Schilder Rudolf J, Marden James H
Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
J Exp Biol. 2004 Feb;207(Pt 5):767-76. doi: 10.1242/jeb.00817.
Maximum isometric force output by single muscles has long been known to be proportional to muscle mass(0.67), i.e to muscle cross-sectional area. However, locomotion often requires a different muscle contraction regime than that used under isometric conditions. Moreover, lever mechanisms generally affect the force outputs of muscle-limb linkages, which is one reason why the scaling of net force output by intact musculoskeletal systems can differ from mass(0.67). Indeed, several studies have demonstrated that force output by intact musculoskeletal systems and non-biological systems is proportional to motor mass(1.0). Here we trace the mechanisms that cause dragonflies to achieve a change from muscle mass(0.67) scaling of maximum force output by single flight muscles to mass(1.0) scaling of dynamic force output by the intact dragonfly flight motor. In eight species of dragonflies, tetanic force output by the basalar muscle during isometric contraction scaled as muscle mass(0.67). Mean force output by the basalar muscle under dynamic conditions (workloops) that simulated in vivo maximum musculoskeletal performance was proportional to muscle mass(0.83), a significant increase in the scaling exponent over that of maximum isometric force output. The dynamic performance of the basalar muscle and the anatomy of its lever, consisting of the second moment of area of the forewing (d(2)) and the distance between the muscle apodeme and the wing fulcrum (d(1)), were used to analyze net force output by the integrated muscle-lever system (F(ind)). The scaling of d(2) conformed closely to the expected value from geometic similarity (proportional to muscle mass(0.31)), whereas d(1) scaled as muscle mass(0.54), a significant increase over the expected value from geometric similarity. F(ind) scaled as muscle mass(1.036), and this scaling exponent was not significantly different from unity or from the scaling exponent relating maximum load-lifting by flying dragonflies to their thorax mass. Thus, the combined effect of a change in the scaling of force output by the muscle during dynamic contraction compared to that during isometric contraction and the departure from geometric similarity of one of the two lever arm lengths provides an explanation for how mass(1.0) scaling of force output by the intact musculoskeletal system is accomplished. We also show that maximum muscle mass-specific net work and power output available scale as mass(0.43) and mass(0.24), respectively.
长期以来，人们一直知道单块肌肉的最大等长力输出与肌肉质量（0.67）成正比，即与肌肉横截面积成正比。然而，运动通常需要的肌肉收缩方式与等长条件下使用的方式不同。此外，杠杆机制通常会影响肌肉 - 肢体连接的力输出，这就是完整肌肉骨骼系统的净力输出缩放比例可能与质量（0.67）不同的原因之一。事实上，多项研究表明，完整肌肉骨骼系统和非生物系统的力输出与运动质量（1.0）成正比。在这里，我们追踪导致蜻蜓从单块飞行肌肉最大力输出的肌肉质量（0.67）缩放比例转变为完整蜻蜓飞行运动动态力输出的质量（1.0）缩放比例的机制。在八种蜻蜓中，基底肌在等长收缩期间的强直力输出与肌肉质量（0.67）成比例缩放。在模拟体内最大肌肉骨骼性能的动态条件（工作循环）下，基底肌的平均力输出与肌肉质量（0.83）成正比，缩放指数比最大等长力输出有显著增加。利用基底肌的动态性能及其杠杆的解剖结构，包括前翅的面积矩（d(2)）和肌肉腱膜与翅支点之间的距离（d(1)），来分析整合的肌肉 - 杠杆系统的净力输出（F(ind)）。d(2)的缩放比例与几何相似性预期值（与肌肉质量（0.31）成正比）非常接近，而d(1)的缩放比例为肌肉质量（0.54），比几何相似性预期值显著增加。F(ind)的缩放比例为肌肉质量（1.036），该缩放指数与1没有显著差异，也与将飞行蜻蜓的最大负载提升与其胸部质量相关的缩放指数没有显著差异。因此，与等长收缩相比，动态收缩期间肌肉力输出缩放比例的变化以及两个杠杆臂长度之一偏离几何相似性的综合作用，解释了完整肌肉骨骼系统如何实现力输出的质量（1.0）缩放比例。我们还表明，最大肌肉质量特异性净功和可用功率输出分别与质量（0.43）和质量（0.24）成比例缩放。
