Emma Bartley burns nearly 600 calories at a high tech, highly toning, high intensity interval training centre

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Speedflex is marketed as “a life-changing way to get fit and healthy” – and it may well be, but to my mind that’s underselling it. Having burnt 580 calories in one 45-minute session at its centre in the City of London, I would personally pitch Speedflex as The Pain-Free Way to Get the Shapeliest Bum in the World. If you want to tone up in time for a holiday, this is the perfect way to do it.

So what is the deal? A high-intensity , low-impact training programme based around a set of cleverly engineered machines. These look a bit like the fixed weights you’ll see in a conventional gym, but instead of using heavy weights their free-motion arms respond to the force you exert on them. The result is a lighter, steadier exercise that cuts out the jolt you’ll get when you lift a weight and momentum kicks in.

A typical class involves a circuit of exercises using the machines, timed at intervals of 30 seconds or less. I first went along to Lombard Street for an induction and was taken through the different movements – the base position is a squat, but you might push up from there on to a standing position, lifting the arms of the machine above your head, or simply lean forward and row. A few “free” exercises like running on the spot, lunges or a plank are included in the circuit to mix it up.

Crucially, everyone is given a full body assessment and a VO2 test before they start, to establish their maximum heart rate. During each class your heart rate is monitored and displayed as a percentage of your maximum on big screens around the room. As a lazy Size 13, I found that very motivating during my first full class, because I didn’t want Emily, our trainer, to see “Emma Bartley: 30%” in big green digits on the screen and start making me do burpees or something.

Over the 45-minute session I started to get quite competitive about it, trying desperately to get my percentage higher than those of the other two people in my class. That was a real novelty, because they were both men, and if we’d been lifting actual weights, I’d never have been able to do the same circuit as them. But at Speedflex you’re working within your own range for cardio and resistance, and simply competing as to how hard you’re each working.

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I did notice that the guys were much fitter and stronger than me after a few circuits, when Emily got us to switch from timed intervals to number of repetitions. During this part of the class, we took it in turns to be the “leader”, doing ten reps on each exercise before switching to the next, with the rest of the group following. Superfit Mark went first, and moved so fast that I could barely manage three reps before he’d done ten. But again, it pushed me to work harder, particularly when I was the leader, because I didn’t want the two of them to have done 25 reps while I was still counting out “Eight… Nine… Heurheugheugh”.

Developed a few years ago in America by a former World Series baseball player, an osteopath and a mechanical engineer, one of Speedflex’s biggest selling points is that the machines are very low impact. That makes it a great way to train if you’re injured, injury-prone, older or out of shape. But because it’s intense, it’s also popular with sporty types: the European brand ambassador is former England football captain Alan Shearer, who trains several times a week at the centre in Jesmond, Newcastle.

Shearer’s involvement, along with the look of the machines and the website, make Speedflex seem quite masculine at first glance, but having tried the workout I think it will really appeal to women. Because you’re doing a lot of repetitions at a low load, you tone up rather than building muscle, and the squat position that’s the basis of most of the exercises makes it great for the upper thighs and bum. A quick (professional) peek at Emily as our session ends confirms my suspicion: doing this regularly gives you pretty perky glutes.

While I’m checking her out, Emily takes us through our training reports. I’ve spent ten minutes in the green zone, working out at 70-79 per cent of my maximum heart rate, 17 minutes in the amber zone (80-89 per cent) and 12 minutes in the red zone (90-100 per cent). My maximum heart rate was 183, which is about what I’d see in a spin class or on a run if I was pushing it, but because of how short the intervals are it didn’t feel like as much work as spinning or running. In 45 minutes, I’ve burnt 582 calories – and because they’re heavier the two men have done even better, with 600 and 1,000 apiece.

There are a couple of catches, of course. At present Speedflex has only two UK centres, in London and Newcastle (there are more in the US and Dubai if you’re a jetsetting type). The pricing isn’t particularly clear; the website advertises sessions for “less than £13”, but if you were doing the recommended three a week, the cost could mount up. But the centres are very luxurious, with rain showers, towels supplied and so on – and the technology makes it fun and incredibly motivating. If you do end up with the World’s Best Arse, I doubt you’ll consider it a bum deal.