Effects of lower limbs muscular fatigue on anticipatory postural adjustments during arm motions in humans.

Background: The purpose of the present experiment was to examine the effects of lower limbs muscular fatigue on the anticipatory postural adjustments during a voluntary arm raising movement.

Methods: Eight adult males (mean age 29+/-6 years) voluntarily participated to the experiment. Subjects' task consisted in performing an unilateral ante-flexion of the right arm over 90 deg, holding a 500 g weight, once having stabilized their upright posture. A similar movement execution was required. Measurements were made in a no-fatigue situation and under a high level of fatigue of lower limbs. Surface EMG of four postural muscles (the ipsilateral and contralateral Gastrocnemius and the ipsilateral and contralateral Semitendinosus) and of one muscle involved in the arm raising (the Anterior Deltoïdeus of the right arm) was recorded. Body sway was also monitored using a force platform.

Results: With fatigue, quantitative EMG analysis showed a decrease of the ipsilateral Semitendinosus activity whereas the temporal EMG analysis showed an increase of its latency with respect to movement onset.

Conclusions: These data suggested a functional adaptation resulting in an invariance of global anticipatory postural adjustments for the two conditions of no-fatigue and fatigue and ensuring an adequate execution of the movement.