Journal Title (Medline/Pubmed accepted abbreviation): Am. J. Clin. Nutr.
Page numbers: 1373-1383
doi (if applicable): 10.3945/ajcn.110.009266
Background:There is substantial evidence that antioxidants provide health benefits in non-exercise settings. However, because exercise is oxidative by nature, there is debate as to whether the combination of antioxidants and exercise has a different effect than exercise alone.
Eccentric exercise – when there is resistance during the lengthening of a muscle (as opposed to concentric exercise, when the muscle shortens). Heavier weights can be used during eccentric exercise than concentric exercise and this exercise has been shown to damage the muscles to a larger extent.
Research question:Does daily antioxidant supplementation, in the form of vitamins C and E, affect muscle performance, redox status (the antioxidant “potential” of the blood), recovery, or extent of hemolysis after a single exercise bout or routine training?
Subjects:Recreationally trained men (n = 28)
Experimental design:random, double-blind allocation to receive vitamin or placebo supplements, repeated measures
Treatments:Vitamin C (1 g) and vitamin E (400 IU) or a placebo (lactose), taken before breakfast. This is 16.7 times the recommended daily intake (RDI) for vitamin C and 13.3 times the RDI for vitamin E.
Protocol:The participants were assessed for height, weight, percent body fat, and maximum isometric torque of the knee extensor muscles (both legs simultaneously) before the study. They were matched for age, BMI, and peak torque before being randomly assigned to the groups. Blood samples were drawn from every participant and muscle biopsies were acquired from 4 volunteers from each group. They then took the supplement for the next 11 wks. At the beginning of week 5, the participants underwent an eccentric exercise protocol (5 sets of 15 knee extensors at 60°/sec with 2 min rest in between sets). For the 5 days after the exercise protocol, participants were assessed for range of motion and peak torque, reported on muscle soreness, and gave blood samples to be measured for creatine kinase and redox potential. The purpose of these assessments was to gauge extent of muscle damage, rate of recovery, and amount of (anti)oxidative biomarkers. For weeks 6-9, the participants performed routine eccentric exercise sessions twice a week. They then rested for 1 wk, and at the beginning of week 11 they repeated the same exercise protocol as week 5 and were again monitored for 5 days.
Daily supplementation with large doses of vitamins C and E did not affect muscle performance or the body’s ability to adapt to eccentric training (one of the most damaging training regimens). The idea that antioxidants affect the body’s responses to exercise, in either a positive or negative fashion, is a highly debated topic. Timing of supplementation and exercise, type of exercise, and even methods of assessing the effects likely play a role in generating these seeming conflicting data. In general, these data do not support positive effects of antioxidant supplementation. However, diets high in fruits and vegetables, which contain a wide range of naturally-occurring antioxidant compounds, are still encouraged.