Balance control under different passive contributions of the ankle extensors: quiet standing on inclined surfaces
Balance control under different passive contributions of the ankle extensors: quiet standing on inclined surfaces
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DOI：
10.1007/s00221-009-1876-4
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发表时间：
2009-07-01
影响因子：
2
通讯作者：
Kanehisa, Hiroaki
中科院分区：
文献类型：
--
作者：
Sasagawa, Shun;Ushiyama, Junichi;Kanehisa, Hiroaki
人类两足站立姿势通常被建模为单个倒立摆，其在矢状面中的踝关节处枢转。由于身体质量中心通常保持在踝关节的前方，因此需要持续的踝伸肌扭矩来防止身体摔倒。在安静的站立过程中，被动和主动机制都有助于产生抵消重力的踝伸肌扭矩。本研究旨在更详细地研究主动稳定机制。八名健康受试者被要求安静地站在三个不同的表面上：1）脚趾向上，2）水平，3）脚趾向下。从腓肠肌（MG）、比目鱼肌（SOL）和胫骨前肌的内侧头记录表面肌电图（EMG）。同时测量身体的倾斜角。结果，我们发现MG和SOL的EMG活动在脚趾向上站立时最低，在脚趾向下站立时最高，表明被动贡献的增加（减少）需要更少（更多）主动肌肉收缩产生的伸肌扭矩。频域分析还表明，摇摆相关的调制踝伸肌活动（0.12-4.03赫兹）是不变的三个脚倾斜。另一方面，这些肌肉的等长收缩强度随着坡度的减小而增加（脚趾向上<水平<脚趾向下）。这些结果支持的想法，通过调节等长收缩强度，中枢神经系统保持恒定水平的肌肉张力和由此产生的踝关节僵硬，而不管被动的贡献。当我们考虑间歇控制器的低带宽时，这种控制方案至关重要。
Human bipedal stance is often modeled as a single inverted pendulum that pivots at the ankle joints in the sagittal plane. Because the center of body mass is usually maintained in front of the ankle joints, ankle extensor torque is continuously required to prevent the body from falling. During quiet standing, both passive and active mechanisms contribute to generate the ankle extensor torque counteracting gravity. This study aimed to investigate the active stabilization mechanism in more detail. Eight healthy subjects were requested to stand quietly on three different surfaces of 1) toes-up, 2) level, and 3) toes-down. Surface electromyogram (EMG) was recorded from the medial head of the gastrocnemius (MG), soleus (SOL), and tibialis anterior muscles. Inclination angle of the body was simultaneously measured. As a result, we found that EMG activities of MG and SOL were lowest during the toes-up standing and highest during the toes-down, indicating that increased (decreased) passive contribution required less (more) extensor torque generated by active muscle contraction. Frequency domain analysis also revealed that sway-related modulation of the ankle extensor activity (0.12-4.03 Hz) was unchanged among the three foot inclinations. On the other hand, isometric contraction strength of these muscles increased as the slope declined (toes-up < level < toes-down). These results support the idea that by regulating the isometric contraction strength, the CNS maintains a constant level of muscle tone and resultant ankle stiffness irrespective of the passive contribution. Such control scheme would be crucial when we consider the low bandwidth of the intermittent controller.