I addressed much of this in a previous; click on the above link to see it.
Below is some of the information that was in it the pertains to you.
Control The Descent
You control (practice) the Descent in approximately the first 3/4 of the movement as Chad stated, as you will with your heavy load of at or near your 1 Repetition Max.
As the saying goes, “Practice doesn’t make perfect. Only Perfect Practice Make Perfect.”
Recoiling Out of The Hole
Learning where to recoil out of the hole is a timing issue that take practice.
You need to learn where to allow the the bar speed in the descent to accelerate and where to stop the recoil and apply concentric force to drive the weight back up.
The Concentric Part of The Squat
In the Concentric Part of The Squat (any movement), you need to drive the weight up as hard and fast as you can, no matter the load.
This has to do with…
CAT, Compensatory Acceleration
This term was categorized by Dr Fred Hatfield, “Dr Squat”, who at one time was the lightest man to Squat over 1,000 at a body weight of 252 lbs.
CAT means driving the weight as fast as you can. What this does is innervate more of the Fast Twitch Type IIa and the “Super” Fast Type IIb/x Muscle Fiber
CAT allso educates the Central Nervous System to quickly engage/recruit more of the Fast Twitch Muscle Fiber.
Think of rate coding/muscle fiber as being able to add more guy to your “Tug of War Rope” pull than the other team has.
Compensatory Acceleration needs to be use with light, moderate and heavy loads.
Optimizing CAT, Compensatory Acceleration
One of the keys in the development of the Fast Twitch Muscle Fiber is…
Band and/or Chains: The load at the top of a Squat is lighter than in the hole. By adding Bands and/or Chains (Accommodating Resistance) it enables you to engage more of the Fast Twitch Muscle Fiber at the top of the Squat.
Going Ballistic: Another method when using a lighter load is to drive up so fast with the weight that you jump with the weight or your feet come slightly off the ground. This ensure you have fully engaged the Fast Twitch Muscle Fiber at the top part of the Squat.