Exercise is certainly a big step toward a healthier lifestyle, but even the most devoted gym rat wonders at some point: How much exercise is too much exercise? A recent study conducted at Monash University has found that there is such a thing as getting too much exercise, like a 24-hour ultra-marathon, and doing so can cause intestinal bacteria to leak into the bloodstream, resulting in blood poisoning.

“Exercising in this way is no longer unusual,” Dr. Ricardo Costa, at the university’s Department of Nutrition and Dietetics, said in a statement. “Waiting lists for marathons, Ironman triathlon events, and ultra-marathons are the norm and they're growing in popularity.”

Costa and his colleagues took blood samples from athletes before and after they completed a 24-hour ultra-marathon. The research team set out to determine if any relationship existed between extreme bouts of exercise and the stress it can place on the gut wall. When the blood samples of athletes competing in a 24-hour ultra-marathon were compared to control subjects, they found that prolonged physical activity caused naturally occurring bacteria, known as endotoxins, to leak into the bloodstream.

As endotoxins seep into the bloodstream, the body’s immune cells trigger an inflammatory response that is similar to a serious infection. This inflammatory response is much greater than what the body required and more than it could handle. If the flood of endotoxins is too much, it can result in a potentially fatal condition known as sepsis induced systemic inflammatory response syndrome. Costa says that participating in over four hours of exercise and repetitive days of endurance training is considered extreme.

"Nearly all of the participants in our study had blood markers identical to patients admitted to hospital with sepsis," Costa explained. "That's because the bacterial endotoxins that leach into the blood as a result of extreme exercise, triggers the body's immune cells into action."

If this is true, then why aren’t more marathon runners suffering from blood poisoning? Simply by training hard and staying fit. By preparing for an ultra-marathon and staying fit, certain athletes from the study had higher levels of Interleukin 10, an anti-inflammatory protein heralded for its healthy properties.

"The body has the ability to adapt and put a brake on negative immune responses triggered by extreme endurance events," Costa added. "But if you haven't done the training and you're unfit, these are the people who can get into trouble."

Costa recommends that anyone hoping to compete in an activity that requires peak endurance get a health checkup first before starting "a slow and steady training program." One month of training is not enough.

Source: Gill S, Hankey J, Costa R, et al. The Impact of a 24-h Ultra-Marathon on Circulatory Endotoxin and Cytokine Profile. International Journal of Sports Medicine. 2015.