Here's one for extreme exercise enthusiasts like Mark Carney and Anthony Jenkins: taking on extreme events like ultramarathons could actually give you blood poisoning, new research has shown.
Researchers at Monash University in Australia looked at the bloodstreams of people taking part in a number of extreme endurance events, such as 24-hour ultra-marathons and multi-marathons, run on consecutive days.
In some cases they found that intestinal bacteria known as endotoxins leaked into the bloodstream and activated a strong immune response, similar to the body's reaction to a serious infection.
"Nearly all of the participants in our study had blood markers identical to patients admitted to hospital with sepsis,” explained Dr Ricardo Costa, lead researcher in the study. “That's because the bacterial endotoxins that leak into the blood as a result of extreme exercise, triggers the body's immune cells into action.”
He added anything over four hours of exercise in one go is considered extreme, as is repetitive days of endurance exercise.
But taking on these kinds of challenges is no longer unusual, with lots of people signing up to marathons, Ironman triathlon events and ultra-marathons.
"It's crucial that anyone who signs up to an event, gets a health check first and builds a slow and steady training program, rather than jumping straight into a marathon, for example, with only a month's training," Costa said.
Training stops poisoning
The danger is found among those who do not regularly do exercise, but occasionally take part in major events. The research team found that people who were fitter and trained over a longer period of time had higher levels of Interleukin 10 - an anti-inflammatory agent, which allowed them to dampen down the negative immune response.
"The body has the ability to adapt and put a brake on negative immune responses triggered by extreme endurance events. But if you haven't done the training and you're unfit - these are the people who can get into trouble," Costa said.