IT's 7.30pm and Bushy Park in Terenure resonates with the sound of people playing sports on this fine August evening. There's the thwack of tennis balls, the roars from what looks like a lively game of footie and the grind of skateboards. And in one corner of the park, a group of 30 flush-faced, perspiring men and women are being put through their paces and shouted at by a scary sounding man called Greg. This is Bootcamp Ireland and it doesn't look like it's for the faint-hearted.

The idea of military-style outdoor exercise classes isn't exactly new but unlike other fitness crazes that suddenly capture the public's imagination and then fade away, this 'PE for adults' has gone the distance. Lorraine Ho started the venture over six years ago, after she came back from travelling. "When I was away, I was always in the outdoors – cycling, walking, hiking – and when I came back to Ireland, I was surprised to see that people weren't using the outdoors, so that's really where the idea came from."

The training happens in the evening in parks all around Dublin, as well as Meath, Cork, Clare and Wicklow – they're always outdoors and they always go ahead, whatever the weather. When the heavy snow brought the country to a standstill in January, the bootcampers still turned up for training. Attendees sign up for eight weeks of training, which means 24 one-hour sessions and free physio class, for €150. And while many gyms offer 'bootcamp'-style sessions, Bootcamp Ireland is the only one where all the instructors actually have a military background. "They're slightly different, they have that little bit of an edge that regular instructors don't have. It just makes you work out harder," Ho says.

But if your impressions of bootcamp is that it's all about intimidation and working out to the point of sheer physical exhaustion, it's not quite as alarming as that. Yes, the trainers shout, but it's rarely personal and no, they won't let you slack but they will encourage you to push yourself as far as you can. "We have all kinds, from people who are training for triathlons and marathon races to the other extreme, where they have been sitting on the couch for the last 10 years. They can all do the same class because we train them all at their own pace," Ho says.

Bootcamp certainly inspires a deep level of devotion in its followers. They cite the lovely feeling of exercising in the outdoor, the diversity of classes, the motivation the instructors give and the excellent level of fitness one can achieve as benefits. Brian Lacey had been going to the gym and felt that he wasn't getting any better or any fitter. A friend recommended Bootcamp Ireland and despite finding it tough going initially – "A friend of mine recommended it and for the first couple of weeks I was wondering what I'd done to annoy her so much," he jokes – two years later, he's still attending the sessions and says that for him, it's simply the best way of getting fit.

It's also acted as a springboard into other things he wanted to try. Bootcamp Ireland organises surfing, hiking and skiing weekends away, and Lacey tried skiing with the group for the first time this year.

There's a massive social aspect to it all, says Ho. "A lot of people are in their 30s and their friends are getting married and having kids and they might feel that the group they used to go out with at the weekends isn't there anymore," she says.

"They join Bootcamp and there are loads of other people in the same boat and they end up going on trips together and on social nights out."

Shelly Browne, who has been attending bootcamp sessions for six years, liked it so much she joined the company. "I had planned to go to London at the end of July and the opportunity came up to work in the office here [marketing] and I just grabbed the chance," she explains. "I just like everything it stands for – I obviously love it because I can't seem to stop doing it.

"Even after all these years, I don't feel like I've reached my limit, there's always further I can go because you can always push yourself more."

Electric Picnic's Siobhan O'Dowd introduced Bootcamp Ireland to revellers at the festival last year and it was a huge success, despite musical festivals and working-out not seeming like obvious bedfellows. But apparently a bootcamp workout is a great cure for a hangover and the instructors will return to Electric Picnic again this year, looking for recruits to arm wrestle and do press-ups.

O'Dowd too has become a bootcamp enthusiast and has started her second eight-week training stint. "It's great because when you're doing sit-ups, you're looking at the sky and because you're so wrecked after that bed just seems to envelop you and you go out like a light."

Lorraine Ho is certainly evangelical about what bootcamping will do for a person. "Your whole attitude to exercise changes. It becomes part of your lifestyle. You become a lot more focused: concentration levels go up; stress levels go down. You start to feel better," she says.

"We don't go on about weight too much but it's just phenomenal how much weight is lost and it just comes naturally."

www.bootcampireland.com

Fitness Fads: the latest exercise crazes

Budokon

A form of martial arts which combines karate, tai kwon do and yoga techniques. While it's not as hardcore as something like kickboxing, it does help with strength and stamina. Good for the mind too, as every session starts with meditation

Power Plate

The work out where you don't sweat but can burn up to 400kcal in one 10-minute session. Here a vibrating plate does all the work for you – stand on it and it causes muscles to contract as much as 50 times a minute.

Kettlebells

These Russian-designed weights are big in 2010. A 15-minute session a day, twice a week is all you need to see results and improve overall strength as you lift, press, swing and pull them.

Zumba

This fun and energetic dance class mixes rumba, salsa and mambo moves so you get your cardio and aerobic exercise, as well as calorie-burning, in one hour-long session.