Valero-Cuevas F J, Cohn B A, Yngvason H F, Lawrence E L
Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA; Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA.
Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA.
J Biomech. 2015 Aug 20;48(11):2887-96. doi: 10.1016/j.jbiomech.2015.04.026. Epub 2015 Apr 22.
Subject-specific and generic musculoskeletal models are the computational instantiation of hypotheses, and stochastic techniques help explore their validity. We present two such examples to explore the hypothesis of muscle redundancy. The first addresses the effect of anatomical variability on static force capabilities for three individual cat hindlimbs, each with seven kinematic degrees of freedom (DoFs) and 31 muscles. We present novel methods to characterize the structure of the 31-dimensional set of feasible muscle activations for static force production in every 3-D direction. We find that task requirements strongly define the set of feasible muscle activations and limb forces, with few differences comparing individual vs. species-average results. Moreover, muscle activity is not smoothly distributed across 3-D directions. The second example explores parameter uncertainty during a flying disc throwing motion by using a generic human arm with five DoFs and 17 muscles to predict muscle fiber velocities. We show that the measured joint kinematics fully constrain the eccentric and concentric fiber velocities of all muscles via their moment arms. Thus muscle activation for limb movements is likely not redundant: there is little, if any, latitude in synchronizing alpha-gamma motoneuron excitation-inhibition for muscles to adhere to the time-critical fiber velocities dictated by joint kinematics. Importantly, several muscles inevitably exhibit fiber velocities higher than thought tenable, even for conservative throwing speeds. These techniques and results, respectively, enable and compel us to continue to revise the classical notion of muscle redundancy for increasingly more realistic models and tasks.
特定个体和通用的肌肉骨骼模型是假设的计算实例，随机技术有助于探索它们的有效性。我们给出两个这样的例子来探索肌肉冗余的假设。第一个例子研究了解剖学变异性对三只猫后肢静态力量能力的影响，每只后肢有七个运动自由度（DoF）和31块肌肉。我们提出了新颖的方法来表征在每个三维方向上产生静态力量时可行肌肉激活的31维集合的结构。我们发现任务要求强烈地定义了可行肌肉激活和肢体力量的集合，将个体结果与物种平均结果相比较时差异很小。此外，肌肉活动在三维方向上的分布并不均匀。第二个例子通过使用具有五个自由度和17块肌肉的通用人类手臂来预测肌肉纤维速度，探索飞盘投掷动作过程中的参数不确定性。我们表明，测量到的关节运动学通过其力臂完全约束了所有肌肉的离心和向心纤维速度。因此，肢体运动的肌肉激活可能并非冗余：在同步α-γ运动神经元的兴奋-抑制以使肌肉遵循由关节运动学决定的对时间要求严格的纤维速度方面，几乎没有（如果有的话）回旋余地。重要的是，即使对于保守的投掷速度，几块肌肉不可避免地会表现出高于认为合理速度的纤维速度。这些技术和结果分别促使并迫使我们继续针对越来越现实的模型和任务修订肌肉冗余的经典概念。
