Maybe it's just me, but I was fairly militant regarding exercise way before I ever joined the fire service. I used to bring a pair of 50's on the bus to knock out thrusters, C&J's and snatches (an olympic movement performed with a DB in this case) in between jobs, "greasing the groove" style. I'd also do bus stop pullups and stuff, although I wasn't as diesel as these guys -
http://www.youtube.com/watch?v=kDCxH88-9X8
I've noticed that a physically weak partner will get the fit one hurt, as they try to compensate for the other's weakness. Ever carry someone down a flight of stairs while your weak partner holds the handles at the bottom of the chair with fully extended arms, too weak and/or lazy to choke up and keep me from having to lean over excessively? How about someone too weak to get the cot up to the top for loading? Why am I always stuck loading the heavy hitters? If you need to rest at every landing while removing a pt on a stair chair, you're useless to me. If you can't roll a pt onto a sheet/blanket and carry them with me down at least one flight of stairs through a narrow hallway to the cot (for those times when the pt doesn't have the time that it takes to do a reeves), you're useless to me. If you can't help me get an unconscious flaccid pt out of the bathtub, you're useless to me. If you gas on compressions after one minute, you're useless to me. If you wake me up in the back of the rig to go to Wendy's at 0130 because you're too irresponsible to pack food for the shift, and absolutely "need" to eat, I'm flinging a box of gloves or something at your head.
Maybe it's just me, but if I were to see the ramifications of an unhealthy lifestyle on a daily basis, for example obese type II diabetics w/ HTN, CHF, amp. limbs etc. COPD'ers, post MI pts, so on and so forth I think that I'd pay a little more attention to my own health.
You don't need to be fit like a Navy Seal, and you can be 400#, as long as you can hang and do the job I won't judge.