Re: working 12hr shifts
I work odd shifts as well, with a minimum of 12 hours a day. This month for instance has been 24 on, 24 off. Not allowed to sleep during my 24 on. My best advice is to listen to your body, once I decided I am never going to be the next Froning, and that I am already more fit then 99% of the population, it made it easier for me to just take a rest day when I needed it. I also have to be extra mindful because we have Unit PT 5 days a week, so I have to put that ahead of my goals sometimes!
Another thing that helps is to use some of this fitness outside of the gym on my off time. Maybe go on hikes, play with the kids at the park, whatever, but just have fun with your body and enjoy life!