How do you build muscles instead of gaining fat?

Work muscles harder: If muscles are used repeatedly until they tire, but are not injured, then they will grow bigger and stronger! if one does not eat or drink more calories than he uses during exercise, then his body will burn up fat for fuel. However, if he drinks a big orange juice (about 300 calories) while exercising, and exercises away only 200 calories, he will still get fatter even though he is exercising.

Muscle building: Lifting weights builds muscle. Doing cardio burns fat. Building muscle can increase your weight, burning off fat will decrease your weight.