In 2017, it’s not enough to be fit and healthy: you need to be strong. The cruel twists and turns of the fitness world: once, you were meant to be lean, limby, elegant, perhaps a ballet dancer. Then you had to prove you could swim for miles or run a marathon (or two). But the latest must-have isn’t just a slim waist: it’s rock-hard abs. You don’t merely run for the bus without breaking a sweat; you could push the bus if it broke down.

In many ways this is just another type of body-shaming, in a more muscly form, but I have to admit it appeals to me. I’ll never be winsome; I’ve never done a second of ballet and I don’t plan to start now. But I do have grit, I like to sweat and I love the idea of knowing that, were push come to shove… well, I could do some efficient pushing and shoving.

I sign up with Fran Finbow, a personal trainer at Frame Gym in London. She is going to get me strong. I will know what to do in the scary weights section of the gym, where men grunt at mirrors. And, hopefully, I’ll look really great in jazzy leggings, just like Fran does.

Happily, the gym is opposite my office. This is crucial to starting a new routine: logistically, it is incredibly easy. All I have to do is add an hour to the beginning or end of a couple of working days, and I’ll have slotted in two workouts. Step two is having someone waiting for you who charges by the hour. Staying in bed and postponing a workout is not an option (depending on how many sessions you book, Fran costs between £55-70 an hour).

We meet to discuss goals and do some basic flexibility analysis, so she can see what she’s working with. I learn a few things: I can do just one proper press-up (chest all the way to the floor and back up again), and I have a “very lean” chin. Yes, chin.

My new trainer seems anxious that I’m vegetarian: eating adequate protein alongside weight training is key to rebuilding muscle (as is good nutrition in general). And, no, she says, lifting weights doesn’t make you big and muscly. Do it right, and you will be leaner, with a smaller waist and firmer, toned legs. Plus it helps stave off osteoporosis, boosts the immune system and improves balance.

After our first proper session, I worry I might actually pass out; Fran has to trail me into the toilets to check that I haven’t. I think my body might be in shock. Until now, my training routine has been enthusiastic but haphazard: apart from my weekly bootcamp in the park with colleagues (which may be more than most do, but is woefully short of the government recommended minimum of 150 minutes’ exercise a week), I might do a burst of 10-minute YouTube video workouts, go on the odd run or swim with friends, or do three days in a row at the gym, followed by weeks where I do very little at all. With gym memberships spiking in January and attendance typically fading by March, will a personal trainer help me stick to a routine?

First Fran focuses on my mobility: we go over very basic moves such as squats, push-ups and lunges, and she looks at how everything is moving. She makes me do a very slow bear crawl across the fitness studio, my hands and toes on the floor, my knees lifted. It appears simple, but it is utter hell. “Just turning on your core,” she sings merrily. When Fran asks if something hurts and I say yes, she cackles with delight. I like her approach: I can’t stand trainers who say, “Do this, and you can have another chocolate this weekend.” I want someone who takes it seriously and pushes me hard.

Every session starts with moves for muscle activation, mobility and technique, and some of them finish with some high-intensity cardio (swinging a kettlebell, or slamming a heavy rope on the floor). Otherwise, we focus on lifting. Weights are all about reps and sets: rep (short for repetition) is one complete movement (for example, one bicep curl). A set is a group of reps. Before I start each set, Fran will tell me what we’re going to do (eg, “three sets of eight to 10 reps”) and check I remember how to do it.

Each week, she ups the ante and encourages me to lift more. And I’m amazed to find that I do: in week one, I manage eight reps of chest presses with two 8kg dumbbells; by week four, I can do sets of 10 reps using a 25kg barbell. I start by doing a deadlift with the 20kg bar on its own, to master the technique; I end up doing 10 reps at 60kg.

I love the endorphin rush that comes from this kind of exertion: Fran teaches me how to breathe properly and how, if I hold my breath, I can use the exhalation effort to help push a heavy weight. It’s also therapeutic; thinking about my technique in such close detail (engage core and bum, and keep my chest high, and breathe, etc) means I cannot possibly think about anything else, such as work stress or to-do lists. It’s just as satisfying as the feeling after a sprint or spinning class.

About four weeks in, I realise that I’m generally feeling really good; in control, fitter and, yes, stronger. I sleep deeply at night and feel calm under pressure. The scribblings in Fran’s book back me up: all weights lifted have gone up. In week eight, she measures me: the shift is not dramatic, but my body fat is down, my muscle mass is up, and my waist and arms are leaner. It’s by no means an end point, but I feel as if I’m on to something. Time to find myself some jazzy leggings.

Start here

• Book at least one hour with a trainer (most gyms offer a free taster session) who can show you the right way to do the basics: squats, deadlifts and presses.

• Your muscles will tighten up, so stretch often, to improve mobility

• Start with light weights (or no weight) and master your technique before increasing the load