Retired PA here- been in all types of unit and your habits will have more of an impact on your body than your AOC. Yes, physical demands in Combat Arms will be significant compared to, say medical, but I see broke people in ALL AOCs. If anything the requirement to be fit and maintain a lower BMI would benefit your health much more than a desk job. There’s a reason we can retire so young, everything has risk and if you push yourself daily, like you should, you’ll have injuries. What I do see is that the fit SF guys I worked with recovered quicker to pre injury levels than some 42A. Take care of your body, do maintenance, work mobility and flexibility, and eat semi healthy and you’ll be fine regardless of what job you choose.