Your muscles have a dual role.
Muscle cells, like any other cells of the body (liver, kidneys, skin, etc.), require energy to perform their normal function at rest; that is to say, the energy expenditure used outside of physical exertion. This is what is referred to as our Resting Metabolic Rate (RMR).
In contrast to other cells that only have to generate enough energy to maintain normal cellular processes, muscle cells have the additional chore of providing enough energy for force generation and movement – from lifting a barbell to doing cartwheels. For the average size man and woman, RMR accounts for the use of about 1,400 to 1,600 calories a day, constituting 60% to 75% of their total daily energy expenditure.i
The effect of lean muscle on RMR.
RMR has several major metabolic origins, but it is our lean body mass - our skeletal muscles (legs, arms and torso muscles) – from which researchers tell us RMR primarily originates. Therefore our resting metabolic rate is highly correlated to the amount of muscle we possess; men, in general having a greater lean body mass, have a higher RMR than women. So the more lean muscle you can maintain, especially as you age, the greater your potential for using more of those food calories you consume daily.
Keep strength training!
This all points back to the value of proper strength training, as there’s no better way to retain or reclaim your lean body mass (muscle) and avoid metabolic slowdown that inevitably leads to more fat and less muscle over time. And that’s the truth.
iFourth edition, Geriatric Nutrition, Ronni Churnoff