The day I was overtaken by someone in a chicken costume was the day I knew I wanted to get serious about my running. It was the summer of 2012 and I was taking part in a 10k race in Regent’s Park in London during a torrential downpour. On the final lap of three, the sodden chicken chased me down and came plodding past, so close that I could smell the damp nylon feathers. I made the usual excuses to myself: this was clearly a much younger man, an experienced club runner who was using a local race to practise in his suit for a marathon. But then something else kicked in: how could I consider myself a runner if I allowed myself to be overtaken by someone in fancy dress?

By the time I had made my decision, the chicken was almost out of sight. But then I saw it struggling up the hill that marked the final kilometre of the race and somehow found something in reserve to speed up. He was still ahead of me as we turned the final corner and I had no idea if he had a sprint finish in his rubbery legs. Something about the daft costume filled me with a kind of lunatic fury and I drew level and passed him on the line.

There were no fancy-dress costumes as I joined more than a thousand runners on the starting line of the English National Cross Country Championships on a freezing day in Sunderland six months later. Since joining my local athletics club, Highgate Harriers, towards the end of 2012, it had been my aim to compete at the event. As I waited for the starting pistol, I thought back to what had driven me to be here, shivering and terrified, ankle-deep in mud. And through the fear and discomfort I found a moment to feel a sneaking pride in what I had achieved.

Until the late autumn of 2011 I had run no farther than the end of my road – and when I first tried that, I struggled to run home again. At 45 years old, the classic journalist’s lifestyle had taken its toll on my waistline. But I was in denial until a particular photo taken in a profoundly unflattering T-shirt made me realise that the lean-and-hungry student I still half-imagined myself to be had been replaced by a fat and thirsty-looking hack. I had to admit that I was having trouble keeping up with my two young sons and was even struggling to bend over to pick up a cricket ball. Worse still, I had become known within the family as “fat dad”, which was blunt, direct and entirely accurate.

I began tentatively, around the wood at the end of my road, a lap at a time, barely above walking pace. After a few weeks I became what used to be called a jogger, at which point a friend arrived for dinner clutching a medal he had won in a race and challenged me to run the next one with him. Towards the end of this, my first 10k event, in December 2011, I was in so much pain that I wondered if this was what dying felt like. But as soon as I saw my time of just over 50 minutes, my first thought was, “I can do better than that.” Within six months, I had lost a stone in weight without consciously changing my diet; the pounds just fell off as I began training three or four times a week.

I decided to dedicate the next year – 2012 – to seeing just how fast a corpulent and ageing journalist could get if he put his mind to it. Friends and family warned me about the strain I would be putting my body under if I took up running seriously yet no one had ever cautioned me of the dangers of being 14 stone, drinking too much and never exercising.

I soon discovered the “parkrun” phenomenon: free 5k runs organised every Saturday morning by volunteers across the country – about 25,000 people take part every week. A simple barcode system allows runners of all abilities to time themselves over a respectable distance in often beautiful surroundings – Hampstead Heath, for example. I soon saw a gratifying improvement in my times at 5k, from more than 23 minutes to 20:30 on Hampstead’s hilly course and a minute faster on flatter circuits across north London such as Alexandra Palace and Highbury Fields, and at Barnstaple in Devon.

I also tried the longer, 10k distance elsewhere, and my improvement was even more dramatic: in the 18 months following my first race, I knocked 10 minutes off my personal best. It now stands at 39:54. I even ran my first half-marathon, the Great North Run, and put in a time of 94:10. To put this in perspective, Britain’s best veteran runner, 60-year-old Martin Rees, does the three distances in about 16, 33 and 71 minutes respectively. But I was still delighted.

So delighted that it became something of an obsession. I began buying Runner’s World and Athletics Weekly to pick up training tips and to persuade myself that I was indeed a real runner. I signed up to websites such as Run Britain and the Power of 10, which allow you to track your performances and compare them against other runners’. These show that I had last year’s 464th fastest time at 5k for an over-45 and the 938th fastest time at 10k in the same category. At the considerably more obscure two-mile distance I was a proud 14th. According to the sites, my latest results put me somewhere in the top 10 per cent of runners my age in the country, which is hugely gratifying. But, of course, the desire to improve these times feeds the obsession. I find myself huddled over the computer after each race waiting for the results to come online and watch the incremental improvement in my times cause minuscule shifts in the rankings.

I see the panic in the faces of colleagues and friends if the conversation happens to turn to running. They know better now than to ask me how it’s going. But if I happen on a fellow enthusiast, the conversation can last for hours as we exchange details of training regimes, injury niggles and race-day war stories. As my running has become more serious, so has the training: a regular 15 miles a week until recently, when I upped it to 25 miles after I found I could manage the six-mile run between work in central London and home in the north of the city. This is nothing compared with seriously competitive runners who will regularly clock up more than 100 miles in a week but it still knocks a significant chunk out of the day.

Martin Bright, runner number 4823, at the English National Cross Country Championships in Herrington Park, Sunderland last year

My wife, a good runner herself in her teens, maintains a weary distance, observing that there are probably worse ways to have a midlife crisis. She finds my range of day-glo running gear mildly amusing and my collection of souvenir race T-shirts and hoodies laughable. She is also the first to point out that, although I now weigh in at just over 12 stone, that still puts me on the chunkier side of the racing community (most good club runners are at least a stone lighter). I like to think she’s secretly proud of me but every now and then I catch a look in her eye that suggests she’s more than a little concerned about my sanity.

As my obsession began to kick in, I visited Rhona Pearce, a physiologist in the sports science service at Loughborough University, who tested my lung capacity, my running economy (how much oxygen I use at a given speed) and my ability to cope with the build-up of lactic acid produced by intensive exercise (that pain you feel in your muscles). I was not a little astonished that on each of these measures, my scores were in line with those expected of a good club athlete. Better still was the conclusion that with training to build my endurance, I would be able to hit times of under 38 minutes at 10k and 18-19 minutes at 5k, something that would have been unimaginable to my podgy former self.

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But the real revelation of the past two years has been the glorious madness of cross-country running. I have Highgate Harriers’ legendary Ben Pochee, one of the fastest men over 40, to thank for introducing me to this strange pursuit, and with his guidance I have now taken part in 16 mud-caked races of varying distances across the country. These included several fixtures of the London Metropolitan League, won for the first time in 2013 by my elite comrades at Highgate. I tasted glory as part of the team that won the Liddiard Trophy, organised by Queen’s Park Harriers in west London. But I have also felt the humiliation of falling flat on my face at the end of the Southern Masters race in Essex, as well as pride at running in the same race as men who compete for their country, including Highgate’s own Shaun Dixon.

Over the winter, each time I took on a new cross-country challenge it felt like the most difficult thing I had ever done in my life. Just a week before tackling the Sunderland course, I had run 15k around Parliament Hill in the Southern Championships and finished a painful 350 out of 541 finishers. I had been told this would be horrible and it was. I was told it would be the most challenging race of my life but nothing prepared me for the misery of Sunderland.

If someone had told me, 18 months earlier, that “fat dad” would be on the starting line of a national competition with some of the best athletes in the country, I would have thought they were cracked. I did wonder about my own sanity when I stared up at the snow-covered hills of Sunderland’s Herrington Park and then down at my poor sodden feet.

By the time a brave 1,100 senior men lined up, the course was 90 per cent mud, churned to sludge by earlier women’s and junior races. My feet were so frozen that they remained numb with the cold until halfway through the race. Although it was a mere 12k, every stride was double the usual effort because of the lack of traction underfoot. Due to my inexperience, I tend to begin my races too quickly and spend long, demoralising periods being passed by runner after runner. At about 10k in Sunderland I noticed that the age profile of the men passing me also increased dramatically as I was overtaken by dozens of wise grey heads, who had sensibly conserved their strength. I was spared the humiliation of being lapped by the leaders by a matter of yards, which helped me through the final circuit of three, but by this time I was almost weeping with the effort of putting one foot in front of the other. You could barely call it running when I squelched over the line in 775th place.

With running there is no arguing with the result. The man who came in 774th that day (Andrew Baker from Guildford & Godalming Athletic Club) was just one second ahead of me but there is no question that he beat me, just as definitively as I beat that chicken in Regent’s Park.

My challenge had been to see how fast I could get from a standing start and I was quietly pleased with the result. I’m no world-beater, but I was officially the 775th fastest senior male cross-country runner in the country in February 2013. I would settle for that. Until next time.*

Martin Bright is a writer and editor. *Last weekend, Martin ran in the 2014 National Cross Country Championships in Nottingham. In a field of more than 1,650, he finished 951st – 205 places in front of Andrew Baker.

Have you pulled off a personal challenge? Either comment below, email magazineletters@ft.com or join the conversation on Twitter using #FTPursuits. You can also tweet us your photos or upload them to Instagram (#FTPursuits)

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What I learnt about myself

• I’m not a world-beater but I don’t give up easily. I haven’t failed to finish a race since I started.

• I have a new-found humility towards the volunteers in the running community: always encouraging to newcomers, whatever their ability.

• I discovered I was quite brave, determined and fitter than I deserved to be. I found I really didn’t mind the rain, could cope with the cold and mud. But one thing still fills me with fear – hills.

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Martin’s tips

• Join a club. There is absolutely no substitute for the expertise and the camaraderie this will bring. It will keep you motivated and push you to improve your technique and times.

• Be thankful for small miracles. Bank incremental improvements, which may seem almost imperceptible, but will add up to significant shifts in fitness and speed over time.

• You don’t have to run a marathon. There are hundreds of races out there from 5k to half-marathons, so set realistic targets and plan towards them.

• Fit in your training with your lifestyle. Set regular times for training runs and rest days. Reserve time for a longer, slower run at the weekend.

• Don’t run on an injury. It is tempting to keep training, even when you are hurt, but there really is no substitute for rest when you have pulled a muscle or damaged a tendon.

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Details

runbritainrankings.com

A site that allows you to log all your races and compare your results with other runners’.

parkrun.org.uk

The running phenomenon that started in Britain but has now gone global. Free, timed 5k runs. Perfect for the beginner but very fast for those who want to push themselves.

eightlane.org

One for the obsessives. An all-in-one news service, discussion forum and training service.