My wife is hesitant. “You want us to work out together?”

“Not work out: train. Elsa and Chris say training together is the key to their relationship.” I’m talking, of course, about Byron Bay’s fittest couple, Elsa Pataky and Chris Hemsworth. She’s Elena in the Fast and the Furious series. He’s Thor. Toned, sculpted, defined: theirs are the bodies of the gods themselves, in his case almost literally.

But how did Elsa and Chris attain such flawless physiques? World-class personal trainers, on-call nutritionists and limitless time and money? Well, yes. But Elsa and Chris have learned a few things through their relentless pursuit of bodily perfection and now they’re sharing them with the world: Elsa in her new book, Strong: How to Eat, Move and Live with Strength and Vitality; Chris through his app Centr, which promises to help one become “fitter, stronger and happier”.

So now I’m attempting to combat my own mid-30s physical ennui with a crash course in Elsa + Chris-style fitness, and my wife is proving a more difficult convert than I had anticipated. “It’ll be fun,” I tell her. “Elsa says we should make it a competition. Who can do the most sit-ups!”

She turns to our one-year-old son. “I think Daddy’s having a breakdown.”

Day one

At Elsa’s urging, I start the first day of my new life with two glasses of tepid water, spiked with lemon juice. As a symbol of what’s to come, it’s both underwhelming and prematurely dispiriting. Breakfast is a leek and goat’s cheese omelette, served with cashew pesto and a leafy green salad. While undeniably delicious, it takes the better part of an hour to prepare and my wife has already left for work by the time I plate up. I try to feed some of her share to our son but he finds the pesto abrasive.

With two healthy, nutritious breakfasts under my belt, it’s time to get to the day’s exercise session. Elsa is a big believer in the power of HIIT – high intensity interval training. As best I can tell, this means doing short bursts of exercise at such pace that you feel like you’re about to die. The health effects are supposed to be significant: increased calorie burn, both during and after training; more muscle growth; greater levels of aerobic fitness. Given that I broke a sweat while watering the garden, HIIT sounds like it could really straighten me out.

Browsing through Strong, I decide to attempt Circuit 4, primarily because it requires no exercise equipment. For 40 minutes I work through an endlessly repeating pattern of bear crawls, squats, push-ups, lunges, planks, crunches and a particularly hellish invention called a sit-through. I complete the first circuit and am horrified to discover that barely five minutes have passed. Still, I am committed, and as the circuits roll on I can feel myself entering a state of near-death transcendence. The sweating is profuse, the grunts laboured and concerning.

Luke Ryan: ‘It’s only after finishing the whole thing that I see the recipe was meant for two.’ Photograph: Mark Gambino

I finally finish and collapse to the ground. As I lie there, letting out small whimpers of discontent, I keep mentally intoning Elsa’s mantra: enjoy the journey, enjoy the journey. Right now the journey feels as though it’s taking place on the Kokoda Track but I’m sure the rewards will be worth it.

Day two

I am so sore I can barely walk. When I sit down I make a noise that could only be described as “agonised”. My wife is enjoying herself far more than I feel is fair.

Day four

My body is beginning to feel normal again. I decide to put aside Elsa’s ministrations and see what Chris has to offer me. I open the Centr app and am peppered with questions: sex, height, weight, exercise frequency, diet. They ask me what my goals are. I choose “Get fit and toned”. They ask me how long I want my subscription to be. I choose “Free 1-week trial”. I’m informed that my Centr Plan is now ready for viewing.

My first impression of my Centr Plan is that I will have to quit my job and hire a PA just to keep up. Breakfast, lunch and dinner are all prescribed. Today there’s a pilates session to attend to, as well as a guided meditation. If I’m feeling really committed I can read a blog about eight ways to stay healthy over the holidays. The production values are high, the imagery sun-kissed and the content extensive. If Elsa’s book feels gently aspirational, Chris’s app feels like a cultish holiday boot camp.

After slurping down a pumpkin spice smoothie for breakfast – ah, so this is why people hate health food – I attempt the pilates. A woman named Sylvia Roberts puts another, unnamed woman through half an hour of pulverising stretches, lifts and holds. I begin, brimming with confidence. I finish, humbled, defeated by the climactic seven-minute “booty sculpter”.

No time to dwell on failure, though: there’s a spinach and feta quesadilla to prepare! An improvement on breakfast, it still leaves one wondering what exactly the health-conscious have against flavour. I distract myself from my gnawing hunger with today’s meditation, a “body scan tension release” with Sergio Perera, who, I discover, is also Chris’s on-set chef. Great, now I’m hungry again. Dinner is a beef vermicelli salad, which I consume like a man rescued from a desert island. It’s only after finishing the whole thing that I see the recipe was meant for two. I look at the empty bowl and open a beer.

Day five

I’ve given up on Elsa and Chris. There’s nothing controversial about what they’re peddling: fresh food, small portions and varied, plentiful exercise would be the expected advice from most health professionals. But I’ve become convinced that these sorts of scorched earth, all-or-nothing campaigns simply offer convenient excuses for failure and a regression back to old habits. Healthy living shouldn’t be something extraordinary, but by making it appear that way it just becomes ever more unobtainable.

I tell my wife all this over breakfast – toast with Vegemite and a giant coffee. “It’s OK,” she says, patting my shoulder supportively. “You were never going to look like Thor anyway.”