Dr Mann
Here is what I've found from the available evidence based on forward dynamic models and Mark Bull 3D system. I will ask Dr Phil Cheetham and Michael Neff whether they have any typical graphs showing the internal/external rotation of lead upper arm in pro-golfers.
Forward Dynamic ModelsSome graphs showing Dr Sasho MacKenzie golf models .
SMK's 1st Golf ModelIf you look at SMK's 1st model, he only allowed rotation of the whole lead arm and no independent rotation of the forearm.
Here is the graph of the optimal swing using his model.
You can see that the arm actually displaced in the internal rotation direction from P4-P5 (ie. went below the zero line) and shallowed the club shaft, probably due to gravity.
The actual torque applied by the upper arm is shown in the graph below (the bolder dashed line M_Arm) and it seems to be positive external rotation torque starting at P5.
To summarise:
1. P4-P5 :The golfer model is shallowing the club (probably by the effect of gravity on the club's COM) , therefore the lead arm is internally rotating.
2. P5-P5.5 :SMK's model does externally rotates about 15 degrees.
3. P5.5-P7 :SMK's model shows a rapid increase in the rate of lead arm external rotation from 15 degrees to 70 degrees.
SMK - 2nd Golfer ModelHere is SMK's 2nd model whose lead upper arm has no ability to externally/internally rotate but does allow forearm supination/pronation.
Look at the SIM3 /SIM5 forearm angle and club COM displacement graph's 'a' and 'b' (ie. the bolded line)
To summarise:
P4-P5: There is a slight amount of forearm pronation which is caused by gravity pulling down on the COM of the club. Quoting from the article : "The forearm angle showed a small decrease during the first half of the downswing due to gravity pulling the club below the swing plane".
P5-P6.5 : There is a gradual supination of the forearm.
P6.5-P7: There is a rapid supination of the forearm.
So if we looked at the 2 models , there seems to be 2 ways to square the clubface by impact. One just using the upper arm while the other just the forearm.
The only other graph I've seen regarding lead internal/external rotation of the upper arm is this one posted on Mark Bull's website .
--------------------------------------------------------------
Copied from Mark Bull's website:
www.bull3dacademy.com/post/shoulder-rotation-what-is-it-reallyLead shoulder
(These patterns and descriptions are for healthy, functioning joint however there are multiple different patterns and values achieved, however it is unusual to see a player achieve a different orientation of the shoulder throughout swing.)
Lead shoulder up/down – elevation of the humerus relative to the forward/backward bend of the ribcage.
Lead shoulder abduction/adduction – the horizontal movement of the humerus across and away from the ribcage relative to ribcage rotation.
Lead shoulder external/internal rotation - the external and internal rotation of the humerus relative to the rotation of the ribcage.
Throughout the backswing, relative to the movement of the ribcage the lead shoulder primarily moves through three patterns, internal rotation, adduction and elevation (this is not the shoulder moving up, it’s the humerus/upper arm bone moving up relative to its start position against the ribcage). Therefore at top of backswing the humerus is internally rotated, adducted and elevated relative to the orientation of the ribcage. Observed ranges the shoulder moves through during the backswing and the values observed across healthy, functioning joint are:
Internal rotation from address to top ~ 35°
Adduction from address to top ~ 40°
Humeral elevation from address to top ~ 35°
Typical in very powerful players the lead shoulder further adducts as the ribcage rotates clockwise at the start of downswing, with the shoulder also externally rotating and moving down where on impact, it is not unusual to observe the lead shoulder values on impact to be:
External rotation from top to impact ~ 30°
Abduction from top to impact ~ 25°
Humeral depression from top to impact ~ 30°
Post impact to finish, this is where the shoulder starts to display the highest rotational value with it moving into significant levels of external rotation, abduction and elevation, ranges achieved can be:
External rotation from impact to finish ~ 60°
Abduction from impact to finish ~ 45°
Humeral elevation from impact to finish ~ 30°
Therefore the shoulder moves through a very defined 4 dimensional pattern (3 orientations over time).
--------------------------------------------------------
From the available evidence I found, it showed 30 degrees of upper arm external rotation from P4-P7. But the net effect of the internal and external rotation of the upper arm from P1-P7 show a slightly larger amount of internal rotation than at address.
DG