The Right Coast
April 20, 2005
By Tom Smith
Exercise is good for you, but is there too much of a good thing? Apparently so. The well-known (but not new) Harvard alumni study, which looked at some 17,000 graduates of Harvard, looked at the relationship of exercise and longevity. (But strangely not head size.) It turns out that even a little exercise is very good for you, so much so that as a rule of thumb, each hour spent exercising adds two to your life. But like most things, there are decreasing returns to scale, and after that even negative returns to scale. Above 3000 - 4000 calories per week, the returns start to be negative.
4000 calories is a lot, but not that much. You might reach that by running 40 miles a week. My own, my Step Mill tells me I expend more than 800 calories climbing somewhat more than 2000 feet (an hour of not slow climbing and very much feeling like a workout). Applying my lawyerly math skills tells me 5 such workouts in a week would put me above 4000 calories. I have had such weeks, but not in a couple of years. You have to log many such weeks I presume before your life expectancy goes down. Maximum benefit seems to be perhaps 2000 calories per week, though what I have read is not clear on that. 2000 cal/week is a wholesome 20 miles per week of running or its equivalent. More than I manage to do regularly, but not that much.
Yes, for some reason I am having a hard time today getting off my butt and onto the bike or into the gym.