I was a volunteer for a few years and became pretty familiar with the system, at least in Colorado. The career and volunteers both had to be capable of performing a certain obstacle course in a certain time annually. It was something like this: in full gear and on air, climb a 100ft aerial ladder, pull a hose line about 100 ft and spray water, hit a heavy sled with a sledge hammer about 5 ft, drag a 170lb dummy 100ft, carry a large fan 100ft, a chainsaw, 100ft, and crawl through a tunnel. There’s probably something else I’m forgetting, but that’s the bulk of it.
I’m pretty sure all departments in the state needed all members to be able to do this at a minimum annually. Additionally, there were other physical assessments that took place periodically, depending on your age, like how many situps you could do, bench press, how far you can stretch, jogging until you hit a certain heartrate, and other misc.
In addition to this stuff, they constantly train. At my department, you trained every shift, time-permitting, doing fireground drills (search and rescue, rapid attack, knot tying, equipment familiarization, truck checks, medical training, throwing ladders, donning gear as fast as possible, roof ventilation, and a whole bunch of other stuff). The guys also went to the gym or worked out at the station nearly every day.
However, there are guys in any department that are fat and lazy. While most guys stay in great shape, there are guys who do little in the way of physical fitness beyond doing the annual obstacle course, which isn’t too hard. Guys in great shape do the course in 3 min or less. Some guys take like 8–10 minutes. But for the most part, fitness is a way of life in the firehouse.
This wasn’t just my house either. I know lots of guys in other departments that are heavy into Crossfit. Some departments make that mandatory for their daily work out, and it’s hardcore. Many departments around the nation are Crossfit certified.
As an aside, most departments in anything other than large/old cities run 80–90% medical calls. Most departments in the nation now provide EMS service to justify their existence since there just isn’t that much fire anymore. Almost everywhere you need to be at least an EMT to even get considered for hire, and there is a steady shift now towards everyone being a medic also.
Since most departments end up running mainly light duty calls, some folks can slide by without being in great shape. Personally, my philosophy as well as that of most others I worked with was to always be fit enough to pull your buddy out of trouble fast.