Influence of knee positions on torque and myoelectric activity of triceps surae at maximum isometric plantar flexion

The aim of this study was to compare the maximum torque of plantar flexors using two knee positions and analyze the mioelectric activity variation of the muscles in both conditions. The sample was composed of 14 healthy men. The participants were positioned on the dynamometer with the right foot attached to the adapter in neutral position (ankle at 90º). Two five seconds of two consecutives maximum isometric voluntary contractions were obtained for each knee position: full extended and 90o. The gastrocnemius lateralis (GNL), medialis (GNM) and soleus RMS value of eletomyography signal and the plantar flexor peak torque average were acquired during three intermediate seconds. The average torques in the knee positions of extension and flexion were 100.4 ± 17.4 Nm and 72.6 ± 18.4 Nm respectively. With the knee flexed, the gastrocnemius presented a decreased activation (40.5 ± 10.5 e 31.7 ± 25.6% for lateral and medial, respectively) while the soleus showed an increased (35.6 ± 28.9%). The reduction of torque appears to result from a compromise between the inhibition of myoelectric activity of the gastrocnemius medialis and lateralis, while the soleus activation is optimized. The results may contribute to exercise prescription plantar flexors muscles emphasizing the different muscles activation varying the knee position.

本研究旨在对比两种膝关节体位下跖屈肌（plantar flexors）的最大扭矩，并分析两种工况下各肌肉的肌电活动变化。研究样本包含14名健康男性受试者。受试者取肌力测试仪（dynamometer）体位，右脚固定于适配器，踝关节处于中立位（踝关节角度为90°）。每种膝关节体位下均完成两次连续的5秒最大等长自主收缩，体位分别为膝关节完全伸展位与膝关节屈曲90°位。本研究采集了腓肠肌外侧头（gastrocnemius lateralis, GNL）、腓肠肌内侧头（gastrocnemius medialis, GNM）及比目鱼肌的肌电（electromyography, EMG）信号均方根（Root Mean Square, RMS）值，以及跖屈肌的峰值扭矩平均值，数据采集时段为每次收缩的中间3秒。膝关节伸展位与屈曲位的平均扭矩分别为100.4±17.4牛·米与72.6±18.4牛·米。当膝关节处于屈曲位时，腓肠肌的肌电激活程度下降（外侧头与内侧头分别为40.5±10.5%与31.7±25.6%），而比目鱼肌的肌电激活程度则上升（35.6±28.9%）。扭矩的下降似乎源于腓肠肌内侧头与外侧头的肌电活动受到抑制，而比目鱼肌的肌电激活得到优化。本研究结果可为跖屈肌的运动处方制定提供参考，强调可通过调整膝关节体位实现各肌肉的差异化激活。