"I'm told that I am getting bored less easily," he explains when I ask him whether all this huffing and puffing is absolutely necessary. "I'm managing my impulse to scream, 'boring alert!' a little better. 'Boredom is self-obsession' - I don't know who said that but I think it applies. So am I becoming less obsessed with myself? I think as a function of age you have to, otherwise you can't stay healthy."The work-out is tough. Not throw-up-all-over-myself-and-fall-back-out-into-the-street-whimpering-to-mummy tough, but hard enough to cause Downey some minor concern. "You OK?" he asks sporadically between swinging 15kg iron kettle bells through his legs (OK, 10kg for me). Gasping, I lie - you have to, right? - and tell Downey I'm "fine", blaming the double espresso with half-and-half I had earlier, but even Jimmy can see I'm feeling pain in muscles I never even knew I had until today.
"Don't worry, British," consoles Downey as we jump into his dealership-pristine ice-white VW Golf, turn down Howard Stern and slipstream into the Venice Beach traffic, just as if he's one of the hundreds of thousands normal Los Angelenos going about their working day, "I've got the cure."
Rebuilt, reborn and restored, Robert Downey Jr has Hollywood at his feet - again - and this time he swears there's to be no reappearance of "Retread Fred, the serial relapser", the term coined by Downey himself to describe his inability to stay off a $4 crack pipe and keep his sorry ass out of a prison-orange jumpsuit. Since director Jon Favreau cast him in Iron Man in 2007 - for which Downey did a screen test for only the second time in his career - Downey's Hollywood credit rating has blown through the roof, smashed the billion-dollar weather balloon at the box office and rocketed into deep space: current position, 45,350 miles past Pluto and climbing. This isn't a comeback. This is a full-scale, karma-reversing body swap.
The three-storey frosted glass and concrete house he takes me to is a monument to Downey Version 4.5. Before I'm shown "the break room" (basically a guest bedroom where I'll shower and change), Downey gives me a tour. "First floor, business": this is the office space where six or so members of Team Downey, the star's production company set up with his wife Susan in 2010 with a first-look deal at Warner Bros, keep a handle on business, which at the moment includes filming Sherlock Holmes 2 in London with Guy Ritchie and Jude Law, pre-production for Yucatan - a heist movie set in Mexico originally devised and worked on by Steve McQueen prior to his death - and looking for a movie for Downey to direct.
"Second floor, pleasure": along with the break room, this is where the Downeys sleep and - well, he said it - pleasure themselves. Their bedroom is a dark affair, the Venetian blinds pulled down with various Conan Doyle books on a dresser, clean wooden surfaces stained the colour of black coffee and a low-riding bed with leather trim and matching bedside tables. The bathroom, with its mosaic tiles and straight-edged, free-standing bath big enough for two, is about as messy as a room can be without it being embarrassing. There's also a small balcony where Downey admits he likes to crouch down in the early evening, alone, and eavesdrop into people's conversations while they stand outside his front door.
"Third floor, sustenance. And access to fish tanks": the uppermost floor is where we'll have brunch, consisting of papaya and mango cubes to start, followed by red-pepper quiche and ending with a gluten-free coffee cake with frosted top, all cooked by his private chef. On this floor there is a square sunken seating area with various Taschen editions, several carved wooden insects, a free-standing piano - a gift from Susan - adorned with a Kerouac inscription from On The Road ("the only people for me are the mad ones") and a plastic Iron Man figurine doing the splits. There is also a rock garden and a terrace, presumably where Downey walks out on occasion, breathes deeply and laughs like a hairdryer into the face of all he surveys and into the narrow minds of all the industry naysayers who doubted his future couldn't be so goddamn sweet.