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

Summary

Objective

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.

Methods

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).

Results

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.

Conclusions

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.

Résumé

But de l’étude

Cette étude avait pour objectif de comparer les effets sur le contrôle postural bipodal de la fatigue unilatérale de la musculature du genou induite par contractions électro-induites (ES) et volontaires (VOL).

Sujets et méthodes

Dix-sept hommes sains (21,5 ± 2 ans) ont réalisé les deux exercices dont la durée (130 répétitions de cinq secondes séparées de deux secondes de repos) et l’intensité (20 % de la force maximale volontaire) étaient équivalentes. La force maximale volontaire et le contrôle postural ont été mesurés grâce à un capteur de force et une plate-forme de force qui enregistre le déplacement du centre des pressions. Nous avons analysé les paramètres spatiotemporels du centre des pressions (condition yeux fermés) et la puissance spectrale par une décomposition en ondelettes du signal stabilométrique. Les mesures ont été réalisées avant (condition PRE) et après la réalisation de chaque exercice (soit immédiatement après : condition POST ; soit cinq minutes après : condition POST 5).

Résultats

En conditions POST et POST 5, ES a davantage affecté la force que VOL mais le contrôle postural a été indifféremment perturbé par les deux exercices.

Conclusions

La perturbation du contrôle postural bipodal à l’issue d’une fatigue unilatérale des extenseurs du genou n’est pas seulement liée à une perte de force musculaire mais semble également (et particulièrement) liée à un affaiblissement de l’efficacité des afférences sensorielles. La fatigue unilatérale de la musculature du genou induite par les contractions ES dégrade le contrôle postural bipodal de la même manière que celle induite par contractions VOL et les vitesses de récupération des capacités posturales ne diffèrent pas entre les deux exercices.

Introduction

Voluntary contractions of unilateral and bilateral lower-limb muscles generate fatigue and deteriorate postural control during monopedal and bipedal stance, respectively [6], [8], [15], [24]. Cross-over fatigue disturbs postural control, which means that the contralateral monopedal postural control after fatiguing muscular contractions of the ipsilateral limb is disturbed [22]. Some studies also analysed the disturbing effects of fatigue of unilateral hip or knee and/or ankle musculature in the bipedal postural control [2], [3], [14], [29], [30]. Overall, in the case of unilateral muscle fatigue, there is an alteration of the bipedal postural control, especially the spatiotemporal parameters of the centre of pressure (COP) under the non-fatigued leg [2], [29], [30]. These authors observed that the contribution of each leg to the control of two-legged stance is modified, which results from neural adjustments and compensatory contralateral strategies to preserve/facilitate bipedal postural control. Compensatory changes take place due to supplementary somatosensory inputs provided to the central nervous system by sensors of the non-fatigued leg's foot [29], [30] and an increase in the motor activity of specific stabiliser muscles of the non-exercised leg [2].

Moreover, electrically stimulated contractions of unilateral and bilateral musculature of lower limbs also affect ipsi- [7], [23], [24] and contralateral [22] monopedal postural control and bipedal postural control [10], respectively. Fatiguing stimulated contractions differently disturb ipsilateral monopedal postural control compared to fatiguing voluntary contractions [23], while they similarly deteriorate contralateral monopedal postural control [22] and bipedal postural control [10]. Nevertheless, we do not know whether unilateral muscle fatigue induced by stimulated contractions affects the bipedal postural control and whether the possible disturbance differs to that induced by voluntary contractions.

Therefore, the aim of this work was to analyse and compare the magnitude and duration of the effects of unilateral muscle fatigue of quadriceps femoris muscle induced by voluntary and stimulated contractions on the bipedal postural control. We concomitantly measured the decrease in muscle force, as this constitutes a basic criterion of fatigue state. Results of this study may have direct applications in the rehabilitation context to prevent possible falls related to loss of balance generated by a session of fatiguing stimulated or voluntary contractions.