What is it? Beat, at Fitness First. It's a cutting-edge range of classes, performed while wearing a monitor that splashes your heart rate across massive screens around the club.

How much does it cost? Free with a membership (from £60 a month), or from £14 pay as you go.

What does it promise? "Heart rate-based training" that "optimises your workouts by ensuring you always train at the right intensity level for you". Basically, it's a hi-tech way to stop you slacking off.

What's it actually like? Intense. I took a 30-minute Cardio Fit 85% HR class, where you have to stay above 85% of your maximum heart rate for the duration of the class. There's five minutes of cardio (on bikes, rowing machines or weird curved treadmills), followed by a minute each of kettlebell swings, rope slams, fast-twitch static running, tyre flips and box jumps. You do that twice, then collapse on the floor, realise that your heart is somehow beating at 102% of its maximum capacity, then receive an email telling you exactly how close to death you came. Quite close, in my case – at one point my heart was beating at 189bpm. It's exhausting. But I burned 515 calories, so it's effective.

Best and worst bit The best bit is the total lack of anywhere to hide – if you skive off for a couple of minutes, everyone will see your heart rate dropping onscreen. The worst bit might be the unfailingly positive feedback from the instructor, who wouldn't stop shouting about how great I was doing, even when I was fairly demonstrably half-arseing it.

Is it worth it? I'm going back next week for more, so let's say yes.