If you’re pushing back-to-back gym classes without seeing major results, try this: Australia’s most hyped workout class that just recently hit U.S. shores. Called F45 (short for function 45), the 45-minute, high-intensity, circuit-style technique has a reputation Down Under for transforming bodies in just a matter of weeks—mine included.
I first tried F45 in 2013 while living in Sydney, back when it was still a relatively undiscovered concept on the Aussie fitness studio circuit. Classes had recently launched at a friend’s gym, so I felt obliged to give it a try. “It’s really hard, but the time goes by crazy fast,” my friend promised as I agreed to a two-week free trial.
I remember three things from that first class: My glutes burned so hard that I avoided stairs for three days, the 45-minute session whipped by in what felt like 20, and I scheduled five more workouts that week on the train journey home. It was just one class, but I was already hooked.
Over the following months, I recruited friends to work out with me, all of whom rapidly fell under the F45 spell. I started attending daily, jumping out of bed for the 5:30 a.m. class, so strong was my addiction to the workout. In the four short years since it launched in Australia, F45 has become a favorite spot to ’gram among the international fitness blogger crowd and has rolled out 750 studios across 26 countries. Today, it’s where almost every young Aussie celeb, model, and Instagram star works out.
There are several different classes on the roster, but each high-intensity, interval training–style circuit follows a winning formula that turns casual gym-goers into bona fide F45 fangirls. For example, you move quickly through exercises, spending about 30 to 40 seconds at each station while large screens count down the time as gif-style graphics clearly demonstrate the movements required at the station. This means you always know what’s coming next and can push through the workout knowing the next break is just seconds away. The variety helps deter boredom too: One minute you could be sprinting on the rowing machine, and the next you might be doing assisted chin-ups or box jumps.
Of course, the real reason everyone loves F45 is that it works. According to my trusty Apple Watch, I burn at least 500 calories in each class, and after my first month, I felt stronger than ever and had trimmed down significantly—while also carving out some actually visible ab muscles. Rob Deutsch, F45’s founder, once told me that it’s not uncommon for class attendees to burn up to 750 calories in a session.
Today, I’m a health and beauty writer with the workout-legging wardrobe to prove it, but despite testing just about every fitness studio fad in New York City, I still haven’t found anything that measures up to F45. After looking on wistfully as locations popped up across California, Texas, Colorado, and other states, the first NYC location finally opened in Flatiron and you know I’ve been attending religiously. Just like the franchise’s Australian locations, each U.S.-based class delivers an ass-kicking that will whip your body in shape stat.
Lucas Catenacci, co-owner of the Flatiron studio, says members who commit to at least three sessions a week experience rapid results: “Typically, body composition changes in one to two weeks [with a] decrease in fat and increase in muscle, and dramatic changes in four to six weeks,” Catenacci told me. Specifically, he’s regularly seeing weight loss in excess of 20 pounds and significant body composition changes in just eight weeks of regular sessions.
Like most good stuff, F45 memberships aren’t cheap: A single session costs $40 (or $35 each when you pre-buy 10), while a month of unlimited workouts is $450. So if new warm-weather threads are typically your seasonal splurge in spring, try investing that cash in an F45 membership instead. Yes, it’s pricey as hell, but if you’re looking to tone up, well, the results speak for themselves.