Background:

To maintain an upright standing posture against external disturbances, the human body mainly employs two types of postural control strategies: “ankle strategy” and “hip strategy.” While it has been reported that the magnitude of the disturbance alters the use of postural control strategies, it has not been elucidated how the level of muscle tone, one of the crucial parameters of bodily function, determines the use of each strategy. We have previously confirmed using forward dynamics simulations of human musculoskeletal models that an increased muscle tone promotes the use of ankle strategies. The objective of the present study was to experimentally evaluate a hypothesis: an increased muscle tone promotes the use of ankle strategies.

Research question:

Do changes in the muscle tone affect the use of ankle strategies?

Methods:

Participants were asked to maintain their standing posture on a movable platform sliding horizontally at several accelerations. Postural reactions for support surface translations were examined under three instructions with or without handgrips: relax state, squeezing a handgrip, and an increased muscle tone of the whole body. Surface-electromyography and marker locations of joints were measured to calculate the index of muscle tone and postural control strategies. The relationship of the indexes was evaluated based on correlation coefficients.

Results:

In half of the conditions, weak negative correlations were noted between the muscle tone index and postural control strategy index. In other words, an increased muscle tone rather promoted the use of the ankle strategy than the hip strategy. These findings are consistent with our previous simulation results.

Significance:

The results recognized a positive response to the research question. This suggests that it is crucial to take muscle tone into account to understand postural control strategies.

中文翻译：

---

肌肉张力的增加促进了在扰动站姿期间脚踝策略的使用

背景：

人体为了对抗外界干扰而保持直立的站立姿势，主要采用两种姿势控制策略：“踝策略”和“髋策略”。虽然有报道称干扰的程度会改变姿势控制策略的使用，但尚未阐明肌肉张力水平（身体功能的关键参数之一）如何决定每种策略的使用。我们之前已经确认使用人类肌肉骨骼模型的前向动力学模拟，增加的肌肉张力促进了脚踝策略的使用。本研究的目的是通过实验评估一个假设：增加的肌肉张力促进脚踝策略的使用。

研究问题：

肌肉张力的变化会影响踝关节策略的使用吗？

方法：

参与者被要求在以几个加速度水平滑动的可移动平台上保持站立姿势。在使用或不使用手柄的三个指令下检查支撑表面平移的姿势反应：放松状态、挤压手柄和全身肌肉张力增加。测量关节的表面肌电图和标记位置，以计算肌肉张力和姿势控制策略的指数。基于相关系数评估指标之间的关系。

结果：

在一半的情况下，肌肉张力指数和姿势控制策略指数之间存在弱的负相关。换句话说，肌肉张力的增加反而促进了脚踝策略的使用，而不是臀部策略的使用。这些发现与我们之前的模拟结果一致。

意义：

结果确认了对研究问题的积极回应。这表明考虑肌肉张力对理解姿势控制策略至关重要。