Can getting and staying fit be really such a bad thing? If nothing else, doing a collective impression of the fat wheezy boys with a note from Matron sitting it out on the sidelines only gives more ammo to our Army chums.
And anyway, having seen the LM from the AFBSC on the matter, if you really feel that strongly about it, it can be counted as one of your 3 so-called recommended / compulsory periods of phys each week. However, if instead of doing a fitness test you were told to go and play football/rugby/sport of choice for an hour, I would put money on the door being off its hinges in the stampede to get out and onto the pitch (and before you say anything, I'm in SH, so no I don't spend all my time doing sports afternoons!). So why should a bit of a jog up and down the gym be a huge problem. If it is, get a girlie to go with you - makes doing sit ups much more enjoyable
If nothing else it should be a matter of personal pride. But if you want to spend the rest of your life trying to remember when you last saw your feet, please be my guest.