Four minutes. In the grand scheme of your whole life four minutes is nothing. At 1 Rebel this is exactly the amount of time you have to complete one of the sections in the 45-minute Reshape class before you get a much-needed 30-second rest. 1Rebel is the brainchild of James Balfour, from the family that founded Fitness First, and Giles Dean. 1Rebel is incredibly high end.

The two-storey space a short walk from the Gherkin is all industrial breeze-block walls and copper piping. There are heated benches in the changing rooms, towels are tri-temperature infused-cold, ambient and hot (the cold ones are housed in a Smeg fridge and doused in Aromatherapy Associates oils), free water is handed out on arrival.

Roots and Bulbs are the resident fit foodies with a bar area serving protein snacks and smoothies, juices and salads. In fact, book in for a 30-minute lunchtime class and rather than pay less than the usual 45-min morning and evening classes you get a free lunch (genius).

I was there to put RESHAPE to the test. A high-intensity group class where you are assigned your own workout station - a padded step (so it doubles as a bench) complete with everything you need including dumbbells and resistance bands, so you don’t waste time retrieving equipment. The session is split between the workout station where we performed upright rows, chest presses, frog jumps, squats and other body-busting moves, before heading to the treadmill. In between each 4-minute section you get a 30 second rest, although this time is taken transitioning to either the treadmill or workout station so it’s more of an 'active recovery'; a heartbeat plays over the sound system to signal the change. On the treadmill you transition from jogs to runs to sprints, with gradients added to build the intensity (and your glutes).

I’m hooked, but next time I book I’ll be trying RIDE where three evenings each week (Mondays and Wednesdays from 6pm, Fridays from 5pm) they invite a live band (a saxophonist and drummer are there on Mondays) to soundtrack your ride.

What You Need: gym kit and a good pair of trainers for Rebel (cleats - bike shoes - are provided for the indoor cycling).

Location: 63 St Mary Axe, London EC3A 8LE. Nearest tube: Liverpool St.

How do I book? First session is free, classes are £25 each but the more you buy the less you pay. 50 session workout at £17 each. Plus look out for regular offers. Visit 1rebel.co.uk for more information.