Four weeks into her Barry's Bootcamp sessions, Charlotte Sinclair is running out of sportswear but not out of steam

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In any form of exercise there is an instant where it all begins to fall into place. Surfers call it the bliss point. I call it the Thank Christ moment. Week four into my four times a week sessions at Barry’s Bootcamp  and it’s not that it’s becoming easier – or that I’m becoming less of a sweat-drenched, red-faced, panting mess by the end of each class – but it isn’t quite as hard as it was.

For instance, I have, voluntarily (and against all rational judgment), begun to run faster, pushing my sprint times up to 10.5 (Barry’s treadmills read miles not kilometres: 10.5 miles is a 16.8km pace). There is a smugness about my newly discovered/recovered fitness levels which, I warn you, verges on the offensive.

When you are doing the same class four times a week you begin to notice things. For instance, I burn more calories with certain teachers than others, (classes led by Anya and Olly seem to especially nuke the calories). On Mondays and Tuesdays, the 5.30pm class seems to be taken up by an immoderate amount of men who take their t-shirts off within two seconds of being on the treadmills. No real hardship there. (Needless to say, you don’t take your top off at Barry’s unless you have concrete abs. There are men here who look like they haven’t touched a carbohydrate since 1998.)

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Similarly – and in the name of equality - there is a particular type of tall, elongated model female who frequents Barry’s 6.30pm classes, girls with high, glossy pony tails, and bright white teeth, who wear – much to the dismay of every other woman in the class, and to quite the opposite effect for every male participant – hotpants. Hotpants! (I’m happy to report they are in the minority.)

Also: with all this questing for hot-bodiedness there comes a good deal of…. manly grunting – and not only from the men. It’s, frankly, rather disconcerting, and also peculiarly un-British.  But this is Barry’s! An American import that’s teaching us that if we’re not grunting our way through our exercise routines, we’re not working hard enough. At the very least, a small, polite squeak of duress every now and then is required. It’s all a bit primal and… meaty down here in the red light, with the sweat and sprinting and cave-man yells. But it’s also a girl haven – women predominate class numbers, run just as hard as the men, and embody the t-shirt slogan: strong is the new skinny. Sometimes you don’t want to do yoga, you want to sweat. This is absolutely the best place to do it.

But did it work for me? Noticeably. My stomach muscles have pinged back into shape, and there has been gratifying all-body toning. The only problem is that Barry’s makes me SO hungry that I’ve probably replaced every calorie I’ve lost. (Unsurprisingly my weight stays unchanged.)

However, the change in my fitness is remarkable: from puffing up the hill sprints, to running confidently. The only drawback? No one has the socks to sustain this amount of exercise. Nor the sports bras.