The eighth of Heartcore's boutique fitness studios, in swanky St John's Wood, is a beautifully-designed space, with decor evoking a Californian beach retreat, complete with bleached wood and instagrammable messages on the walls. It offers Heartcore's signature classes, which focus on honing and strengthening that all-important core. We tried a TRX HIIT class, which uses straps to get you burning fat and calories (up to 1000 per 55-minute session) using your own body weight – and to put it mildly, it was challenging, leaving even the fittest among us a flapping mess on the floor at times. But the instructor was kind and encouraging – none of the militant barking you'll get at other places – and the resulting glow was well worth the effort (and had us sadistically signing up for more).
Heartcore is also renowned for its top-notch Dynamic Reformer Pilates and Barre classes, the former of which takes place in a gorgeous room whose vaulted windows reveal the building's former life as a church.