Usherwood James R
Structure and Motion Laboratory, The Royal Veterinary College, Hatfield, UK.
J Exp Zool A Ecol Integr Physiol. 2020 Jan;333(1):9-19. doi: 10.1002/jez.2268. Epub 2019 Apr 29.
The majority of terrestrial mammals adopt distinct, discrete gaits across their speed range. Though there is evidence that walk, trot and gallop may be selected at speeds consistent with minimizing metabolic cost (Hoyt and Taylor, 1981, Nature, 291, 239-240), the mechanical causes underlying these costs and their changes with speed are not well understood. In particular, the paired, near-simultaneous contacts of the trot is puzzling as it appears to demand a high mechanical work that could easily be avoided with distributed contacts, as with a "running walk" gait or "tolt." Here, a simple condition is derived-a ratio including the pitch moment of inertia and back length-for which trotting is energetically advantageous because it avoids the energetic consequences of pitching. Pitching could also be avoided if the impulses from the legs were orientated through the center of mass. A range of idealized gaits is considered that achieve this zero-pitch condition, and work minimization predicts a transition from trot to canter at intermediate speeds. This can be understood from the geometric principles of achieving a "pseudoelastic" collision with each impulse (Ruina et al., 2005, J Theoretical Biol, 14, 170-192). However, at high speeds, a transition back to trot is predicted that is not observed in nature.
大多数陆生哺乳动物在其速度范围内采用独特、离散的步态。尽管有证据表明，行走、小跑和疾驰可能是在与将代谢成本降至最低相一致的速度下被选择的（霍伊特和泰勒，1981年，《自然》，第291卷，第239 - 240页），但这些成本背后的机械原因以及它们随速度的变化尚未得到很好的理解。特别是，小跑时成对且近乎同时的接触令人费解，因为它似乎需要很高的机械功，而像“竞走”步态或“托尔特”步态那样通过分散接触很容易避免这种情况。在此，推导出一个简单的条件——一个包括俯仰转动惯量和背部长度的比率——对于这个条件，小跑在能量方面具有优势，因为它避免了俯仰的能量后果。如果来自腿部的冲量通过质心定向，也可以避免俯仰。考虑了一系列理想化的步态，这些步态实现了这种零俯仰条件，并且功最小化预测在中等速度下从小跑过渡到慢跑。这可以从与每个冲量实现“伪弹性”碰撞的几何原理来理解（鲁伊纳等人，2005年，《理论生物学杂志》，第14卷，第170 - 192页）。然而，在高速时，预测会出现回到小跑的转变，而这在自然界中并未观察到。
