I've seen exaggerated claims pro and con about the question of strength training and metabolism. Some authors imply that if you pump iron for a week or two you'll be able to pound down an extra Big Mac and quart of ice cream per day.
The most pessimistic authors declare that there is almost no increase in metabolism from strength training. In the middle the statement that gaining an extra pound of muscle boosts metabolism by about 50 calories per day is often made. So who's right?
The 50 calorie per day notion comes from looking at studies like that by Campbell, et al [Campbell, 1994], which showed about a 7% increase in metabolims among participants in a 12 week resistance training program.
This amounts to around 150 calories per day, and the participants gained on average about 3 pounds of muscle, so it appears that each pound of muscle boosted metabolism by 50 calories per day. Similar results have been found in other studies, e.g. [Pratley, 1995].
On the other hand, the calorie consumption of muscle has been directly measured and found to be about 6 calories per pound per day[McClave, 2001]. Further, each pound of fat burns up 2 calories per day, so if you lose a pound of fat and gain a pound of muscle there should only be a net boost in your metabolism of 4 calories per day, as one author put it, maybe enough for a celery stick.
Based on this result, science writer Gina Kolata in her book claimed that strength training does not boost metabolism Ultimate Fitness [Kolata, 2003], and similar reasoning was used in an article in Runner's World by well-known running writer Amby Burfoot.
The two results, both from careful scientific studies, seem to present a paradox. But it turns out the 50 calorie per day argument is a misinterpretation of the Campbell results. It's not that 3 extra pounds of muscle boosted the participants metabolism 7%, instead the strength training revved up all their muscle, leading to a significant increase in resting metabolic rate (RMR).
This was stated by the authors of the Campbell study, who never made the 50 calorie per pound per day claim: "The increase in RMR is due to an increase in the metabolic activity of lean tissue and not an increase in the amount of lean tissue mass". [Campbell, 1994]. Various factors may cause this increase, including repair of tissue damage, increased protein synthesis, etc. Using the 6 calorie per pound per day result as justification that there is very little increase in metabolism is also a misinterpretation, again based on the wrong assumption that it's the extra pounds of muscle that matter.
So strength training will increase your metabolism, by making all your muscles a bit more active. This revving up lasts at least a couple of days after training- the 7% boost mentioned above was measured 45 hours after the participants' last training session.
Personally its not my main reason for doing it, I'm after things like bone health and fighting off age-related decline in muscle. But I don't mind any help my metabolically challenged old body can get.
References
-Campbell, W, Crim, M, Young, V, and Evans, W.
"Increased Energy Requirements and Changes in Body Composition With Resistance Training in Older Adults", American Journal of Clinical Nutrition,60: 167, 1994.
-Kolata, G, Ultimate Fitness: The Quest for Truth about Health and Exercise, Farrar Straus Giroux, 2003.
-McClave, Stephen A.; Snider, Harvy L., "Dissecting The Energy Needs Of The Body", Current Opinion In Clinical Nutrition And Metabolic Care, 4(2):143-147, 2001.
-Pratley R, et al, "Strength Training Increases Resting Metabolic Rate And Norepinephrine Levels In Healthy 50- To 65-yr-old Men", J. Appl Physiol., 79(3):818-23, 1995.
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