Effects of Muscle Activity and Muscle Strength According to Verbal Command Volume in Isokinetic and Isometric Exercise of Quadriceps

Purpose: The purpose of this study was to investigate the effects of muscle activity and muscle strength according to verbal command volume during isokinetic and isometric quadricep exercises. Methods: To measure muscle activity and muscle strength, surface electrodes were attached to the participants, as they sat on a Biodex chair. The isometric exercise was performed three times, with maximum exercise at 30° bending angle, based on a maximum extension state of the knee at 0°. The average holding time was unified to three seconds. In addition, the isokinetic exercise was performed three times, at 60°/sec. The verbal command ranged between 0∽60 dB and 0∽75 dB. Muscle activity was measured using surface electromyography (4D-MT, Relive, Gimhae, Korea). The Biodex System 4 was used to measure the isometric and isokinetic strength of the nodal line, and 4D-MT was used to measure muscle activity. Results: There were significant improvements in the maximal and relative muscle strengths, when the 0∽ 60 dB and 0∽75 dB verbal commands were applied with isokinetic extension/flexion (p<.05). The isokinetic exercise (0∽75 dB) group showed a significant difference in the vastus medialis oblique muscle activity change (p<.05), while the isometric exercise (0∽75 dB) group showed a significant difference in the rectus femoris muscle activity change (p<.05). Conclusions: Our results reveal that verbal commands effectively improve muscle activity and muscle strength during isokinetic and isometric quadricep exercises.