When you think of the difference between fast twitch vs. Slow Twitch, I want you think of runners:
Marathon runners are predominantly slow twitch. They have many mitochondria which allow for them to not get tired and sustain over a long people of time. Look at the marathon runner. This is by no means meant to be disrespectful to marathoners, but they do not have a lot of muscle mass and their bodyfat tends to be on the higher side.
Sprinters are predominantly fast twitch. Fast twitch fibers are strong, fast and explosive. They tend to tire quickly and also tend to get hurt more easily than slow twitch due to the explosive manner in which they function. Sprinters are usually lean, muscular and look athletic. When is the last time you saw more than a handful of marathon runners looking like Ben Johnson or Carl Lewis? Not many times I can remember.
What I am saying is you want to have more TypeII fibers because they are strong, explosive, large and fast. You can go down on the rep slower if you want because it will increase time under tension....which I think is a little overrated in my opinion....but I digress. When you do the concentric (Positive portion of a lift), make sure to explode up in everything. Remember, Force=mass x acceleration. The body doesn't know that you are using 135lbs for it to adapt. It only knows the force that you are putting behind it...so explode the reps to work the TypeII(fast twitch) fibers.
Does that make sense?