I am not a runner. That's not to say I don't run: I've jogged back from nights out, cutting a weaving path down empty streets, phone in one hand, pilfered beer mat in the other.
On the last day of year six, I ran home through pouring rain, half crying, half gasping for breath. I've done a run-skip-shuffle to Tesco in a coat and pyjamas for milk. I've run cross-countries and pounded pavements. I even planned to run the London Marathon.
But still, I'm not a runner. A runner is a strange thing – a neon-Lycra-clad, grilled-chicken-and-a-salad type of person.
They are light-footed and competent; I recently discovered that I've been incorrectly bending my knees my whole life. What kind of a person can't even bend their own knees?
Running has been part of my life since I was 11, or maybe 12. The reason I started was to be good at something. I was ungainly and lanky, and I didn't have many friends, so the more activities I could be good at, the less I had to worry about feeling good.
I'd go running after school, slink into the gym at lunchtime and even do laps of the field. I was the only person sick with excitement, not dread, on cross-country days. I'd finish every time with a ferrous tang of blood in my mouth and my lungs burning, but I'd still want more. I wanted to win.
I never did, of course, but I couldn't stop myself from pulling on my trainers and setting off around the track. I loved the feeling of it, no matter how deeply average I was. I'll never forget turning up to the borough cross-country after a summer of training and being effortlessly lapped by a girl called Naomi, who to my knowledge had not trained once.
I hated her, but I was proud of how far my body could take me, and how fast.
Other than these spikes of emotion, I find it difficult to remember the thoughts I have while running; it sends my mind to a strange place. Running is so often a world of high-performance sportswear, heart-rate trackers and go-faster stripes, but my shambolic kind of jogging is a long way from all that.
When I run, I don't think about personal bests. Fragments of words and phrases get stuck on a loop in my head until the words barely make sense. Other times, it's a broken thought – recently, I silently role-played ordering a pain au chocolat for the entirety of a five-mile run.
I end up remembering all the tiny details that were useless then and are even more useless now, but that somehow stay in my head after being drummed in by the rhythm of my trainers hitting the ground. I know the exact weight of my old running bottle, and the grassy smell of my cross-country races.
Recently, I silently role-played ordering a pain au chocolat for the entirety of a five-mile run
These things make me so nostalgic that I almost want to get off the sofa, take to the streets and run, right now. There was one summer in my early teens when I ran nearly every day.
A family friend called Angela took me out running during the summer holidays. We ran along the Thames, through the cobbled streets of Leigh-on-Sea in Essex, and along the traffic-choked roads into Southend town centre. I kept a journal listing how far we'd run, and where, and in what time. It was perhaps the happiest school holidays I ever had.
Later, I joined my grandmother's running club. She didn't take up running until her forties, but to this day – even now, with her knee replaced and her body hosting a million aches and pains – she stays active.
The running gave way to jogging, which became power walking, but she's my inspiration. With the running club, I went on a few of their shorter jogs, through hilly Hadleigh and along the beach at Chalkwell, gulping in the sharp sea air.
On one of these runs I pushed myself so hard that I threw up, 100 yards from the finish line, into a stiff breeze that sent my vomit flying over the man who had been my pacesetter. I got a good time, though.
As I grew older, my teenage body began to fill out and become strange and new to me, and my running took on a different role. Suffering from bulimia, running became a way to make my body smaller. I knew all kinds of terrible things, like how many miles equalled a Mars bar, or how long I'd have to run to earn a packet of Mini Cheddars.
I'd purge after a day of compulsive eating and then go running, desperate to sweat out any fat that might have come to rest on my bum or thighs. I ached after every run.
With this history, it might seem dangerous to choose to run a marathon only a few years after finally shaking off my eating disorder. To run it for Beat, an eating disorder charity, is an extra twist of irony.
But that's exactly what I planned to do; I wanted to rediscover the kind of running that punctuated those carefree summer holidays more than a decade ago. I was ready to become a real runner, once and for all.
I didn't want to run for my weight, or my speed, or my fitness. In fact, it barely had anything to do with my body any more: being a real runner meant wholeheartedly throwing myself into a sport that I love, that keeps me active and floods my mind with endorphins.
I put the idea of running the marathon to my fiancée, Leah, during a half-hearted midweek jog. It was one of the first times we'd gone for a jog since moving to Sheffield. We hadn't done much running together before, but as soon as our competitive anxieties had worn off, we found it was the perfect way to stave off the boredom of those dull weekday jogs.
As we were walking the final leg of the run, I said, 'Maybe I should run the marathon.' 'Maybe we should run it,' she said. And that was that. Exactly two-and-a-half runs into our new life together, we decided to run the London Marathon.
Training was hard. Sheffield is a city of hills, and even the gentlest jog can feel like a mountain hike.
There were some sparks of glory, such as when I ran my first 10k in December: it was called Percy Pud, where (and I'd be lying if I said this hadn't swayed me to enter) all finishers get a free Christmas pudding and a sachet of instant custard.
But mostly, it was tough. We would head out to train when the sun was sinking low in the sky, and the pavements were slippery with mulch. In winter, we ran into the countryside, cutting through frosty grass, our skin smarting with the chill of the icy air.
And then I developed shin splints, which made every step feel like running on glass, and the marathon dream was over – for the moment, at least. Leah and I have had to defer our marathon places until next year. But somehow, it doesn't even matter.
Running has become so much more than this one race.
What's caught me off guard is I've barely given a thought to my changing body. I'm sure parts of me have grown fatter and others have become leaner, but I've hardly noticed.
With all this running, I've started thinking about health in a way that's so different to the calorie-counting, mile-tracking kind of fitness that used to interest me.
Now, it's my mind that I'm working out when I stretch my legs: I'm getting better at running off the anxiety and I'm becoming stronger at batting away creeping feelings of depression.
My mental health is better than ever. You can't run off mental illness, of course, any more than you can stride away from diabetes, but the physical outlet helps to distract me from the mess of my mind.
What's caught me off guard is I've barely given a thought to my changing body
When your brain is tying itself in knots, it can be cathartic to work your limbs, fill your lungs, and remember that you are a miraculous, living, breathing human body.
I'm still not a 'real' runner. I haven't got the hang of sportswear; my bedtime and running outfits are one and the same.
But when that familiar feeling of anxious energy comes over me, I hit the streets. I nurse my bad legs back to health. The first few steps are like wading through treacle, then my body starts to move a bit faster, and I gain momentum and my legs begin to stretch out in joyous strides. I am up and running again.
You can find Ruby's London Marathon charity page for Beat at uk.virginmoneygiving.com/RubyTandoh
This article originally appeared in the June issue of ELLE on sale now