There is no arguing that exercise is a good thing. Regular exercise can improve your mood, your body composition, and, in most cases, your cardiovascular health. However, an extensive review of studies that was published in the April issue of the Canadian Journal of Cardiology, has come up with some interesting findings. The review found that intense exercise, like very high-intensity, endurance exercise, can cause irreparable structural damage to the heart through an increase risk of atrial fibrillations (AFib). The lead researcher, Dr. Andre La Garche, M.D., Ph.D., and head of Sports Cardiology at Baker IDI Heart and Diabetes Institute in Melbourne, Australia, and his team reviewed 12 different studies on abnormal heart rhythms in athletes and endurance runners. They reviewed studies focused specifically on AFib, which can lead to stroke or heart failure. The researchers found an impossible to ignore correlation between intense exercise and AFib. Even La Garche's very own 2011 study supports these new findings. In his study, La Garche examined AFib in people who did not previously suffer from heart disease and found that they were 4 times as likely to have engaged in endurance sports. [bctt tweet="Is Too Much Exercise Bad For Your Heart?"] But that doesn't mean you have to give up training for that triathalon! The review is careful to point out that the benefits of exercise are far greater than the risks. Besides, the exercise you are doing needs to be both vigorous and sustained over a long period. In this review, extreme exercise was considered to be vigorous exercise, sustained over several hours, nearly every single day. It was more like the type of exercise you'd see from a professional athlete as opposed to your daily 30 minute HIIT session. La Garche says there needs to be more research and studies done to determine at exactly what point the risk for AFib increases. He says he conducted the review because he wanted to "discuss the often questionable, incomplete, and controversial science behind the emerging concern that high levels of intense exercise may be associated with some adverse health effects." Until that new research is done, you might want take a closer look at your own goals. If you aren't aiming to be an Olympic marathoner, there is no need to push yourself beyond your limits every day. As you do with everything else in life, keep things moderate and balanced. There is no reason to give up the daily HIIT session you've been doing on Sweatflix℠. With these program you will push your body to its limits but you will not be pushing it to the point of exhaustion. And, of course, rest days are built into these programs so your body has time to repair and rebuild. Remember: taking time to rest and recover is every bit as important as the workouts themselves! What do you think of these findings? Does this change your approach to training?