Document Type : Original Articles


Department of Physical Therapy, Faculty of Medical Sciences, Tarbiat Modares University



Background. Standing on an unstable platform needs more effort of the neuro-musculoskeletal system. This study was about to highlight the joint regulations in keeping balance while standing on an unstable platform using spectral analysis. Methods. Thirteen healthy young males were participated to stand on an unstable platform with two levels of support stiffness, two visual, and three cognitive dual-task conditions. Motion analysis was utilized to measure postural regulations at the lower extremity joints. Power spectral analysis was applied on the joint rotations to discriminate the joint behaviors in different standing conditions. Results. Results showed that the body used higher levels of the postural adjustment by more joint regulations as the standing conditions become more difficult. Support stiffness of the platform and vision were effective in keeping balance (p < .05) while the cognitive dual tasks had no significant effect (p > .05). In simpler standing conditions, the ankle-hip strategy was responsible for body stabilization in lower frequencies. However, increasing the standing difficulty by eliminating the vision or use of looser support of the platform was led to the predominance of the ankle strategy. Conclusion. Standing in different conditions prevailingly relied on the ankle strategy. Enhancement of the postural difficulty may revert to dominantly use the ankle strategy.