Maybe they should try caging them with enough room to flap their wings and get some blood flow and oxygen into those muscles.
Agree.
The growth hormones could possible add to it...Most of the breasts I come across could have come off an ostrich...Even if you pound them they are as tough as leather...And they probably couldn't 'free range' if they wanted...They'd fall over on their beaks...
If you’ve ever raised Cornish Cross birds, you’d know their inclination is to lay down by the feeder, and eat. That’s about it. If confinement alone were the problem, I would think they’d all be affected.