Do you want to know the problem with being an actor so talented you can play a maths genius, stranded Martian and the pop-punk singer of ‘Scotty doesn’t know’ (that’s right, that’s Matt Damon in EuroTrip)? Beyond finding time to sleep it’s that, unlike most action stars, you’re not eternally in excellent nick. So when the producer of Jason Bourne comes calling, you have to hone a normal bloke’s body into blockbuster muscle. Even at the age of 45.

For the Bourne reboot, Damon needed a reboot up the backside, to return to Treadstone-taming shape. Enter celebrity trainer, Jason Walsh, an expert so overqualified he has more letters after his name that in it (that’s CSCS NSCA-CPT, for anyone playing PT bingo).

He’s the man who beefed up Bradley Cooper for American Sniper and leaned down John Krasinski, better known as Jim from the American Office, to play a Navy SEAL in 13 Hours: The Secret Soldiers of Benghazi (no, we didn’t see that one either).

But don’t be intimidated. For a man working in the world of fiction he is refreshingly matter of fact about achieving a silver screen physique. Slow and steady beats overnight transformations, he says. As he puts it, you need to hit all the letters between A and Z if you want that body to last beyond the wrap party.

So guess again if you thought this was going to be an exercise in building a beach physique. Military men – fictional or not – carry total-body strength that keeps them injury-free. In fact, for Walsh, mirror muscle work is “stupid”: training for aesthetics creates imbalances that make back pain worse. Not an option for a super-spy approaching middle age.

Which is where Walsh’s favourite piece of gym kit comes in: the Versaclimber. His US workout base, Rise Nation, is full of them. He hosts sessions similar to the spin classes you see at gyms nationwide – dark rooms, strobe lights, dance remixes and buckets of sweat.

But while the classes may seem similar, swapping spin bike for Versaclimber gears the training to those clad in actual camo, not the Sweaty Betty lycra kind. The climbing motion is a primitive movement, so you get the total-body benefits of animal flow, without having to spend an hour crawling around on the floor like a bear.

Never tried a Versaclimber? There’s probably one gathering dust in the corner of your gym, left fallow because, well, it’s bloody difficult. But used correctly it’s the ultimate piece of fitness kit, says Walsh: it’s kind to joints, forces you to work in proper movement patterns, and makes your heart work harder than almost any other piece of kit in the gym. So you get in shape faster – and won’t get sidelined by injury.

Intrigued? Probably. Nervous? You should be. Take on this exclusive workout, fresh from Walsh’s Californian fitness Mecca, to build a body like Jason Bourne. Soundtracked by Moby’s ‘Extreme Ways’, of course.

The 30-minute Jason Bourne Versaclimber Workout

Warm-Up: 4 mins 30 secs

Perform 4 reps of 60 second long-range strokes, at a pace of 130 feet per minute.

Rest for 30 seconds.

Set 1: 3 mins 30 sec

Do a sprint segment of short strokes, at 200 feet per minute, for 45 seconds.

Before you can catch your breath, follow with a sprint of long range strokes, at 130 feet per minute, for 45 seconds.

Repeat the interval again.

Rest for 30 seconds.

Set 2: 5 mins

Sweating? Well here’s where things get Paris-car-chase intense. Start with short strokes, at 220 feet per minute, for 20 seconds.

Without rest, move onto short strokes, at 120 feet per minute for 10 seconds.

Repeat the interval 8 more times.

Rest for a minute.

Set 3: 7 mins

Repeat set 1, including the rest, twice.

Set 4: 3 mins 30 sec

Start with long strokes, at 140 feet per minute, for 30 seconds.

Keep the length but up the pace to 200 feet per minute, for 60 seconds.

Repeat both intervals again.

Rest for 60 seconds.

Recover: 5 mins

Short, slow strokes at 150 feet per minute.