Jorge, whether we like it or not, bowling is not a one size fits all sport.
During one of my USBC certifications, we did some one the lane work with volunteer subjects.
Palmer Falgren was our instructor. Palmers a former PBA champion, an accomplished coach, an wrote numerous articles for magazines including Bowling This Month.
One of the bowlers was a well muscled woman bowler. He drew our attention to how her shoulder musculature was not conducive to a free swing.
This video features two PBA pros neither of which fits a mold. Jeff Lizzi is heavily muscled, Ryan Shafer is not a smoothie either.
Both are good enough to compete at the PBA level.
There was a Tom Kouros article using Jeff Lizzi as a subject.
viewtopic.php?f=3&t=4172The subject of ball weight boils down to what the bowler can effectively impart a quality release on a consistent basis.
A ball can be too light as well as too heavy. The fit of the ball is extremely important as a well fitted ball is handled easier. The fit is ideally assessed right after it is drilled and the bowler rolls a few in the shop.
The bowler has to trust the driller, sometimes the bowler does not know or already is a squeezer. The driller can't work with him too long if there are customers waiting.
Ball fit and letting it release itself from the hand should be lesson one or pretty close to one.
If we are talking about a petite woman or slender man, they are probably not going to succeed with muscled swings.
There are probably varying degrees of free or muscled swings. A big key is a relaxed grip, one where the bowler is not grabbing. A big key, is whatever they do, can they do it well and repeat it enough to succeed at the level of their choice.
When considering the way a bowler can achieve their potential, we have to factor in how they are built, their temperament, in short, who that bowler is. Coach Fred Borden used the term, match that bowler with their inner drum beat. A Hallmark of a top coach (and I am not one, I'm just a bowling enthusiast) is successfully obtaining that bowlers best on a consistent basis. That coach will determine what to fix and when. This is not to say they get it all done like flipping a switch, sometimes it might take time.
Admittedly, gravity is consistent and humans are not as consistent, but humans have muscle, tendons, and bones so "free" and "relaxed" will come in degrees.
Now I said, I'm not a top coach. I just certified upnto the Silver level, to see if I could do it. USBC does not really train or groom coaches. Some are born. What's really missing from their coaching program is a mentoring/apprenticeship program. I would have certainly welcomed the opportunity.
Passing tests is easy, what Jim does takes talent.
Be that as it may, I thought I'd get the ball rolling so to speak.
Also, in coaching analysys you might have several top coaches assess a bowler who might offer a different remedial list or sequence.
I would consider studying bowlers of similar stature.
Of course, one does not want to fix what is not broken.