I needed a bike fit. That’s what I learned the last time I went for a ride with Belinda, the woman made of iron filings from the Bella Velo cycling club. I had such a suite of learnings from that day – about my fitness, backbone, endurance, valour and preparedness – that this didn’t seem like the most important, even though when Belinda said it, all her cycling friends nodded sagely, and one added, “You do look like you’re at a funny angle.”

It’s gait analysis – you get on a treadmill and someone critiques your tread – only for bikes. Matt Wallace, at Richmond Cycles, hitched my bike up to a machine at the back so I could pedal without moving, and observed these various angles. Certain things he could tell before I even got on, such as that I had flat tyres and my drop handlebars were pointing downwards. I had a spill a while back and just bent them back into serviceable shape, so I’ve been cycling with my head pointed at the pavement for about three months. We (OK, he) fixed that. He did some old-fashioned tape measurements, and then another one with a laser, which establishes how far the end of the saddle is from the bottom bracket, and therefore where your centre of gravity is. You can have a racing fit, or a comfort fit, or anything in between, though I sense from the off that “comfort” is a bit looked down upon.

“I won’t get you sitting up like you’re on a town bike,” Matt said.

“No, no, no,” I replied. “I don’t want to look like Miss Marple.” (Though I do a lot more civic detective work than I do racing if, by “racing”, we mean “going faster than anyone else”.)

Matt asked if I’d made any adjustments, which of course I hadn’t. Then I remembered that I gave the bike to my uncle when I was pregnant 10 years ago, and he probably spent the entire time I was gestating a human tinkering with it.

“Is he taller than you?” Matt said.

“God knows. He’s 82. He’s never the same height twice and he keeps replacing his knees.”

“He must have a longer reach.”

My saddle was too low, so I wasn’t getting a full range of movement from my leg. Matt raised that a full three-and-a-half centimetres, which makes it a bit of a white-knuckle ride getting on the bloody thing, but I will admit makes me faster.

My bars were too far forward, too, so I was having to reach too far, which Matt could tell from an arched back. So he brought the saddle forward and replaced the stem at the front with a shorter one. That made a difference of four centimetres, which is, improbably, all the difference in the world.

The whole frame is probably a bit too big for me – 56cm – but you can work with a bike that’s one size out if you make the right adjustments. My posture is livelier and more aggressive. Zero effort, this cost me, and I’m significantly faster. It’s a fitness miracle.

What I learned this week

If your seat moves forward, it has to go up as well to keep the same extension in your leg. Because, if you imagine a big circle, from seat to chain to bars, you have to be at the same point of the circle. Galileo, innit.

• Zoe wears top from My Gym Wardrobe. Hair and makeup: Sarah Cherry