This is in response to your question, "is the modern swing totally free of muscle?"

Most elite bowlers (PBA) do in fact, deploy varied degrees of "muscle" somewhere
within the swing cycle. Ronnie Russell appears to be such a bowler. Keep in mind that
elite bowlers are blessed with tons of natural ability. This natural ability is what sets
them apart from everybody else. They are able to use muscle and still be able to
repeat quality shots again and again. However, it is a fact that the more you let gravity dictate the pace and timing of your swing, the more consistent you will be---shot after shot. Gravity swings the ball at the same rate of speed all the time.
And, by allowing gravity to dictate swing timing, a bowler is better able to synchronize their footwork WITH their armswing speed.

In regards to bowlers who have low pushaways and "quiet" shoulders it
is also important to remember that the forward motion of the body (the footwork)
contributes to backswing height all by itself. This forward motion generates
inertia that exerts a forward (pulling) force against the bowler's (bowling ) arm . As the body
moves forward in the initial phases of the approach, it wants to pull the ball along with it. But, the ball "responds" with an equal but opposite force of its own--in the opposite direction. This
force contributes to backswing height. This force gets interrupted however, if muscle
is applied at this point--leading to a LOWER backswing height. When this happens,
bowlers will try to make up for it by adding MORE muscle in an effort to increase backswing height.

As JustRico stated, it is extremely difficult to have good timing
when muscle is introduced because it is very hard to repeat shot after shot. Not so with a gravity fed swing. In the past there were a few elite bowlers who generated
little or no pushway, and kept their bowling shoulders stationary, but still managed to generate sufficient backswing height, without using muscle to pull the ball into the backswing. Jim Stefanich and John Handegard were two of the best at this. This
technique was known as 'walking past the ball". They had extremely loose armswings that were dictated by the force of gravity alone. You can see this technique by
watching these 2 greats on old videos that can be accessed on You Tube.

If muscle is to be used, it should be minimized. Muscling on the downswing is
the worst place to deploy it because it usually results in squeezing the ball and a loss of balance
at release. It is better to wait for the ball to arrive at the release. Don't pull down on it. Don't get anxious and try to bowl before the ball wants to "bowl".

Like they say in golf- effortless power vs. powerless effort.

Tension free is probably a better description. 

People have told me I have one of the purest pendulum arm swings they have ever seen.  I use leverage and timing to minimize the effort in my swing, but I am very aware of using muscle to get my back swing higher, and am also aware of accelerating at the bottom. 

Like they say in golf- effortless power vs. powerless effort.

Tension free is probably a better description. 

That sounds better than:

"TOTALLY muscle free arm swing" from BTM article I read.

In karate/boxing, An effective, smooth, quick, and powerful punch (release) has to have the body working in the right manner (technique) and right timing. Understanding when to activate muscles and when to deactivate them is key. good bowlers do this but most are unaware of it.

Another way to think of it is, if you are inconsistent with your targeting or shot making it lends itself towards too much muscle in the swing causing the inconsistencies (can't muscle it the same way twice) and improper movements in the approach and/or timing

More times than not, muscling is created by too heavy a bowling ball (lack of strength) improper fit (undue or unnecessary squeezing - muscle) or improper timing...

Brick I'm sorry but please read your post and tell me the logic in it lol

Can you explain to be the thought process of going up in weight other than to lower your scores (: