As at least one major base I know of has facilities worse than my old primary school unless you want to pay to join the fitness suite I fail to see how can be expected to maintain an arbitrary standard in your own time.
Prior to yet another lengthy detachment I strolled into the gym and asked for a fitness programme from the 4 PTIs discussing their next fun run. Sorry only do those on Thursdays, told them I was detached on Thursday, reply:shame!
I learnt to swim at 3, learnt to ride a bike at 5 and can still operate for 24 hours without sleep and fly at low level without throwing up. As for fitness to survive, the chances of surviving the missile strike are slim and wher would you run to, coupled with the rest the crew being possibly less fit or injured and the appalling kit we are/are not issued with seems pointless on balance.
Scrap the PTI branch along with "swimming tests" and "fitness tests".