By counteracting gravity, triceps surae sets both kinematics and kinetics of gait.
By counteracting gravity, triceps surae sets both kinematics and kinetics of gait.
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DOI：
10.1002/phy2.229
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发表时间：
2014-02-01
影响因子：
2.5
通讯作者：
Do, Manh-Cuong
中科院分区：
文献类型：
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作者：
Honeine, Jean-Louis;Schieppati, Marco;Gagey, Oliver;Do, Manh-Cuong
在步态的单站姿阶段，重力作用于重心会产生不平衡力矩，从而产生推进力。小腿三头肌活动通过抑制胫骨向前旋转来抵抗重力，从而调节COM动量。我们假设，小腿三头肌活动的时间和幅度调制决定了步态的运动学(步长和节奏)和动力学。19名年轻受试者参加了两个实验。在步态启动(GI)方案中，受试者故意以不同的速度开始行走，以相同的步长。在平衡恢复(BR)方案中，受试者在意外地从倾斜姿势中释放后，执行不同长度的步数。用大力台记录地面反作用力，用无线表面电极采集比目鱼肌、腓肠肌内侧肌、外侧肌、胫前肌的肌电。在两种方案中，三头肌活动持续时间与单站持续时间高度相关(GI，R2=0.68；BR，R2=0.91)。步长与单步站立持续时间高度相关(BR，R2=0.70)。通过调节三头肌的活动幅度来减速COM下落，从而获得COM动量的控制。通过调节三头肌的活动，中枢神经系统(CNS)改变COM相对于压力中心(COP)的位置。矢状面上的COP间隙是决定不平衡力矩和步行速度的决定因素。因此，通过控制间隙，中枢神经系统改变了步行速度(GI，R2=0.86；BR，R2=0.92)。这项研究首次强调，仅仅通过抵消重力，三头肌的活动决定了步态的运动学和动力学。它还提供了证据表明，快速行走过程中三头肌活动的激增是因为为了实现更平稳的步态过渡，需要在较晚的姿势下制动COM的下落。文章表明，通过垂直控制重心的下落，中枢神经系统能够设定全局步态运动学和动力学。这种控制是通过小腿三头肌活动的时间调制来完成的。文章还表明，增加后位三头肌的活动幅度，可以阻止重心的下降，为后续的步步执行提供了顺畅的条件。
In the single‐stance phase of gait, gravity acting on the center of mass (CoM) causes a disequilibrium torque, which generates propulsive force. Triceps surae activity resists gravity by restraining forward tibial rotation thereby tuning CoM momentum. We hypothesized that time and amplitude modulation of triceps surae activity determines the kinematics (step length and cadence) and kinetics of gait. Nineteen young subjects participated in two experiments. In the gait initiation (GI) protocol, subjects deliberately initiated walking at different velocities for the same step length. In the balance‐recovery (BR) protocol, subjects executed steps of different length after being unexpectedly released from an inclined posture. Ground reaction force was recorded by a large force platform and electromyography of soleus, gastrocnemius medialis and lateralis, and tibialis anterior muscles was collected by wireless surface electrodes. In both protocols, the duration of triceps activity was highly correlated with single‐stance duration (GI, R2 = 0.68; BR, R2 = 0.91). In turn, step length was highly correlated with single‐stance duration (BR, R2 = 0.70). Control of CoM momentum was obtained by decelerating the CoM fall via modulation of amplitude of triceps activity. By modulation of triceps activity, the central nervous system (CNS) varied the position of CoM with respect to the center of pressure (CoP). The CoM‐CoP gap in the sagittal plane was determinant for setting the disequilibrium torque and thus walking velocity. Thus, by controlling the gap, CNS‐modified walking velocity (GI, R2 = 0.86; BR, R2 = 0.92). This study is the first to highlight that by merely counteracting gravity, triceps activity sets the kinematics and kinetics of gait. It also provides evidence that the surge in triceps activity during fast walking is due to the increased requirement of braking the fall of CoM in late stance in order to perform a smoother step‐to‐step transition. The article shows that by vertically controlling the downward fall of the center of mass the central nervous system is capable of setting global gait kinematics and kinetics. The control is done via temporal modulation of triceps surae activity. The article also shows that increasing the amplitude of triceps activity in late stance brakes the fall of the center of mass providing smooth conditions for the subsequent step‐to‐step execution.