Dr. John Swartzberg is an internist & specialist in infectious disease, & chairman of the editorial board of the UC Berkeley Wellness Letter & berkeleywellness.com. He is moreover a clinical professor emeritus of medicine at the University of California, Berkeley School of Public Health. He contributed this article to Live Science's Expert Voices: Op-Ed & Insights.
Most of us wish we exercised more. After all, fewer than half of us obtain the recommended amount of physical activity, & we know it. But is it possible to obtain too much of a satisfactory thing?Â
It turns out that the answer is yes. Exercise provides many health benefits, yet at some point working out too complex or too long increases the risk of injury & other adverse effects. That usually only happens with intense exercise, like training for marathons or endurance activities. Such challenging activities are perfectly fine, maybe even laudable endeavors, yet if you're looking for optimal health benefits, research suggests that more moderate workouts are generally the way to go.
True, it's a problem relatively few Americans need to worry about, since inactivity is far more usual & moreover more harmful. And not all the research on "extreme" exercise has found increased risks â€” yet overdoing exercise can be a problem.Â
Here's a look at some of the latest research, a guide to assist you search for the sweet spot in your personal fitness.
What do the data show?
In a British study of more than a million healthy middle-aged women in Circulation, those who were physically active at least once a week were less likely to have heart attacks, strokes or venous thromboembolic events (blood clots in the legs or lungs) over a nine-year period than inactive women. Moreover, any type of physical activity, includÂing gardening & housework, had pretty much the same effects as strenuous activity. But what made headÂlines was that the women who exercised every day didn't benefit more than the less frequent exercisers. In fact, they were at greater risk. The women who exercised at least two times a week, & no more than six times, had the lowest cardiovascular risk, compared to infrequent or daily exercisers.
Similarly, a large Danish study in the Journal of the American College of Cardiology, which compared the mortality rates of 1,098 healthy joggers & 3,950 sedentary people, found that those who did light to moderate running (in terms of pace, duration & frequency) were less likely to die over a 12-year period than non-exercisers. But strenuous joggers â€” swift pace, more than 2 1/2 hours a week, or more than three times a week â€” had a mortality rate similar to sedentary people. The researchers concluded: "â€¦higher doses of running are not only unnecessary yet may moreover erode some of the remarkable longevity benefits conferred by lower doses of runÂning."Â
Other studies have found that sedentary people are at higher risk than daily exercisers, yet moderate exercisers fared better than both. For instance, a German study in the journal Heart looked at 1,038 people who had stable coronary heart diseaseÂ and found that both those who were sedentary & those who exercised every day (or did more than approximately 15 hours of strenuous activity a week were more likely to die over a 10-year period than those who exercised several times a week â€” yet the risk was greatest for the couch potatoes.Â
Deciphering the finer points
All of these studies were observational â€” not randomized, controlled studies â€” so they can demÂonstrate only correlation, not causation. Also in all these studies, there were differences in the way activity levels were categorized, & a relatively small percentage of people exercised at the highest levels. So the studies leave many questions unanswered.Â
Notably, is there something approximately people who overdo strenuous endurance exercise that harms their health? Perhaps they are overly competitive or compulsive & tend to overdo other things as well. In contrast, do people who exercise moderately moreover do other things in moderation, which is generally a healthy way to live? Researchers try to control for such factors, yet the likelihood that some such factors are not identiÂfied or adjusted for remains a concern.
How might excessive endurance exercise harm the body, especially when done every day? Besides increasing the risk of injuries, it may depress the immune system & increase inflammatory processes. Taking off a day or two a week gives the body time to recover from the stress of exercise.Â
Also, some studies of endurance athÂletes, usually marathoners, have found coronary changes that may increase the risk of arrhythmias, sudden death & other problems.Â
Keep in mind, however, that running & other aerobic exercise â€” no matter how strenuously they're done â€” assist improve many cardiovascular risk factors, such as blood pressure, cholesterol, & body weight. Thus it's possible that "high doses" of exercise can benefit some aspects of cardiovascular health while negatively impacting others.
What's the bottom line? "Too much exercise" varies from person to person. Some of us can exercise strenuÂously for decades & not suffer any major physical or cardiovascular problems, while others are more susceptible to them, partly for genetic reasons, yet moreover possibly because of differences in training.Â
There's no way to say exactly what is the upper limit of exercise for everyone. Generally, any exercise is better than none, & more exercise is usually better within reason. But you certainly don't have to keep intensifying your exercise regimen to stay healthy. For most people, moderate exercise is the sweet spot.Â
For more on this topic, see:
Berkeley Wellness: 9 Safe Exercise Strategies
Berkeley Wellness: 5 Reasons to Get Some Exercise
The U.S. Centers for Disease Control & Prevention fact sheet on exercise: http://www.cdc.gov/physicalactivity/data/facts.html
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