It was with fear, and almost a touch of loathing, that I hauled my weary self from under a warm duvet before the clock struck nine on a Saturday morning. But instead of the smell of bacon frying or the promise of a smouldering hot cup of coffee, my early-morning inspiration was men in shorts – and the chance to get fit alfresco, of course – as I headed to Pittville Park to join the latest British Military Fitness session in Cheltenham.

Promising the perfect antidote to sweaty gyms, the sessions, which are essentially exercise classes held outside, sounded superb – offering a unique challenge to everyone regardless of fitness levels, or lack of them. As I laced-up a pair of shamefully dusty trainers, that haven’t seen the light of day for far longer than I care to share, Mother Nature was on my side. The skies were dry, and the session was in a park – so just how hard could it be?

Met by friendly Ex-Royal Marine Giles Heeks, who was duly decked in camouflage trousers and rucksack – no shorts, though – I was handed a blue bib with the number 88 emblazoned across and realised that this was going to be exactly what it said on the tin: British. Military. Fitness. Gulp.

After a warm-up we ran, we rolled and we carried each other – yes, piggy-backs are classed as exercise. We circled the trunks of Pittville Park’s huge oak trees, working the abs, arms, and every other muscle in between, simultaneously taking in huge lungfuls of crisp air, and soaking up the sun’s vitamin D as we worked out.

The infectious enthusiasm of exercising in a team proved refreshing – pairing-up with a friendly face, playing frisbee-netball and having more than a few laughs gave me a rosy glow and feel-good-factor that you rarely enjoy after a jog on the treadmill with only your iPod for company. Giles confirmed the benefits of this type of exercise, promising that studies show you get seven minutes of real cardiovascular exercise during an average gym workout, compared to a whopping 40 minutes with British Military Fitness sessions.

I wasn’t surprised by the stats – outdoor exercise with army style encouragement and direction is hard work, very hard work. I pushed myself because I wanted to keep-up and join in, but it’s not for the faint-hearted. Wearing your numbered bib, ‘nice press up 88!’, means even if you loiter at the back the instructors will see you – and will shout your number, not to embarrass, but to encourage. A motivational tool my fellow fitness fanatics for the day confessed to loving.

While I’ve heard about the famous post work-out high as serotonin levels peak, as I walked home – albeit at a somewhat slower post-session pace – I felt a buzz I have never experienced from an aerobics class or gym workout. Yes, my kit was grass-stained, my face was red, my bedraggled hair may have shocked passers-by and I hadn’t been treated to the men in shorts I was hoping for, but I was walking with a smile.

British Military Fitness sessions at Pittville Park in Cheltenham are held Tuesdays, Thursdays and Saturdays and cost between £20 and £33 a month. To take advantage of a free trial class and find out more about British Military Fitness Cheltenham call 020 7751 9742, visit www.britmilfit.com or email fitness@britmilfit.com