Free Radicals Inhibit Some Exercise Fitness Adaptations

Free radicals are typically thought of as having only negative effects on the body, but in reality they have both positive and negative effects. This is the case in the specific context of exercise. Free radicals formed during exercise cause acute muscle fatigue and muscle cell damage, but they also stimulate some of the physiological adaptations that enhance fitness. Thus it is reasonable to speculate that supplementation with antioxidants that inhibit free radical formation may also inhibit some of the free radical-dependent fitness adaptations to exercise, and a new study from the University of Jena, Germany, provides evidence that this speculation is indeed accurate.

Researchers recruited a group of perviously untrained and trained volunteers and put them through a four-week exercise protocol. Half of the subjects received daily vitamin C and vitamin E supplementation and the other half received placebo. The effects of exercise training on insulin sensitivity in all subjects was measured. The researchers found that insulin sensitivity increased only in subjects who did not receive vitamin supplementation, whether previously untrained or trained. The authors of the study concluded, “Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.”