For the two hundred people assembled on the rooftop of Lahore’s swankiest new mall, Fortress Square, braving the May heat is the least of their problems. It’s the thought of conquering the burpees and the squats that’s making their heads spin and their bodies sweat. The group is diverse, consisting of everyone from young professionals looking to get into shape, new moms seeking to banish their muffin tops, body conscious aunties and a smattering of the city’s socialites who want to be part of the latest fitness fad raging across the city. But they are on a singular mission to not be the ones to face the wrath of the trainers and be shamed for doing the sit-ups like a lazy 5-year-old.

This is the 42-Day Challenge - a fitness programme that was introduced in Karachi in 2013 and found its way to Lahore only a few months ago. Developed by med student Torsam Tajik and aspiring lawyer Nusrat Hidayullah, the 6-week, bootcamp-style intensive workout routine is complemented by an equally stringent diet plan. Torsam describes the exercise part of the programme as a compilation of routines pioneered by fitness experts around the world as well as scientific research in the field, coupled with his own understanding, gathered through his medical training, of the workings of the human body.

The workout regime is based on High-Intensity Interval Training or HIIT, a form of exercise that is having a serious moment worldwide. From super athletes like David Beckham to Victoria’s Secret supermodels, celebrities around the globe favour this form of intense workout to fulfill their fitness goals. So what exactly is HIIT? It’s a type of cardiovascular exercise that alternates short bursts of high intensity intervals with equally short ‘rest’ or ‘recovery’ periods. Because of its ability to burn fat and build muscle, it’s considered a healthier alternative than traditional exercises such as running for hours on the treadmill in the gym.

"Most people, especially us Lahoris, want a quick-fix weight loss solution," says Anushka Paracha, the woman who runs the Lahore chapter of the 42-Day Challenge. "But the traditional methods often have negative health benefits. Most people will either starve themselves and end up losing muscle, or will exercise for hours in the gym and not control their diets. Both methods do the body no good nutritionally."

The goal of the programme is to focus on fat loss instead of weight loss - a healthier option in the long run. So while you may not be dropping kilos on the scale, you will be losing inches around your body as the HIIT workout, combined with the meal plan, allows the body to cut out the fat and build muscle that gives you strength.

"There are many misconceptions surrounding fitness routines in Pakistan, especially amongst women. A majority of the women here tend to follow diets that make them lose muscle strength along with fat, making their bodies weak as a result," explains Anushka. "Or if you tell women to lift free weights even of 4 kgs, which is part of our routine, they will hesitate to do so thinking it will bulk them up. Which is strange, considering a lot of them carry their own kids who definitely weigh more than 4kgs," explains Anushka.

Styled like a fitness bootcamp anywhere in the world, where trainers are meant to use the occasional unkind word as a form of motivation, the 42-Day Challenge is definitely not for you if you prefer cushy, air-conditioned gyms where you can give up the minute you feel the workout getting too strenuous. The 45-minute session, held six days a week, is brutal and has been known to reduce grown men and women to tears.

"You are thrown in the deep end," says PR guru Selina Rashid of Lotus, who recently completed her first session in Lahore. "Whether you’ve been a regular gym buff all your life or never worked out before, you are all doing it together. Of course, it’s very difficult but then that’s why it’s a bootcamp. They will kill you!" Selina, who had two kids in two years and piled on the pounds, wanted a jolt to the system and the 42-Day Challenge worked like a charm. "My husband and I did it together, so it was quite motivating. I’m happy with the results and will join again post-Ramzan."

The tough love doesn’t work for everyone though, and there are many dropouts in the first few days. "I know the participants all hate me the first week," smiles Anushka. But that’s something that she says she can live with, because the paradigm shift in those who make it through to the end of the 6 weeks is huge. "It’s not just about dropping inches, it’s about adopting a whole new lifestyle that is healthier and better for you." Encouraging Lahoris to give up biryani for lunch in favour of 5 small meals weighing between 60 to 100 grams hasn’t been easy but the glowing testimonials that crop up daily on the Challenge’s Facebook page show that people are slowly but surely opening up to the idea of embracing a healthier lifestyle.

While the 42-Day Challenge pioneered the concept of HIIT bootcamps, it’s no longer the only programme in Lahore that offers fat-loss workout regimes. The 40-Day Bootcamp, run by a company known as 180 Degrees, offers a similar programme for the very same price (PKR 15,000); in fact many people confuse one for the other. That’s understandable because the 40-Day Bootcamp was introduced by ex-participants of the Challenge who say they were dissatisfied with the service they were getting. With certified trainers on board and sessions that span four weeks as well as six, the bootcamp is finding its share of takers. "We started in February and we’ve trained as many as 500 people so far, including the Pakistan Polo Team," says Natasha Qizalbash of 180 Degrees. "Our groups vary in age from twelve to sixty, so we make sure we cater to everybody."

No matter which programme you opt for, according to nutritionist Amna Sultan, the key to undergoing such an intense workout challenge is to trust your instincts. "We all know what our limitations are and how much we can push ourselves. In most instances, the workouts cater to those who have physical limitations, such as a bad back, but I would still advise people to watch out for signs that mean the body cannot be pushed any further. Having said that, an exercise that doesn’t challenge you to push your boundaries isn’t working. So be intelligent and know when to stop."