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Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Is Exercise Always Good for You?

February 27, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

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:

  • Obesity — itself a risk factor for many health problems, including diabetes and hypertension.
  • Elevated cholesterol — a well-established risk factor for heart disease and other vascular problems, including stroke and poor circulation.
  • Diabetes — For the majority of people with type 2 diabetes, excess weight contributes to insulin resistance, a potential cause of the disease.
  • High blood pressure — While there are genetic, nutritional, hormonal and even developmental causes of hypertension, exercise can be a powerful adjunct to lowering blood pressure, especially by promoting weight loss.
  • Depression — It's clear that for many people, exercise improves mood and sense of psychological well-being.
  • Insomnia — Sleep experts generally agree that regular exercise can help ward off sleep problems and hasten improvement when sleep is difficult.

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:

  • Stretch well before, after and, if possible, during exercise.
  • Use appropriate protective gear.
  • Cross train. Reduce the chances of overusing or injuring any one group of muscles by doing different activities that use different muscle groups.
  • See your doctor for blood pressure and cholesterol measurement, along with other assessments of cardiac risk, and consider taking low-dose aspirin (81 milligrams) daily if you have risk factors for heart disease. If you participate in marathons, some experts suggest that aspirin may be a good idea for a few days before and after the day of the race.
  • Resist the temptation to do too much too soon. If you are starting from a state of poor conditioning, start slowly and work up very gradually.
  • Listen to your body's signals. If you are "under the weather," take a day off. Don't exercise if you have a fever. If your periods have stopped, you may be exercising too much and an evaluation with your doctor is warranted. Persistent pain is not normal and should prompt a re-evaluation of your exercise program.
  • Change your program to lower impact activities, such as an exercise bike instead of running, especially if you are over 30 years old. As we age, our muscles, bones and joints become less forgiving of repetitive or forceful impact.
  • Be careful. Pay attention to general safety and the "rules of the road" if you are walking, jogging, biking, or otherwise sharing the road with automobiles, especially at night.

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.

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