The study will evaluate the change in gastrointestinal (GI) flora following probiotic supplementation, and expected to lead to an increase in the intestinal epithelial integrity and to improvement in its health. Concurrently with the reduction in the amount of toxins in the GI tract following an intensive exercise, a lower incidence of symptoms of discomfort will improve the quality of the training sessions which will be exhibited by an improvement in endurance capacity and in physiological responses to rigorous exercise. Half of the participants will receive probiotic supplement while the other half will receive a placebo.