Department of Medical Informatics and Image Analysis, Aalborg University, Fredrik Bajersvej 7D, DK-9220 Aalborg, Denmark.
J Electromyogr Kinesiol. 1993;3(2):67-77. doi: 10.1016/1050-6411(93)90001-D.
The electrically elicited muscle twitch has been used to identify mechanical muscle properties in relaxed muscles. We attempted to characterize the mechanical muscle properties in an active muscle. Each subject was seated and his/her left foot was strapped to a platform. The ankle torque and electromyogram (EMG) of the ankle extensors and flexors were measured while the subject was asked to match the ankle torque to a pseudo randomized rectangular tracking signal. A system identification technique was used to determine the impulse response from EMG to torque at various contraction levels. The amplitude of the impulse response decreased markedly with the contraction level when the amplitude of the tracking signal was constant, whereas the amplitude of the impulse response increased with the amplitude of the tracking signal. An explanation for these findings could be seen in the results from the properties of individual motor units. Our results suggest that the rate modulation that occurs during rapid changes in the force in an already isometric contracted muscle is very efficient in generating force in the newly recruited motor units, but inefficient in motor units approaching tetanus.
电诱发的肌肉抽搐已被用于识别放松肌肉的机械肌肉特性。我们试图在活跃的肌肉中描述机械肌肉特性。每位受试者都坐在座位上,将左脚绑在一个平台上。当要求受试者将脚踝扭矩与伪随机矩形跟踪信号匹配时,测量了脚踝伸肌和屈肌的扭矩和肌电图(EMG)。使用系统识别技术确定了在不同收缩水平下从 EMG 到扭矩的脉冲响应。当跟踪信号的幅度恒定时,脉冲响应的幅度随收缩水平显着降低,而脉冲响应的幅度随跟踪信号的幅度增加。在个体运动单位特性的结果中可以看到对这些发现的解释。我们的结果表明,在已经等长收缩的肌肉中力的快速变化期间发生的速率调制对于在新募集的运动单位中产生力非常有效,但是对于接近强直的运动单位效率低下。