Effects of lower limb muscle fatigue on movement strategies for maintaining postural stability

Abstract

Introduction: Fatigue is a distressing symptom inversely related to postural stability in adults with neuromuscular and systemic diseases. However, there is no information about the effects of lower limb muscles fatigability on the movement strategies for balance control in the upright standing. Methods: This study enrolled 41 healthy subjects (female/male: 22/19; age 23±3 years; body mass index 25.4±3.7 kg/m2). Participants underwent posturography and surface electromyography of the gastrocnemius medialis during a sustained, fatiguing voluntary contraction of the gastrocnemius preceded and followed by quiet standing (120s). Muscle
excitation and fatigability were evaluated using the mean square root (RMS) RMS values and the RMS and spectral median frequency (f'()) slopes. Balance control was evaluated using the center-of-pressure elliptic area (Area) and average velocity (Vavg). Movement strategies for balance control were evaluated using the number of high-density regions (nHDR) and spatial patterns of the three-dimensional statokinesigram. Results: Mean time to muscle fatigability was 258 ± 190 s. Wilcoxon’s signed rank test showed both Area and Vavg increased after the fatiguing task with statistical evidence of difference (Area: p = 0.002, W = 191.0; Vavg: p <0.001, W = 126.5), but not for nHDR (p = 0.557, W = 153.0). Single-centered spatial patterns were predominant in both tasks (pre-fatigue: n=22/41; post-fatigue: n=19/41), with no statistical evidence of an association between the spatial patterns and tasks (g=0.237, 95%CI=[-0.338; 0.542]). Conclusion: Lower limb muscle fatigability increases postural instability, but it is not associated with changes in movement strategies for balance control in the upright stance.