Emma Bartley is still struggling to shift the baby weight. Her glossy magazine colleagues are super fit and beautiful. What happened when they all went running?

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Joining the office running club seemed like a good idea in theory. I mean, no, I’m not a regular runner. Yes, I’m hopelessly out of shape after having a baby. No, there won’t be much opportunity to improve – I’m only here doing a fortnight’s freelance work. But none of those, I reasoned, were good enough excuses not to even try.

I quickly realised my mistake, however, as I stepped blinking into the midday sun last Wednesday lunchtime. This isn’t your average group of unfit office workers going for a shuffle round the park: my Lycra-clad colleagues are part of the ELLE Running Club, a brand thought up last year by the magazine’s dynamic Editor, Lorraine Candy. The team are taken out by high-profile personal trainers – this week it’s Claire from Reebok – and they blog and tweet their exploits to thousands of followers. Most intimidatingly of all, they are tiny.

“You can’t say that,” says Georgia Simmonds, ELLE’s acting commissioning editor. “That’s not what it’s about at all.” She’s worried the ELLE runners will sound like stuck-up fashion types – The Devil Wears Puma – so I promise to clarify that this is a lovely, friendly team who go out of their way to include me. But seriously, they are TINY. Georgia is Forties movie-star beautiful, even in her kit; willowy fashion assistant Esperanza de la Fuente should have been a model; and one section editor has a waist so tiny I’d think it was corseted if she wasn’t revealing her midriff. Looking around the group of ten I realise that the only person here who might be in my weight category is Claire – and she is a semi-professional bodybuilder.

I think about running back inside, but it’s too late; we’re off into the Carnaby Street crowd, dodging the lunchtime shoppers and the odd slightly leery local worker (“That’s what I’m talking about! The ELLE Running Club!” a man tells his friend as I barge in between them, bringing up the rear). For the first two minutes I’m in a blind panic, but as the crowds thin and we head up towards Regent’s Park I start to think that maybe I can do this. The park really isn’t far, probably about a mile, and I’m told that when we get there, we’ll be stopping to stretch.

Which we do. Unfortunately, the stretching doesn’t last very long before we have to run further on in the 29C heat. After a few minutes we stop again to do some exercises, but it’s high kicks and knee raises rather than the nice, sedate sit-ups I’d pictured. Now I’m really feeling the fact that I’ve had a baby, and not because I’m struggling – although I am, cutting every corner I can, my knee-ups slow and lacklustre while fitter ELLE runners seem to be aiming for their chins. Rather, I’m painfully aware that I had a load of coffee this morning, I’ve drunk a load of water along the way, and my pelvic floor exercise regime is not what it could be. But just as I’m about to pee myself, Claire urges us on to the next visible landmark, the boating lake, from where we loop back round and head home.

The first ELLE runner stops to walk at this point, and shockingly, it isn’t me. We’ve been out for half an hour and I’m starting to panic about what time I’ll be back. My boss is letting me work 10am-5pm so that I can get back for the baby, and I feel guilty taking a lunch break. If it takes us another half hour to get back and I have to stop in at the gym for a shower (which I will, I’m absolutely bright red and sweating profusely), I’ll have been out for over an hour. Not cool. So I keep running at the same pace, trying to keep sight of Georgia and a few others at the front as the rest of the group slows down a little.

Slightly ahead of me, Espe stops to walk – I chuck her my water (I’m too scared to take another sip anyway) but keep going, aware that I have no means of paying for a bus or taxi back. Yes, seriously, I’m thinking about bus routes at this point.

But as we reach the edge of the park and turn right, heading south back to the office, I start to catch up with the front runners. Simultaneously, I start to think I might do it. There’s very little distance left to run, and we have to stop for a few traffic lights, which gives me a chance to take deep breaths and try to slow my heart rate. As I do so I realise that, while I’m unbearably hot, my body feels reasonably OK.

Along we go in a group of four, getting closer and closer to the office until finally we’re back and it’s time for me to jump in a cold shower. As I change, it sinks in that I’ve done the whole run (around four miles) without stopping, and largely keeping pace with the regulars.

Perhaps, I think, I’m fitter than I’d thought. But my crimson face gives the lie to that theory; I spend the next two hours sweltering at my desk like a sweaty Satan. Maybe the ELLE team aren’t as hardcore as I’d thought? But we are talking about a group of women who recently ran the Paris half-marathon between appointments at Paris Fashion Week. In the end, I conclude that it’s the group itself that has kept me going. I’d never have done it by myself, but in a pod of runners I just got on and did it. It also really helped that I knew I’d be supported if I did have to stop: everyone took it at their own pace, and Claire hung back to make sure any stragglers were OK.

Will I be back next week? Definitely, and I might even time myself. But I will be laying off the coffee beforehand…

Join the ELLE Running Club at  elleuk.com/beauty/running , on  facebook.com/elleuk  and on Twitter @elleukrunning