Camilleri M J, Hull M L
Biomedical Engineering Program, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
J Biomech. 2005 Nov;38(11):2172-80. doi: 10.1016/j.jbiomech.2004.09.037. Epub 2004 Dec 16.
Mathematical models of the inter-relationship of muscle force, velocity, and activation are useful in forward dynamic simulations of human movement tasks. The objective of this work was to determine whether the parameters (maximum shortening velocity V(max) and shape parameter k) of a Hill-type muscle model, interrelating muscle force, velocity, and activation, are themselves dependent on the activation. To fulfill this objective, surface EMG signals from four muscles, as well as the kinematics and kinetics of the arm, were recorded from 14 subjects who performed rapid-release elbow extension tasks at 25%, 50%, 75%, and 100% activation (MVC). The experimental elbow flexion angle was tracked by a forward dynamic simulation of the task in which V(max) and k of the triceps brachii were varied at each activation level to minimize the difference between the simulated and experimental elbow flexion angle. Because a preliminary analysis demonstrated no dependency of k on activation, additional simulations were performed with constant k values of 0.15, 0.20, and 0.25. The optimized values of V(max) normalized to the average value within a subject were then regressed onto the activation. Normalized V(max) depended significantly on the activation (p<0.001) for all values of k. Furthermore, the estimated V(max) values were not sensitive to the selected k value. The results support the use of Hill-type models in which V(max) depends on activation in forward dynamic simulations modeling muscles with mixed fiber-type composition recruited in the range of 25-100% activation. The use of more accurate models will lend greater confidence to the results of forward dynamic simulations.
肌肉力量、速度和激活之间相互关系的数学模型在人体运动任务的正向动力学模拟中很有用。这项工作的目的是确定一个将肌肉力量、速度和激活相互关联的希尔型肌肉模型的参数（最大缩短速度V(max)和形状参数k）本身是否依赖于激活。为了实现这一目标，从14名受试者身上记录了四块肌肉的表面肌电信号以及手臂的运动学和动力学数据，这些受试者在25%、50%、75%和100%激活（MVC）水平下进行快速释放的肘部伸展任务。通过对任务的正向动力学模拟来跟踪实验性肘部屈曲角度，在每个激活水平下改变肱三头肌的V(max)和k，以最小化模拟和实验肘部屈曲角度之间的差异。因为初步分析表明k不依赖于激活，所以使用0.15、0.20和0.25的恒定k值进行了额外的模拟。然后将归一化到受试者内平均值的V(max)的优化值与激活进行回归分析。对于所有k值，归一化的V(max)都显著依赖于激活（p<0.001）。此外，估计的V(max)值对所选的k值不敏感。结果支持在正向动力学模拟中使用V(max)依赖于激活的希尔型模型，该模型用于模拟在25%-100%激活范围内募集的具有混合纤维类型组成的肌肉。使用更精确的模型将为正向动力学模拟的结果带来更大的信心。
