Postural control in single-limb stance.

Postural control in single-limb stance has previously been shown to be impaired among soccer players with functional instability (FI) of the ankle joint. The aim of the present study was to further study the role of the ankle in postural control. A dynamic method was used involving optoelectronic movement recordings of body segments and force-plate recordings of the reaction ground force. Surface electromyography was recorded for the peroneus longus muscle. Thirty physically active men were selected. Fifteen of them had FI of the ankle chosen for recording. The results show that different patterns exist for maintaining equilibrium in single-limb stance. The ankle has a central role for postural corrections. The position of center of pressure is highly correlated to the position of the ankle and peroneal muscle activity. When the body was in disequilibrium, corrections were made at the hip. It is proposed that a change from an inverted pendulum model to a multisegmental chain model takes place when adjustments at the ankle joint no longer suffice to maintain postural control. The men with FI showed impaired postural control associated with increased upper segmental corrections.