Camilleri M J, Hull M L, Hakansson Nils
Biomedical Engineering Program, One Shields Avenue, University of California, Davis, CA 95616, USA.
J Biomech. 2007;40(7):1423-32. doi: 10.1016/j.jbiomech.2006.06.009. Epub 2006 Sep 1.
Mathematical models of the muscle excitation are useful in forward dynamic simulations of human movement tasks. One objective was to demonstrate that sloped as opposed to rectangular excitation waveforms improve the accuracy of forward dynamic simulations. A second objective was to demonstrate the differences in simulated muscle forces using sloped versus rectangular waveforms. To fulfill these objectives, surface EMG signals from the triceps brachii and elbow joint angle were recorded and the intersegmental moment of the elbow joint was computed from 14 subjects who performed two cyclic elbow extension experiments at 200 and 300 deg/s. Additionally, the surface EMG signals from the leg musculature, joint angles, and pedal forces were recorded and joint intersegmental moments were computed during a more complex pedaling task (90 rpm at 250 W). Using forward dynamic simulations, four optimizations were performed in which the experimental intersegmental moment was tracked for the elbow extension tasks and four optimizations were performed in which the experimental pedal angle, pedal forces, and joint intersegmental moments were tracked for the pedaling task. In these optimizations the three parameters (onset and offset time, and peak excitation) defining the sloped (triangular, quadratic, and Hanning) and rectangular excitation waveforms were varied to minimize the difference between the simulated and experimentally tracked quantities. For the elbow extension task, the intersegmental elbow moment root mean squared error, onset timing error, and offset timing error were less from simulations using a sloped excitation waveform compared to a rectangular excitation waveform (p<0.001). The average and peak muscle forces were from 7% to 16% larger and 20-28% larger, respectively, when using a rectangular excitation waveform. The tracking error for pedaling also decreased when using a sloped excitation waveform, with the quadratic waveform generating the smallest tracking errors for both tasks. These results support the use of sloped over rectangular excitation waveforms to establish greater confidence in the results of forward dynamic simulations.
肌肉兴奋的数学模型在人体运动任务的正向动力学模拟中很有用。一个目标是证明与矩形激励波形相比，倾斜的激励波形可提高正向动力学模拟的准确性。第二个目标是展示使用倾斜波形与矩形波形时模拟肌肉力的差异。为实现这些目标，记录了14名受试者肱三头肌的表面肌电信号和肘关节角度，并计算了肘关节的节段间力矩，这些受试者以200和300度/秒的速度进行了两次周期性肘关节伸展实验。此外，在一项更复杂的蹬踏任务（250瓦，90转/分钟）中记录了腿部肌肉组织的表面肌电信号、关节角度和踏板力，并计算了关节节段间力矩。使用正向动力学模拟，进行了四项优化，其中针对肘关节伸展任务跟踪实验节段间力矩，还进行了四项优化，其中针对蹬踏任务跟踪实验踏板角度、踏板力和关节节段间力矩。在这些优化中，改变定义倾斜（三角形、二次型和汉宁窗）和矩形激励波形的三个参数（起始和结束时间，以及峰值激励），以最小化模拟量与实验跟踪量之间的差异。对于肘关节伸展任务，与矩形激励波形相比，使用倾斜激励波形进行模拟时，节段间肘关节力矩均方根误差、起始时间误差和结束时间误差更小（p<0.001）。使用矩形激励波形时，平均肌肉力和峰值肌肉力分别大7%至16%和20 - 28%。使用倾斜激励波形时，蹬踏的跟踪误差也有所降低，二次型波形在两项任务中产生的跟踪误差最小。这些结果支持使用倾斜激励波形而非矩形激励波形，以增强对正向动力学模拟结果的信心。
