Because they’re working at such a high intensity, bodybuilders (and anyone who does a large amount of resistance training) often have a significantly altered metabolic rate after exercise. “It can take hours for the muscle cells to return to their normal state, and during that time the body uses a higher percentage of fat as fuel,” explains Len Kravitz, Ph.D., coordinator of exercise science at the University of New Mexico. Because bodybuilders work out so often, this enhanced fat-burning effect becomes cumulative.
However, adds Kravitz, these metabolic changes take a significant amount of time—up to five days a week of hard training in the weight room. That’s why the rest of us, who may complete only a moderate strength-training program two or three days a week, still need to do three or four aerobic workouts to burn fat and get lean.