It’s not uncommon to hear or read claims that, “if you gain one pound of muscle you will burn about 50 extra calories per day.” If only it were that easy...
In fact, the resting metabolic rate of skeletal muscle is frequently confused with the resting metabolic rate of the lean body mass as a whole. Lean body mass however includes all our organs (liver, brain, heart, and kidneys) which burn 15 to 33 times more calories by weight than skeletal muscle.
Here’s a more detailed look at the data: [Enlarge Chart]
Elia M: Organ and Tissue Metabolism: Tissue Determinants and Cellular Corollaries. New York, NY: Raven Press, Ltd.; 1992:61-77.
So back to the weight training. Skeletal muscle, which is what is increased with weight training, is the least metabolically active component of lean body mass. Further, the average exerciser doesn’t actually add much lean body mass, but let’s assume for example that they did gain 2 kilograms (4.5 pounds) of skeletal muscle over a few months. Let’s also assume that they lost 4.5-pounds of fat, and their actual weight stayed the same. The net change in their resting metabolic rate would be 17 calories a day, which is equivalent to one teaspoon of sugar!
Here's the math (numbers from white area of above Body Tissue chart):
2kg (13 – 4.5) = 17 calories/day
- Skeletal muscle metabolic rate = 13 calories/kg,
- Adipose tissue metabolic rate = 4.5 calories/kg
So the fact is, that strength training doesn’t turn anyone into a calorie burning machine, as is commonly claimed. According to Dr. Robert Ross, clinical assistant professor of medicine at Baylor College of Medicine and co-author of the exercise science text, Understanding Exercise for Health and Fitness, “you would have to double your skeletal muscle to increase your resting metabolic rate by 20%." The reference male in the Body Tissues chart above would have to add 12.3-pounds of skeletal muscle (a 20% increase) to increase his resting metabolic rate by 67-calories a day. The amount in an Oreo!
The tissue metabolism rates in this article, from Elia, have been validated in numerous studies by several metabolic labs in the U.S. and United Kingdom.
Best!
-Dorene
For more on this topic see Metabolism: Facts & Fiction, which is from my Healthy Eating & Weight Management Guide workbook).
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