Aerobic exercise involves the cardiovascular system of heart and lungs to a greater extent then does anaerobic exercise. The type of activity, heart rate level, and time spent doing the exercise non-stop determines whether it is aerobic or anaerobic . Your body supplies your muscles with energy in overlapping phases. It depletes your short duration anaerobic energy while phasing in your long term aerobic energy. Muscle building is a short duration activity.
Muscle building is anaerobic.
The total workout takes a long time because of the starts and stops between sets . It has little benefit on your heart and lungs. Walking, on the other hand, is aerobic. The workout may take less time than muscle building, but it is non-stop and has a major benefit on your heart and lungs. The physics of Form and Function cause your body to adapt to the type of exercising you do.