Getting fit isn't easy. I've always hated gyms, but now the pre- baby cycle-to-work routine has crashed as well. After breakfasting, bathing and dressing our child, I just can't manage to find my bike, pack clothes and remember a tie - I know I'll forget something. And how could I justify a subscription at that lovely yuppie pool near work: to prevent a heart attack in 20 years time? Sorry, Child Benefit is meant for a higher purpose.

Like our baby's keep-fit class. They said PE kit was not required. Dress in your usual clothes, they suggested. Come before work and play along with the music. Sounds good. However, I leave my suit at home as a precaution. Cords (tie scrunched in pocket) are best for crawling around. And I keep my pager, that badge of office life, clipped on belt. So everyone knows that this isn't my whole world, that another life could at any time claim me back, that Something Very Important might need my attention.

We're sitting on the mat, me and toddler, trying to keep up with the others. It all feels very familiar: hall with wood-blocked floor; tall windows you swing open with a big pole; the start of a new class where everyone seems to know what to do; the whiff of smelly feet. I remember being somewhere like this as a child, the panic of falling off the wooden horse, landing winded on my back. And then there's that old self-consciousness - when asked to remove my shoes, why do I always find a hole in my sock?

"Heads and shoulders, knees and toes, knees and toes" sings a very nice, very brisk lady. But I keep putting my hands on my head when they should be on my toes. Child looks lost and bemused. And before we've got the hang of that, we're on to the next verse: "Eyes and ears, mouth and nose, mouth and nose..." Oh dear, I think, here I am, a grown man with his own pager, still uncomfortable about not keeping up with teacher.

It's meant to be fun. What could be more innocuous than singing "Row, row, row your boat/ Gently down the stream"? But I know it's a sneaky abdominal exercise (or "abs", as grown-up gym aficionados always call them), designed for developing a washboard stomach.

Suddenly, we're out of the boat, standing up and bending over. "I'm a little teapot/ Short and stout/ Here's my handle/ Here's my spout." Aha - here comes a sideways stretch: "When the kettle's boiling/ Hear me shout/ Lift me up/ And pour me out."

But our child isn't interested. She's not conforming to gym culture, not bothered about being a teapot. Up she gets and wanders off to the trampoline. That's my girl.