The determinate factor in how quickly to lower the weight in the Squat is dependent of the load in regard to your 1 Repetition Squat Max.
The Lighter the load in regard to your 1 Repetition Max, the faster you can lower the weight.
However, as the load in regard to your 1 Repetition Max increases, the Descent Squat Speeds need to slow down. That based on research by Dr Tom McLaughlin (PhD Exercise Biomechanics/Former Powerlifter) as well as the empirical data.
Here’s what McLaughlin research found…
Novice/Intermediate Lifter’s Descent Bar Speed
Novice/Intermediate Lifter tended to lower the bar quickly. McLaughlin’s finding was that in doing so the bar weight was magnified by 147%.
This has to do with Newton’s Second Law: Force = Mass X Acceleration.
300 lb Squat Example
Novice/Intermediate Lifter who allowed the bar to drop too fast would have magnified the bar load from 300 lbs to 441 lbs.
Now let look at at the…
Elite Lifter’s Descent Bar Speed
Elite Lifter were tended to ride the brake at the beginning of the Descent.
Doing so only magnified the bar weight 112%.
300 lb Elite Squat Example
That meant that the Elite Lifter would only magnify the bar weight from 300 lbs to 336 lbs; a much more manageable load vs the 441 lb load for the Novice/Intermediate Lifters.
However, there needs to be some Descent Speed/Acceleration in the Squat to evoke the Stretch Reflex to “Sling Shot” you out of the hole.
With that in mind, here is the rest of McLaughlin’s research on how to…
Minimize The Reversal Force and Evoke The Stretch Reflex
Initially “Ride The Brakes” during the first part of a near 1 Repetition Max Load. Doing so, decreases the Acceleration/Speed which decreases the Force/Bar weight.
Once you are a couple of inches from the hole, allow the Decent Speed to Accelerate. The purpose of this is to provide enough tension to elicit the Stretch Reflex.
As per McLaughlin…
The last word on squats
Men’s Fitness, Sept, 1998 by Jeff O’Connell
“You want to lower the weight slowly, even during the first six inches of the descent,” says McLaughlin. “Too many lifters start the squat very quickly and think they’ll slow down halfway, but the momentum of the bar increases very quickly, and they end up effectively lifting more than the actual weight. The top lifters have velocity and acceleration patterns that are uniquely geared this way compared to beginners and intermediates.”
“You want a slight recoil - enough that the change in direction utilizes some of the energy transfer in your body.”
Chad Wesley Smith
Chad states the same in his training video at the 3:40 minute mark in his video.
“…Be slower, more controlled in the top three quarters of the Squat. …Then accelerate into the bottom of the Squat…”
Shane Hamman’s Dive Bomb Squat
Hamman is The Exception To The Rule". Hamman’s method isn’t going to work for the majority of lifters.