By focusing on opposing muscles in different exercises, the non-working muscle has an opportunity to rest while the working one is performing all the work. This is beneficial because the intensity of your workouts is easily increased with increasing the time you spend building muscles at the gym.XL Test Plus Use as many repetitions as possible when training. Do at least 15 repetitions of each exercise, and do not take a long break between sets. By doing this, you are letting your lactic acids flow, which in turn, helps muscle growth. You can grow your muscles tremendously by following this advice.