I think that if one has damaged cells, with damaged mitochondria, which is one current theory about PN now and other diseases, that exercise would be limited by that damage.

You might be able to do some, but not what you would like or what others might tell you to. The mitochondria process glucose and fatty acids, for energy, for the muscles etc. And if they don't work properly, you are limited by that loss.

I think CMT would fall into this category of poor metabolism.

In other words, don't push...pay attention to what is weak and set limits. One sign would be a lack of tolerance ...if you build slowly and hit a wall and can't get past it...that would be a poor sign for further exercise limits.