Kaya Motoshi, Leonard Tim R, Herzog Walter
Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
J R Soc Interface. 2008 Apr 6;5(21):415-26. doi: 10.1098/rsif.2007.1158.
It has been shown that cat soleus (SOL) forces remain nearly constant despite increases in electromyography (EMG) activity for increasing speeds of locomotion, while medial gastrocnemius (MG) forces and EMG activity increase in parallel. Furthermore, during jumping, average cat SOL forces decrease, while average EMG activity increases dramatically compared with walking conditions. Finally, during rapid paw-shake movements, SOL forces and EMG activities are nearly zero. Based on these results, we hypothesized that the SOL is deactivated, despite ankle extensor requirements, if the contractile conditions limit SOL force potential severely. The purposes of this study were to (i) investigate SOL EMG activity and force as a function of its contractile conditions during jumping, (ii) test whether SOL EMG activity is associated with SOL contractile conditions, and (iii) determine the functional implications of SOL EMG activity during jumping. It was found that the SOL was prematurely deactivated in two distinct phases during the propulsive phase of jumping, in which shortening speeds approached or even exceeded the maximal speed of muscle shortening. We concluded that the SOL was prematurely deactivated to save energy because its mechanical work output approached zero, and speculated that the first phase of deactivation might be caused by a decrease in group Ia firing associated with active shortening and the second by a pre-programmed response inherent to the central pattern generator.
研究表明，尽管随着运动速度增加肌电图（EMG）活动增强，但猫比目鱼肌（SOL）的力量在运动速度增加时几乎保持恒定，而腓肠肌内侧头（MG）的力量和EMG活动则平行增加。此外，在跳跃过程中，猫比目鱼肌的平均力量下降，而与行走状态相比，平均EMG活动显著增加。最后，在快速抖爪运动中，比目鱼肌的力量和EMG活动几乎为零。基于这些结果，我们推测，如果收缩条件严重限制比目鱼肌的力量潜力，尽管有踝关节伸展的需求，比目鱼肌仍会失活。本研究的目的是：（i）研究跳跃过程中比目鱼肌的EMG活动和力量与其收缩条件的关系；（ii）测试比目鱼肌的EMG活动是否与比目鱼肌的收缩条件相关；（iii）确定跳跃过程中比目鱼肌EMG活动的功能意义。研究发现，在跳跃的推进阶段，比目鱼肌在两个不同阶段过早失活，此时缩短速度接近甚至超过肌肉缩短的最大速度。我们得出结论，比目鱼肌过早失活是为了节省能量，因为其机械功输出接近零，并推测失活的第一阶段可能是由于与主动缩短相关的Ia类神经放电减少，第二阶段是由于中枢模式发生器固有的预编程反应。
