Lead knee movement in downswing

[RussUK]

I played a couple of rounds last week and my ball striking with my irons was a little up and down. Some of it is mental as at the range its fine but i hit the course and it can get a lttle hairy.

As im thinning the ball at times im thinking i may be unconciously straightening my left leg too soon. I was watching the masters to see what the pros did and noticed Tiger seems to have his left knee pretty flexed at impact (giving a sort of squatting look), so my question is when should the knee straighten/begin to straighten, before, at or after impact?

Lee Westwood says he likes to start the downswing by moving his left knee away from the right which makes sense but when to extend the leg?

Thanks all

p.s. pretty annoyed about the masters, forgot ot put my bet on Jordan

[mvmac]

Lee Westwood says he likes to start the downswing by moving his left knee away from the right which makes sense but when to extend the leg?

Have you seen this video, should help with your question.