Energy balance

Sustained high levels of physical activity expenditure trigger compensatory metabolic adaptations that decrease resting metabolic rate (RMR), thereby constraining total energy expenditure and facilitating long-term weight loss maintenance.

If you are maintaining significant weight loss through high levels of exercise, expect your resting metabolism to drop as a compensatory mechanism. This is not a sign that your exercise is ineffective; rather, it is a physiological adaptation that helps you keep the weight off. Do not interpret a plateau in weight loss despite high activity as a failure of your regimen, but as evidence of metabolic adaptation constraining total energy expenditure.