LIZ HOGGARD: Can Michelle Obama’s exercise class cure my gymphobia?

My practice coach, Louis, reassures me, “Don’t worry. This isn’t going to be a beast,” as he straps a heart rate monitor to my arm. ‘Together we look for the right intensity and then you set your own pace.’

Puzzled, I look up the definition of beasts on my phone – “punishment intended to humiliate, go to extremes, and hurt (usually military).” What did I let myself go for?

I haven’t set foot in the gym in over 35 years, put off by the garish male instructors, harsh lighting and general air of body fascism back then.

Like many middle-aged women, I like endorphin-stimulating exercise, but it has to be gentle and non-competitive. I run 30 miles a week, swim three times, do Pilates. But when it comes to Lycra, count me out.

Yet Orangetheory Fitness, the franchise of cult gym studios founded in America and growing in popularity in the UK, where there are now nine studios, claims to offer a different type of exercise class.

Community and inclusiveness are the keywords. It is for people of all ages, shapes and sizes. Michelle Obama is a fan and if you watch the Netflix show Queer Eye you will recognize it as the place where the Fab Five take clients.

Can this cure my gym phobia?

Orangetheory (or “Orange Therapy” as fans call it) teaches hour-long circuit classes, split between time on the treadmill and rowing machine, and weight and strength exercises like lunges and floor squats. It’s a group class, but you go at your own pace according to your own heart rate data.

Everyone is set up with an arm heart rate monitor. It tracks your beats per minute and the data is projected next to your name on digital screens around the room, so you can see how many calories you’re burning and what your average heart rate percentages are.

The goal isn’t to be flat all the time, but to get your heart rate up, boost your metabolism, and improve cardiorespiratory health.

Unfortunately heart health is not good in my family. My father and all my grandparents died of heart attacks at a young age.

A family history of heart disease is defined by having a first-degree male relative who had a heart attack at age 55, or a first-degree female relative at age 65. My father had his first age at 54 years old.

When I recently consulted a leading cardiologist, he bluntly told me to cut out weekly chips, follow a Mediterranean diet, and increase fat-burning exercise. I am fit but a bit chubby – which is dangerous with my family history.

So could heart rate-based interval training at the dreaded gym at age 60 make a difference?

I am booking into Orangetheory’s studio in Fulham, South West London. I expect an orange-clad cult. And yes, the lighting makes the whole room look orange and the super-fit coaches have a hint of Baywatch about them, but they’re nice, enthusiastic, and make you feel that their biggest goal is to get beefy midlifers in shape.

At the beginning, Louis walks me through the five heart rate zones people go through during exercise. Gray is when you are relaxed; blue is the easy warm-up zone; green – the ‘endurance zone’ – is when you feel challenged; then there’s the orange zone when things start to feel awkward. The red zone – the upper one – is reached at maximum effort.

“It’s like your mother-in-law’s house,” jokes Sean Johnson, Orangetheory’s regional fitness manager. “It’s fine to walk in, but no one wants to stay too long.”

The goal is to spend a third of the workout (20 minutes) in the orange zone and the rest in the green zone. But the effort required depends on your body and medical history.

I’ve never done interval training. The session starts on the rowing machine, where I enjoy the workout of muscles, abs, legs.

Louis encourages us to increase our efforts, raise our heart rates and move from the gray zone of warming to green.

Soon everyone’s profiles will light up green, orange, and red on the parent leaderboard. Unfortunately mine doesn’t go beyond gray (aka a relaxed pace).

Then, It’s A Knockout style, the group sprints to the other side of the room to do strength exercises. While everyone else is spinning weights around their heads, I’m still trying to get my feet out of the Velcro straps of the rowing machine.

I enjoy the Total Body Resistance exercise (stretching with resistance bands on the wall), and it’s good to see my profile has moved to blue. I already lift 3 kg hand weights at home, but combining weights with lunges is difficult. I cry on the third set of reps and am shocked at how unfit I feel.

We continue with the treadmills where you can run, jog or walk. I choose power walking at four miles per hour. As we increase the grade to 10 percent (to increase the grade), I finally get my first green zone readout and feel triumphant.

Then Sean takes me through my results (regulars get them by app). After an energizing, adrenaline-pumping class, I burned 308 calories in an hour and walked 3,000 steps. For comparison, I had to walk seven miles (14,000 steps in five hours) the day before to burn off that amount.

I was in the green zone for 16 minutes. My peak heart rate was 131 beats per minute (ideally for my age it should be 80-136). Walking vigorously on an incline has little impact, but will strengthen my posterior chain (the muscles in the back and glutes), Sean says tactfully.

The day after my session my thighs hurt – have they ever moved so much before? When I test my blood pressure with my Omron home monitor, it has dropped from Grade 1 Hypertension to High Normal. I hate interval training, but even I see the point in getting out of your comfort zone.

Orange Theory is less about bodybuilding and more about “training for life”; improving strength and coordination so you can climb stairs, carry groceries, and other things that can slip out later in life.

So yes, I agree to go back every week. And really do! I’ve even managed to hit the orange zone once or twice and I’m less breathless when climbing hills. I have a bad feeling that I am converted.

• Orangetheory Fitness studios in the UK offer a free trial class. Membership options in London start from £109 per month or £199 for ten lessons, orangetheory.com