Samya, my instructor, adopts a hands-on approach, which involves much prodding and poking. It’s literally an attempt to get me “into shape”. And apparently I shouldn’t have worn loose clothing. “I need to see exactly what’s going on,” she says ominously. The first few exercises seem ridiculously easy. Nothing to it. This, it turns out, is because I’m cheating, cutting corners by bringing other parts of my body into play, rather than isolating individual areas.

But even when I’m doing the exercises properly - and you know when you’ve got them right because you feel the stretch - some of them seem much easier than others. Samya insists that this is not unusual. We all have favourite muscles, which we use habitually. But this means other muscles get neglected and grow weak. My inner thighs, for example. “Weak, weak, weak,” says Samya. “But your shoulder and abdominal muscles aren’t so badI they’re only a little weak.”

After the mat exercises, she disappears into the store cupboard and comes back with a huge rubber ball. It looks like an over-sized space hopper. The idea is to repeat some of the exercises while lying on the ball. Sounds simple enough, but within seconds I’m face down on the floor. “Not really for beginners,” she laughs. As someone used to football and tennis, it’s strange to reach the end of the class without the hint of a sweat. It certainly doesn’t feel like I’ve had any kind of work-out.

But I do feel refreshed and relaxed. Walking back to the Tube I catch sight of my reflection in a shop window. Taller. More upright. A little regal, even. And that’s the point at which I think “wow”. I feel good about myself. After all, no one need ever know about my weak inner thighs.