Antibiotics Can Hurt Your Aerobic Performance Come Race Day

If you’ve been fighting an infection and your doc recommends antibiotics, consider waiting until after your 10K or half-marathon to begin taking them. Researchers at the University of California at Riverside found that, in lab studies, a 10-day course of antibiotics decreased aerobic performance by 21 percent.

“Antibiotics can kill many, if not most, bacteria in your gut that play an essential role in normal bodily functions,” says co-author Theodore Garland. Antibiotics don’t just kill off the harmful bacteria causing your infection, he explains, they also remove important bacteria from the gut that provide energy for muscles in the body.

On the positive side, researchers found no indication of other negative health side effects from the antibiotics. Your takeaway? Weigh the severity of your symptoms against the importance of your sporting event. If the race takes precedence, hold off on your antibiotics until you cross the finish line to preserve your aerobic performance.