When you target a muscle group during weight training, you're priming those muscles to grow by tearing down muscle fibers. The rest period between training sessions gives your muscles a chance to heal and grow. If you train a specific muscle group too often, you compromise your body's natural response to weight training. Although individuals respond to exercise differently, training a muscle group once a week is generally sufficient.
You need to rest a muscle group at least 24 to 48 hours before training it again. However, this doesn't necessarily mean that training a muscle group every two to three days is the best way to gain mass. Muscles recover and grow during rest, and larger muscles, such as those in your chest, take more time to recover than smaller muscles, such as your triceps and biceps. If you work a muscle group too often, you risk losing muscle tissue and strength.
Targeting each muscle group once a week ensures that your muscles have time to recover and repair before you train them again. When you give your muscles adequate rest between training sessions, you improve their capacity to handle weight increases, which is essential to adding muscle mass. Overtraining depletes glycogen stores, which hinders your muscles' ability to work at full capacity. Training fatigued muscles may also compromise your form, increasing your risk of injury.
Muscles in your arms and shoulders tend to get worked more often, since you engage these muscles during isolated movements as well as when you target muscles in your chest and back. Schedule your training to avoid engaging a muscle group in both primary and secondary work on the same day. Target the hamstrings, trunk flexion and calves together; your upper back and triceps together; your quads, calves and abs together; and your chest and biceps together, taking the third, sixth and seventh day off.
Signs of Overtraining
Hitting the weights too often can interfere with your goal to gain muscle mass and may even compromise your health. Symptoms of overtraining include elevated blood pressure, constant muscle fatigue, decreased immunity, injury, restlessness and loss of appetite. General fatigue, irritability and moodiness are also potential indicators that you're overdoing your training. Evaluate your schedule to ensure that you're not working the same muscle group on back-to-back days, make rest days a priority and cut back on your sets if you experience any of these symptoms.