Cresswell A G, Löscher W N, Thorstensson A
Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Exp Brain Res. 1995;105(2):283-90. doi: 10.1007/BF00240964.
The present study was designed to determine the relative contribution of the gastrocnemius muscle to isometric plantar flexor torque production at varying knee angles, while investigating the activation of the gastrocnemius muscle at standardised non-optimal lengths. Voluntary plantar flexor torque, supramaximally stimulated twitch torque and myoelectric activity (EMG) from the triceps surae were measured at different knee angles. Surface and intra-muscular EMG were recorded from the soleus muscle and the medial and lateral heads of the gastrocnemius muscle in 10 male subjects. With the ankle angle held constant, knee angle was changed in steps of 30 degrees ranging from 180 degrees (extended) to 60 degrees (extreme flexion), while voluntary torque from a 5-s contraction was determined at 10 different levels of voluntary effort, ranging from 10% of maximal effort to maximal effort. To assess effort, supramaximal twitches were superimposed on all voluntary contractions, and additionally during rest. Maximal plantar flexor torque and resting twitch torque decreased significantly in a sigmoidal fashion with increasing knee flexion to 60% of the maximum torque at 180 degrees knee angle. For similar levels of voluntary effort, the EMG root mean square (RMS) of gastrocnemius was less with increased knee flexion, whereas soleus RMS remained unchanged. From these data, it is concluded that the contribution of gastrocnemius to plantar flexor torque is at least 40% of the total torque in the straight leg position. The decrease of gastrocnemius EMG RMS with decreasing muscle length may be brought about by a decrease in the number of fibres within the EMG electrode recording volume and/or impaired neuromuscular transmission.
本研究旨在确定在不同膝关节角度下，腓肠肌对等长跖屈扭矩产生的相对贡献，同时研究在标准化非最佳长度下腓肠肌的激活情况。在不同膝关节角度测量了比目鱼肌的自主跖屈扭矩、超强刺激引发的抽搐扭矩和肌电活动（EMG）。对10名男性受试者的比目鱼肌以及腓肠肌内侧头和外侧头记录了表面肌电和肌内肌电。在踝关节角度保持恒定的情况下，膝关节角度以30度步长从180度（伸展）变化到60度（极度屈曲），同时在10种不同的自主用力水平下测定5秒收缩产生的自主扭矩，自主用力水平范围从最大用力的10%到最大用力。为了评估用力程度，在所有自主收缩期间以及休息时叠加超强抽搐。随着膝关节屈曲增加，最大跖屈扭矩和静息抽搐扭矩以S形显著下降，在膝关节角度为180度时降至最大扭矩的60%。对于相似的自主用力水平，随着膝关节屈曲增加，腓肠肌的肌电均方根（RMS）减小，而比目鱼肌的RMS保持不变。从这些数据得出结论，在直腿位置，腓肠肌对跖屈扭矩的贡献至少占总扭矩的40%。腓肠肌肌电RMS随肌肉长度减小而降低，可能是由于肌电电极记录容积内纤维数量减少和/或神经肌肉传递受损所致。
