Department of Ecology & Evolution, University of California, Irvine, CA 92697-2525, USA.
Integr Comp Biol. 2012 Nov;52(5):588-96. doi: 10.1093/icb/ics111. Epub 2012 Sep 2.
A skeleton amplifies the minute contractions of muscles to animate the body of an animal. The degree that a muscular contraction displaces an appendage is determined by the gearing provided by the joints of a skeleton. Species that move rapidly commonly possess joints with relatively high gears that produce a large output displacement. However, the speed of an appendage can depend on dynamics that obscure how this motion is influenced by the skeleton. The aim of this review is to resolve mechanical principles that govern the relationship between the gearing and speed of skeletal joints. Forward dynamic models of three rapid force-transmission systems were examined with simulations that varied the gearing of a joint. The leg of a locust, the raptorial appendage of a mantis shrimp, and the jaw of a toad are all driven by the conversion of stored elastic energy into kinetic energy. A locust achieves this conversion with high efficiency when it kicks and thereby applies nearly all stored energy into fast movement. This conversion is unaffected by differences in the leverage of the knee joint, as demonstrated by a maximum kicking speed that was found to be independent of gearing. In contrast, the mantis shrimp creates drag as it strikes toward a prey and thereby loses energy. As a consequence, high gears displace the raptorial appendage relatively far and yield slower motion than do low gears. The muscle that opens a toad's jaw also dissipates energy during ballistic capture of prey. This loss of energy is reduced when jaw opening occurs from the slower muscle contraction produced by a high gear within the jaw. Therefore, the speed of these lever systems is dictated by how gearing affects the efficiency of the conversion of potential energy into kinetic energy. In this way, the energetics of force transmission mediate the relationship between the gearing of a skeletal joint and the maximum speed of its motion.
骨骼放大肌肉的微小收缩，从而使动物的身体活动起来。肌肉收缩使附肢移动的程度取决于骨骼关节提供的齿轮传动比。快速移动的物种通常具有相对较高齿轮比的关节，从而产生较大的输出位移。然而，附肢的速度可能取决于动态因素，这些因素掩盖了骨骼对运动的影响方式。本综述的目的是解决支配骨骼关节传动比和速度关系的机械原理。通过模拟改变关节的传动比，检查了三个快速力传递系统的正向动力学模型。蝗虫的腿、螳螂虾的捕食附肢和蟾蜍的下巴都是通过将储存的弹性势能转化为动能来驱动的。蝗虫在踢腿时效率很高，几乎将所有储存的能量都转化为快速运动，从而实现了这种转化。膝关节的杠杆作用的差异对这种转化没有影响，因为最大踢腿速度被发现与传动比无关。相比之下，螳螂虾在向猎物猛击时会产生阻力，从而失去能量。因此，高齿轮会使捕食附肢相对远地移动，并产生比低齿轮更慢的运动。蟾蜍张开下巴的肌肉在捕捉猎物时也会消耗能量。当通过下巴内的高速齿轮产生较慢的肌肉收缩来实现下巴张开时，能量损失会减少。因此，这些杠杆系统的速度取决于传动比如何影响势能转化为动能的效率。通过这种方式，力传递的能量学调节了骨骼关节的传动比与运动的最大速度之间的关系。
