The influence of goal-directed reaching distance on standing postural control variability in non-disabled individuals

BACKGROUND: Performing everyday standing tasks is relevant to the individuals independence. It is a challenging postural action that requires upper extremity (UE) movements to interact with objects of the environment. Postural movement variability is a strategy of the postural system for exploring postural boundaries during the action. The distance to the target to be reached may affect the variability in postural control parameters. AIM: To test if the variability in postural control parameters is enhanced by reaching beyond the UE-length during a goal-directed standing task. METHOD: Twelve non-disabled adult individuals performed reaching to turn on a light switch (target) while standing, which was placed at 100% and 130% of the UE-length distance. The kinetic data were recorded using a force plate during the UE movement, and the centre of pressure (CoP) displacement variability index was calculated. RESULTS: The variability index of the CoP displacement for reaching was greater at the distance of 130% of UE-length compared to 100% in both anterior-posterior and medial-lateral directions (p = 0.019). No differences in time to complete the task were observed. CONCLUSION: Postural system increases the variability in postural controlling variable CoP displacement for reaching beyond the UE-length while standing. This movement variability helps individuals explore the boundaries of this standing action and may be useful for learning processes and counterbalancing postural disturbances.