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.