I think that Sasho MacKenzie got many facts wrong in his discussion with Andrew Rice and here are some examples of why I believe that some of his opinions are wrongheaded.
At the 13:00 minute time point of the video, Sasho implied that he could generate greater clubhead speed at impact by creating a greater degree of torso-pelvic separation (= dynamic X-factor) at the transition - by starting the counterclockwise pelvic rotation while the club is still moving back to its final end-backswing position. Jim McLean first promoted this dynamic X-factor ideology and he wrote an entire book on the subject of the "X factor", but there is no definitive scientific evidence that proves that a golfer will generate a greater clubhead speed at impact if he produces a stretch-shorten cycle of his core abdominal muscles using this dynamic X-factor approach. Although many pro golfers (eg, Bubba Watson) use this dynamic X-factor approach, many pro golfers (eg. Hideki Matsuyama and Rory McIlroy) do not use this approach and there is no evidence that they are therefore handicapped by a slower clubhead speed at impact.
At the 13:30 minute time point of the video, Sasho stated that he likes the idea of turning the upper torso into (against) the proximal part of the lead arm in order to stretch the left shoulder girdle muscles. However, there is no scientific evidence that a small increase in the degree of stretch of those left shoulder girdle muscles will increase clubhead speed at impact. Swing power due to the release of the left arm (called the release of PA#4 in TGM terms) mainly happens between P4 and P5.5, and the left arm mainly moves downwards in the plane of left arm elevation => left arm lowering during that time period, and it is not moving very much away from the upper torso in the plane of left arm adduction => abduction (which mainly happens between P5.5 and impact). Therefore, there is no reason to believe that stretching those left shoulder girdle muscles will increase the speed of release of PA#4 between P4 and P5.5.
At the 13:38 minute time point of the video, Sasho stated that he also wanted to stretch the external rotator muscles of the right humerus in the right shoulder socket at the end of the backswing, but he did not explain how this could increase clubhead speed. It is theoretically possible (but not yet scientifically proven) that an active right arm adduction maneuver between P4 and P5.5 can synergistically help to increase the speed of release of PA#4 (release of the left arm), but the speed of right arm adduction is not dependent on stretching muscles that externally rotate the right humerus in the right shoulder socket.
At the 14:08 minute time point of the video, Sasho states that he also wants to stretch the left wrist muscles by creating a greater degree of left wrist upcocking in the later backswing (or during the early downswing via the phenomenon of "float loading"). However, although there is scientific evidence demonstrating that having a greater degree of left wrist upcocking can increase clubhead speed by impact, it is not based on the stretch of the left wrist muscles that can cause left wrist ulnar deviation. It is simply based on the increased degree of clubhead lag that can be obtained by float loading the left wrist during the transition.
Between the 20:26 minute time point and the 21:17 time point of the video, Sasho claims that the average tour player has 20 degrees of left wrist extension at P4 and that he then massively flexes the left wrist during the first 95% of the downswing before finally moving the left wrist from flexion in the direction of left wrist extension during the last 5% of the downswing's time period. Sasho even irrationally claims that the biomechanical phenomenon of the left wrist moving from being flexed at P6 to becoming less flexed at impact would hugely increase clubhead speed at impact, and he seemingly also believes that the left wrist must be significantly extending very soon after impact (between P7 and P7.2) to "allow energy to get out from the arm to the club" - see Sasho demonstrating left wrist breakdown at the 21:21 minute time point of the video. I think that Sasho is totally wrong about all these points.
First of all, consider Sasho's claim that all pro golfers are significantly flexing their left wrist during the first 95% of the downswing.
Here is a graph from Phil Cheetham's study of 92 tour pro golfers.
The green graph represents the left wrist extension-flexion graph of the "average" pro golfer. Note that the left wrist is extended about 10-15 degrees at P4 ("top") and that it actually becomes increasingly extended during the early downswing before moving significantly in the direction of flexion during the later downswing before reaching its greatest degree of flexion just before impact. Note that the left wrist graph shows that it is slightly less flexed soon after impact, which means that it is moving in the direction of extension - but it is not frankly extended soon after impact. An example of a pro golfer who manifests this left wrist motional pattern is Ben Hogan.
Here is an animated gif showing Ben Hogan's left wrist behaviour as he transitions between the mid-downswing to his late downswing between P5.5 => P6.2.
Note how cupped (extended) Hogan's left wrist is at P5.5 and note how he significantly flexes his left wrist between P5.5 and P6.2. In other words, Ben Hogan is doing the exact opposite of what Sasho claims should happen when he states that pro golfers are significantly flexing their lead wrist during the early-mid downswing time period and then moving towards left wrist extension in the later downswing.
At the 22:03 minute time point of the video, Sasho demonstrates the "reverse motorcyle move" and he asserts that it promotes increased clubhead speed at impact because a golfer does not have to "down-regulate" during the later downswing in order to get a square clubface by impact. I think that his explanation is totally invalid! First of all, I agree that it is perfectly acceptable to use the "reverse motorcyle move" during the early-mid downswing time period, but there is no scientific evidence that it will decrease the amount of left forearm supination required in the later downswing in order to square the clubface by impact (and which is called the release of PA#3 in TGM terminology) and there is no scientific evidence that it will enable a pro golfer to swing the club faster. The majority of pro golfers do not use the "reverse motorcyle move" and they are not subsequently hampered from a swing power generation perspective, or from a clubface-squaring perspective, as a result of not using the "reverse motorcycle move". I discussed the controversial issue of the "reverse motorcyle move" in great detail in topic number 1 of the following review paper at
www.perfectgolfswingreview.net/TylerReview.html and I featured many pro golfers who do not use the "reverse motorcyle move".
Andrew and Sasho also discussed the issue of the rate-of-closure (ROC) of the clubface through impact. Sasho correctly stated that there is no scientific proof that a pro golfer who has a high ROC of his clubface through impact will hit the ball less straight than another pro golfer who has a low ROC of his clubface through impact - because of the confounding factor of talent (hand-eye coordination skills) that will enable a pro golfer, who uses a high ROC through impact (like Phil Mickelson), to still hit the ball straight. However, Sasho then asserted that an amateur golfer, who does not play regularly, could benefit by adopting a golf swing technque that promotes a low ROC through impact. As an example of a low ROC technique, Sasho refers to the "reverse motorcyle move". However, there is no evidence that using a "reverse motorcyle move" will decrease the clubface's ROC through impact - considering the "fact" that the clubface-closing effect of the "reverse motorcyle move" (which is is due to a finger-torquing action secondary to the isotonic contraction of the left forearm's flexor digitorum profundus muscles to the left hand's 3rd, 4th and 5th fingers) automatically/naturally dissipates in the later downswing between P6.5 and impact, and there is no evidence that the golfer (who uses the "reverse motorcyle move") uses less left forearm supinatory motion during their release of PA#3. Most importantly, Sasho never even discusses the difference between a drive-hold (DH) and a non-DH hand release action through impact, which will likely have a much greater effect on a golfer's clubface ROC through impact than golf swing techniques used to vary the amount of left forearm supination happening during a PA#3 release action (which is a pre-impact phenomenon).
At the 38:37 - 38:45 minute time point of the video, Sasho states that the average tour pro has to close the clubface by 70 -110 degrees between P6 and impact, and he then asserts that it would probably be better to use body rotation to help close the clubface (thereby implying that it will enable the golfer to use less left forearm supination in the later downswing). That claim is totally wrong! Having more body rotation between P6 and impact, so that the golfer comes into impact with a more open pelvis/upper torso, will not decrease the amount of left forearm supination required during a PA#3 release action (which is inversely proportional to left hand grip strength). I demonstrated that "fact" in the following you-tube video (
www.youtube.com/watch?v=2izM_uLPmYY&t=1814s ) between the 30:22 minute - 34:20 minute time point of the video.
Jeff.