FUNCTIONAL EVALUATION SECTION   

Medicina dello Sport 2004 March;57(1):31-9

Copyright © 2004 EDIZIONI MINERVA MEDICA

language: English

Contractile changes in knee extensor muscles after repetitive maximal isokinetic contractions in male power-lifters and untrained subjects

Ereline J., Gapeyeva H., Pasuke M.

Institute of Exercise Biology and Physiotherapy, University of Tartu, Tartu, Estonia

Aim. ­Changes in iso­metric max­imal vol­un­tary (MVC) and electri­cally ­evoked sub­max­imal ­tetanic con­trac­tion char­ac­ter­is­tics of the ­knee ­extensor (KE) mus­cles ­after ­short-­term ­high-inten­sity ­fatiguing iso­ki­netic exer­cise ­were com­pared in ­male ­power-­lifters (n=11) and ­untrained sub­jects (n=15) as con­trols.
­Methods. ­During meas­ure­ment of iso­metric MVC and ­evoked ­tetanic con­trac­tion char­ac­ter­is­tics the sub­jects ­were ­seated on a ­custom-­made dyna­mo­metric ­chair. Sub­max­imal iso­metric (~25%MVC) ­tetanic con­trac­tion of KE mus­cles was ­evoked by per­cut­aneous ­electrical stim­u­la­tion ­using rec­tan­gular ­pulses of 1-ms dura­tion ­with the fre­quency of 50Hz. ­Fatigue ­test con­sisted of 30 repet­i­tive max­imal iso­ki­netic ­knee exten­sions at ­angular ­velocity 1.57 rad·s-1 and at 0.5 Hz fre­quency on the ­Cybex II iso­ki­netic dyna­mom­eter. Iso­metric MVC ­force, ­peak ­force of ­evoked ­tetanic con­trac­tion (­PFES), and ­rates of ­force devel­op­ment ­during max­imal iso­metric vol­un­tary (RFD) and ­evoked ­tetanic (­RFDES) con­trac­tions, as ­well as ­half-relax­a­tion ­time of ­evoked ­tetanic con­trac­tion (­HRTES) ­were meas­ured ­before, and 1 and 10 min ­after the exer­cise.
­Results. A ­total mechan­ical ­work ­output (TWO) ­during iso­ki­netic exer­cise was 38% ­greater (p<0.05) in ­power-­lifters ­than in con­trols. ­Power-­lifters had a ­greater (p<0.05) ­fatigue ­index as com­pared to con­trols. Iso­metric MVC ­force, RFD, ­PFES and ­RFDEs ­were ­decreased (p<0.05), and ­HRTES was prol­on­gated (p<0.05) 1 min ­after exer­cise for ­both ­groups as com­pared to pre-exer­cise ­level. ­These char­ac­ter­is­tics recov­ered to pre-exer­cise ­level for ­untrained men ­within 10 min ­after the ces­sa­tion of exer­cise, ­while ­they did not ­recover for ­power-­lifters.
Con­clu­sion. It was con­cluded ­that ­power-­lifters pro­duced a sig­nif­i­cantly ­greater ­work ­output and ­fatigued ­faster ­during repet­i­tive max­imal iso­ki­netic ­knee exten­sions com­pared ­with ­untrained sub­jects. The ­recovery of iso­metric MVC and electri­cally ­evoked sub­max­imal ­tetanic con­trac­tion char­ac­ter­is­tics of KE mus­cles ­within 10 min ­after the iso­ki­netic exer­cise was ­more ­delayed in ­power­lifters ­than in con­trols.