Exclusive: try this 15-minute workout from Barry's Bootcamp

London workouts are high-octane. January is a month for picking up new habits and forsaking old vices, though Londoners go hard in the gym whatever the month — the collective insanity persists all year.

As a result, the capital offers intense disciplines and cross-disciplines for most tastes.

But those chiselled of cheek and whittled of core know that Barry’s Bootcamp is one of the biggest beasts in town. The Hollywood export, which is responsible for the lissom bodies of stars including David Beckham and Kim Kardashian, has a tribe of fervent fanatics who are delighted that it’s opening its fourth studio in Victoria this month.

Hour-long classes alternate between weight-training sections and intervals on the treadmill. Your heart rate is stoked, which in turn triggers the metabolism: you can burn up to 1,000 calories in a session, and continue to chew through them after a class. Recovery periods are fleeting, intended to keep the heart rate elevated throughout the session.

There are six class types, focusing on different muscle groups: arms and abs, butt and legs, chest, back and abs, hardcore abs and full body. My first class, hardcore abs, was brutal; floor work involved crunches, planks, jack-knifes and bicycle kicks, while struggling with a medicine ball.

Treadmill intervals were fast and often at an incline. Curiously, afterwards I feel euphoric rather than weepy, or shellshocked. I have gulped the Kool-Aid.

Follow Phoebe Luckhurt on Twitter at @phoebeluckhurst