Monitoring Treadmill Physical Exercise and Recovery in Elite Water Polo Players with Local Muscle Oxygen Saturation Measurements—Regional and Sex Differences

Background: Despite numerous data on whole-body responses, we have less information about local muscular changes during physical exercise in athletes. Oxygen saturation (SmO2) changes in the working muscles follow phases of load and are useful, as local metabolism could influence physical fitness. Methods: A total of 100 asymptomatic elite water polo players (63% male, age: 17.2 (interquartile range: 16.1–18.9) years) were examined using near-infrared spectroscopy to measure SmO2 in both vastus lateralis and left deltoid muscles during continuous uphill running treadmill exercise. Results: Differences were observed between upper and averaged lower limb resting SmO2 (82.1% (77.0–89.0%) vs. 68.3% (59.2–73.6%), p < 0.001). During exercise, the relative decrease in averaged lower limb SmO2 was greater compared to the upper limb at the anaerobic threshold (−0.371 (−0.539–−0.200) vs. –0.224 (−0.340–−0.099), p < 0.001) and at maximal exercise (−0.557 (−0.750–−0.411) vs. –0.420 (−0.556–−0.271), p < 0.001). Higher averaged lower limb relative SmO2 was recorded compared to the upper limb after 5 min cool-down (+0.081% (−0.046–+0.195%) vs. –0.047% (−0.140–+0.000), p < 0.001). No differences were found between males and females in resting lower limb SmO2. Both sexes showed a monotonic decrease in SmO2 during exercise, with differences in the relative values at the anaerobic threshold and at maximal intensity. Females exhibited a rebound in SmO2 after a 5 min cool-down. Conclusions: We provide insights into SmO2 alterations during maximal-intensity exercise and recovery through the measurements of elite water polo athletes, also highlighting sex differences in SmO2. Measuring local SmO2 changes is a promising additional method in physical fitness follow-up.