Structure and Motion Laboratory, The Royal Veterinary College, London NW1 0TU, United Kingdom.
Proc Natl Acad Sci U S A. 2010 Apr 13;107(15):7078-82. doi: 10.1073/pnas.0911396107. Epub 2010 Mar 29.
The structure and motion of elephant limbs are unusual compared with those of other animals. Elephants stand and move with straighter limbs (at least when walking), and have limited speed and gait. We devised novel experiments to examine how the limbs of elephants support and propel their mass and to explore the factors that may constrain locomotor performance in these largest of living land animals. We demonstrate that elephant limbs are remarkably compliant even in walking, which maintains low peak forces. Dogma defines elephant limbs as extremely "columnar" for effective weight support, but we demonstrate that limb effective mechanical advantage (EMA) is roughly one-third of that predicted for their size. EMA in elephants is actually smaller than that in horses, which are only one-tenth their mass; it is comparable to human limb values. EMA drops sharply with speed in elephants, as it does in humans. Muscle forces therefore must increase as the limbs become more flexed, and we show how this flexion translates to greater volumes of muscle recruited for locomotion and hence metabolic cost. Surprisingly, elephants use their forelimbs and hindlimbs in similar braking and propulsive roles, not dividing these functions among limbs as was previously assumed or as in other quadrupeds. Thus, their limb function is analogous to four-wheel-drive vehicles. To achieve the observed limb compliance and low peak forces, elephants synchronize their limb dynamics in the vertical direction, but incur considerable mechanical costs from limbs working against each other horizontally.
与其他动物相比，大象的四肢结构和运动方式较为特殊。大象直立行走时四肢较为挺直（至少在行走时如此），移动速度和步态受限。我们设计了新颖的实验来研究大象的四肢如何支撑和推动它们的身体，并探索可能限制这些最大陆生动物运动性能的因素。我们证明，即使在行走时，大象的四肢也具有惊人的柔韧性，从而保持较低的峰值力。传统观念认为，大象的四肢非常“柱状”，有利于有效承重，但我们证明，其肢体的有效机械优势（EMA）大约只有其体型预测值的三分之一。大象的 EMA 实际上比马的还要小，马的体重只有大象的十分之一；与人类的肢体数值相当。大象的 EMA 随速度的增加而急剧下降，就像人类一样。因此，随着四肢的弯曲，肌肉力量必须增加，我们展示了这种弯曲如何转化为更多用于运动的肌肉量，从而导致代谢成本增加。令人惊讶的是，大象的前肢和后肢在制动和推进方面发挥着相似的作用，不像以前假设的那样或其他四足动物那样将这些功能分配给不同的肢体。因此，它们的肢体功能类似于四轮驱动车辆。为了实现观察到的肢体柔韧性和较低的峰值力，大象在垂直方向上同步它们的肢体动力学，但在水平方向上，肢体相互作用会产生相当大的机械成本。
