Lai Qian Qi, Gouwanda Darwin, Gopalai Alpha A
School of Engineering, Monash University Malaysia, Selangor,Malaysia.
Motor Control. 2022 Oct 10;27(2):179-193. doi: 10.1123/mc.2021-0138. Print 2023 Apr 1.
Balance control is essential for postural adjustment in physical activities. This study investigates the behavior of human postural control and the coordination and adaptation strategy of hip, knee, and ankle when standing on an unstable surface. Twenty participants were recruited. Four different conditions were investigated: a quiet bipedal stance with eyes open and eyes closed, and standing on an unstable surface with eyes open and eyes closed. Other than the joint angle, the standard body sway measures, such as sway area and sway velocity, were computed. A nonlinear time series measure, that is, sample entropy, was used to determine the regularity of the time series and body adaptability to change and perturbation. The results show that the body sway increases as the difficulty increases. This study also confirms the coordination of the hip, knee, and ankle to maintain body balance on the unstable surface by decreasing the joint angle and adopting a lower posture. Even though the individual joint has lower sample entropy value and is deemed to be rigid and less adaptive to perturbation, the postural control exhibits higher sample entropy value, particularly in the anterior-posterior direction, and has the ability to stabilize the body by manipulating the joints simultaneously. These outcomes suggest that an unstable surface not only challenges the human postural control, but also reduces the hip, knee, and ankle adaptability to perturbation, thus making it a great tool to train body balance.
平衡控制对于身体活动中的姿势调整至关重要。本研究调查了人类姿势控制的行为以及在不稳定表面上站立时髋、膝和踝关节的协调与适应策略。招募了20名参与者。研究了四种不同的情况：睁眼和闭眼的安静双足站立，以及睁眼和闭眼站在不稳定表面上。除了关节角度外，还计算了标准的身体摆动测量值，如摆动面积和摆动速度。使用一种非线性时间序列测量方法，即样本熵，来确定时间序列的规律性以及身体对变化和扰动的适应性。结果表明，随着难度增加，身体摆动增大。本研究还证实了髋、膝和踝关节通过减小关节角度并采用更低的姿势来在不稳定表面上维持身体平衡的协调性。尽管单个关节的样本熵值较低，被认为较为僵硬且对扰动的适应性较差，但姿势控制表现出较高的样本熵值，尤其是在前后方向上，并且能够通过同时操纵关节来稳定身体。这些结果表明，不稳定表面不仅对人类姿势控制构成挑战，还会降低髋、膝和踝关节对扰动的适应性，因此使其成为训练身体平衡的理想工具。
