Carrying 45lbs-110lbs of gear including the gun also ammo for anywhere from 6-72 hours. If he's not physically fit enough to do a few push-ups then how is he suppose to do that? The answer is that he couldn't. That's not even to mention that you're constantly moving a lot of heavy shit around even outside of combat roles because everything the military is built to last almost forever so everything tends to be big, thick, and heavy. Even the shipments of food tend to have very heavy boxes weight 50-100lbs and the storage is almost never a close walk or straight walk. You don't have to be the Incredible Hulk but you at least need to be average strength. Also every military member has to pass a Physical fitness test every 6 months, if you fail 3 in your entire career then you're automatically kicked out. He would of 100% been gone in 1.5 years.