A muscle must be subjected to a stimulus that compels it to adapt and grow. If there is no reason for a muscle to grow, no hypertrophy will occur. Muscles increase their strength and size when they are forced to contract at levels close to their maximum. Much more weight can be lifted with compound exercises than isolation movements. More weight, more overload and in turn more muscle. A compound exercise is a movement that involves more than one major muscle group. It involves a primary muscle and one or more secondary muscles.
