Arm Motion in the Lawn Bowling Delivery

When I was provided my first lessons in lawn bowling (three years ago), I was instructed to draw back my arm along the aiming line keeping the plane of the running surface of the bowl precisely vertical. Subsequently, I saw that many experienced bowlers when they started their pendulum delivery turned the palm in towards the side of the body as it passed through the plane of the body and only turned the hand back to its starting orientation as it reached the point where the bowl was to be released. When I was given instructional material during my winter sojourn in Australia, this was proposed as a useful modification in the delivery. For the past two years, I couldn’t understand what advantage this could bring. Now, I see that when I try to keep the plane of the bowl’s running surface fixed, if there arises a need for the backswing to be more pronounced, I can feel my shoulder muscle stretching excessively. This stress causes the top of the backswing to deviate in a direction away from the body. This would cause one to bowl narrow on the forehand and wide on the backhand.

If one turns one’s palm in through the backswing this stressing doesn’t occur.
So it might make sense, at least for heavy drive shots or when bowling on particularly slow greens, to turn the wrist in. One might think that changing one’s delivery for drive shots might complicate life; however, there is a hypothesis that making the drive delivery significantly different from the draw has an advantage: because the two shots follow a different style, your mental computer that is supposed to automatically control the proper weight of your shots, does not confuse the weight for a drive with the proper weight for a draw shot. As a consequence according to this hypothesis,  a draw shot delivered immediately after a drive will not be as likely to be overweight. Apparently, if drive and draw have much in common, drives tend to cause draws immediately following to be too heavy.