Thursday, December 31, 2009

Exercise: How Much is Enough?

The New York Times' Well Blog published a piece today entitled "How Little Exercise Can You Get Away With?" -- a headline which, besides being ungrammatical, is somewhat deceptive. While the article appears at first glance to have been prompted by research about how much exercise is enough to maintain a baseline of good physical health, it's actually the amount of exercise needed to keep people from "feeling gloomy."
The answer, according to a study published in this month’s British Journal of Sports Medicine: a mere 20 minutes a week of any physical activity, whether sports, walking, gardening or even housecleaning, the last not usually associated with bringing out the sunshine. The researchers found that more activity conferred more mental-health benefits and that “participation in vigorous sports activities” tended to be the “most beneficial for mental health.” But their overall conclusion was that being active for as little as 20 minutes a week is sufficient, if your specific goal is mental health.
The Times does point out, though, that such scant exercise "won't do much for your cardiovascular fitness and is unlikely to lessen your risks for a multitude of diseases and, ultimately, of premature death, benefits that a greater amount of exercise may provide." According to the U.S. Department of Health and Human Services' 2008 Physical Activity Guidelines for Americans, the "minimum amount of exercise required to see a significant lowering of your risk of dying prematurely was ... 500 MET minutes of exercise a week."
A single MET, or Metabolic Equivalent of Task, is the amount of energy a person uses at rest. Two METs represent twice the energy burned at rest; four METs, four times the energy used at rest; and so on. Walking at three miles per hour is a 3.3-MET activity, while running at 6 miles an hour is a 10-MET activity. The committee concluded that a person needs to accumulate a weekly minimum of 500 MET minutes of exercise, which does not mean 500 minutes of exercise. Instead, 150 minutes a week (two and a half hours) of a moderate, three- to five-MET activity, such as walking, works out to be about 500 MET minutes. Half as much time (an hour and 15 minutes per week) spent on a 6-plus MET activity like easy jogging seems, according to the committee, to have similar health effects.
Interestingly, they did not find that exercise beyond a certain point conferred significant additional health benefits. Instead, the “dose response” for exercise, the committee found, is “curvilinear.” In other words, people who are the least active to start with get the most health benefit from starting to exercise. People who already are fit don’t necessarily get a big additional health benefit from adding more workout time to their regimens.
That doesn't mean we should stop doing daily intense workouts, though: "According to the Physical Activity Guidelines report, 'It has been estimated that people who are physically active for approximately seven hours a week have a 40 percent lower risk of dying early than those who are active for less than 30 minutes a week.'

(Nice! I may actually have a greater chance of not dying early! (That is, if I don't keel over and die while doing some super-fucking-crazy Insanity routine.)

But the lesson aimed at people like my pre-P90X self (i.e., couch potatoes hoping to remain as guiltlessly immobile as possible) is simple: "Do something."
“Inactivity is looking more and more like one of the underlying causes of many chronic diseases,” [Frank Booth, a professor in the department of biomedical sciences at the University of Missouri at Columbia] says. If, he adds, “you want to live to be 100,” which happens to be my New Year’s resolution, “then don’t just sit all day.”