I always wonder when I feel her if it's fat or muscle...anyway what do you mean by projection?
I’m going to have a go at this.

Fat, lets assume it accumulates evenly over the chickens body.

To test for fat on a human you might pinch an area of skin and depending on the thickness of the piece of flesh you’ve pinched gives an indication of the amount of fat.
I’ve just pinched fat bird and Tackle here and you would need calipers to tell the difference, neither seemed very pleased at the fat test.

If you have a hen that doesn’t do tricks, you know, a bit of a sofa lounger then you could make a comparison.
You could test leg strength by making a very simple squat machine.
A pole stuck in the ground with another pole attached at the top by a hinge of some description able to move in a full 180 degree arc. In the middle of this pole, attach weights; maybe a piece of cloth like a sling shot. Use kitchen scale weights to put in the pouch.
Pad the end of the pole and make your chicken squat underneath with the end of the pole resting on her back. Then, get her to stand. By adding weights eventually she’ll get to a struggle point. That would give you her leg strength.
Wing strength I’m still thinking about.