What is Eccentric Loading? by B Pak

In order to lift a weight, muscular force muscle exceed the downward force of the load. The opposite occurs when you lower a weight - motor units are turned off until the downward force of the load is greater than the muscular force acting upon it. With less motor units active, greater tension and more damage occurs to the remaining muscle fibers, to promote hypertrophy.

What's the take away? To grow, you'll have superior gains when exposing your muscles to loads greater than 85% your 1RM via eccentric enhanced exercises in your workouts front time to time. This will activate Type II fibers to "initiate" muscle growth.