Ettema G J, Huijing P A
Department of Anatomical Sciences, University of Queensland, Australia.
J Biomech. 1994 Aug;27(8):1015-22. doi: 10.1016/0021-9290(94)90218-6.
The effect of vibration frequency during small amplitude (approximately 0.25% of muscle-tendon complex length) vibrations on muscle stiffness and phase angle of the rat gastrocnemius medialis muscle (n = 7) was investigated at four different force levels. Frequencies varying from 5 to 180 Hz were studied. Furthermore, series elastic stiffness was determined as a function of muscle force. The experiments were also simulated, using a Hill-type muscle model representing the fundamental characteristics of the experimental muscles. The frequency response found in the experiments deviated from the simulation results: stiffness and phase were lowest at about 30 Hz, whereas the simulations showed a rapid asymptotic increase of stiffness and decrease of phase angle with increasing frequency. The values levelled off at about 60 Hz. The discrepancy between experimental and simulation results is thought to be due to changes of the contractile properties of muscle, especially at low movement frequencies, where the contractile machinery has a significant influence on muscle stiffness. At frequencies of 120 Hz and above, the muscle stiffness resembled series elastic stiffness in both experimental muscles and simulations. This suggests that the contractile element contracts approximately isometrically. Functional implications of the frequency response are discussed.
研究了在四种不同力水平下，小幅度振动（约为肌腱复合体长度的0.25%）频率对大鼠腓肠肌内侧肌肉（n = 7）的肌肉刚度和相位角的影响。研究了从5到180赫兹的频率。此外，还确定了串联弹性刚度作为肌肉力量的函数。使用代表实验肌肉基本特征的希尔型肌肉模型对实验进行了模拟。实验中发现的频率响应与模拟结果不同：刚度和相位在约30赫兹时最低，而模拟结果显示随着频率增加，刚度迅速渐近增加，相位角减小。这些值在约60赫兹时趋于平稳。实验和模拟结果之间的差异被认为是由于肌肉收缩特性的变化，特别是在低运动频率下，收缩机制对肌肉刚度有显著影响。在120赫兹及以上的频率下，实验肌肉和模拟中的肌肉刚度都类似于串联弹性刚度。这表明收缩元件近似等长收缩。讨论了频率响应的功能意义。
