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大象的“四轮驱动”运动

一项研究表明,大象的腿很可能在运动的时候发挥与其它四足动物的腿不同的功能。John Hutchinson及其同事利用特制的平台用高速红外摄影机记录下大象运动,从而分析了六头亚洲象行走或奔跑的时候的步态。大多数四足动物的前腿和后腿各司其职:后腿主要是用于推动,而前腿的功能是制动。然而,这组科学家发现他们研究的大象利用前腿和后腿制动和推动,它的运动类似于各个轮子独立运作的四轮驱动的汽车。这组作者提出,大象和其他动物运动的差异可能是由于大象的尺寸以及大象比更小、更轻的动物更需要稳定性。这组科学家还发现大象的腿所发挥的杠杆作用远弱于这种尺寸的预期作用。这组作者说,和其他四足动物不同,大象腿的力产生的有用运动的数量随着大象速度的增加而减少,这很可能需要比其他动物更多的能量消耗,而且限制了大象在奔跑时的耐久力。

参考文献:Published online before print March 29, 2010, doi: 10.1073/pnas.0911396107

Integration of biomechanical compliance, leverage, and power in elephant limbs

Lei Rena,b, Charlotte E. Millera, Richard Lairc, and John R. Hutchinsona,1

Abstract
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.

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