Article

Muscle fatigue is associated with reduced power output and work capacity of the
skeletal muscle. Fatigue-induced impairments in muscle function are believed to
be a potential cause of increased injury rates during the latter stages of
athletic competition and often occur during unexpected perturbations. However the
effect of fatigue on functionally relevant, full body destabilizing perturbations
has not been investigated. This study examines the effect of muscle fatigue on
the activation of the quadriceps and hamstrings to fast, full body perturbations
evoked by a moveable platform. Surface electromyographic (EMG) signals were
recorded from the knee extensor (vastus medialis, rectus femoris, and vastus
lateralis) and flexor muscles (biceps femoris and semitendinosus) of the right
leg in nine healthy men during full body perturbations performed at baseline and
immediately following high intensity exercise performed on a bicycle ergometer.
In each condition, participants stood on a moveable platform during which 16
randomized postural perturbations (eight repetitions of two perturbation types: 8
cm forward slides, 8 cm backward slides) with varying inter-perturbation time
intervals were performed over a period of 2-3 min. Maximal voluntary knee
extension force was measured before and after the high intensity exercise
protocol to confirm the presence of fatigue. Immediately after exercise, the
maximal force decreased by 63% and 66% for knee extensors and flexors,
respectively (P<0.0001). During the post-exercise postural perturbations, the EMG
average rectified value (ARV) was significantly lower than the baseline condition
for both the knee extensors (average across all muscles; baseline:
19.7+/-25.4muV, post exercise: 16.2+/-19.4 muV) and flexors (baseline:
24.3+/-20.9 muV, post exercise: 13.8+/-11.0 muV) (both P<0.05). Moreover the EMG
onset was significantly delayed for both the knee extensors (baseline:
132.7+/-32.9 ms, post exercise: 170.8+/-22.9 ms) and flexors (baseline:
139.1+/-38.8 ms, post exercise: 179.3+/-50.9 ms) (both P<0.05). A significant
correlation (R(2)=0.53; P<0.05) was identified between the percent reduction of
knee extension MVC and the percent change in onset time of the knee extensors
post exercise. This study shows that muscle fatigue induces a reduction and delay
in the activation of both the quadriceps and hamstring muscles in response to
rapid destabilizing perturbations potentially reducing the stability around the
knee.
CI - Copyright (c) 2012 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS