There's been lots of sensible advice for you Sean; get a good physio, Mackenzie works for alot of patients; and the "watch the training" story from Canuck physio gives a message. It's tough that your back doesn't seem to have taken to life in the marines but I'm sure you will manage in the long run even if you have a complete change of career direction. When I was a sporty young newly qualified physio 20 plus in the UK then in Switzerland I did: walking -climbing -trekking -aerobics -tennis-jazzdance- ski touring -mountaineering -jogging -swimming etc etc and of course physio full time. All the resisted manual exercises I did for my patients combined with my energetic free time carrying heavy backbacks gave me two central disc protusions and weird pains down both lages that bothered me for years and made me rethink and redirect my sports. And believe me there is a life out there after the initial confrontation with the awful truth that not all backs like everything we do with them! Now aged 53 I do long cycle tours over walking paths for fun (uphill downhill) and ride horses for hours every week. Being a physio I of course believed I needed physio training exercises and mackenzie and fitness gym stuff to be fit to ride. So I irritated my back 10 years ago again by doing it all under expert supervision. Shit happens. No more gym workouts. Today I have the best core stability I've ever had by riding and grooming horses. I also help the blacksmith now and then lifting the hooves for up to 2 hours without dying horrrible deaths afterwards. Also work as a physio half time. Never felt better! Wish you all the best and good luck with all the decisions that are coming up.