F stands for functional - as in "functional fitness training", which runs for 45 minutes. It's been spreading like wildfire through Sydney, and other parts of the country, with a cult set to form in Wollongong. But does it live up to the hype? I decided to find out.

I discover there is a military connection, as Ben Keith bought into the franchise late last year as a potential career change following 13 years in the navy.

The clearance diver is on long-service leave, and is testing the waters in the fitness industry with hopes of a new life direction.

"[F45 training is] something we do a lot of at work [in the navy], a lot of cardio-based and circuit-based, high-intensity training ... and I want to pass on my knowledge to everyone else," Keith says.

"We don't do any Olympic lifting movements or heavy movements, everything's under 30 kilos ... anyone can do it."

I guess by anyone, he means a 67-kilo female who's weakness is chocolate - I'm in!

According to its Facebook page, F45 Training Wollongong offers "life-changing" workouts. I'm not sure in what sense, but if I end up looking like Bruce Jenner I may be concerned.

I tried two 6.45am classes on two different days before work - one was strength-based, the other cardio endurance. I find the gym on Kenny Street, and it's like one big open-plan box with "stations" set up, and a strip of fake grass for sprints - I hate sprints!

First question, "where are the showers". They don't have any. I can't exactly travel 30 minutes home again to change - I feel sorry for my co-workers that day.

Before both sessions, the instructor quickly demonstrates the different circuit stations and the exercises.

You're in a group of two or three, and do short bursts (between 20 to 40 seconds) of intense exercises with 10-20 seconds rest in between. Once you've done two to four sets of one exercise, you move to the next station. My most hated exercise of the strength session was pullups - even when they fitted two resistance bands under my feet, I struggled.

Of the cardio workout, my most hated was the burpee with the box jump - mainly because I'm unco-ordinated and kept slipping off the box (ouch).

It's all systems go for the entire session, sweat dripping, mascara running (not mine, of course), moans and groans. The girl in my cardio team and I converse on how difficult it is, but she tells me she loves it and "has to get back into it".

The team aspect is fun, and there's certainly lots of high-fives. At the end everyone seems hyped and bouncing off the walls - a stark contrast from the sleepy faces that wandered in 45 minutes earlier.

I think F45 would appeal to people who are bored of their current gym and love a good challenge - it's definitely not for the faint-hearted. If you've never lifted a weight before or have health issues, this may be a little out of your reach.