The greatest delusion an old man or woman can entertain when they take up exercise hits them about six months in. They imagine they are young again.

Picture it. You are stronger and faster than you have been in decades. You can eat up miles and turn on bursts of speed. You feel you can go back to being a 17-year-old. All you need is to push yourself a little further, lift a little heavier until … a muscle rips or a bone fractures and you are incapacitated for months.

Perhaps it is sexist stereotyping but men strike me as most likely to ignore the basic rule to build gradually. Certainly, the tale of the 2019 athletic career of this particular man should serve as a warning.

I had a place in the London Marathon at the end of April. In March, the training was going well, too well in fact. It went to my head. Determined to post a decent time, which in my vanity I thought would be three and a half hours, I had completed five training runs of 20-miles plus, when in truth I only needed to run two or three.

A week into April and I was running along the seafront in Barcelona. My left foot hit an incline and my hip flexor tore. Physiotherapists told me to do nothing until the marathon and see what happened.

Perhaps it is sexist stereotyping but men strike me as most likely to ignore the basic rule to build gradually.

I reached the start line three weeks later not knowing if I would have to pull up after 100 metres. Miraculously, I felt fine. My hip hurt but I could run. A few miles in, I thought I could carry on as if nothing had happened. I upped my speed. It felt good, and I completed the first half of the marathon in 1:44:09 which was close to my personal best half-marathon time of 01:43:53.

The race was going marvellously apart from one tiny detail: I had another 13 miles to run. I remember very little of the second half. The pain, I remember the pain. And the paracetamol I kept gulping. And counting each stride as if somehow it would make it easier. And wishing it would end, which it did when I got across the line in 04:16:45.

My first thought was to run another marathon but do it properly and post a time I could boast about to my friends. Instead of convalescing, I went out for a little jog at the start of May. My foot hit rubbish on the pavement. It twisted over and a metatarsal snapped.

For the 10 weeks I was in a surgical boot, I yearned to return to running. I imagined I could go back to my previous levels of fitness and run a half-marathon in September over the South Downs just like that.

Inevitably, I came back too fast and ran too far. My body pretty much closed down, and I tore a calf muscle in September. I waited for it to heal, came back too fast again, and tore it again. I am now doing what I should have done in the first place: four intervals of four minutes of running and one minute walking, and then a day off, three times this week.

Next week it will be nine-minute runs and one-minute walks. The week after, I will move to 30-minute slow three-mile runs. The week after that, I will start running four times a week, and move up to five times a week and longer runs in March, as I start to train seriously for the Hackney half-marathon in May.

If you are now working through your couch-to-5k running plan –—and if you are not, see me after class — you will recognise the pattern. You start slowly and gradually build strength: three minutes running, 90 seconds walking one week; five minutes of running, three minutes of walking the next, and so on.

Consistency is everything. If you run three times a week, it is astonishing how quickly you improve. Everyone who has taken up running can remember when they could not run 100 yards without collapsing. If you stick at it, your body will change as will your ability to run off stress. But only if you don’t let the stress of meeting absurd expectations overwhelm you.

Running is like life should be but isn’t: you get out what you put in. If you train, you will see the most incredible changes and take as normal feats you would once have thought impossible.

Running is like British culture should be but isn’t. It favours the patient and the modest, who know there are no flash shortcuts, and that if a thing is worth doing it is worth doing for its own sake, not because you want to show off — most especially to yourself.