Cathers I, O'Dwyer N, Neilson P
Department of Biomedical Sciences, Faculty of Health Sciences, University of Sydney, Australia.
Exp Brain Res. 1999 Nov;129(2):278-87. doi: 10.1007/s002210050898.
The tonic stretch reflex was investigated using small-amplitude displacements (<4.2 degrees ) of the wrist while subjects maintained average contraction levels of 25% of maximum in flexor carpi radialis. The wrist displacements were designed to preclude voluntary following but at the same time were confined to the frequency range most relevant to voluntary movements. They included a broad-frequency band (0-12 Hz) signal as well as sets of narrow-band signals spanning the range from 0 to 10 Hz. The maximum frequency was set so as to remain within the linear encoding bandwidth of the reflex system and thereby minimize distortion. The effects of frequency bandwidth and amplitude of the displacement perturbations were tested in separate experiments. The coherence square, gain and phase between the EMG and angular displacement were calculated in order to characterize the stretch reflex under these conditions. It was found that the phase of the reflex response was dependent on both bandwidth and amplitude. For narrow-band displacements, the phase advance was about 30 degrees greater over the frequency range tested than for broad-band displacements, suggesting that the reflex response may be influenced by the predictability of the perturbation. At the smallest amplitude of 0.3 degrees, the peak phase advance was about 20 degrees greater than at the largest amplitude of 4.2 degrees. The gain was also higher and rose more steeply with frequency at smaller amplitudes. In the frequency range up to 12 Hz, the tonic stretch reflex responds most effectively to smaller-amplitude, more regular, higher-frequency inputs and this is consistent with a role for the reflex in counteracting small-amplitude oscillations, tremors and errors of voluntary movement.
在受试者保持桡侧腕屈肌平均收缩水平为最大收缩力的25%时，通过对腕关节进行小幅度位移（<4.2度）来研究紧张性牵张反射。腕关节的位移设计为排除自愿跟随动作，但同时又限制在与自愿运动最相关的频率范围内。它们包括一个宽频带（0 - 12 Hz）信号以及一系列从0到10 Hz的窄带信号。设置最大频率是为了使其保持在反射系统的线性编码带宽内，从而将失真降至最低。在单独的实验中测试了位移扰动的频率带宽和幅度的影响。计算肌电图（EMG）与角位移之间的相干平方、增益和相位，以便在这些条件下表征牵张反射。结果发现，反射反应的相位取决于带宽和幅度。对于窄带位移，在测试的频率范围内，相位超前比宽带位移大约30度，这表明反射反应可能受扰动可预测性的影响。在最小幅度0.3度时，峰值相位超前比最大幅度4.2度时大约大20度。在较小幅度时，增益也更高，并且随频率上升得更陡峭。在高达12 Hz的频率范围内，紧张性牵张反射对较小幅度、更规则、更高频率的输入反应最有效，这与反射在抵消小幅度振荡、震颤和自愿运动误差方面的作用是一致的。
