ANTIOXIDANTS & PERFORMANCE
When researchers in the early 1980s first looked at the relationship between exercise and free radical production, they found a two to three fold increase in free radicals in the muscles and livers of rats during physical activity. Today, this relationship continues to be studied, using human subjects under specific training conditions, with a focus on trying to identify specific ways that free radical production hurts performance. In general, research into free radicals and antioxidants has been plagued by inconsistency in the measurements used to gauge the role of dietary and supplemental antioxidants on oxidative stress. As a result, while we know that antioxidants offer some health benefits for athletes related to combating free radicals, it's difficult to be much more specific than that.
Studies have used widely varying exercise conditions, modalities, training intensities, genders, ages, and measures of oxidative stress through blood and urine. One newer test, called Raman spectroscopy, involves a laser light pointed at the fat pad of the palm to measure the amount of carotenoids in the body. So while progress continues, there are still many questions left to answer.
We do know that the importance of antioxidants for performance varies greatly from one sport to the next. For example, a 2006 study of endurance-training athletes working out at altitude for six weeks found that antioxidant levels in these athletes were below normal after the training sessions. This suggests that the antioxidants were doing their job neutralizing free radicals, and being used up in the process, helping to limit oxidative stress and likely boosting performance. But a 2009 study by the same researchers found that elite swimmers training for 13 days at altitude did not experience decreased antioxidant levels, suggesting that the antioxidants in their bodies (both endogenous and exogenous) didn't have to fight off free radicals and thus didn't play a significant role in performance. Other studies have looked at specific antioxidant vitamins, such as vitamin C, and produced conflicting results on whether high doses can reduce post-workout muscle soreness and damage. Vitamin E, meanwhile, has been shown to enhance oxygen utilization at altitude, but does not seem to be as effective for that purpose at sea level.
What does all this mean? Essentially, it's not yet clear just how much oxidative stress affects athletic performance, but it likely contributes to muscle damage, decreased power, fatigue, and slow recovery. And while antioxidants' precise effects are still being debated and likely vary greatly from person to person and sport to sport, they can help limit oxidative stress and thus help protect the body. In summary, antioxidants can help many athletes, though the precise benefits are variable and not always well defined.