In addition to bumping up the metabolism by adding pounds of new muscle, we missed three ways to get even leaner with weight training.
Expenditure. Obviously, building that muscle mass required some type of hard physical effort. That is, training with weights to stimulate the body to develop those fresh 10 pounds of muscle mass requires energy. Assuming the individual did not radically alter his caloric intake during the time it took to build the muscle, it is prudent to say many of the calories required to do the physical work came from two places; fat stores or food.Obviously, had some of these calories come from fat stores, body fat levels would have decreased. And, if some of the fuel came from the foods he ate, this leaves “less net calories” available to be stored as body fat. In other words, he either burned some body fat as fuel or he burned much of his food intake which leaves less fuel available for the body to make body fat.
Recovery. Weight training is very different than aerobic training in its need for fuel to recover. When an individual trains with weights, the stress placed upon the muscles causes tiny micro-tears within the individual muscle fibers. Energy (calories) is required to mend these damaged fibers. Put another way, it “costs” the body energy to repair itself. Building back broken down fibers requires energy even at rest! This means the individual who leaves the gym after having engaged in a hard weight training session will continue to experience an elevated metabolism until those fibers are completely repaired. He’s literally burning calories outside of the gym to repair his muscles. Aerobic exercise does not cause this effect. Once the aerobic session is completed, net calorie burn returns to zero. In other words, an aerobic session will only burn calories during the exercise. Never after. The metabolic edge of the individual training with weights; he burns fuel during and after each workout session.
Glucose Metabolism. Adding muscle to your frame changes the metabolism of sugar which impacts body fat levels. Recall, there are receptors for insulin on both muscle and fat cells and these receptors act in a see-saw fashion. If the receptors on muscle tissue are more sensitive, they tend to dominate over those located on fat cells. Adding muscle makes muscle cells more insulin sensitive which translates into a decrease in insulin output by the pancreas. When insulin levels are on the lower side, as opposed to chronically elevated, the body is more apt to burn fat as fuel and to store glucose from carbohydrate foods as muscle glycogen. When glucose is being deposited as muscle glycogen, it is less likely to effect fat storage.