Chest development, big space in the middle

[401Delta]

Anything that brings the upper arms as far as you can across the chest will hit the that inner area.

This is true, but it will also hit the 'middle' and 'outer' chest as well.

Even if a non-spanning fiber is innervated independently from the spanning fibers (and for the sake of this argument, let's incorrectly assume that all of the non-spanning fibers are located only at the 'inner' chest [WHICH THEY ARE NOT]), they must still be pulling from something (i.e. spanning fiber), and that spanning fiber is going to have to contract as well in order to ultimately transmit force to the tendon.

Your statement assumes the following:

1. That you can independently innervate a non-spanning fiber.
2. That you can isolate local non-spanning fibers with a particular movement.
3. That non-spanning fibers make up a significant portion of the 'inner' chest.