Changes in the relative contribution of each leg to the control of quiet two-legged stance following unilateral plantar–flexor muscles fatigue
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We used unilateral plantar–flexor muscles fatigue to assess the capacity of the central nervous system to adapt quiet two-legged stance control to a unilateral ankle neuromuscular perturbation. Eighteen young healthy adults stood barefoot with their eyes closed and were asked to sway as little as possible. The Experimental group (n = 9) executed this postural task in two conditions, before (pre-test) and following the completion of a fatiguing exercise designed to induce a muscular fatigue in the plantar–flexor muscles of their dominant leg (post-test). For the Control group (n = 9), this fatiguing exercise was replaced with a standing rest period corresponding to the fatiguing exercise. Results of the Experimental group showed no significant difference between the weight-bearing index measured in the pre-test condition and that observed in the post-test condition. Results further revealed that unilateral plantar–flexor muscles fatigue yielded different effects on the centre of foot pressure (CoP) displacements under the non-fatigued leg and under the fatigued leg: a wider surface area of the CoP displacements was observed under the non-fatigued than under the fatigued leg, and a higher mean speed of the CoP displacements was observed under the non-fatigued leg only in the post-test relative to the pre-test condition. These findings evidenced that the contribution of each leg to the control of quiet two-legged stance is modified as a result of muscle fatigue of unilateral plantar–flexor muscles. The greater contribution of the non-fatigued leg could be viewed as a fatigue-induced adaptive change in the control of quiet two-legged stance in response to an alteration of the unilateral ankle neuromuscular function induced by unilateral plantar–flexor muscles fatigue.
KeywordsAdaptation Balance Muscle fatigue Ankle Centre of foot pressure Unilateral Humans
The authors would like thank subject volunteers and the anonymous reviewers for helpful comments and suggestions. Special thanks also are extended to C. Hoxinel for various contributions. Results of a pilot study of this research have been presented at the XIII Congrès de l’Association Posture-Équilibre, Marseille (France), 8–10 Dec 2006. This manuscript has been presented in abstract form at the XVI Congrès de l’Association Posture-Équilibre, Lille (France), 13–14 Nov 2009.
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