Document Type : Original Articles


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


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
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.


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