Purpose: To determine (1) the effect of a 40-minute steady-state run on muscle membrane integrity of elite athletes as reflected by serum creatine kinase (CK), (2) whether antioxidant supplementation (AS) with vitamins E and C has a protective effect, and (3) if a minimal blood concentration of vitamin E or C is required for any such protection. Methods: Fifteen elite-level endurance athletes (VO2max=71.5±1.2mL·kg-1min-1) were randomly assigned to 6 weeks AS (1000 IU·d-1 natural vitamin E and 1000 mg·d-1 vitamin C) or placebo. Using a double-blind crossover design and 4-week washout period, each treatment was followed by a 40-minute steady-state run at 3 mM blood lactate. Blood samples before and 0 and 24 hours after the run were assayed for serum and red cell a-tocopherol (a-TOH), serum ascorbate, and CK. Results: The AS produced a 2.5-fold, well-correlated (r = .84) increase in serum and red cell a-TOH (P < .001) that attenuated the increase in postrun CK (P = .01). There was no change in serum ascorbate with AS and no relationship with CK (P > .1). Curvilinear regression revealed some evidence that a critical level of serum a-TOH in the vicinity of 12 mg·L-1 was required to attenuate CK efflux, a level only achieved with AS. Conclusion: The muscle membrane integrity of elite-level athletes is compromised even during steady-state running of moderate intensity and duration. The AS provided a protective effect, with evidence that a serum a-TOH concentration of around 12 mg·L-1 is required.
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