What is it? A heart rate-based circuit class that makes the splashy – if intimidating – claim that you can burn up to 1,000 calories per session.

How much does it cost? Membership at the London studio I visited is £69 per month, although it varies around the country – currently there are YourZones in London, Essex, Kent and Yorkshire, and they’re spreading quickly.

What does it promise? As well as the heart-rate sensors – which project your effort on to a giant screen for all to see – and the impossible-sounding 1,000-calorie claim, YourZone boasts calorie afterburn. The theory is that, if you work hard enough, your body will continue to burn hundreds of calories for 36 hours after your session.

What’s it actually like? Heart-rate training is easily my favourite type of workout, since you’re left with nowhere to hide. However, YourZone is a little different from similar classes I’ve done. The session is split equally between cardio (treadmill, bike and rowing) and strength (shoulder presses, lunges, ball slams, curls). The circuits are staggered, so you’re barely in direct competition with anyone but yourself. The session lasts for a full hour, which means that you can really blast through the calories. Before I started, the trainer told me that he’d only ever seen one person hit a thousand calories before. I managed 976. I may or may not have made up the difference by doing star jumps in the shower, like an overcompensatory moron.

Best and worst bit In terms of sheer, concentrated effort, YourZone is hard to beat. I just wish I’d worked 24 calories harder.

Is it worth it? Yes.