It is true that what works for one may not work for somebody else. However, the mechanics used for a power player differ greatly from the mechanics deployed by a
typical stroker style. I am a stroker and have been for my entire bowling life, which spans over 50 years. I had the very good fortune to have taken lessons from many of the greats including Fred Borden, John Jowdy (now deceased), Bill Hall and others.
Each of these great teachers contributed enormously to my bowling knowledge and their keen eyes did wonders in helping me with my physical game. It is important to point
out that the physical movements needed to master today's style (power player) are
very different than what's necessary to excel as a "stroker". Unfortunately, many
well-intentioned, but very competent instructors make the mistake of trying to incorporate the movements of one style with the other, often with less than satisfactory results.
This leads me to make a few of my own comments about the "thumb down" issue.
The thumb down notion is indeed, intended to assist the bowler in rotating the
bowling shoulder as the swing reaches its highest point. It more easily allows the power player to get their bowling hand behind the ball while increasing the height
of the backswing. Combined, this allows the power player to project the ball left-
to-right (rt. hander). This, combined with exaggerated side (spine) tilt allows the ball
to get under the shoulder at release. In fact, it assists the ball in getting INSIDE the shoulder at the point of release. In this position, the ball is "most heaviest". This causes the bowling wrist to collapse under the increased ball "weight" at the bottom of the swing, which effects the high rev release that we see so often today. It's not muscle that creates the power release. In fact, "muscle" inhibits it if applied at the release point. Such are the mechanics of the modern power release. They differ greatly from the movements necessary in a stroker's game. By necessity.
For a stroker, trying to incorporate elements of the above can lead to all sorts of problems. For most strokers, rotating the bowling shoulder (opening it up) will
often lead to accuracy problems, among other things, unless the bowler is gifted
enough to be able to close the shoulder consistently, shot after shot. Pete Weber
is probably the very best at doing this. Most strokers cannot, even good ones.
The less the bowling shoulder opens, the better the results for them. So "thumb down", which in reality means getting the BACK of the non-bowling hand facing to the right at the top of the backswing, is not a good thing for them. Instead, they should concentrate on
keeping their palm facing the floor, and the (non) bowling arm either at their side or
EVER SO SLIGHTLY in front of their left shoulder at this point. "Squareness" will always rule the day with the stroker. By necessity.
Some will argue (and have), that "squareness" inhibits the stroker from projecting the ball from right to left. They are correct if they are comparing it with the power player's ability to "open up" the lane when needed. They can do it better, no doubt about it. But the stroker can come close and do it best by staying within his own physical game. They do this through a combination of equipment /speed changes, and most of all by realigning their bodies to "fit" the trajectory they are using-- all the time being sure to remain square in relation to their ball's intended path.
Aside from the thumb down, another factor that differs between the 2 styles is the amount of forward spine tilt that is deployed. The power player of today deploys much more forward tilt than most strokers use. Yet, many instructors are
now teaching "one -for-all" strategy when it comes to forward spine tilt, which is incorrect.
Again, it is important to say that by "stroker", this also defines a bowler
who stays on the side of the ball at release, more or less. A stroker with excessive
forward spine tilt at release dramatically raises the ball's rotational axis, often causing
the ball to excessively skid and not being able to effectively read the mid lane. By necessity, this group of bowlers fare much better with less (forward) spine tilt . This
gets their bowling hand in a better position to impart side rotation on the ball at release.
In contrast, the power player, being more behind the ball, and by virtue of the
automatic wrist collapse, can effect a more powerful "roll" with increased spine tilt
because their hand is able to more effectively uncoil over a larger circumference of the ball. This is much, much different than a the stroker's release mechanics.
Concluding, it cannot be emphasized enough how these 2 styles contrast so differently in terms of the mechanics needed to effect them and how important it
is for bowlers and well -intentioned instructors to acknowledge these differences.
Most importantly, they should be very cautious when attempting to incorporate
the mechanics of one style with the other. It can lead to significant problems
down the road for a lot of bowlers (and a lot of unnecessary frustration).