F45: Inside The World’s Biggest Fitness Movement

Hot, sweaty and high on endorphins. F45 classes – some of which are said to burn 1,000 calories in 45 minutes – leave devotees dripping with the fruits of their labour.

A mix of strength training and cardio, the F in F45 stands for ‘functional training’: exercises that mimic or recreate everyday movement (think lifting, squatting, jumping, rowing and biking) to build strength and make the body more efficient. But unlike a traditional gym session, you’ll never do the same routine twice. Experts at F45 headquarters release fresh routines every four to five weeks, and there are currently around 3,500 exercises in their encyclopaedia. This means they can create a range of classes suitable for everyone, from total beginners to seasoned pros.

The F45 scene in London is booming. There are currently 24 studios across the UK’s capital, and plans to open at least 20 more over the next year, bringing the F45 workout to every corner of the city.

While F45-ers are encouraged to train at their own pace and work towards individual goals, one of the reasons F45 (and indeed any form of heart-raising exercise) is so effective is the focus on intensity.

The style of training, known as high-intensity interval training (HIIT), has been proven to be one of the fastest ways to improve overall fitness. It achieves this by throttling your body into what’s known as a state of ‘excess post-exercise oxygen consumption’ (EPOC). During this period – also referred to as the ‘afterburn’ – your body is essentially recalibrating, using increased amounts of oxygen to replenish depleted energy levels and reset hormones and body temperature. When in EPOC (which can last up to 48 hours), the body continues to burn calories, explains Haydn Elliott, co-owner of, and trainer at, F45 Oxford Circus in London.

The F45 8-Week Challenge, another of the company’s drawcards, is deemed the ultimate fitness test for its members. Eight weeks of as many classes as you can fit in (“you should aim for at least five a week,” says Elliott), along with a meal plan (you’re encouraged to eat meat and nuts for breakfast) and a motivational app guarantees impressive results. Those who lose the most weight can expect to win anything from far-flung holidays to cash prizes.

F45 was born out of Deutsch’s desire to create a group-based, results-driven workout and a model customers would keep coming back to. “There was a clear gap in the market,” he explains. “On the one end of the spectrum, there are individuals who spend $20 [approx. £15] a week on a gym membership but get no motivation so they … stop going. Then you have the people paying up to $80 [£60] for personal training sessions. I wanted to create something that combined the two in a fun environment.”

F45, he says, falls somewhere between the two: group sessions, led by fitness instructors, priced in the mid-way mark (£25 per session) while offering a premium experience.

But F45’s pared-back aesthetic – bright lights and branded equipment such as battle ropes, sandbags and medicine balls – puts it in stark contrast with the low-lit, Instagram-friendly boutique studios that have become trendy in today’s fitness world.

“Does trendy always mean effective?” asks Elliott. “When it comes to fitness, you don’t need to overcomplicate it. These basic components are what make [F45] easy to follow and fun. McDonald’s only sold burgers and chips for 25 years and became the biggest franchise in history. I’m not promoting fast food, but F45’s simplicity is a reason for its success.”

Deutsch started franchising in 2014, and there are now branches in 35 countries. Most recently, F45 studios opened up in the Czech Republic, Finland and India.

But in an age of fleeting fitness trends, does F45 run the risk of becoming another fad? HIIT training – which is at the crux of F45’s philosophy – has had its fair share of bad press in recent months. Critics point out that, if you’re doing HIIT properly, you shouldn’t be able to do it five times a week – it’s designed to push your body to its limits.

Personal trainer and biomechanics coach Anthony Fletcher tells Culture Trip that HIIT training should be approached with caution. “Five HIIT sessions a week is a huge amount. Unless you’re a trained athlete, it’s all too easy to injure yourself and in classes like F45, you’re often left to your own devices,” he says. “For the best results, HIIT should be incorporated as a part of a wider training plan. By popping up on every street corner, F45 are playing a numbers game – but this doesn’t mean it’s the be all and end all of fitness.”

These days, hardcore fitness sells, but will enthusiasm for pushing our bodies to the limit push us to the fitness brink? Is it time we all slowed down?

Deutsch is adamant that F45 has long-term potential. Unlike spin or boxing studios, which offer just one discipline, F45 is able to adapt to workout trends, he says. But with fitness fads moving faster than a HIIT session, F45 may well need to rethink its strategy before it burns out.