that's when training. But when at rest, the body uses mostly fat. Also during Aerobic activity, the body uses 75% fat and 25% muscle(protein) for energy. once it turns into anaerobic(lifting) your body uses only glycogen, be it from what you've eaten or stored). Your body used stored energy first but yes since you're lifting and it's anaerobic your body will need glucose so after all that is stored is used it will turn to using muscle. But that's only during the anaerobic activity.