Idiens is nothing if not consistent. She started teaching online at the beginning of lockdown, for 40 of her local friends and clients in Berkshire. ‘We thought it’d be as a nice way for us to come together,’ she says. Five years on she has thousands logging on to her live workouts. ‘We still do a 30-minute session at the same time on the same days, 9am on Mondays, Wednesdays and Fridays,’ she says.

We’re meeting because she’s launching her first book, Fit At 50: Your Guide To A Stronger, Fitter & Happier (Mid)life In Just 6 Weeks. She also has a growing membership and app with hundreds of workouts on demand, as well giving free classes on Instagram, her website and on YouTube.

Why does she think she got so popular, so fast? I ask. ‘It’s helped that I’m part of this huge conversation around midlife, menopause and staying strong and healthy that’s been happening in the past few years,’ she says. ‘I always say that strength training makes your muscles strong… but it does so much more. The exercises I do in classes aren’t, for example, isolated bicep curls on a machine. They’re functional, working the muscles you need to put things away in a high cupboard, to turn as you get out of the car.’

Idiens’ daily posts on Instagram to her two million followers explain the benefits of strength work for health and fitness, posture and balance, flexibility and co-ordination into later life, and how it helps bone health too. ‘People think the bone you’re born with is the bone you have for life, but in fact you can make a massive difference to it by lifting weights. You can grow new bone and improve your bone density. Members have told me about their improved DEXA bone density scan results after doing my workouts regularly.’

Idiens often talks about how exercise makes us feel mentally, too. ‘Lifting weights gives you inner confidence. You feel stronger, but it’s more than that. You really have to focus on the weights, and on your muscle groups and form and technique. The 30 minutes you spend in the class is time you’ve carved out for yourself. A lot of people tell me that exercise is their headspace.’

We laugh over what used to be thought about women lifting weights, back when Idiens first became a PT in the early 2000s. ‘There was a myth that weights would bulk you up into a bodybuilder overnight,’ she says. ‘Exercise for women meant cardio, a way to run off what they’d eaten the night before.’

A lot of women still come to her doing mainly cardio, she says. ‘If running gives a release and mental clarity, you don’t have to give it up. I advise strength work three to four times a week, cardio for 150 minutes a week. If you’re not a runner, that can be walking. You can get your heart rate up with weights too.’ (If you don’t believe her, try the Friday 9am Strength HIIT class!).

There’s a focus in classes on the core, the back, and especially, the glutes. ‘Most women spend a lot of time sitting at laptop or driving a car, leaving the glutes weak. If those muscles aren’t firing, it can lead to back pain.’ And there’s plenty of arm work too (Caroline has impressive arms). ‘One client told me that at her son’s wedding, she wore a sleeveless dress for the first time in 15 years,’ she says.

The book is a based on a six-week programme, including Caroline’s other three pillars of midlife health too. As well as exercise, there’s sleep (‘it’s your superpower!’) and mindset (‘by beginning an exercise regime you will start to notice how amazing endorphins make you feel’). For the fourth pillar, nutrition, Idiens worked with a dietitian Laura Clark to create over 50 satisfying, easy recipes – tuna crunch wrap, anyone? ‘The right nutrition is important alongside exercise. Your body changes so much during the menopause that it can be a bit of a shock. One of the side effects I hear from women all the time, is weight around the middle. At this age, it’s not about cutting things out, it’s about moderation. It’s about fuelling your body correctly to be able to exercise correctly.’

What can women expect to see if they follow the plan for six weeks? ‘I always say that in two weeks you’ll feel it, in four weeks you’ll see it and in six weeks it’ll become a habit,’ she says.

Idiens argues it doesn’t matter what age you are, anyone will feel the difference. ‘There are women in my classes of all ages. And why wouldn’t you start now, when you know it’s going to help you into your 70s and 80s?’

Caroline’s best fitness advice

1) Always warm up and cool down. And listen to your body.

2) Start small. Remember, changes take time. Build up gradually.

3) Take regular rest days. Muscles need time to recover and grow stronger.

4) Schedule your workouts into your diary.

5) Write down your workouts to keep track of your progress.

6) Start with bodyweight exercises, then light weights, and gradually go heavier. The ideal weight is when your last two reps feel hard.

7) Even when you’ve built up to heavier weights, there’s still a place for light weights and resistance bands, to train smaller muscles.

8) Remember, a little exercise goes a long way.

Fit at 50 by Caroline Idiens

Caroline’s 20-minute full-body workout for Red

One circuit is three sets. Do each exercise for 30 seconds per exercise with a 15-second rest after each exercise. Take 30 seconds of rest between sets. For the exercises with dumbbells, use the weights which are right for you (or none). Make sure you warm up and cool down. You can watch the full video of the workout above.

1) Squat and press

With all your weight in your heels, hips back, straight back, squat as if sitting into a chair. Keep your chest lifted and shoulders back. Come back to standing. Keeping your knees soft and abs tight, slowly press the arms up above the head. Return to the start position.

2) Reverse lunges (alternate legs)

With shoulders back and core engaged, step back so your front leg is at 90 degrees. Power through the supporting heel to stand. Switch sides.

3) Deadlift into upright rows

With a soft bend to the knee, hinge from the hips, sending them back. Keep the back straight. As soon as the chest is parallel with the floor, drive up to stand. Try not to round through the spine or dip the head. Standing tall with knees soft, bring your elbows up.

4) Bent-over rows

Hinge from the hips, with arms extended for full range of motion. Keep your back straight and your head in line with the spine. Slowly bring arms back towards the pocket of your leggings. Core tight. Do not round spine.

5) Press-ups

Start on hands and knees. With your hands wide on the mat, come forward in one movement (without dipping the head), back straight and elbows back. Try to keep core engaged and come up in one movement. If the exercise is too hard from your knees, start against a wall or on a bench and progress to on knees (as in pictures), then to on toes.

6) Slow mountain climbers

From a plank position, keep your hips down, back straight, core tight, shoulders over wrists. Bring one knee into the chest, then alternate. Do these at the right pace for you.

7) Dead bugs

On your back, head down, extend one arm and opposite leg slowly. Switch sides. Keep the back on the floor and core engaged throughout. You can also do this holding light weights.

Fit At 50: Your Guide To A Stronger, Fitter & Happier (Mid)life In Just 6 Weeks by Caroline Idiens is out on 6 March

For 20% off the first month of Caroline’s Circuits, use the code Red20 at carolinescircuits.com