Kelso J A
Am J Physiol. 1984 Jun;246(6 Pt 2):R1000-4. doi: 10.1152/ajpregu.1984.246.6.R1000.
Conditions that give rise to phase shifts among the limbs when an animal changes gait are poorly understood. Often a "switch mechanism" is invoked that has a neural basis which remains speculative. Abrupt phase transitions also occur between the two hands in humans when movement-cycling frequency is continuously increased. The asymmetrical out-of-phase mode shifts suddenly to a symmetrical in-phase mode involving simultaneous activation of homologous muscle groups. The boundary between the two coordinative states is indexed by a dimensionless critical number, which remains constant regardless of whether the hands move freely or are subject to resistive loading. Coordinated shifts appear to arise because of continuous scaling influences that render the existing mode unstable. Then, at a critical point, bifurcation occurs and a new stable (and perhaps energetically more efficient) mode emerges.
当动物改变步态时，导致肢体间相位变化的条件目前还知之甚少。人们常常援引一种具有神经基础的“转换机制”，但其神经基础仍属推测。当运动循环频率持续增加时，人类的两只手之间也会发生突然的相位转变。不对称的异相模式会突然转变为对称的同相模式，涉及同源肌肉群的同时激活。两种协调状态之间的边界由一个无量纲的临界数来表征，无论双手是自由移动还是受到阻力负载，该临界数都保持不变。协调的转变似乎是由于持续的缩放影响导致现有模式不稳定而产生的。然后，在一个临界点，会发生分岔，一种新的稳定（可能在能量上更高效）模式出现。
