What is it? A treadmill surrounded by a tent that covers your lower body. The tent is inflated until it takes your weight, and then off you go.

How much does it cost? Balance Physio in Clapham, London, where I went, charges between £8 and £17 per 30 minute session, depending on the size of the package purchased, though says you can have a 10% discount if you quote “Guardian”. The treadmills are also found at select gyms and physiotherapy practices across the UK.

What does it promise? Something called “unweighting technology”, which makes you feel lighter than you actually are. It also reduces impact, which is handy for a number of reasons. If you’re injured, it’s a recovery aid. If you’re obese, it makes running more comfortable. If you’re elderly, it offers support. But it’s also a great training tool for the healthy; which is how I used it.

What’s it actually like? Once you get over the sheer alien weirdness of the machine – you have to wear cycling shorts that zip into the tent of the treadmill – it’s incredibly effective. You reduce or increase your percentage of bodyweight in increments. During my session, I dropped down to 60% bodyweight and ploughed along comfortably at 18km/h, which is usually a full-tilt sprint for me. Then, gradually, I added weight back on. It’s a clever riff on interval training: instead of speeding up and slowing down, you just make yourself heavier and lighter. I quickly ended up exhausted and drenched in sweat, so that has to be a good thing, right?

Best and worst bit You will never feel as powerful as when you’re bounding along at top speed in one of these. But you’ll never feel as heavy as when you get off.

Is it worth it? If you have the chance to try one, absolutely.

• This article was amended on 14 December 2015. An earlier version said Balance Physio in Clapham, London, charges £100 for 20 minutes. This has been corrected to say between £8 and £17 per 30 minute session, depending on the size of the package purchased.