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The left knee move is more than a stable base, it is a critical part of why Hogan could create lag pressure the way he did.

Many of those that learned from Hogan speak of moving the left knee as a key start to the downswing. It is well worth trying if you are a swinger.

Edz,
You can try maintain flexion with your left knee although this won't work for people.
Hogan was able to maintain knee flexion was a reaction from being able to create normal and shear forces. The down swing acceleration the center of pressure shifts forward toward the front foot. It is this action creating forward momentum that facilitates the production of shear force at the feet/ground interface. Ground reaction to the shear force created by the feet produces a force couple, which is translated through the legs to the hips segment.This creates lower body stabilization and maintain left knee flexion.
The force couple acts on the hips segment to produce torque and rotary acceleration.

How hogan created Lag was a chain of events, in his initial downswing Hogan created separation between his lower body and upper body. This loaded his muscle group between his hips and upper body relationship. The stabilization of Hogans lower body allowed Hogan to fire his upper body with his muscles.His arms Lagged behind and his muscles in is upper body arms relationship loaded, As his upper body started to slow prior to impact, This again allowed hogan to fire the muscles (arm /upper body).His upper body would momentarily slow and square up to his hips at impact.The slowing of the upper body allow hogan to fire his arms. Hogan arms fired and they slowed down just prior to impact allowing hogan to release the club.
This is how hogan created Lag.
It's a little more complex than this although I hope this gives a general understanding.

Hogans secret was a chain of the events although his key to his golf swing was the ability to create ground forces.
With out ground force you can not maintain knee flexion like hogan did. A chain of events lead to how Hogan created Lag.

In golf people don't know how to create ground forces. Although even if they are aware of them it's not something you can physically apply on the practice fairway. You need to train your body the right movement patterns to create ground forces.
What is important is how you create the right moves to create ground forces.

Took years of research to work out how to train someone to achieve ground forces, research found the body has to be trained to achieve ground forces.