"We are more bacteria than we are human. The bugs in our gut affect our energy metabolism, making it easier to break down carbohydrates, protein and fibre," said Jonathan Scheiman, a postdoctoral fellow at Harvard University in the US.
"They are also involved in inflammation and neurological function. So perhaps the microbiome could be relevant for applications in endurance, recovery and maybe even mental toughness," Scheiman said.
Researchers collected fecal samples on a daily basis from 20 athletes training for the 2015 Boston marathon one week before and one week after the race.
On comparing the pre-race and post-race samples, they found a sudden spike in the population of one particular type of bacteria after the marathon.
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"This bug's natural function is to break down lactic acid," Scheiman said.
They found that during intense exercise, the body produces more lactic acid than usual, which can lead to muscle fatigue and soreness. This bacteria could potentially help with that.
Researchers are now feeding the bacteria to mice to measure its effects on lactic acid levels and fatigue.
They found a type of bacteria in ultra-marathoners that can help break down carbohydrates and fibber - which is key during a 100-mile run - that was not present in the rowers, suggesting that different sports may foster niche microbiomes.