It is important to include rest periods between sets when working out. Effective rest periods last from a few seconds to as much as five minutes.
Energy is stored in the muscles as creatine. Creatine is a type of phosphate that helps the body restore its levels of adenosine triphosphate (ATP). ATP is a molecule of energy within the cells of the muscle. It takes approximately three minutes for the body to build up its ATP after heavy exercise.
Athletes such as powerlifters and football players who train for the purpose of developing short bursts of strength with low repetitions usually need up to five minutes of rest between sets. Bodybuilders and other athletes who train for a muscular build are probably only going to need approximately one minute or less to rest up between sets.
When beginning a workout program for the first time or after being away from working out for an extended period of time, it is best to use some caution and take longer breaks between sets. Due to the risk of injury, it is counter-effective to begin a rigorous activity without first building up endurance.