Perry A K, Blickhan R, Biewener A A, Heglund N C, Taylor C R
CFS, Museum of Comparative Zoology, Harvard University, Bedford, MA 01730.
J Exp Biol. 1988 Jul;137:207-19. doi: 10.1242/jeb.137.1.207.
Terrestrial animals have 'preferred speeds' within each gait, that are used much more frequently than others for moving along the ground. Energy costs reach minimal values at these speeds within each gait. In this study we asked whether these speeds are mechanically equivalent among different animals (i.e. speeds where the same levels of peak muscle stress occur). If so, this would help in establishing a link between the energetics and the mechanics of the active muscles at these speeds, providing a first step in understanding why energy costs are minimal. We also asked whether peak muscle stress reaches a similar fraction of the maximal isometric stress at these speeds. If so, this would suggest that muscles are structured so that a similar reserve capacity remains, with a similar safety factor for avoidance of injury in response to prolonged repetitive loading. We compared two species that use quite different locomotory methods at their preferred speeds: white rats that gallop and kangaroo rats that hop. We measured peak stress in the ankle extensor muscles of these two species, as they moved at their preferred speeds, using a force platform/ciné analysis technique. We also measured the maximum isometric force that this muscle group could develop in situ in the same individuals. We found the ankle extensors of white rats and kangaroo rats developed virtually identical levels of peak stress at their preferred speeds (70 +/- 6 kPa and 69 +/- 6 kPa, respectively, mean +/- S.E.), despite a fourfold difference in peak ground reaction force per unit body mass exerted on each limb. The values of peak isometric stress in situ were also virtually identical (206 +/- 17 kPa and 200 +/- 9 kPa, respectively). Our finding that the peak muscle stress is about one-third of maximum isometric stress at the preferred speeds is consistent with the idea that these are mechanically equivalent speeds, where the same fraction of available muscle fibres is recruited. Finding nearly identical values in two species that move in such different ways (galloping vs hopping), and have such large differences in ground reaction force exerted by each limb, suggests this may be true more generally for terrestrial vertebrates.
陆生动物在每种步态下都有“偏好速度”，它们在地面移动时使用这些速度的频率远高于其他速度。在每种步态下，能量消耗在这些速度时达到最小值。在本研究中，我们探讨了这些速度在不同动物之间是否在力学上等效（即产生相同水平峰值肌肉应力的速度）。如果是这样，这将有助于在这些速度下建立活跃肌肉的能量学与力学之间的联系，为理解能量消耗为何最小提供第一步。我们还研究了在这些速度下峰值肌肉应力是否达到最大等长应力的相似比例。如果是这样，这将表明肌肉的结构使得保留了相似的储备能力，对于因长时间重复负荷而避免受伤具有相似的安全系数。我们比较了两种在偏好速度下使用截然不同运动方式的物种：奔跑的白鼠和跳跃的更格卢鼠。我们使用力平台/电影分析技术，在这两个物种以偏好速度移动时，测量其踝伸肌的峰值应力。我们还测量了同一动物个体中该肌肉群在原位能够产生的最大等长力。我们发现，白鼠和更格卢鼠的踝伸肌在偏好速度下产生的峰值应力水平几乎相同（分别为70±6千帕和69±6千帕，均值±标准误），尽管每只肢体上单位体重的峰值地面反作用力相差四倍。原位峰值等长应力的值也几乎相同（分别为206±17千帕和200±9千帕）。我们发现在偏好速度下峰值肌肉应力约为最大等长应力的三分之一，这一发现与这些速度在力学上等效的观点一致，即在这些速度下募集了相同比例的可用肌纤维。在两种运动方式如此不同（奔跑与跳跃）且每只肢体施加的地面反作用力差异如此之大的物种中发现了几乎相同的值，这表明对于陆生脊椎动物而言，这可能更具普遍性。
