Temple University, Philadelphia, PA, USA.
J Neurophysiol. 2012 Mar;107(5):1513-21. doi: 10.1152/jn.00256.2011. Epub 2011 Dec 7.
Anthropological and biomechanical research suggests that the human foot evolved a unique design for propulsion and support. In theory, the arch and toes must play an important role, however, many postural studies tend to focus on the simple hinge action of the ankle joint. To investigate further the role of foot anatomy and sensorimotor control of posture, we quantified the deformation of the foot arch and studied the effects of local perturbations applied to the toes (TOE) or 1st/2nd metatarsals (MT) while standing. In sitting position, loading and lifting a 10-kg weight on the knee respectively lowered and raised the foot arch between 1 and 1.5 mm. Less than 50% of this change could be accounted for by plantar surface skin compression. During quiet standing, the foot arch probe and shin sway revealed a significant correlation, which shows that as the tibia tilts forward, the foot arch flattens and vice versa. During TOE and MT perturbations (a 2- to 6-mm upward shift of an appropriate part of the foot at 2.5 mm/s), electromyogram (EMG) measures of the tibialis anterior and gastrocnemius revealed notable changes, and the root-mean-square (RMS) variability of shin sway increased significantly, these increments being greater in the MT condition. The slow return of RMS to baseline level (>30 s) suggested that a very small perturbation changes the surface reference frame, which then takes time to reestablish. These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity.
人类学和生物力学研究表明，人类的脚进化出了独特的推进和支撑设计。从理论上讲，足弓和脚趾必须发挥重要作用，但许多姿势研究往往侧重于踝关节的简单铰链作用。为了进一步研究脚解剖结构和姿势传感器控制的作用，我们量化了足弓的变形，并研究了在站立时向脚趾（TOE）或第 1/2 跖骨（MT）施加局部扰动的影响。在坐姿下，在膝盖上分别加载和提起 10 公斤的重量会使足弓分别降低和抬高 1 到 1.5 毫米。只有不到 50%的变化可以用足底表面皮肤压缩来解释。在安静站立时，足弓探头和胫骨晃动显示出显著的相关性，这表明当胫骨向前倾斜时，足弓变平，反之亦然。在 TOE 和 MT 扰动（以 2.5 毫米/秒的速度将脚的适当部分向上移动 2-6 毫米）时，胫骨前肌和腓肠肌的肌电图（EMG）测量显示出明显的变化，胫骨晃动的均方根（RMS）变异性显著增加，在 MT 条件下增加更为明显。RMS 缓慢恢复到基线水平（超过 30 秒）表明，一个很小的扰动会改变表面参考框架，然后需要时间重新建立。这些发现表明，脚不是作为刚性支撑基础，而是在主动状态下具有柔韧性，并且对微小变形敏感。总之，脚的结构和生理学似乎对双足姿势控制任务具有高度敏感性。
