[This article originally appeared in the
April 2002
issue of Northwest Runner
magazine.]
Since retiring from my position as a monthly Northwest Runner columnist, I've been asked some excellent questions on training and fitness. This guest column discusses two such questions that may be of general interest.
Q.Can metabolism be changed (i.e., sped up or slowed down)? I think it has been assumed and talked about much especially in the past decade, yet are there data confirming this? Also, what is the definition of metabolism? --Heidi Messner, Kirkland, WA
A. In the context of your question, I would define metabolism as the rate at which the body uses energy (burns calories). Many other definitions are possible, of course.
As you know, it's easy to temporarily speed up one's metabolism by getting off the couch and exercising; the body burns calories at a higher rate during exercise than at rest. I assume you're specifically asking about resting (basal) metabolism -- e.g., does an athlete burn more calories than a couch potato while they're both sitting on the couch?
The first important point is that the more muscle mass you have, the more calories you burn, even while at rest. (Even resting muscle tissue requires some energy to stay alive.) Therefore, if you bulk up your body by lifting weights, you'll burn more calories at rest than you used to (Dolezal & Potteiger, Journal of Applied Physiology 85: 695-700, 1998) simply because you now have extra muscle doing all the things that resting muscle does (pumping ions in and out, synthesizing and breaking down proteins, etc.).
What if you exercise regularly but your body composition (muscle mass, percent body fat, etc.) doesn't change? Does exercising still lead to changes in resting metabolism? The answer to this question depends on exactly what is meant by "resting metabolism."
The idea that metabolism remains temporarily elevated after exercise is
also supported by several studies (summarized by Van
Etten et al., Journal of Applied Physiology 82: 298-304, 1997, and Westerterp,
American Journal of Clinical Nutrition 68: 970S-974S, 1998) of previously inactive
subjects who enroll in exercise programs. These studies have found that if someone starts
working out every day and burns, say, 200 calories during each workout, he/she then has
to consume an extra 400 or so calories per day (on average) in order to
maintain his/her body weight.
Q.At a recent coaching conference for track coaches in Ohio, one of the speakers stated that static stretching is best if done after a workout. The speaker said that static stretching should not be done before a workout because it can reduce muscle strength by up to 15% for up to an hour. This is of great significance if true since most high school athletes are still employing the jog - stretch - drills - workout - cooldown model. I am hoping you might have access to research that has some supporting evidence for this loss of strength after stretching. Can you help? --Mark Shafer, track/cc coach, Chardon Schools, Chardon, OH
A. The short answer to your question is: yes, static stretching (in which a stretched position is held for several seconds or more, hence the term "static") can reduce muscle strength. However, as far as I know, the relevant studies have only demonstrated a reduction in strength after a particular muscle group has been stretched for TWENTY TO SIXTY MINUTES. (For references to the original scientific studies, please see paragraph 6 of my previous article on stretching. As you know, most athletes don't stretch each muscle group for more than a minute or two. I am not aware of any evidence that such short periods of stretching impair strength, so there is no reason to assume that brief stretches before a workout or race hurt performance.