Changes in oxygen consumption of human muscle and tendon following repeat muscle contractions

The purpose of this study was to investigate changes in the oxygen consumption (VO₂) of muscle and tendon following repeat muscle contractions. During endurance tests (50 repetitions at 70% of the maximum voluntary contraction with 5-s contractions and 5-s rest) and the recovery period (0–10 min), we measured the blood volume and oxygen saturation (StO₂) of the medial gastrocnemius muscle and Achilles tendon using near infrared spectroscopy and red laser light. Nine male subjects performed the endurance tests three times on separate days (tests-1, 2, and 3). Before and after (test-1: immediately after, test-2: at the 5-min recovery point, test-3: at the 10-min recovery point) the endurance tests, the rate of StO₂ during 8-min period of arterial occlusion was measured to estimate the VO₂ of muscle and tendon. In test-3, after the end of exercise, the THb and StO₂ of the Achilles tendon increased gradually, and these values were higher than the pre-exercise levels until the end of the recovery period. The VO₂ of tendon as well as muscle increased significantly after the repeat muscle contractions. Furthermore, the VO₂ of tendon returned to the pre-exercise level at the 10-min point of recovery, although that of muscle was significantly higher compared to the pre-exercise level until the end of the recovery period. These results indicate that the difference between oxygen supply and consumption within tendon was greater after compared to before exercise.