Effect of Ankle Joint Angular Position on Postural Control of Upright Stance

People frequently perform activities of daily living that require maintaining the upright balance over inclined surfaces with altered ankle joints position. Such postures might affect the postural control and lead to increased incident of falls. The aim of the thesis was to evaluate the postural control in static and dynamic tasks when standing over inclined surfaces inducing ankle joints dorsiflexion and plantarflexion. The static task (Chapter two) involved a quiet standing with dorsiflexed and plantarflexed ankles. Ten young adults stood on a force platform or on a firm 15° inclined wedge that induced either dorsiflexion or plantarflexion. A piece of foam was placed on top of the force platform and on the wedge. The center of pressure (COP) distance and velocity in the anteroposterior (AP) and mediolateral (ML) directions were calculated. Significantly larger magnitudes in most of the investigated variables were seen while standing with ankles in the dorsiflexion when compared to standing naturally (p<0.05). Plantarflexion increased the COP velocity in the anteroposterior direction (COPAP) when compared to a natural stance. Standing on the foam surfaces resulted in increases in all of the COP measures in all of the ankle conditions. The dynamic task (Chapter three) involved standing with dorsiflexed and plantarflexed ankles and performing bilateral arm movements. Another group of 10 young adults were asked to stand erect on the fore platform and on the 15 inclined wedge inducing either ankle joints dorsiflexion or plantarflexion and perform a self-paced discrete bilateral shoulder flexion. The muscles activity was acquired using adhesive EMG electrodes attached to the bellies of the major postural muscles. The analysis of muscles activity performed prior to performing the arm movement in the anticipatory postural adjustments phase (APAs) and after the arm movement in the compensatory postural adjustments phase (CPAs). The coactivation (C) and reciprocal activation (R) indexes were calculated for the ventral and dorsal muscles in the trunk, leg and shank segments in the APA and CPA phases. The COPAP displacement was acquired from the force platform signals. The study outcomes showed a modification of shank muscles activity across the experimental conditions in the APAs and CPAs. Noticeably, the dorsiflexion standing was associated with an inhibition in the tibialis anterior muscle and activation in the gastrocnemius muscle. The C index was significantly larger than R index in all the body segments in the natural and plantarflexion standing. The COPAP displacement was similar across the experimental conditions. The outcomes of the thesis could provide a basis for future research studying the effect of prolonged standing over inclined surfaces on the control of vertical posture. Furthermore, future research could include a sample population with diminished balance ability as elderly and people with neurological conditions