance with 18 U.S.C. Sect ion 1734solely to indicate this fact.

J . A p p l . P h y s i ol .

88: 109112, 2000.

8750-7587/00 $5.00 C opyr igh t 2000 t h e Am er ica n P hysiologica l S ociet y 109ht tp ://w w w.ja p.or g


2/4

Electrode placement and EMG instrumentat ion. A bipola r(2.54-cm center-to-center) surface electrode (Quinton Quickprep s ilver-s ilver chloride) a rra ngement w a s pla ced on t her i g h t t h i g h ov er t h e l a t e r a l p or t i on of t h e v a s t u s l a t e r a l is(V L ), midw a y bet w een t he grea t er t rocha nt er a nd t he la t era lcondyle of the femur. The reference electrode w a s placed overt he i l ia c cres t . I nt erelect rode impeda nce w a s kept below 2,000 by careful abrasion of the skin. The EMG signal wasprea mplified (ga in: 1,000) by using a differential amplifier(EM G 100, B iopa c Sys t em, Sa nt a B a rba ra , CA ). The EM Gsigna l wa s sam pled at 1,000 points/s an d fi ltered at 10500H z . Th e r oot m ea n s q ua r e E M G a m p li t ud e v a lu es w e r e

ca lcula t ed for t he 10-s t ime fra me for ea ch s a mple t a ken(MP 100, B iopac Syst ems).

Determination of PWCFT. The PWC FT va lues w ere det er-mined from the VL muscle by using the protocol of deVries etal. (3). Figure 1 illustrates how the PWC FT w a s det erminedus ing t he da t a from subject 7 in t he C r g roup (Ta ble 1). Thesubjects bega n peda ling (wit h toe clips) a t 60 W (70 rpm) on acalibrated, electronically braked cycle ergometer (Corval 400,Quinton In strum ents, S eatt le, WA). The power output wa sthen increased by 30 W every 2 min until th e subject could nolonger maint ain 70 rpm. During ea ch 2-min int erval, six 10-sEM G s a mples w ere recorded from t he V L . The P WC FT w a sd e t er m i n ed b y a v e r a g in g t h e h i gh e st p ow e r ou t p ut t h a tres ult ed in a nons ignifica nt (P 0.05; single-tailed t-test)slope value for th e EMG am plitude vs. t ime relationship, wit ht he low es t pow er out put t ha t res ult ed in a s ignifica nt (P 0.05) slope value (Fig. 1).

R e li a b il it y of t h e P WC FT w a s d et er m in ed b y u si n g asubsample of subjects (n 11) mea s ured 7 da ys a pa rt . Thet es t -ret es t int ra cla s s correla t ion coeff icient (R) w a s 0. 94(S E 6 W), which is similar to values reported by deVries etal. (2, 3) in older (R 0.976) and younger male subjects (R0.947). I n a ddit ion, t he t es t -ret es t mea n difference for t heP WCFT values 0.5 Ww as not statist ically signifi cant (t 0.09;P 0.05).

Stati st i cal an alysis. C h a n g e s i n b o d y w e i g h t ( B W ) a s a

res ult of s upplement a t ion w ere a na lyzed by us ing a 2 2[t rea t ment (P l , C r) t ime (pretest , postest)] mixed fa ctorialANOVA. Differences in the mean posttest PWC FT va lue w ered e t er m i n ed b y u s in g a n a l y s i s of cov a r i a n ce , w i t h p r et e stP WCFT serving as the covariat e. Da ta w ere considered signifi-cantly different when the probability was P0.05.

RESULTS

Th e d e scriptive ch aracte rist ics of th e su b je cts , asw e l l a s t h e c h a n g e s i n B W a n d P W C FT f o r t h e t w ogroups, ar e shown in Ta ble 1. There w ere no signifi cantchanges in B W from pretesting t o posttesting for eitherg rou p . Ho we ver, th e ad ju sted m e an p ostte st P WC FT

va lue for th e Pl group (mea n

155 W) wa s significant lyless tha n tha t of the Cr group (mean 186 W).

Fig. 1. I llustrat ion of method used for determining physical workingcapacity a t fa t igue thr eshold (PWC FT) for subject 7 in creatine group.

EMG, electromyographic voltages; NS, not s ignificant ; uVrms, rootmean square EMG amplitude.

Ta ble 1. Char acter isti cs of the subjects (n15 )

S u bject Age, y r H eigh t , cm B W-P r e, kg B W-P ost , kg P WC FT-P r e, W P WC FT-Post, W

Pl acebo group

1 18 163 75.5 75.0 165 1352 19 165 51.4 51.8 135 1353 19 167 56.4 56.0 135 1354 20 167 59.0 59.6 165 1655 17 170 80.5 81.8 135 1656 19 164 70.5 69.9 165 1657 21 160 60.5 59.0 105 1058 19 163 56.0 56.0 165 165

MeanS D 19.01.2 164.93.1 63.710.4 63.610.6 146.322.3 146.322.3

Cr ea t i n e g r ou p

1 17 172 74.3 76.4 165 2252 21 154 66.7 68.2 165 1953 20 163 67.3 65.0 195 2254 22 159 64.0 64.5 165 1955 18 166 78.9 78.7 225 2256 18 167 62.7 63.4 165 1657 20 178 65.5 64.7 105 135

MeanS D 19.41.8 165.68.0 68.55.9 68.76.3 169.336.4 195*34.6

P WCFT, physical w orking capa city a t fa t igue threshold; BW, body weight ; Pre, before treat ment ; P ost , a f ter trea tment . * Mean P WC FT-P ostvalues significantly different from mean P WC FT-Pre values (P0.05).

110 CRE ATINE LOADING ON NEU ROMUSC ULAR FATIGU E


3/4

DISCUSSION

Re ce n t in vestig at io n s (6, 10) u sin g m ale su b je ctsh a v e s h ow n t h a t C r l oa d i n g (20 g /d a y ) f or 5 d a y ss i g n i fi c a n t l y e l e v a t e d w h o l e m u s c l e C r s t o r e s b y a na vera ge of 20%, wit h a s much a s 20%stored in th e formo f PCr. V an d e n b e rg h e e t a l . (20) d e m o n strate d a 6%increase in muscle PC r concentr a tion in college-a ge

women (1922 yr old) after 4 days of Cr loading. Thefem ale su b je cts in th e p rese n t s tu d y (Tab le 1) w e resimila r in a ge (1821 yr old) a nd closely follow ed the Crloa ding regimen used in the st udy by Van denberghe etal. (20) (5 g, four times per day for 5 days). Therefore,a lthough muscle PC r levels were not directly mea suredin t he present study, the results of previous investiga -t io n s (6, 10, 20) su g g e st th at i t is l ik e ly th at th e Crloa ding resulted in an increa se in muscle P Cr concentra -tion.

S e ve ral s tu d ie s th at h ave e xam in e d th e e rg o g e n iceffect of Cr loa ding on performa nce by using supra ma xi-m a l w o r kl oa d s on a cy cl e e r g om et e r h a v e r e por t e dsig n ifi can t in cre ase s in to tal wo rk d u rin g b o th sin g le

and multiple bouts of exercise (1, 11, 17, 22). Recently,J a cobs et a l . (11) a nd P revost et a l . (17) demonstra tedsig n ifi can t in cre ase s in t im e t o e xh au st ion (8.5 a n d24%, r espectively) dur ing cycle ergometry a t 125 a nd150%maxima l oxygen consumption ra te a fter Cr loa d-ing in physically active men and women. Prevost et al .hypothesized tha t Cr loa ding increa sed exercise ca pac-ity and diminished the exercise-induced rise in plasmalacta te levels by dela ying a na erobic glycolysis. In con-trast , F e b b raio e t a l . (5) d e m o n strate d n o sig n ifi can td if fe re n ce s in t im e to e xh au stio n an d in tram u scu larlacta te levels during cycle ergometry a t 115120% ofm a xim a l o xyg e n con su m ption rat e a f te r Cr load in g in

u n tra in ed m e n .Fewer st udies have been conducted to determine theeffects of Cr loading on submaximal exercise perfor-mance (16, 18). Nelson et al. (16) recently reported thatC r l o a d i n g i n m a l e a n d f e m a l e a t h l e t e s ( a g e r a n g e2127 yr) resulted in a 12%increa se in th e ventilat oryt h r e sh ol d a s w e ll a s a d ecr ea s e i n b l ood l a ct a t e a n dammonia concentrations during incremental cycle er-gometry. In contr a st, S tr oud et a l . (18) reported t ha t C rload in g h ad n o e ffect on re spirato ry g as e xch an g e orb lood lactat e a ccum u latio n d u rin g in cre m en ta l tre ad -mill exercise in physically a ctive men. Discrepan cies inth e l i te ratu re re g ard in g th e e f fe cts o f Cr lo ad in g o np erform a n ce m ay b e at tr ib u te d to th e h ig h ly var iab le

in te rin d ivid u al re spon se in m u scle Cr re te n tion as aresult of Cr loading (1, 6). Recently, Casey et al . (1)d e m o n strate d a p o si t ive re lat io n sh ip (r 0.71, P 0.05) betw een a na erobic exercise performa nce duringcycle ergometr y a nd t he ma gnitude of muscle Cr reten-t i on f r om C r l oa d i n g , a n d t h e y c on cl ud ed t h a t t h eimprovement in anaerobic performance was criticallyd e p e n d e n t o n th e m ag n itu d e o f m u scle Cr re te n tio nfollowing loadin g.

McClaren et al . (13) have suggested that a decreasein muscle pH, a s a result of the accumulation of H orin tra - an d e xtra cel lular am m on ia, m ay b e re spon sible

for fatigue-induced increases in MU recruitment andt h e cor r es pon d in g i n cr ea s e i n E M G a m p li t u de . I na g r e em en t , Ta y l or e t a l . (19) a l s o f ou n d t h a t , f ori n cr e m en t a l c y cl e e r g om e t r y, t h e a c cu m u l a t i on ofp l a s m a l a c t a t e a n d a m m o n i a w a s a s s o c i a t e d w i t h a nincrease in EMG amplitude measured from the rectusfemoris mus cle. Therefore, th ere is evidence to suggestt h a t a r el ia n c e on a n a er ob ic g l y col y si s l e a d s t o a n

increase in E MG a mplitude from t he working musclesa s a result of chan ges in muscle a nd blood lact a te levelsand the corresponding decrease in pH.

In the present study, Cr loading resulted in a delay inth e o n se t o f N M F (as m e asu re d b y th e PWC FT test),w h i ch m a y h a v e b ee n d u e t o t h e ef fe ct of e lev a t e dmuscle P Cr on the tra nsition from a erobic to an a erobicmetabolism. Prevost et al. (17) and Volek and Kraemer(22) h a ve h yp o th esize d th a t in cre asin g m u scle P Crco n te n t b y Cr lo ad in g m ay d e cre ase th e re l ian ce o nanaerobic glycolysis, reduce intramuscular lactate accu-m u latio n , an d , th e re fo re , d e lay th e o n se t o f fat ig u e .Th u s t h e r e s u lt s of t h e p r es en t s t u d y s u gg es t t h a td u rin g in cre m e n tal cycle e rg o m e try Cr lo ad in g m ayd e lay th e o n se t o f N M F an d th e fat ig u e - in d u ce d in -crea se in EMG a t subma ximal power outputs by reduc-in g th e re lian ce on an a e rob ic g lycolysis a n d at te n u at-i n g t h e a ccu m u la t i on of l a c t a t e a n d a m m o n ia i n t h ew orking muscles and blood.

I n su m m ary, Cr lo ad in g re su lte d in a s ig n ifi can tlyh ig h er P WC FT va l u e (186 W) c om pa r e d w i t h a P l(155 W), indicat ing tha t C r loading ma y delay t he onsetof NMF during incremental cycle ergometry in femalea t h l e t e s . T h e d e l a y i n N M F m a y h a v e b e e n d u e t oau g m e n te d PC r le vels in th e m u scle , wh ich m a y h a veresulted in a great er ca pacity t o delay a na erobic glycoly-sis (16, 17, 22). F u tu re stu d ies th a t wo u ld d irectlymeasure muscle P Cr, la ctat e, a nd am monium levels arewa rra n te d to val id at e th e se re sults .

We t h a n k F or t r es s I n t e r n a t ion a l ( O m a h a , N E) f or f u n d in g t h isstudy.

Address for reprint request s an d other correspondence: J . R. Stout ,Creighton Univ., Exercise Science Dept., 2500 California Pl., Omaha,NE 68178 (E-mail: [email protected]).

Received 14 Ma y 1999; accepted in fi na l form 31 August 1999.

REFERENCES

1. Casey, A., D. Constantin-Teodosiu, S. Howell, E. Hultman,and P. L. Greenhaff. Cr e a t in e in g es t ion f a v or a b ly a f f ec t sperformance and muscle metabolism during maximal exercise inh u m a n s . A m . J . P h y si o l . E n d ocr i n o l . M et a b. 271: E31E37,1996.

2. DeVries, H. A., G. R . Brodowicz, L . D. Robertson, M. D.Svoboda, J . S. Schendel, A. M. Tichy, and M. W. T ichy.Es t im a t in g p h y sica l w or k in g c a pa c i t y a n d t r a in in g c h a n g e s int h e e ld e r ly a t t h e f a t ig u e t h r e s h old ( P W C FT). Ergonomics 32:967977, 1989.

3. DeVries,H. A.,T. J . Housh,G. O.J ohnson,S.A.Evans,G. D.Tharp, D. J . Housh, and R. A. Hughes. Factors affect ing theest imation of physical w orking capacity a t t he fa t igue threshold.Ergonomics33: 2533, 1990.

4. DeVries, H. A., M. W. Tichy, T.J . Housh, K. D. Symth, A. M.Tichy, and D. J . Housh. A m e t h od f or e s t im a t in g p h y sica lworking capacity a t the fa t igue threshold (PWC FT). Ergonomics30: 11951204, 1987.

5. Febbraio,M., T.F lanagan,R. Snow, S.Zhao, and M. Carey.Effect of creat ine supplementa tion on intra muscular TCr, metabo-

111CREATINE LOADING ON NEUROMUSCULAR FATIGUE


4/4

lism and performance during intermit tent , supramaximal exer-cise in huma ns. Acta Ph ysiol. Scand.155: 387395, 1995.

6. Harris, R. C., K. Soderlund, and E . Hultman. Elevat ion ofcreat ine in rest ing and exercised muscle of normal subjects bycreat ine supplementat ion. Cli n. Sci. (Colch.)83: 367 374, 1992.

7. Hela, J . N., C. Y. Guezennec, and F. Goubel. The aerobic-ana erobic tra nsit ion: re-examinat ion of th e th reshold conceptincluding and electromyographic approach. Eur. J. Appl . Physiol.56: 643649, 1987.

8. Housh,T. J ., H.A. deVries, G. O. J ohnson,S. A. Evans, andS. McDowell. The effect of a mmonium chloride a nd sodiumb ica r b on a t e in g e s t ion on t h e p h y s ica l w or k in g c a p a ci t y a t t h efat igue t hreshold. Eur. J. Appl. Physiol.62: 189192, 1991.

9. Housh,T.J ., H.A. deVries,G. O.J ohnson,S.A.E vans, G.D.Tharp, D. J . Housh,and R. J . Hughes. The effect of glycogendepletion and supercompensation on the physical working capac-ity a t the fa t igue threshold. E u r . J . A p p l . P h y s i ol . 60: 391394,1990.

10. H ultman, E., K. Soderlund, J . A. Timmons, G. Cereblad,and P. L. Greenhaff. Muscle creat ine loading in m en. J . A p p l .Physiol.81: 232237, 1996.

11. J acobs, I., S. Bleue, and J . Goodman. Creat ine ingest ionincreases a naerobic capacity a nd ma ximum a ccumulat ed oxygendeficit . Can. J. Appl. Physiol.22: 231243, 1997.

12. McCartney, N., G. J . F. Heignehauser, and N. L . J ones.Ef f ec t s of p H on m a x im a l p ow e r ou t pu t a n d f a t ig u e d u r in g

short-term dynam ic exercise. J . A p p l . P h y si o l . 55: 225229,1983.

13. McClaren, D. P., H. Gibson, M. Parry-Billings, and R. H. T.Edwards. A review of metabolic and physiological factors infat igue. Exerc. Sport S ci. Rev.17: 2968, 1989.

14. Matsumoto, T., K. Ito, and T. Moritani. The relat ionshipb et w e e n a n a e r ob ic t h r e s h old a n d e le ct r om y og r a p h ic f a t ig u ethreshold in college women . Eur. J. Appl. Physiol.63: 15, 1990.

15. Moritani, T., T. Takaishi, and T. Matsumoto.Determinat ionof maximal power output a t neuromuscular fa t igue thr eshold.J .Appl. Physiol.74: 17291734, 1993.

16. Nelson, A., R. Day, E. Glickman-Weiss, M. Hegstad, and B.Sampson.Creat ine supplementat ion ra ises ana erobic threshold(Abstract). F A S E B J . 11: A589, 1997.

17. Prevost, M. C., A. G. Nelson, and G. S. Morris. Cr e a t in es u p ple m en t a t ion e n h a n c es in t e r m it t e n t w or k p e r for m a n c e .Res. Q. Exerc. Sport68: 233240, 1997.

18. Stroud, M., D. Holliman, D. Bell, A. Green, I. Macdonald,and P. Greenhaff. Effect of oral creat ine supplementat ion onrespirat ory gas exchange and blood lactate a ccumulat ion duringsteady-state incremental treadmill exercise and recovery in man.Cli n. Sci. (Colch.)87: 707710, 1994.

19. Taylor,A. D., R. Bronks, and A. L. Bryant. The relationshipbetween electromyography and work intensity revisited: a briefr e v ie w w it h r e fe r en c es t o la c t ic a cid os is a n d h y p er a m m on ia .El ectromyogr. Cli n. N eur ophysiol. 37: 387398, 1997.

20. Vanderberghe,K.,M. Goris,P.Van Hecke,M. Van Leeputte,L. Vangerven, and P. Hespel. Long-term creat ine intake isbeneficial to muscle perfomance during resistance training. J .Appl. Physiol.83: 20552063, 1997.

21. Viitasalo, J . T., P. Luhtanen, P. R ahkila, and H. Rusko.Ele ct r om y og r a p h ic a c t iv it y r e la t e d t o a e r obic a n d a n a e r ob icthreshold in ergometer bicycling. A c t a P h y si o l . S ca n d . 124:287293, 1985.

22. Volek, J . S., and W. J . Kraemer.Creat ine supplementa t ion: itseffect on human muscular performance and body composition. J .Strength Cond. Res.10: 200210, 1996.

112 CRE ATINE LOADING ON NEU ROMUSC ULAR FATIGU E

Documents

Effect of Creatine Loading on Neuromuscular Fatigue Threshold