Department of Zoology, University of British Columbia, 4200-6270 University Blvd, Vancouver, BC V6T 1Z4, Canada.
Department of Biology, California State University, Sacramento, 6000 J St., Sacramento, CA 95819, USA.
J Exp Biol. 2019 Apr 5;222(Pt 7):jeb195578. doi: 10.1242/jeb.195578.
Control of wing shape is believed to be a key feature that allows most birds to produce aerodynamically efficient flight behaviors and high maneuverability. Anatomical organization of intrinsic wing muscles suggests specific roles for the different motor elements in wing shape modulation, but testing these hypothesized functions requires challenging measurements of muscle activation and strain patterns, and force dynamics. The wing muscles that have been best characterized during flight are the elbow muscles of the pigeon (). studies during different flight modes revealed variation in strain profile, activation timing and duration, and contractile cycle frequency of the humerotriceps, suggesting that this muscle may alter wing shape in diverse ways. To examine the multifunction potential of the humerotriceps, we developed an work loop approach to measure how activation duration and contractile cycle frequency affected muscle work and power across the full range of activation onset times. The humerotriceps produced predominantly net negative power, likely due to relatively long stimulus durations, indicating that it absorbs work, but the work loop shapes also suggest varying degrees of elastic energy storage and release. The humerotriceps consistently exhibited positive and negative instantaneous power within a single contractile cycle, across all treatments. When combined with previous studies, our results indicate that both within and across contractile cycles, the humerotriceps can dynamically shift among roles of actuator, brake, and stiff or compliant spring, based on activation properties that vary with flight mode.
翅膀形状的控制被认为是大多数鸟类能够产生空气动力学效率高的飞行行为和高机动性的关键特征。内在翅膀肌肉的解剖组织表明，不同的运动元素在翅膀形状调节中具有特定的作用，但测试这些假设功能需要对肌肉激活和应变模式以及力动力学进行具有挑战性的测量。在飞行过程中，研究得最好的翅膀肌肉是鸽子的肘部肌肉（）。在不同的飞行模式下的研究表明，肱三头肌的应变曲线、激活时间和持续时间以及收缩周期频率存在差异，这表明该肌肉可能以多种方式改变翅膀形状。为了研究肱三头肌的多功能潜力，我们开发了一种工作循环方法来测量激活持续时间和收缩周期频率如何在整个激活起始时间范围内影响肌肉的工作和功率。肱三头肌主要产生净负功率，可能是由于刺激持续时间相对较长，表明它吸收了工作，但工作循环的形状也表明了不同程度的弹性储能和释放。在所有处理中，肱三头肌在单个收缩周期内始终表现出正功率和负功率。当与以前的研究相结合时，我们的结果表明，无论是在收缩周期内还是跨收缩周期，肱三头肌都可以根据激活特性（这些特性随飞行模式而变化）在执行器、制动器和刚性或顺应性弹簧之间动态切换。
