I think most people do. All you have to do is watch a youtube video of any pro bowler and you'll see as they approach the foul line...the ball speeds up so they can release it near their front leg and not go over the foul line.
The two things I look for that tell me it's NOT a true pendulum, pure gravity swing is:
1) Does the backswing go higher than the initial ball position? If it does, which it will for most pro bowlers...it can't be simply gravity/pendulum...because the increase in speed due to gravity's effect on the ball will be almost equally cancelled out as the effect of that same gravity works against it on the backswing. Push a person on a swing set...give them one push...and see if they go higher coming back (without trying) than going forward. It's physically impossible. Therefore, a backswing higher than the initial ball point means the bowlers is ADDING energy to his/her backswing.
2) Watch pros as they start into their final step...the ball is still quite a ways back..just starting it's downswing...you can see it "speed up" as they get their sliding foot close to the foul line. A true pendulum swing wouldn't need chest rotation. The shoulders could stay perfectly straight....just pendulum the ball at the shoulder...and the only speed increase would be how fast you approach...but you'd have to approach at the same speed...because otherwise the timing would be off.
There was a pro bowler in the 80s...can't remember who...but he started his approach with his ball hanging down at his side in one hand. He then pushed his arm straight forward...it would go back (like a pendulum)...and then forward again using gravity. That was the closest thing I've ever seen to a "true pendulum swing".
I think most bowlers use "muscles" in their forward and back swings. It's just not noticeable because MOST of the swing is due to the ball weight and gravity. You couldn't throw a bowling ball without the pendulum effect...it's too heavy. You'd have a blown rotator cuff in a matter of months. And...your shoulders could never stay paralell to the foul line...it'd be impossible to stop your ball side shoulder from going forward just due to the momentum. But to say it's not at all part of the proper swing...then your approach timing would have to be "perfect" to get that ball at that release point the same each time. I think swings are very individualized...no 2 are exactly the same. And like you said...trying to totally tear that apart...you end up getting totally out of whack.
I tried switching to a 3-step approach...a really short approach...I tried releasing way earlier...I tried a really super-short backswing....it's tough. I guess over time you could get used to it...but wow...it felt SO weird to start my approach that close to the foul line.
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