F45 Training [1] is a circuit-based workout class that is guaranteed to push you out of your comfort zone and get you sweating up a storm. A group training method offering 45-minute gym classes that combine functional exercises designed to work your entire body, each class is dedicated to either cardio, resistance, or on Saturdays, a combination of both.

But, is F45 technically High Intensity Interval Training (HIIT) [2]? We sat down with Fran Whitfield, an REPs Level 3-certified trainer who is also the Head Trainer at F45 Vauxhall in London [3], to find out.

What Is High Intensity Interval Training?

High intensity interval training (commonly referred to as HIIT) has received a lot of buzz in recent years, and that's for good reason. Most notably, HIIT helps you burn body fat more efficiently and in a shorter period of time [4] than traditional low-intensity sustained state (or LISS) [5] cardio.

According to Whitfield, HIIT is a specific exercise concept characterised by "very intense periods of time and then resting in slower recovery period". HIIT, Whitfield says, is a "time-efficient workout that also increases your Excess Post-Exercise Oxygen Consumption (EPOC); also known as the calorie 'afterburn'". Simply put, that means your metabolism will be higher, and therefore, your body will burn more calories, long after you've finished your workout when compared to a more steady-state cardio workout.

"There are several different forms of HIIT," Whitfield says. "Tabata, being one type, is pushing through hard 20-second bursts and resting for 10 seconds. There are also several other styles of HIIT training such as work for 40 seconds rest for 20 seconds, work for 45 seconds rest for 15, and [there are also] AMRAPs and ENOMS," but that's a conversation for another day.

Is F45 High Intensity Interval Training?

In short: yes. In long: not every single workout will be the type of HIIT you are picturing — i.e. the type of workout that will leave you huffing, puffing, and sweating your arse off. According to Whitfield, "every workout in F45 is designed as HIIT training as we operate on a work/rest style"; however, she does believe the cardio workouts, which happen at every F45 gym every single Monday, Wednesday, Friday, and Saturday, could be considered more classically HIIT than the resistance-based classes on Tuesday and Thursday.

"On cardio days, members will be encouraged to go as hard as they can in each exercise and complete as many reps, distance, speed as they can for the whole set" until the timer runs out, explains Whitfield. "Whereas, during the resistance days, I will encourage the members to lift a heavy enough weight to reach a certain repetition range dependent on the work interval timing," which is important to maintain correct form and avoid injury.

F45 has also introduced their own heart rate monitor, called an F45 Lionheart monitor, so you can tangibly track how hard your body is working throughout a work out. "It's an incredible device to use during HIIT training," says Whitfield. "Being able to see your heart rate and what this equates to in percentage of your maximum heart rate [means] you are able to ensure you're pushing yourself as hard as you can during those work intervals." She says that often, you won't even know how hard you're working (or not working) "until you see the results on the screen [and] you realise you could give a bit more". While not essential to an F45 workout, it is a great way of ensuring that you're pushing yourself to your full potential and reaping all the of HIIT training by maximising every single work interval.