Movement Variability and Muscle Activity Relative to Center of Pressure during Unipedal Stance on Solid and Compliant Surfaces

in Motor Control

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James L. Croft
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Vinzenz von Tscharner
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Ronald F. Zernicke
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Compliant surfaces are used to challenge postural stability, but assessments are frequently limited to summary measures of center of pressure that do not provide insights into the temporal dynamics of motor coordination. Here, we measured center-of-pressure changes on three surfaces (solid, foam, and air-filled disc) and quantified the relative timing of changes in joint angles and muscle activity with respect to center-of-pressure changes. Nine active male subjects (20–30 years old) performed ten 30-s trials of unipedal stance on each of the three surfaces. Sway range, mean sway, mean sway velocity, path length, and fitted ellipse area increased, monotonically, from solid surface to foam to air-filled disc. The number of significant cross-correlations was greater for the compliant surfaces compared with the solid surface. Muscle activity preceded changes in center-of-pressure displacement, with the type of surface affecting the magnitude of the lead in the mediolateral direction. Center of pressure was more constrained on less stable surfaces and in the mediolateral direction.

Croft is with the Institute of Sport and Recreation Research, New Zealand School of Sport and Recreation, Faculty of Health & Environmental Sciences, AUT University, Auckland 1142, New Zealand. von Tscharner is with the Faculty of Kinesiology, University of Calgary, Calgary, AB Canada. Zernicke is with the Dept. of Orthopaedic Surgery and the Division of Kinesiology, Dept. of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48105.

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