The hip shift is where we should generate the power in our swing. I think of the legs and hips as the engine of the golf swing and the arms and hands as the transmission system. OK, additional power is applied through the arms and hands but without the drive from the lower body it would not allow us to hit long.
I don't go along entirely with this guys interpretation though, I prefer to think of the hips carrying out a composite movement where the legs push to the left, this starts the hips in a powerful composite movement where they both slide and rotate to the left as the left hip also raises, this pulls the arms and right shoulder into action.
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