it helps to isolate the muscles. But do not expect your benchpress or squat to go up 100 lbs. Isolation exercises do very little to increase your strength on compound exercises. For the compound exercises you need to make the muscles stronger AND learn how to use them together. Strength is attributed largely to the nervous system. If you ever look around, you will see some guys that are stronger that guys that have much more muscle mass. The small guys have trained their nervous system to recruit a larger % of motor units when lifting.
