Effects of postural and cognitive difficulty levels on the standing of healthy young males on an unstable platform.

Standing on an unstable platform requires continuous effort of the neuro‑musculoskeletal system. The aim of the present study is to evaluate the ability to remain standing on an unstable platform at different levels of postural and cognitive difficulty. Healthy young males stood in the sagittal plane on an unstable platform supported by a pair of springs with modifiable stiffness. The balance test also assessed different levels of vision and cognitive function. Linear and nonlinear metrics of standing, based on motion captured kinematic data, were assessed to analyze the stability of standing. Results showed that vision plays a significant role in maintaining balance in terms of linear metrics. Elimination of visual feedback changed the direction of body sway and increased standing instability. Placement of low stiffness springs led to unstable standing. The cognitive dual task, however, had no effect on the stability metrics and merely could be revealed in the simplest test condition. Standing on an unstable platform was closely related to visual feedback and decreasing the spring stiffness significantly reduced stability. The roles of cognitive involvement were subdued by increasing the postural difficulty in standing on an unstable platform.