Do antioxidant supplements interfere with skeletal muscle adaptation to exercise training?

Abstract

A popular belief is that reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced during exercise by the mitochondria and other subcellular compartments ubiquitously cause skeletal muscle damage, fatigue and impair recovery. However, the importance of ROS and RNS as signals in the cellular adaptation process to stress is now evident. In an effort to combat the perceived deleterious effects of ROS and RNS it has become common practice for active individuals to ingest supplements with antioxidant properties, but interfering with ROS/RNS signalling in skeletal muscle during acute exercise may blunt favourable adaptation. There is building evidence that antioxidant supplementation can attenuate endurance training-induced and ROS/RNS-mediated enhancements in antioxidant capacity, mitochondrial biogenesis, cellular defence mechanisms and insulin sensitivity. However, this is not a universal finding, potentially indicating that there is redundancy in the mechanisms controlling skeletal muscle adaptation to exercise, meaning that in some circumstances the negative impact of antioxidants on acute exercise response can be overcome by training. Antioxidant supplementation has been more consistently reported to have deleterious effects on the response to overload stress and high-intensity training, suggesting that remodelling of skeletal muscle following resistance and high-intensity exercise is more dependent on ROS/RNS signalling. Importantly there is no convincing evidence to suggest that antioxidant supplementation enhances exercise-training adaptions. Overall, ROS/RNS are likely to exhibit a non-linear (hormetic) pattern on exercise adaptations, where physiological doses are beneficial and high exposure (which would seldom be achieved during normal exercise training) may be detrimental.

Figure 1. Effects of antioxidants on skeletal muscle during exercise training

Effectors of antioxidants that may be negatively affected are marked in red, effectors of antioxidants that may be beneficially affected are marked in blue.

Figure 2

Acute skeletal muscle signalling during exercise, and interference of antioxidants to hamper training adaptations

Figure 3. Non‐linear/hormetic effects of ROS/RNS on exercise training adaptations and performance

Lower doses of ROS/RNS exert beneficial effects, whereas theoretical high ROS/RNS exposure (which would rarely be achieved during training) would impair training adaptations and performance. Antioxidant supplementation during an exercise task that results in an increase in ROS/RNS production which promotes training adaption and improves performance would be detrimental (blue and green bars, respectively). However, if the exercise task resulted in ROS/RNS exposure that exceeds this level then antioxidant supplementation may potentially be beneficial. We suggest that the level of ROS/RNS stress required to reduce performance would be lower than what would be necessary to hamper training adaptation.