All of the studies in the review focused on abnormal heart rhythms among endurance athletes — people who routinely expose themselves to highly vigorous exercise (as in multiple hours of intense activity almost daily). Taken together, the research suggests a connection between intense and excessive exercise and a type of heart arrhythmia called atrial fibrillation, where the heart beats very rapidly and irregularly. This condition can lead to irreversible damage to the heart muscle.The lead author of the review concluded that more research is needed to have a more exact idea of just how much exercise can prompt these effects, Shape reports.Related: 6 Ways To Relieve Sore Muscles After Overtraining However, the review makes it very clear that exercising is still incredibly beneficial. The kind of exercise that might be "overboard" is the kind a professional athlete would do, not your average SoulCycle devotee. So, if you have a sensible routine that you enjoy and doesn't leave you feeling burned out, there's no reason to stop.Related: You Don't Have To Run Very Far To Reap The Benefits Of Running