Effects of unilateral knee extensor muscle fatigue induced by stimulated and voluntary contractions on postural control during bipedal stance

Abstract

This study aim was to compare the effects of unilateral knee extensor fatigue induced by electrically stimulated (ES) and voluntary (VOL) contractions on postural control during bipedal stance. Seventeen healthy active males (21.5±2 years) completed these two fatiguing exercises of the quadriceps femoris muscle. Both exercises were of equal duration (130 repetitions of 5 seconds, each separated by a rest period of 2 seconds) and intensity (20% isometric maximal voluntary contraction [MVC]). Both MVC and postural control were recorded using an ergometer and a force platform that registered the centre of foot pressure (COP). We analyzed the spatiotemporal COP parameters (in eyes closed condition) and the spectral power density given by the wavelet transform. Recordings were performed before (PRE condition) and after the completion of each fatiguing task (immediately: POST condition; and after a 5-minute recovery: POST 5 condition). In the POST and POST 5 conditions, the ES exercise affected MVC more than the VOL exercise but the bipedal postural control was similarly deteriorated for both exercises. The disturbance of the bipedal postural control after unilateral knee muscle fatigue is not only related to a reduction in muscle strength but also (especially) to an impairment of the effectiveness of sensory inputs. Unilateral knee muscle fatigue induced by ES similarly degrades the bipedal postural control as that induced by VOL, and the duration of the recovery of postural control did not differ between both fatiguing exercises.