When I was at primary school, I wasn't just an unsporty child: I was positively anti-sporty. One of my earliest memories is of being instructed to run to a wall on the other side of the football pitch and back at breaktime. By the time I turned round for the return leg, all my classmates were happily tucking into their Marmite sandwiches while sniggering at my snail-like speed. Things were even worse on the netball field, where the A-list girls simply refused to throw the ball to me, even when I was standing directly underneath the goal.
As a result, I had always associated sport with hot-faced humiliation and avoided any sort of activity for over 20 years, faking a case of athlete's foot for five years to avoid swimming and sneaking to the back of the queue in rounders so I wouldn't even have to trot a few steps.
Adverts extolling exercise didn't help either - the proud owner of a bottom that always looks big in everything, I simply couldn't identify with the lithe whippets who were supposed to be my role models. It was almost as if sporty types had membership to an exclusive club with a 'curvy types need not apply' policy. When was the last time you saw a plus-size fit kit?
Fast forward to 2015, however, and it's an entirely different story. Having run 67 marathons so far, I'm an aspiring member of the 100 Marathon Club and my goal is to do at least another 15 this year in addition to a 100-mile walk in Holland. So what changed? What turned me into a marathon convert after decades of extreme exercise avoidance?
Age definitely had something to do with it. Firstly, I didn't want to spend my thirties feeling as unhealthy as I did in my twenties. And secondly, I cared a lot less about what others thought. In my younger days I'd have been mortified to learn that I'd come last (yes, really, last!) in no fewer than five marathons. In my forties I'm thrilled that I've plucked up the courage to attempt them at all.
Older and wiser, I no longer judge myself against other people's criteria for what being 'sporty' involves. 'Talented, athletic and competitive' - I'm none of these things. What I am now is 'active', a word that to me implies that I'm doing my own sweet thing to keep moving, for my own sweet reasons, and I don't care how 'well' I'm doing it. Instead of being mortified that I don't look like a runner, I take great delight in proving that running isn't only for those who look fabulous in Lycra.
Watching Sport England's - which aims to 'inspire women to wiggle, jiggle, move and prove that judgement is a barrier that can be overcome' - I was impressed by how well the filmmakers captured what being active is all about. Yes, the ad says, there's absolutely nothing wrong with wanting to be competitive, but there's also room for the rest of us - the ones with wobbly bits, who find being competitive stressful and demotivating. Stop judging yourselves, urges the ad, forget about whether you're sporty or not and just get moving.
I can vouch first-hand for the benefits of adopting this philosophy. Whenever I look at my burgeoning medal collection I'm reminded that being active gives me the greatest sense of achievement I've ever known - which is heightened because, well, I'm 'bad' at running, and each and every medal has been so hard won. They are mementoes of success measured in my own terms: in every race it's not about the time I've done, but the fun time I've had; not about the people I've beaten, but the friends I've made.
This new sense of self-belief has benefited innumerable other areas of my life: I ditched my career as an editor, which wasn't really going anywhere, and retrained as a clinical hypnotherapist; I wrote the books I'd always dreamed of writing; I reinvented myself as The World's Slowest Marathon Correspondent and now travel the world reporting on marathons for three running publications.
So perhaps us 'unsporty' types should ignore the 'sporty' label entirely and adopted a new one - 'active' - instead. It's time we rebelled against the way fitness is sold to us - as a glamorous and aspirational lifestyle choice reserved for the firm of thigh and fleet of foot. Only once we shatter the stereotype of what a fit person looks and acts like will we be able to realise our true potential.
Lisa is the co-author of Running Made Easy. Find out more here.