“Don’t push it if you don’t feel well, certainly don’t faint. It’s just not worth it, and it’s annoying for me.” My yoga instructor tells it how it is. Fierce Grace yoga has gained a lot of traction among the hardcore: Bikram-high temperatures, 90-minute sessions, postures I have never seen outside the internet.

In truth, when you’re doing their 30-day challenge, which is as it sounds, one class a day, to see if you can form the habit, you meet quite a lot of instructors. Some are more soothing than the sound of the sea; some are hard as nails, in a fun way (there is one who lives near me, called Shirley Williams, whom I would choose as my satnav voice); some are firm but fair; some are philosophers (“You can feel this any way you choose; you can feel it in your skin, you can feel it in your muscles; you can feel it in your bones; you can feel it in your spirit,” said a guy whose name I couldn’t compute, because I was too hot). The fierceness doesn’t really come from them; the fierceness comes later, from within.

There’s no way of gilding this, the first hot yoga session, if you’ve done almost none before and you haven’t processed what they mean by hot, is a nightmare. Hell on Earth. I asked the receptionist whether I should keep my socks on, and she laughed in my face. Half an hour in, my veneer of civilisation was battling hand-to-hand with my animal spirit over whether or not to strip to my pants. The room, at weekends, is packed: the sweat from someone’s toe is dripping on your nose, and your warrior pose, as you thwack your neighbour, is truly an act of war. You can pretty much smell the last three days of all the people in the room: all they’ve eaten and drunk, the things they’ve thought.

Everything that looks easy is actually hard; everything that looks hard is ridiculous. Everyone else is amazing. “Dancers in the room, go ahead and move your knee behind your shoulder,” an instructor will say casually, which surely must be a joke, then they bloody do. The time inches past, and there’s so much of it. Truthfully, if I wasn’t on the challenge, it would have been a one-time event. But the idea of committing to a month of yoga (hot or cold) is to force yourself to break through this barrier.

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The class is so intense that after three hours of it – which is two days’ worth – the world is already different. It started with a shift in my perception of time. “Oh God, 45 more minutes” turned into “Oh no, only 45 minutes” overnight; then I began inwardly smirking about “finding my stillness” and started to actually look for some stillness. It was the gateway drug to all kinds of other annoying behaviours: finding green chai delicious; making a batch of dal for the week ahead; listening to my heart. Fighting with my Mr on day three, I said, “Maybe I was wrong. I’m sorry”, and he reared back in horror and said, “Urgh, I hate Yoga You.”

I still suck at the practice itself; I still cannot keep my back straight in any scenario. I still cannot touch my legs with my face except in the most unorthodox postures. I am light years away from performing a crow. I’ll get back to you in 27 days’ time.

Where to try it

There are lots of 30-day yoga challenges – find a class near you, or try Yoga With Adriene’s series on YouTube.