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Articles in PresS, published online ahead of print September 20, 2002
J Appl Physiol, 10.1152/jap.00600.2002
Submitted on July 8, 2002
Accepted on September 19, 2002
1 INSERM/ERIT-M 0207 Motricite-Plasticite, Faculte des Sciences du Sport, Dijon, France
* To whom correspondence should be addressed. E-mail: gmillet{at}u-bourgogne.fr.
The aim of this study was to identify the mechanisms that contribute to the decline in knee extensor muscles (KE) strength after a prolonged running exercise. During the two days preceding a 30 km running race (mean ± SD duration: 188.7 ± 27.0 min) and immediately after the race, maximal percutaneous electrical stimulations (single twitch, 0.5 s tetanus at 20 Hz and 80 Hz) were applied to the femoral nerve of 12 trained runners. Superimposed twitches were also delivered during isometric maximal voluntary contraction (MVC) to determine the level of voluntary activation (%VA). The vastus lateralis electromyogram was recorded. KE MVC decreased from pre- to post-exercise (188.1 ± 25.2 to 142.7 ± 29.7 Nm ; P < 0.001) as did %VA (98.8 ± 1.8% to 91.3 ± 10.7%, P < 0.05). The changes from pre- to post-exercise in these two variables were highly correlated (R = 0.88 ; P < 0.001). The modifications in the mechanical response following the 80 Hz stimulation and M-wave peak-to-peak amplitude were also significant (P < 0.001 and P < 0.05, respectively). It can be concluded that (i) central fatigue, neuromuscular propagation and muscular factor are involved in the 23.5 ± 14.9% reduction in MVC after a prolonged running bout at racing pace and (ii) runners with the greatest knee extensors strength loss experience large activation deficit.
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