Philip J. Goscienski, M.D.
Until only a few generations ago everyone exerted plenty of energy because the age of labor-saving devices had not yet arrived. Except for the moderately wealthy, the rest walked to work, to the fields, to the village or town to shop. Having a horse saved walking long distances but if you think that caring for a horse - or even riding one - is not physically demanding you probably have never owned one. We were still an agricultural nation 200 years ago and everything from drawing water to preparing a meal, gathering firewood to raising a few vegetables, washing diapers to building furniture, took lots of human effort. In terms of how much physical activity was required for ordinary living, things really had not changed much for several hundred thousand years. The wheel made life easier but just barely.
Those activities were enough to keep most folks fit throughout life. Fewer than 5 percent of Americans were obese only a century ago. As we turned the corner on the 21st century more and more of us became exercisers. Walkers, runners, bikers and gym buffs saw the need for more physical activity in order to postpone or to avoid the chronic diseases that had overtaken most adults because of their sedentary lifestyle.
It is still true that regular, moderately intense physical activity prevents heart disease, stroke, type 2 diabetes and other chronic ailments but some physicians have begun to notice that extreme exercise may be responsible for heart disease and early death. Marathon runners and triathletes represent such extremes.
It has been known for decades that long-distance runners often develop upper respiratory infections in the days following competition. It's possible that the stress of such exertion lowers their immunity. Another factor is that intense exercise causes the body to form inflammatory chemicals that play a role in several diseases, including heart disease and stroke. Runners' hearts are also larger than normal. This was once thought to be a healthy adaptation to their intense activity but there may be some harmful consequences. If there is any risk of exercise it appears to occur in those athletes who run - not walk - more than 30 miles per week. Few casual runners reach that distance in a week and the benefits of more modest exercise far outweigh the risk
The bottom line: It's far more dangerous to exercise too little than too much.
Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at email@example.com.