WRONG: MAINTAIN KNEE FLEX
For many years now, much instruction has stated the opposite. Players have been encouraged and taught to maintain the same flex at address in the rear knee on the backswing under the guise that this would create more coil and allow you to hit the ball farther. Carefully posed pictures have been shown to demonstrate this, but what hasn’t been shown is images of the world’s best demonstrating these characteristics.
Why is that? Because that is not what the best players do or have ever done. There may be a select few, but instruction should be about the rule, not the exception. Theories are nice, but I prefer facts.
Here, is what is portrayed in those posed positions:
If the case for the flexed rear leg was tried in court. it would lose. There is ZERO evidence to support such teaching. It was grounded on the idea that by restricting the hip turn (through maintaining flex in the right leg), you would create more coil and thus produce more power.
This is one of the bromides in golf instruction that has made golfers worse and created a lot of business for orthopedics and chiropractors. Restricting the hips besides destroying your swing, has caused untold lower back and hip pain in millions of golfers. By learning to side-bend and extend correctly, you create more stretch and more hip and shoulder turn, thus more power and minimal to zero pain.
One point to note: the rear leg extends, that doesn’t mean it locks up. Leading orthopedics and chiropractors agree more hip turn creates less lower back issues. The only way you can achieve this is through the left knee flexing forward and the right knee/leg straightening.