Exercise induces an increase in free radicals production in human skeletal muscle. The amount of production depends on the intensity of exercise, with strenuous exercise generating high amount of free radicals and, consequently, oxidative cellular damage. Electronic Paramagnetic Resonance (EPR) is the only non-invasive technique available to detect and quantitate Reactive Oxygen Species (ROS) concentration. Ten masters swimmers (mean age 30±5; males) were trained for 8 weeks with a low-volume/high-intensity program. ROS generation kinetic in capillary blood were evaluated by means of a recently developed EPR micro-invasive determination at rest and after incremental arm-ergometer test until exhaustion, both before (PRE) and after (POST) training period.

Results: At the end of exercise, a significant increase (p<0.05) of ROS production was observed both in PRE and POST. For training effects: 1) ROS resting values recorded in POST were significantly lower than in PRE and, 2) ROS blood concentration at the end of exhaustive exercise was lower (10 vs 16%) in POST than in PRE. Conclusion: Strenuous aerobic exercise increases ROS resting production, as demonstrated in our previous study and others studies with different athletes. A good training scheduling reduces ROS production values at rest and at the end of an exhaustive exercise. This results could be due to a more efficient mitochondrial respiratory chain or antioxidant capacity in whole body.