Trail Arm Pronation

+Tyler F
Thanks Tyler, this is an extremely helpful and well illustrated explanation.

+Ed C Sorry for the delay, this week we went back to work :)

1 - How much it compares at set up varies a lot. It's dependent on grip and release pattern. As a general rule, both arms are about 30 degrees more pronated at impact than it was at set up, but remember, the amount of pronation/supination depends on the shoulder position...so this might not the best marker for comparing numbers.
2 - I think the timing difference is natural given the different shoulder movements that take place in the downswing. But yes, the difference in the arm movements does contribute to the club moving a bit in the hands.

+Seb J Good observation. I definitely prefer to see the inside of the forearm longer through impact. When I see the back of the elbow show up quickly, we usually have to fight pulls and pull hooks.

Here's a graph of Grant Waite's trail arm. You'll see in transition that the blue line is decreasing during the first part of transition. When the blue line is moving negative, the arm is pronating. So there is some truth to the idea of starting the downswing pattern with pronation. Now' you'll see that the motion actually starts prior to the change of direction of the club. Here's a video of his swing to show the timing of when the pronation is happening. You'll see that it's a subtle amount of movement, so I'd be careful not to go too crazy with it. It has to be off-set by shoulder external rotation and scapular depression so that it doesn't actually steepen the shaft.

I have a couple of videos on the trail arm in transition.
https://www.golfsmartacademy.com/golf-instruction/throw-ball-in-transition/
https://www.golfsmartacademy.com/golf-instruction/open-trail-hand-full-swings/
https://www.golfsmartacademy.com/golf-instruction/connecting-lead-and-trail-arm-shallow/?list=jj,5499

The trail arm corkscrew builds through the downswing, but yes, it starts in transition.

happy Golfing,
Tyler