I don't really know if I buy this. Is it really that your body doesn't respond to exercise, or is it that these individuals don't have the mental capability to push them selfs. I've been lifting for ten years myself, and I have seen plenty of people in the gym who go every day and never seem to obtain any gains. You can take the nice route and say that's due to genetics, or you can sit down and actually watch them and start to notice a few things. These are usually the people that do the following, never switch there routine, never pick up a heavier weight, to long of breaks between sets, and worst of all have a very low tolerance for pain.