Overtraining is characterized by persistent soreness or stiffness, a rise in the resting heart rate, fatigue, lack of motivation, irritability or depression. If these symptoms are ignored, an injury will eventually force you to rest, and much longer time will be needed than if you were already scheduling recovery time. It is important to cooperate with your body's cycles of work and recovery. The anaerobic or peripheral system is the muscles. Strenuous exercise tears down the muscles on a microscopic level, placing stress on muscles, tendons and connective tissue.
Proper rest builds up the muscle stronger than before the workout.
Each muscle group needs 24-48 hours of rest in between workouts, to recover, repair, and rebuild muscle tissues, replace energy stores and remove exercise waste products. If you train the whole body with weights in one session, you can workout three times a week with at least one day of rest in between sessions. Some more advanced exercisers train more often, but they alternate the muscle groups they work, such as the upper body one day and the lower body the next. The aerobic system is the central system composed of the heart, lungs and blood vessels. This system recovers fairly fast in a conditioned person.