In older adults who exercise regularly, the extent to which their resting metabolic rate changes during periods of lower energy intake is closely related to how much their body's beta-adrenergic signaling contributes to that change.

In older adults who exercise regularly, the contribution of beta-adrenergic receptors to resting energy use is detectable when energy expenditure is high but disappears when energy expenditure is lowered, suggesting that higher energy flux maintains this physiological mechanism.

Regular physical activity that keeps energy use high may help maintain a higher resting metabolic rate and lower the risk of losing metabolic function and gaining weight as people age.

In older adults who regularly exercise, lowering both physical activity and food intake reduces the number of calories burned at rest and decreases nerve activity in skeletal muscle, indicating that higher energy use is linked to a higher resting metabolic rate.

In trained men, resting metabolic rate increases only when both physical activity and food intake are high and balanced, not when calorie intake is higher or lower than expenditure alone.

In people who train regularly, a higher resting metabolic rate is not due to long-term changes from exercise, but rather to temporary increases in energy use during and after intense activity. When those high-energy conditions are removed, the metabolic rate difference between trained and untrained individuals disappears.