Physical and Sensory Perturbations Changed Joint Regulations in Control of Posture: A Power Spectral Analysis

Background: Standing on an unstable platform needs more effort from neuromusculoskeletal 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 in this cross-sectional study 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 postural adjustment by more joint regulations as the standing conditions became more difficult. Support stiffness of the platform and vision were effective in keeping balance (P<0.05), while the dual cognitive tasks had no significant effect (P>0.05). 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 ankle strategy. Conclusion: Standing in different conditions prevailingly relied on the ankle strategy. The enhancement of postural difficulty may revert to dominantly use the ankle strategy.