How much exercise is too much?

Most of us know keeping active is crucial to our health and happiness. So it's not surprising that making exercise a regular habit was one of the top three New Year’s resolutions for 2015. But just how much exercise should we be doing – and is it possible to exercise too much?

The current exercise guidelines for adults recommend at least 150 minutes per week of moderate physical activity – or 75 minutes per week of vigorous physical activity. These guidelines also suggest that an increased amount of exercise is associated with additional health benefits.

Although increased amounts of exercise above the minimum guidelines are encouraged for health benefits, no upper limit exists. While the guidelines caution that high-intensity exercise may increase the risk of injuries and heart issues, there is no fixed point at which exercise definitively becomes detrimental to one’s health. In other words, we don’t have a clear sense of what constitutes “too much” exercise.

Recent research is at least beginning to shed some light on the notion that there may be a point at which large volumes of exercise begin harming, rather than improving, our health. For instance, while a regular exercise routine is highly effective for boosting longevity and cardiovascular health and ameliorating many common chronic diseases, such as obesity, diabetes and stroke, long-term endurance exercise has been linked with pathologic structural remodeling of the heart, enlarged arteries and increases in anxiety and depression.

Chronic training for and competing in extreme events such as marathons, ultramarathons, Ironman distance triathlons and very long distance bicycle races may cause short-term negative cardiovascular effects. For example, among a group of patients diagnosed with coronary artery disease, those who exercised beyond the recommended 60-minute maximum saw decreases in their antioxidant levels as well as stiffening of their blood vessels. In comparison, those exercisers who exerted themselves within a more reasonable range – i.e., in 60 minutes or less – saw a reduction in free radicals, in addition to improved circulation.

Another study found a very high rate of myocardial fibrosis among lifelong endurance athletes. More specifically, the researchers found that 50 percent of athletes who underwent cardiac magnetic resonance imaging displayed signs of the tricky-to-detect hardening of heart cells. This hardening of heart cells may play a role in precipitating sudden cardiac arrest or, at the very least, induce an irregular heartbeat. And while runners who log between .15 and 15 miles per week (a wide range, indeed) benefit from an estimated 19 percent reduction in mortality rates, those who consistently surpass 25 weekly miles have a risk of death comparable to those who don’t exercise.

Although this preliminary research is finding that for some individuals, long-term excessive endurance exercise may cause adverse health issues, further investigation is warranted to determine if an upper cutoff for the health benefits of exercise exists.

Pinning down just how much exercise qualifies as “too much” will likely vary between individuals and depend on a variety of factors – including their age, health history and lifestyle. But determining the point at which physical activity begins posing a threat to our health is critical in ensuring we don’t accidentally cause our bodies – and brains – more harm than good. Understanding this potential upper-level cutoff is important as researchers examine the concept of people becoming addicted to exercise.

In the meantime, make sure you're at the very least meeting the minimum amount of exercise for health benefits and reaching your New Year’s resolutions for your well-being. Even if you don’t reach every single one of your fitness goals, remember that something is always better than nothing.

Copyright 2014 U.S. News & World Report