BackgroundAlthough physical exercise training is highly recommended, physical exercise causes oxidative stress, which is potentially injurious. This study evaluates this ‘exercise paradox’ by evaluating the effect of physical exercise on exercise-induced lipid peroxidation.MethodsMeasurement of lipid peroxidation (ie, expired ethane and pentane and plasma malondealdehyde) taken during cardiopulmonary exercise stress testing were compared between a group of 10 cardiac patients who underwent physical exercise training in a cardiac rehabilitation setting and a group of 10 nonexercising cardiac patients.ResultsOur findings indicate that physical exercise training increased physical work capacity without a concomitant increase in expired markers of lipid peroxidation (ethane and pentane) and decreased malondealdehyde levels.ConclusionsBecause physical exercise-trained people can perform more intense physical work with less oxidative stress, we conclude that physical exercise training can reduce potential chronic health effects associated with daily activities by contributing to an overall reduction in exercise-induced free radical production.