Raichlen David A
Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA.
J Exp Biol. 2006 Feb;209(Pt 4):633-44. doi: 10.1242/jeb.02061.
Many researchers have suggested that cursorial mammals concentrate limb muscle mass proximally to reduce energy costs during locomotion. Although supported by experiments where mass is added to an individual's limbs, mammals with naturally occurring distally heavy limbs such as primates have similar energy costs compared with other mammals. This study presents a new hypothesis to explain how animals with distally heavy limbs maintain low energy costs. Since distal mass should increase energy costs due to higher amounts of muscular power outputs, this hypothesis is based on the divergent effects of stride frequency on internal and external power outputs (the power output to move the limbs and the body center of mass, respectively). The use of low stride frequencies reduces limb velocities and therefore decreases internal power, while associated long strides increase the vertical displacement of the body center of mass and therefore increase external power. Total power (the sum of internal and external power) may therefore not differ among mammals with different limb mass distributions. To test this hypothesis, I examined a sample of infant baboons (Papio cynocephalus) during ontogeny and compared them with more cursorial mammals. Limb mass distribution changes with age (from distal to more proximally concentrated) in baboons, and the infants used shorter strides and higher stride frequencies when limb mass was most proximally concentrated. Compared with non-primates who have more proximally concentrated limb mass, the infants used longer strides and lower stride frequencies. Relatively low internal power was associated with low stride frequencies in both the intra- and inter-specific samples. However, only in the inter-specific comparison were relatively long strides associated with high external power outputs. In both the intra-specific and the inter-specific samples, total power did not differ between groups who differed in limb mass distribution. The results of this study suggest that a trade-off mechanism is available to quadrupeds with distally heavy limbs allowing them to maintain similar total power outputs (and likely similar energy costs) compared with mammals with more proximally concentrated limb mass.
许多研究人员认为，善于奔跑的哺乳动物将肢体肌肉质量集中在近端，以降低运动过程中的能量消耗。尽管在将质量添加到个体肢体的实验中得到了支持，但具有自然远端较重肢体的哺乳动物，如灵长类动物，与其他哺乳动物相比，能量消耗相似。本研究提出了一个新的假设，以解释具有远端较重肢体的动物如何保持低能量消耗。由于远端质量因更高的肌肉功率输出量而应增加能量消耗，该假设基于步频对内部和外部功率输出（分别为移动肢体和身体质心的功率输出）的不同影响。使用低步频会降低肢体速度，从而降低内部功率，而相关的大步幅会增加身体质心的垂直位移，从而增加外部功率。因此，不同肢体质量分布的哺乳动物之间的总功率（内部和外部功率之和）可能没有差异。为了验证这一假设，我在幼年期检查了一组婴儿狒狒（黄狒），并将它们与更善于奔跑的哺乳动物进行了比较。狒狒的肢体质量分布随年龄变化（从远端到更集中在近端），当肢体质量最集中在近端时，婴儿使用较短的步幅和较高的步频。与肢体质量更集中在近端的非灵长类动物相比，婴儿使用更长步幅和更低步频。在种内和种间样本中，相对较低的内部功率都与低步频相关。然而，只有在种间比较中，相对较长的步幅才与高外部功率输出相关。在种内和种间样本中，肢体质量分布不同的组之间总功率没有差异。这项研究的结果表明，对于具有远端较重肢体的四足动物来说，一种权衡机制是可行的，这使得它们与肢体质量更集中在近端的哺乳动物相比，能够保持相似的总功率输出（以及可能相似的能量消耗）。
