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Groupe Analyse du Mouvement, Faculté des Sciences du Sport, Université de Bourgogne, 21078 Dijon Cedex, France
Neuromuscular fatigue of the knee
extensor (KE) and plantar flexor (PF) muscles was characterized after a
65-km ultramarathon race in nine well-trained runners by stimulating
the femoral and tibial nerves, respectively. One week before and
immediately after the ultramarathon, maximal twitches were elicited
from the relaxed KE and PF. Electrically evoked superimposed twitches
of the KE were also elicited during maximal voluntary contractions
(MVCs) to determine maximal voluntary activation. MVC and maximal
voluntary activation decreased significantly after the ultramarathon
(
30.2 ± 18.0% and 27.7 ± 13.0%, respectively;
P < 0.001). Surprisingly, peak twitch increased after
the ultramarathon from 15.8 ± 6.3 to 19.7 ± 3.3 N · m for PF (P < 0.01) and from 131.9 ± 21.2 to 157.1 ± 35.9 N for KE (P < 0.05). Also,
shorter contraction and half-relaxation times were observed for both
muscles. The compound muscle action potentials (M wave) were not
significantly altered by the ultramarathon with the exception of the
soleus, which showed a slightly higher M-wave amplitude after the
running. From these results, it can be concluded that 65 km of running
1) severely depressed the maximal voluntary force capacity
mainly because of a decrease in maximal voluntary activation,
2) potentiated the twitch mechanical response, and
3) did not change significantly the M-wave characteristics.
electrically evoked twitch; potentiation; M wave; central activation; electromyography
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