Loram Ian D, Lakie Martin
School of Sport and Exercise Sciences, The University of Birmingham, Birmingham B15 2TT, UK.
J Physiol. 2002 May 1;540(Pt 3):1111-24. doi: 10.1113/jphysiol.2001.013077.
In standing, there are small sways of the body. Our interest is to use an artificial task to illuminate the mechanisms underlying the sways and to account for changes in their size. Using the ankle musculature, subjects balanced a large inverted pendulum. The equilibrium of the pendulum is unstable and quasi-regular sway was observed like that in quiet standing. By giving full attention to minimising sway subjects could systematically reduce pendulum movement. The pendulum position, the torque generated at each ankle and the soleus and tibialis anterior EMGs were recorded. Explanations about how the human inverted pendulum is balanced usually ignore the fact that balance is maintained over a range of angles and not just at one angle. Any resting equilibrium position of the pendulum is unstable and in practice temporary; movement to a different resting equilibrium position can only be accomplished by a biphasic 'throw and catch' pattern of torque and not by an elastic mechanism. Results showed that balance was achieved by the constant repetition of a neurally generated ballistic-like biphasic pattern of torque which can control both position and sway size. A decomposition technique revealed that there was a substantial contribution to changes in torque from intrinsic mechanical ankle stiffness; however, by itself this was insufficient to maintain balance or to control position. Minimisation of sway size was caused by improvement in the accuracy of the anticipatory torque impulses. We hypothesise that examination of centre of mass and centre of pressure data for quiet standing will duplicate these results.
站立时，身体会有微小的晃动。我们感兴趣的是利用一项人为任务来阐明这些晃动背后的机制，并解释其幅度变化的原因。受试者通过踝关节肌肉控制一个大型倒立摆保持平衡。该倒立摆的平衡是不稳定的，并且观察到类似安静站立时的准规则晃动。当受试者全神贯注于尽量减少晃动时，他们能够系统地减少摆的运动。记录了摆的位置、每个踝关节产生的扭矩以及比目鱼肌和胫骨前肌的肌电图。关于人体如何平衡倒立摆的解释通常忽略了一个事实，即平衡是在一定角度范围内保持的，而不仅仅是在某一个角度。摆的任何静止平衡位置都是不稳定的，实际上只是暂时的；要移动到另一个静止平衡位置只能通过双相的“抛接”扭矩模式来实现，而不是通过弹性机制。结果表明，通过不断重复神经产生的类似弹道的双相扭矩模式可以实现平衡，该模式能够控制位置和晃动幅度。一种分解技术表明，踝关节固有机械刚度对扭矩变化有很大贡献；然而，仅靠它本身不足以维持平衡或控制位置。晃动幅度的减小是由于预期扭矩脉冲精度的提高。我们假设，对安静站立时的重心和压力中心数据进行检查将得到相同的结果。
