Musculoskeletal modelling of an ostrich (Struthio camelus) pelvic limb: influence of limb orientation on muscular capacity during locomotion.
Musculoskeletal modelling of an ostrich (Struthio camelus) pelvic limb: influence of limb orientation on muscular capacity during locomotion.
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作者：
Hutchinson JR;Rankin JW;Rubenson J;Rosenbluth KH;Siston RA;Delp SL
我们开发了一个三维的，生物力学的计算机模型的36个主要的骨盆肢肌肉群的鸵鸟（鸵鸟骆驼），调查肌肉功能，在这个最大的现存鸟类和模式生物的运动力学，身体大小，解剖学和进化的许多研究。结合实验数据，我们使用该模型来检验两个主要假设。我们首先询问鸵鸟是否使用肢体方向（关节角度），优化他们的肌肉在步行或跑步时的力矩产生能力。接下来，我们测试鸵鸟是否使用肢体的方向，在中期的立场，保持他们的伸肌肌肉接近最大，屈肌肌肉接近最小，时刻武器。我们的两个假设涉及到控制的优先级，一个大的双足动物可能会演变下的生物力学约束，以实现更有效的静态重量支持。我们发现，鸵鸟不使用肢体的方向来优化他们的肌肉的力矩产生能力或力矩臂。我们推断，肌肉或肌腱的动态特性可能是运动优化的更好的候选人。无论如何，解释为什么物种在运动过程中选择特定关节方向的一般原则是缺乏的，这就提出了这样的一般原则是否存在或者分支是否进化出不同的模式（例如，在选择姿势时对肌肉力量-长度或力量-速度特性进行加权）。这使得对灭绝动物估计的肌肉力矩臂的理论研究陷入僵局，直到对现存分类群的研究回答这些问题。最后，我们比较我们的模型的结果对鸵鸟四肢肌肉力矩武器的两个先前的研究，发现许多肌肉的一般协议。一些屈肌和伸肌表现出自我稳定的模式（屈肌/伸肌动作之间的姿势依赖性开关），鸵鸟可以用来协调他们的运动。然而，在我们的研究结果中，一些明显的不一致之处说明了一些值得警惕的原则。重要的是，肌腱旅行的肌肉力矩臂的经验测量必须仔细设计，以保持3D肌肉几何形状，以免他们的准确性相对于解剖学上的现实模型。鸟类肌肉的3D力矩臂的精确实验测量的缺乏留下了关于不同建模或实验数据集（例如鸵鸟）的相对准确性的不确定性。然而，我们的模型首次提供了鸵鸟肌肉动作的一组全面的3D估计，强调鸟类肢体力学是高度三维和复杂的，以及没有肌肉纯粹在矢状面中起作用。像我们这样的实验和模型的比较合成可以提供强大的合成解剖学，力学和控制如何在运动过程中相互作用，以及这些相互作用如何演变。这样一个框架可以消除阻碍分析灭绝类群肌肉功能的障碍。
We developed a three-dimensional, biomechanical computer model of the 36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to investigate muscle function in this, the largest of extant birds and model organism for many studies of locomotor mechanics, body size, anatomy and evolution. Combined with experimental data, we use this model to test two main hypotheses. We first query whether ostriches use limb orientations (joint angles) that optimize the moment-generating capacities of their muscles during walking or running. Next, we test whether ostriches use limb orientations at mid-stance that keep their extensor muscles near maximal, and flexor muscles near minimal, moment arms. Our two hypotheses relate to the control priorities that a large bipedal animal might evolve under biomechanical constraints to achieve more effective static weight support. We find that ostriches do not use limb orientations to optimize the moment-generating capacities or moment arms of their muscles. We infer that dynamic properties of muscles or tendons might be better candidates for locomotor optimization. Regardless, general principles explaining why species choose particular joint orientations during locomotion are lacking, raising the question of whether such general principles exist or if clades evolve different patterns (e.g., weighting of muscle force–length or force–velocity properties in selecting postures). This leaves theoretical studies of muscle moment arms estimated for extinct animals at an impasse until studies of extant taxa answer these questions. Finally, we compare our model’s results against those of two prior studies of ostrich limb muscle moment arms, finding general agreement for many muscles. Some flexor and extensor muscles exhibit self-stabilization patterns (posture-dependent switches between flexor/extensor action) that ostriches may use to coordinate their locomotion. However, some conspicuous areas of disagreement in our results illustrate some cautionary principles. Importantly, tendon-travel empirical measurements of muscle moment arms must be carefully designed to preserve 3D muscle geometry lest their accuracy suffer relative to that of anatomically realistic models. The dearth of accurate experimental measurements of 3D moment arms of muscles in birds leaves uncertainty regarding the relative accuracy of different modelling or experimental datasets such as in ostriches. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in ostriches for the first time, emphasizing that avian limb mechanics are highly three-dimensional and complex, and how no muscles act purely in the sagittal plane. A comparative synthesis of experiments and models such as ours could provide powerful synthesis into how anatomy, mechanics and control interact during locomotion and how these interactions evolve. Such a framework could remove obstacles impeding the analysis of muscle function in extinct taxa.
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