Smith J L, Chung S H, Zernicke R F
Department of Physiological Science, University of California, Los Angeles 90024-1568.
Exp Brain Res. 1993;94(2):308-22. doi: 10.1007/BF00230301.
To assess speed- and gait-related changes in semitendinosus (ST) activity, EMG was recorded from three cats during treadmill locomotion. Selected step cycles were filmed, and hip and knee joint kinematics were synchronized with EMG records. Swing-phase kinetics for trot and gallop steps at 2.25 m/s were compared for gait-related differences. Also, swing kinetics for different gallop forms were compared. With few exceptions, ST-EMG was characterized by two bursts for each step cycle; the first preceded paw off (STpo), and the second preceded paw contact (STpc). The two-burst pattern for the walk was defined by a high-amplitude STpo burst and a brief, low-amplitude STpc burst; at the slowest walk speeds, the STpc burst was occasionally absent. For the trot, the STpo burst was biphasic, with a brief pause just after paw off. With increasing walk-trot speeds, the duration of both bursts (STpo, STpc) remained relatively constant, but recruitment increased. Also, the onset latency of the STpo burst shifted, and a greater proportion of the burst was coincident with knee flexion during early swing. At the trot-gallop transition, there was an abrupt change in the two-burst pattern, and galloping was characterized by a high-amplitude STpc burst and a brief, low-amplitude STpo burst. At the fastest gallop speeds, the STpo burst was often absent, and the reduction in or elimination of the burst was associated with a unique pattern of swing phase kinetics at the knee. Knee flexion during the gallop swing was sustained by two inertial torques related to hip linear acceleration (HLA) and leg angular acceleration (LAA); correspondingly, muscle contraction was unnecessary. Conversely, knee flexion at the onset of the trot swing relied on a flexor muscle torque at the knee acting with an inertial flexor torque (LAA). Rotatory and transverse gallops at 4.0 m/s had similar swing phase kinetics and ST-EMG. Gait-related changes in ST-EMG, particularly at the trot-gallop transition, are not congruent with neural models assuming that details of the ST motor pattern are produced by a spinal CPG. We suggest that motor patterns programmed by the spinal CPG are modulated by input from supraspinal centers and/or motion-related feedback from the hindlimbs to provide appropriate gait-specific activation of the ST.
为评估半腱肌（ST）活动中与速度和步态相关的变化，在三只猫进行跑步机运动期间记录了肌电图（EMG）。拍摄选定的步周期，并将髋关节和膝关节运动学与EMG记录同步。比较了2.25米/秒时小跑和疾驰步的摆动期动力学，以分析与步态相关的差异。此外，还比较了不同疾驰形式的摆动动力学。除少数例外情况外，每个步周期的ST-EMG特征为两个爆发；第一个爆发先于爪子离地（STpo），第二个爆发先于爪子接触（STpc）。行走的双爆发模式由高振幅的STpo爆发和短暂、低振幅的STpc爆发定义；在最慢的行走速度下，STpc爆发偶尔会缺失。对于小跑，STpo爆发是双相的，在爪子离地后有短暂停顿。随着行走-小跑速度增加，两个爆发（STpo、STpc）的持续时间保持相对恒定，但募集增加。此外，STpo爆发的起始潜伏期发生变化，且在摆动早期，爆发的更大比例与膝关节屈曲同时出现。在小跑-疾驰过渡时，双爆发模式发生突然变化，疾驰的特征是高振幅的STpc爆发和短暂、低振幅的STpo爆发。在最快的疾驰速度下，STpo爆发常常缺失，爆发的减少或消除与膝关节摆动期动力学的独特模式相关。疾驰摆动期间的膝关节屈曲由与髋关节线性加速度（HLA）和腿部角加速度（LAA）相关的两个惯性扭矩维持；相应地，肌肉收缩是不必要的。相反，小跑摆动开始时的膝关节屈曲依赖于膝关节处的屈肌肌肉扭矩与惯性屈肌扭矩（LAA）共同作用。4.0米/秒时的旋转疾驰和横向疾驰具有相似的摆动期动力学和ST-EMG。ST-EMG中与步态相关的变化，尤其是在小跑-疾驰过渡时，与假设ST运动模式细节由脊髓中枢模式发生器（CPG）产生的神经模型不一致。我们认为，由脊髓CPG编程控制的运动模式受到来自脊髓上中枢的输入和/或后肢与运动相关的反馈调节，以提供适合特定步态的ST激活。
