DG,
I agree that some of what Dave Philips says makes no sense.
So, I cannot understand why bigger grips will increase the amount of force/torque being applied to the club handle. Also, I cannot understand how his larger mass means that he doesn't have to move his weight as much and how that contributes to a greater clubhead speed.
However, I can understand how jumbo grips are helpful. they force BD to use a high palmar grip, and not a finger grip, and that decreases left wrist joint mobility and therefore potential "wobble".
Here is my explanation of how BD uses "end-range" to become more consistent.
First, watch this video.
Then, watch this video.
Here is my explanation using these capture images.
Image 1 is at address. Note that he markedly internally rotates his left humerus and fully supinates his left forearm to its end-range. The end-range of left forearm supination is much reduced when the left humerus is both fully straight and internally rotated.
Image 2 is at P4. He uses an one-piece takeaway and delays any left forearm pronation to later than P3.5. Also, he uses less pronation than normal. That is possible because i) his left shoulder socket is very protracted at P4, ii) his left humerus is very internally rotated and ii) he is capable of a large amount of shoulder (upper torso) rotation.
Image 3 is at P5.5. BD adducts his right upper arm superfast and retains his 90 degree right elbow angle bend that allows him to maintain clubhead lag very well.
Image 4 is at P6.7. He has a small accumulator #3 angle (like Phil Mickelson), which means that he is delaying his PA#3 release action.
Image 5 is at impact. Note how much he has rotated the back of his lead hand showing that he performed a PA#3 release action between P6.7 => P7.
Image 6 is at P7.2. Note that he is a DHer, and not a roller like Phil Mickelson - despite having a small accumulator #3 angle at impact.
Why is he not a roller if he has a small accumulator #3 angle at impact?
There are many factors in play.
First of all, at impact his left humerus is internally rotated and his left forearm is at its end-range of supination (which means that it is less likely to continue to supinate as seen in PM's roller release action). Secondly, he does not "run-out-of-right arm" which can predispose to pronation of the trail forearm. Instead, he keeps his trail forearm supinated and he also uses a clockwise circumductory roll motion of his trail wrist to keep his trail hand partially under the club handle at impact, which helps him to avoid rolling his right palm over his left palm. Thirdly, he likely has a negative hand couple torque scenario at impact, which can help stabilise his lead wrist and prevent flipping or rolling. Fourthly, he does not rapidly externally rotate his left humerus between P7 => P7.2 and he uses a no-roll DH-hand release action technique where he rotates his upper torso counterclockwise and keeps the impact triangle intact.
Watch the video to note that he starts to bend his left arm and externally rotate his left humerus between P8 => P9 and that allows him to get much more left forearm supination. That shows that the end-range of left forearm supination depends on whether the left arm is bent or straight and also dependent on whether the left humerus is internally rotated or externally rotated. The combination of a straight left arm + internally rotated left humerus decreases the end-range limit of left forearm supination, which helps him to be a more efficient DHer between P7 => P7.2.
In terms of his increased swing power, I think that the following factors are in play.
1) His increased muscle strength allows him to rotate much faster in the backswing and induce a stretch-shorten cycle of his shoulder girdle muscles, abdominal muscles an dhis right-sided lateral pelvic rotator muscles.
2) He has very strong lats, which allow him to adduct his right upper arm very fast between P4 > P5.5, and that allows him to maintain clubhead lag to P5.5+.
3) His increased core muscle strength increases his counterclockwise speed of pelvic and upper torso rotation, which combined with number 2) allows him to release PA#4 faster and more efficiently.
Jeff.