Last reviewed February 27, 2013
It is among the most common recommendations you will hear: Get more exercise. In fact, it is so commonly recommended, I suspect many people stopped listening long ago. My mother says she hates going to the doctor because all she's ever told is to eat right and exercise more. At least, that's her version.
The Problems of Too Little Exercise
In all fairness to my mother's doctors, it is hard to overstate the benefits of regular exercise in reducing the risk of a variety of diseases. Among the many illnesses or conditions that become less likely when you exercise regularly are:
Even with all these benefits, it is worth acknowledging that exercise is not always beneficial. If you are looking for a reason not to exercise, this is news you may welcome: It can be bad for you. Researchers interested in the effects of exercise have noticed that sometimes the health effects of exercise are in the "wrong" direction. Injuries, heart attacks, and other negative effects of exercise can be observed in certain situations. Although on balance, the effect of exercise is overwhelmingly positive, there are some "costs" to consider when seeking the benefits.
The Problems With Exercise
Some health problems associated with exercise are self-evident: sports related injuries, such as a fracture or ligament injury (sprain) that follows trauma. But others are not so predictable: back pain related to twisting motions, stress fracture due to repetitive minor trauma (including running), knee pain or tendonitis due to overuse.
And not all exercise has the same risks. For example, fractures and sprains are more likely if you are subject to significant trauma or if you do too much. Sudden, high intensity exercise, especially if you are not used to it, can put more stress on the heart. In fact, studies have found a small but increased risk of sudden death (presumably from a heart attack or irregular heart rhythm) in people who exercise heavily after being inactive. Young women who exercise to the point of having little body fat may not ovulate or menstruate. This puts them at risk of osteoporosis and at higher risk of fracture. When associated with an eating disorder such as anorexia nervosa, excessive (or obsessive) exercise can lead to even more serious health problems.
A recent study found that marathoners had changes in their blood during and just after the race that might put them at risk of a heart attack. This followed the observation that approximately one in 50,000 seemingly healthy marathoners experiences sudden death from cardiac cause. The study looked at healthy runners who ran a marathon without incident and had blood tests after the race. A pattern of "thickened" blood was observed that could increase the risk of heart attack. Perhaps unrecognized heart disease or other risk factors combine with such changes to contribute to or provoke the rare cases of sudden death.
Trying To Do the Right Thing
If you are trying hard to exercise regularly, the "dark side" of exercise should not deter you. Instead, look at your current or planned exercise to see if there are ways to reduce your chances of encountering an exercise-related health problem. Here are some general guidelines:
The Bottom Line
While it can be easy to define what constitutes too little exercise (especially if you don't exercise at all), it is much harder to define what is too much. And even if you aren't doing too much, problems can arise. Ideally, exercise should only improve our health without putting it at risk; unfortunately, as with many things, there are two sides to the equation. Try to put the sensational news items in perspective. With some minor adjustments, it is possible to avoid the significant risks associated with slothfulness as well as those smaller ones associated with exercise.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.