Gait & posture · 2026
Voluntary ankle contraction reproduces centre of pressure features commonly attributed to automatic postural control.
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Michaud Lucas, Lajoie Yves
Аннотация
BACKGROUND: Postural control is often assessed through centre of pressure (COP) analysis to infer underlying control mechanisms. For example, during dual-tasking, measures such as sample entropy have been interpreted as reflecting changes in automaticity, whereas shifts in frequency content have been associated with stiffening, often attributed to ankle co-contraction. However, the specificity of these metrics remains unclear.
RESEARCH QUESTION: The objective of the present study was to compare the effects of dual-tasking and voluntary ankle contraction on COP and electromyographic (EMG) activity to determine whether commonly used metrics reflect specific control mechanisms.
METHOD: Fifteen healthy young adults completed 60-second standing trials under four conditions: baseline, voluntary contraction of the muscles around the ankle, and two dual-task conditions of different difficulty. EMG was recorded from the medial gastrocnemius, tibialis anterior, rectus femoris, and biceps femoris. COP measures (sway area, mean velocity, sample entropy, and wavelet-derived frequency content), EMG activity, co-contraction index, and intermuscular coherence were compared across conditions.
RESULTS: Dual-tasking and voluntary ankle contraction both altered sample entropy and frequency content, although their effects differed across axes and frequency bands. Dual-tasking reduced sway area, whereas voluntary ankle contraction did not. Dual-tasking produced little change in EMG activity, whereas VAC elicited a more pronounced neuromuscular response, particularly in TA activity and the co-contraction index.
SIGNIFICANCE: COP metrics should be carefully interpreted in isolation, as control strategies associated with dual-tasking and voluntary ankle contraction may produce overlapping outcomes. Studies lacking neuromuscular measures or experimental context should therefore be interpreted cautiously.
RESEARCH QUESTION: The objective of the present study was to compare the effects of dual-tasking and voluntary ankle contraction on COP and electromyographic (EMG) activity to determine whether commonly used metrics reflect specific control mechanisms.
METHOD: Fifteen healthy young adults completed 60-second standing trials under four conditions: baseline, voluntary contraction of the muscles around the ankle, and two dual-task conditions of different difficulty. EMG was recorded from the medial gastrocnemius, tibialis anterior, rectus femoris, and biceps femoris. COP measures (sway area, mean velocity, sample entropy, and wavelet-derived frequency content), EMG activity, co-contraction index, and intermuscular coherence were compared across conditions.
RESULTS: Dual-tasking and voluntary ankle contraction both altered sample entropy and frequency content, although their effects differed across axes and frequency bands. Dual-tasking reduced sway area, whereas voluntary ankle contraction did not. Dual-tasking produced little change in EMG activity, whereas VAC elicited a more pronounced neuromuscular response, particularly in TA activity and the co-contraction index.
SIGNIFICANCE: COP metrics should be carefully interpreted in isolation, as control strategies associated with dual-tasking and voluntary ankle contraction may produce overlapping outcomes. Studies lacking neuromuscular measures or experimental context should therefore be interpreted cautiously.