Department of Kinesiology, Texas Christian University, Fort Worth, TX,USA.
Motor Control. 2022 Jul 19;26(4):591-607. doi: 10.1123/mc.2022-0005. Print 2022 Oct 1.
During upright standing, individuals often use co-contraction muscle activity at the ankle joint when encountering increased postural difficulty; however, this strategy has been shown to be maladaptive. The purpose of the current investigation was to examine the effect of sloped standing on postural sway and muscle co-contraction at the ankle joint as a function of postural difficulty. Twelve young (21.67 ± 1.11 years) adults performed upright standing on flat, declined, and inclined support surfaces. Center of pressure displacements indexed postural sway while electromyography data were collected for the tibialis anterior and gastrocnemius medialis muscles. A co-contraction index and a nonlinear coupling metric (cross-approximate entropy) were computed between ankle dorsiflexor and plantar flexor muscles (tibialis anterior/gastrocnemius medialis) activity. The results showed that higher degrees of postural difficulty led to increased amounts of sway as well as increased sway regularity. Lower co-contraction index was observed for higher degrees of postural difficulty; however, increased dynamic coupling occurred with deviations from the flat standing condition. Overall, increased postural difficulty as manipulated by sloped standing (in either inclined or declined conditions) resulted in individuals adopting a more regular sway trajectory that may be due, in part, to a stronger dynamic coupling strategy occurring at the neuromuscular level.
在直立站立时，个体在遇到更大的姿势困难时通常会在踝关节处使用协同收缩肌肉活动；然而，这种策略已被证明是不适应的。本研究的目的是探讨倾斜站立对姿势摆动和踝关节协同收缩的影响，以及其作为姿势困难的函数。12 名年轻成年人（21.67±1.11 岁）在平面、倾斜和倾斜支撑表面上进行直立站立。中心压力位移指标表示姿势摆动，同时采集胫骨前肌和腓肠肌内侧的肌电图数据。在踝关节背屈肌和跖屈肌（胫骨前肌/腓肠肌内侧）活动之间计算了协同收缩指数和非线性耦合度量（交叉近似熵）。结果表明，更高程度的姿势困难会导致更大的摆动幅度和更高的摆动规律性。对于更高程度的姿势困难，观察到更低的协同收缩指数；然而，随着偏离平面站立条件，动态耦合增加。总体而言，倾斜站立（无论是倾斜还是倾斜）引起的更大程度的姿势困难导致个体采用更规则的摆动轨迹，这可能部分归因于在神经肌肉水平发生更强的动态耦合策略。
