Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, Royal Veterinary College, Hatfield, United Kingdom.
Geosciences Program, Queensland Museum, Brisbane, Australia.
PLoS Comput Biol. 2021 Apr 1;17(4):e1008843. doi: 10.1371/journal.pcbi.1008843. eCollection 2021 Apr.
The arrangement and physiology of muscle fibres can strongly influence musculoskeletal function and whole-organismal performance. However, experimental investigation of muscle function during in vivo activity is typically limited to relatively few muscles in a given system. Computational models and simulations of the musculoskeletal system can partly overcome these limitations, by exploring the dynamics of muscles, tendons and other tissues in a robust and quantitative fashion. Here, a high-fidelity, 26-degree-of-freedom musculoskeletal model was developed of the hindlimb of a small ground bird, the elegant-crested tinamou (Eudromia elegans, ~550 g), including all the major muscles of the limb (36 actuators per leg). The model was integrated with biplanar fluoroscopy (XROMM) and forceplate data for walking and running, where dynamic optimization was used to estimate muscle excitations and fibre length changes throughout both gaits. Following this, a series of static simulations over the total range of physiological limb postures were performed, to circumscribe the bounds of possible variation in fibre length. During gait, fibre lengths for all muscles remained between 0.5 to 1.21 times optimal fibre length, but operated mostly on the ascending limb and plateau of the active force-length curve, a result that parallels previous experimental findings for birds, humans and other species. However, the ranges of fibre length varied considerably among individual muscles, especially when considered across the total possible range of joint excursion. Net length change of muscle-tendon units was mostly less than optimal fibre length, sometimes markedly so, suggesting that approaches that use muscle-tendon length change to estimate optimal fibre length in extinct species are likely underestimating this important parameter for many muscles. The results of this study clarify and broaden understanding of muscle function in extant animals, and can help refine approaches used to study extinct species.
肌肉纤维的排列和生理学可以强烈影响肌肉骨骼功能和整个生物体的性能。然而，在体内活动期间对肌肉功能的实验研究通常仅限于给定系统中的少数几种肌肉。通过以稳健和定量的方式探索肌肉、肌腱和其他组织的动力学，肌肉骨骼系统的计算模型和模拟可以部分克服这些限制。在这里，开发了一种具有 26 个自由度的小型地面鸟类后肢的高保真肌肉骨骼模型，即优雅凤头鸠（Eudromia elegans，~550 克），包括肢体的所有主要肌肉（每条腿 36 个执行器）。该模型与双平面荧光透视（XROMM）和力板数据集成，用于行走和跑步，其中动态优化用于估计整个步态中的肌肉激发和纤维长度变化。在此之后，进行了一系列跨越生理肢体姿势总范围的静态模拟，以确定纤维长度可能变化的范围。在步态中，所有肌肉的纤维长度都保持在 0.5 到 1.21 倍的最佳纤维长度之间，但主要在主动力-长度曲线的上升支和平台上运作，这一结果与之前对鸟类、人类和其他物种的实验发现相似。然而，纤维长度的范围在个体肌肉之间差异很大，尤其是在考虑整个关节运动的总可能范围时。肌肉肌腱单位的净长度变化大多小于最佳纤维长度，有时变化很大，这表明使用肌肉肌腱长度变化来估计已灭绝物种中的最佳纤维长度的方法可能会低估许多肌肉的这个重要参数。本研究的结果阐明并拓宽了对现存动物肌肉功能的理解，并有助于改进研究已灭绝物种的方法。
