This is Scientific American's 60-Second Science. I'm Karen Hopkin.The microbes in our intestines help keep us healthy, strengthening our immune systems and promoting metabolism.But they may also give us a leg up when it comes to moving our legs up―and down again, rapidly and repeatedly―because a new study finds that mice that are fed bacteria isolated from elite athletes log more time on the treadmill than other mice that are treated only to bacteria found in yogurt.The results appear in the journal Nature Medicine.Aleksandar Kostic, a microbiologist at Harvard Medical School,was initially interested in how the gut microbes of people with diabetes might differ from folks without the condition―the idea being that tweaking the microbiome might help to treat the disease.But the question of enhancing overall health and fitness can also come from the other direction:"But here the question was more, what's unique in the gut microbiome of someone who is supremely healthy?And can we use that feature of the microbiome to transfer into other people to potentially make them healthier?"And a handy window into the gut is poop.So Kostic and his crew asked 15 runners who competed in the Boston Marathon in 2015 to provide daily stool samples from a week before the race to a week after.They also collected samples from 10 people who are decidedly more sedentary, and they tallied the bacteria present in each.