Knee Extensor Activity Patterns at Various Movement Velocities and Muscle Tension Levels

[Purpose] To compare knee extensor activity patterns at various velocities and muscle tension levels. [Participants and Methods] We instructed 12 healthy adult males to perform maximal voluntary knee extension using an isokinetic exercise machine as a motor task, and measured their knee extensor activity using a surface electromyography device. The motor task was performed at 3 different velocities: 30, 60, and 120 °/s. [Results] Significant decreases in rectus femoris muscle activity were observed when performing the motor task at 120 °/s compared with 30 and 60 °/s, and at 60°/s compared with 30 °/s. In contrast, there was a significant increase in vastus intermedius muscle activity at 120 °/s compared with 30 and 60 °/s. There were no significant differences in vastus lateralis or medialis muscle activity. [Conclusion] The results suggest tendencies of the rectus femoris and vastus intermedius to depend on the muscle tension level and movement velocity, respectively.