Essentially, pushing it too much can weaken your immune system, leaving you open to infection, says biochemist Mike Gleeson, PhD, a professor at the UK’s Loughborough University. He cited research that found you can be up to six times more likely to get sick when you work out too hard (think: training for a half marathon, going for a run, then doing yoga, regularly taking a 90-minute spin class.).
That doesn’t mean you should abandon your workouts altogether: Not doing anything can put you in the danger zone, too. People who don’t exercise at all typically get up to three colds a year, and a recent study published in the British Journal of Sports Medicine found that people who are active at least five days a week have shorter colds.
The solution? Regular moderate exercise, like taking a 30-minute pilates class, doing the elliptical for 20 minutes, or even just going for a fast walk. Gleeson told us that you’ll reap the most benefits when you can do this three or more times a week, reducing your odds of getting sick by 30 percent.
