Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
Philos Trans R Soc Lond B Biol Sci. 2011 May 27;366(1570):1530-9. doi: 10.1098/rstb.2010.0345.
Muscles actuate movement by generating forces. The forces generated by muscles are highly dependent on their fibre lengths, yet it is difficult to measure the lengths over which muscle fibres operate during movement. We combined experimental measurements of joint angles and muscle activation patterns during walking with a musculoskeletal model that captures the relationships between muscle fibre lengths, joint angles and muscle activations for muscles of the lower limb. We used this musculoskeletal model to produce a simulation of muscle-tendon dynamics during walking and calculated fibre operating lengths (i.e. the length of muscle fibres relative to their optimal fibre length) for 17 lower limb muscles. Our results indicate that when musculotendon compliance is low, the muscle fibre operating length is determined predominantly by the joint angles and muscle moment arms. If musculotendon compliance is high, muscle fibre operating length is more dependent on activation level and force-length-velocity effects. We found that muscles operate on multiple limbs of the force-length curve (i.e. ascending, plateau and descending limbs) during the gait cycle, but are active within a smaller portion of their total operating range.
肌肉通过产生力来驱动运动。肌肉产生的力高度依赖于它们的纤维长度，但很难测量肌肉纤维在运动过程中的作用长度。我们结合了行走过程中关节角度和肌肉激活模式的实验测量值，以及一个能够捕捉下肢肌肉纤维长度、关节角度和肌肉激活之间关系的肌肉骨骼模型。我们使用这个肌肉骨骼模型来模拟行走过程中的肌肉-肌腱动力学，并计算了 17 条下肢肌肉的纤维工作长度（即肌肉纤维相对于其最佳纤维长度的长度）。我们的结果表明，当肌肉-肌腱顺应性较低时，纤维工作长度主要由关节角度和肌肉力臂决定。如果肌肉-肌腱顺应性较高，纤维工作长度则更多地取决于激活水平和力-长度-速度效应。我们发现，在步态周期中，肌肉在力-长度曲线的多个支上（即上升支、平台支和下降支）起作用，但在其总工作范围内的活动范围较小。
