Influence of ankle muscle fatigue on postural strategy selection


The nervous system (NS) combines sensory feedback, reflexes and descending central commands to generate effective postural control in changing environments. Although it is clear that neuromuscular fatigue alters sensory feedback, its impact on postural control is poorly understood. We investigated the effect of ankle neuromuscular fatigue on postural strategies used to control standing balance in conditions of support surface perturbations. We hypothesized that following ankle fatigue the NS will regulate the center of mass (COM) through a combination of ankle and hip strategies. Fifteen young healthy adults completed 10 pre- and 10 post-fatigue perturbations trials, each consisting of 1-minute sinusoidal anterior/posterior support surface oscillations with an unexpected postural perturbation generated by an increase in the oscillation frequency from 0.25 Hz to 0.5 Hz. Ankle plantar and dorsiflexors were fatigued to 50% of maximum contraction. Displacement of the hip, COM and temporal activation of the postural muscles were used to identify changes in postural control due to fatigue. Analysis demonstrated a post-fatigue shift from predominantly ankle-based control to a complex combination of ankle and hip muscle activity. The COM displacement was maintained while hip displacement increased significantly post-fatigue. The data suggest that post- ankle fatigue individuals ensure stability by shifting from isolated ankle control to one incorporating aspects of a hip strategy.