because you have to be within a certain bpm band which maximises fat burning....this is roughly 130bpm or a fast walking/ slow jog pace on a treadmill. If you run you'll be working cardio ie: lungs and fitness. It will still burn fat but not as much.

Weight training will still burn fat but if not done right your body will burn muscle too or become catabolic.....a fine balance of diet and exercise will burn fat AND build muscle