Compensatory Oxygenation Changes in Non-active and Active Muscles During Incremental Exercise in Healthy Adults

We aimed to clarify the compensatory changes in oxygenation in non-active versus active muscles during incremental exercise.

Fifteen male volunteers (age, 21.1 ± 0.5 years) underwent cardiopulmonary exercise testing (CPET) using a cycle ergometer ramp protocol, while maintaining the left upper extremity in a drooping position. We continuously recorded oxygenated hemoglobin (O₂Hb), deoxygenated hemoglobin (HHb), total hemoglobin (THb), and tissue oxygen saturation (StO₂) in the left vastus lateralis (active muscle) and triceps brachii (non-active muscle), as well as cardiopulmonary parameters, during the test.

There were significant interactions between time and muscles for all changes in O₂Hb (p < 0.001), HHb (p < 0.001), THb (p < 0.001), and StO₂ (p < 0.001). In the non-active muscle, O₂Hb and StO₂ remained higher than at rest until the 40% point of the test, unlike in the active muscle. HHb increased from the 80% point in the non-active muscle, but it increased immediately after the start of the test in the active muscle. THb showed no significant change in the non-active muscle, but it continued to increase immediately after the start of the test in the active muscle.

During CPET, O₂Hb and StO₂ in the non-active muscle remained higher in the low- to moderate-intensity phases than in the rest phase and decreased in the high-intensity phase, unlike in the active muscle.