Hutchinson John R
Biomechanical Engineering Division, Stanford University, Stanford, California 94305-4038, USA.
J Morphol. 2004 Oct;262(1):421-40. doi: 10.1002/jmor.10241.
I used a simple mathematical model of the inverse dynamics of locomotion to estimate the minimum muscle masses required to maintain quasi-static equilibrium about the four main limb joints at mid-stance of fast running. Models of 10 extant taxa (a human, a kangaroo, two lizards, an alligator, and five birds) were analyzed in various bipedal poses to examine how anatomy, size, limb orientation, and other model parameters influence running ability. I examined how the muscle masses required for fast running compare to the muscle masses that are actually able to exert moments about the hip, knee, ankle, and toe joints, to see how support ability varies across the limb. I discuss the assumptions and limitations of the models, using sensitivity analysis to see how widely the results differed with feasible parameter input values. Even with a wide range of input values, the models validated the analysis procedure. Animals that are known to run bipedally were calculated as able to preserve quasi-static equilibrium about their hindlimb joints at mid-stance, whereas non-bipedal runners (iguanas and alligators) were recognized as having too little muscle mass to run quickly in bipedal poses. Thus, this modeling approach should be reliable for reconstructing running ability in extinct bipeds such as nonavian dinosaurs. The models also elucidated how key features are important for bipedal running capacity, such as limb orientation, muscle moment arms, muscle fascicle lengths, and body size. None of the animals modeled had extensor muscle masses acting about any one joint that were 7% or more of their body mass, which provides a reasonable limit for how much muscle mass is normally apportioned within a limb to act about a particular joint. The models consistently showed that a key biomechanical limit on running ability is the capacity of ankle extensors to generate sufficiently large joint moments. Additionally, the analysis reveals how large ratite birds remain excellent runners despite their larger size; they have apomorphically large extensor muscles with relatively high effective mechanical advantage. Finally, I reconstructed the evolution of running ability in the clade Reptilia, showing that the ancestors of extant birds likely were quite capable runners, even though they had already reduced key hip extensors such as M. caudofemoralis longus.
我使用了一个简单的运动逆动力学数学模型，来估算在快速奔跑的中间 stance 阶段，维持四肢四个主要关节准静态平衡所需的最小肌肉质量。分析了 10 个现存分类单元（一个人类、一只袋鼠、两只蜥蜴、一只短吻鳄和五只鸟类）在各种双足姿势下的模型，以研究解剖结构、体型、肢体方向和其他模型参数如何影响奔跑能力。我研究了快速奔跑所需的肌肉质量与实际能够在髋、膝、踝和趾关节产生力矩的肌肉质量相比如何，以了解支撑能力在整个肢体上的变化情况。我讨论了模型的假设和局限性，使用敏感性分析来查看结果在可行的参数输入值范围内差异有多大。即使有广泛的输入值范围，模型也验证了分析过程。已知双足奔跑的动物被计算为能够在中间 stance 阶段保持其后肢关节的准静态平衡，而非双足奔跑者（鬣蜥和短吻鳄）被认为肌肉质量太少，无法以双足姿势快速奔跑。因此，这种建模方法对于重建已灭绝的双足动物（如非鸟恐龙）的奔跑能力应该是可靠的。模型还阐明了关键特征对于双足奔跑能力的重要性，例如肢体方向、肌肉力臂、肌肉束长度和体型。所建模的动物中没有一个在任何一个关节上的伸肌质量占其体重的 7%或更多，这为肢体中通常分配用于围绕特定关节起作用的肌肉质量提供了一个合理的限制。模型一致表明，奔跑能力的一个关键生物力学限制是踝伸肌产生足够大的关节力矩的能力。此外，分析揭示了大型平胸鸟类尽管体型较大，但仍然是优秀的奔跑者；它们具有形态上较大的伸肌，具有相对较高的有效机械优势。最后，我重建了爬行纲动物奔跑能力的进化，表明现存鸟类的祖先可能是相当有能力的奔跑者，尽管它们已经减少了关键的髋伸肌，如长股尾肌。
