No effect of antioxidant supplementation on muscle performance and blood redox status adaptations to eccentric training


Journal Title (Medline/Pubmed accepted abbreviation): Am. J. Clin. Nutr.
Year: 2011
Volume: 93
Number: 6
Page numbers: 1373-1383
doi (if applicable): 10.3945/ajcn.110.009266

Summary of Background and Research Design

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.

Summary of research findings:
  • Vitamin C and E supplementation increased the fasting vitamin C and E concentrations in the blood at weeks 4 and 10 compared to baseline.
  • Supplementation did not increase muscle function, redox status, or hemolysis index.
  • The exercise protocol that was performed before the month of routine eccentric training caused peak torque and range of motion to decrease and not return to pre-exercise until 5 days afterwards. The muscles were also sore for the 4 days following and markers of oxidative damage were elevated accordingly. Moreover, the ratio of reduced:oxidized glutathione in the blood fell.
  • After the 4 wks of performing eccentric exercise twice a week, peak torque, the reduced:oxidized glutathione ratio and range of motion increased in the immediate postexercise period. At the same time, muscle soreness, and markers of oxidative damage decreased significantly after the exercise for the 5 days following. This shows that the body adapted to the exercise protocol.
  • There were no differences in performance between the vitamin group and the placebo group after either exercise protocol.

Interpretation of findings/Key practice applications:

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.
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