muscle, it turns out, makes a fairly small contribution to RMR.
"Brain function makes up close to 20% of RMR," he said. "Next is the heart, which is beating all the time and accounts for another 15-20%. The liver, which also functions at rest, contributes another 15-20%. Then you have the kidneys and lungs and other tissues, so what remains is muscle, contributing only 20-25% of total resting metabolism."
So, if you slave at weightlifting and increase your muscle mass by an ambitious 20%, this translates into only a 4% to 5% increase in RMR. Since a 200-pound man has an RMR of roughly 2,000 calories, a 20% increase in muscle mass equals only an 80- to 100-calorie increase.