A study published in Current Microbiology, has shown that probiotic supplements substantially prevent oxidative stress under periods of intense training. Subjects were 24 male cycling athletes, who were undergoing 4 weeks of intense off-season training. They were split into two groups, where one was given probiotics and the other nothing (control). Blood samples were analyzed before and after the supplementation, and plasma levels of reactive oxygen metabolites and biological antioxidant capacity were evaluated.

After intense training, the control group had very high levels of reactive oxygen metabolites, but those who received probiotic supplements saw very little oxidative stress. In this study it seemed that probiotic supplements increased antioxidant production during exercise, as plasma antioxidant levels were elevated with exercise in the probiotic supplemented group only.

Although this study is intriguing, more research needs to be done investigating how probiotics may promote ergogenic effects. For example, it is known that elevated levels of reactive oxygen species limit nitric oxide (a vasodilator) production and lead to vascular dysfunction. Thus, in this case, keeping antioxidants high and oxidative stress low would help to increase blood flow to working muscles.

Martarelli D, Verdenelli MC, Scuri S, Cocchioni M, Silvi S, Cecchini C, Pompei P.
Effect of a probiotic intake on oxidant and antioxidant parameters in plasma of athletes during intense exercise training. Curr Microbiol. 2011 Jun;62(6):1689-96. Epub 2011 Mar 12.