What Should I do to prevent my body and joints from breaking down on me while in the military?

Good luck. No matter what you do.....your body will eventually start breaking down the longer you stay in. Use proper lifting techniques as much as humanly possible. Ibuprofen (Motrin). Heat/Ice packs. The minute something hurts, go to sick call. Follow all medical advice/instructions. Proper ergonomics when sitting.

The best medicine is preventive medicine. Get in shape. Stay in shape. A well-conditioned body is far harder to break than one that isn't

Watch your weight. Every extra pound is 5X on your knees and back. Careful lifting, follow safety guidance. Never ignore small stuff so it gets bigger

I would strongly recommend cross-training n an aquatic environment.
This, in conjunction with, proper training techniques, proper (?) diet, and adequate (?) sleep.
Unfortunately, being on Active Duty doesn’t afford you the option of ‘adequate’ or scientifically recommended. So, you do ‘what you need to do to get done what needs to be done’...Adapt & Overcome

If you are going to take calcium, make sure that it has magnesium also. The calcium will go straight though. Magnesium will bind it to the body.

This is a tough question., but fundamentally, all other things being equal, you've got to avoid gaining excess weight which is terrible for your joints. Although subject to controversy, to this end, I recommend avoiding carbohydrates in your diet as much as you can. They are highly inflammatory to your body. Stick with the good fats and protein. Doing this may be very difficult for you because mess halls and U.S. government guidelines, since their establishment in 1978 or so, will push you in the other direction. Unfortunately, those guidelines were not written based on their value for proper nutrition, but by politically motivated junk science. The solution is to stick to good science. Personally, I stick as closely as I can to the regimen advocated by the doctors at dietdoctorDOTcom. Proof of effectiveness: I can still comfortably wear the service dress uniform I wore for my last 10 years of active duty. Height 6 feet 3 inches, Chest 44 inches, Waist 34 inches; weight fluctuating plus or minus 2-4 pounds centered on 200 pounds. People around me are amazed at my energy levels and mental acuity. And, I'm only 87 years old, by the way.

There really isn’t a trick to it, the best thing you can do is to take care of your body. That includes eating healthy, watching your diet, and continuing to strengthen your muscles. Stretch daily! Don’t get caught up in “training breaks” or temporary lulls in physical training. If you have a schedule that allows you to do pt on your own then take advantage and do it. Find out about proper stretching for whatever muscle group you are working. Most musculoskeletal injuries in the military ( or at least Army) are due to overuse. The military is bound to break you down a tad; we do more than the average civilian and then you add aging into it, but you will have an easier time if you take care of yourself.

I'll second what SGT Bollum said, lift with your legs. I have seen a lot of guys in my Signal MOSes lift with their backs. Some of our equipment was pretty heavy. I don't know how many of them ended with back problems, but I always lifted with my legs. I was a catcher on my high school softball team so I may have already been in the habit of doing that type of movement without thinking about. Lift with your legs.

If you want supplements try - MSM / glucosamine /chondroitin these are all beneficial for the joints. But be sure to keep the exercises done correctly and be very careful to lift properly at ALL times (do not bend the back to pick up anything, use the knees), also follow the other advice you see here weight is important as is staying hydrated.

Its called aging son. Grunt/Arty MOS are harder on the body than most- goes with the choice,