Moon Brad R, Hopp J Johanna, Conley Kevin E
Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA.
J Exp Biol. 2002 Mar;205(Pt 5):667-75. doi: 10.1242/jeb.205.5.667.
Rattling by rattlesnakes is one of the fastest vertebrate movements and involves some of the highest contraction frequencies sustained by vertebrate muscle. Rattling requires higher accelerations at higher twitch frequencies, yet a previous study showed that the cost per twitch of rattling is independent of twitch frequency. We used force and video recordings over a range of temperatures to examine how western diamondback rattlesnakes (Crotalus atrox) achieve faster movements without increases in metabolic cost. The key findings are (i) that increasing muscle twitch tension trades off with decreasing twitch duration to keep the tension-time integral per twitch nearly constant over a wide range of temperatures and twitch frequencies and (ii) that decreasing lateral displacement of the rattle joint moderates the mechanical work and power required to shake the rattle at higher frequencies. These mechanical trade-offs between twitch tension and duration and between joint force and displacement explain how force, work and power increase without an increase in metabolic cost.
响尾蛇发出的嘎嘎声是脊椎动物最快的运动之一，涉及脊椎动物肌肉维持的一些最高收缩频率。发出嘎嘎声在更高的抽搐频率下需要更高的加速度，但先前的一项研究表明，发出嘎嘎声的每次抽搐成本与抽搐频率无关。我们在一系列温度下使用力和视频记录，以研究西部菱背响尾蛇（Crotalus atrox）如何在不增加代谢成本的情况下实现更快的运动。关键发现是：（i）增加肌肉抽搐张力与缩短抽搐持续时间相互权衡，以使每次抽搐的张力 - 时间积分在广泛的温度和抽搐频率范围内几乎保持恒定；（ii）响尾关节横向位移的减小降低了在更高频率下摇动响尾所需的机械功和功率。抽搐张力与持续时间之间以及关节力与位移之间的这些机械权衡解释了力、功和功率如何在不增加代谢成本的情况下增加。
