When AJ Calitz does his interval training, he partners up with Monty, a two-year-old Labrador.

Calitz, the winner of the recent Red Bull Lion Heart – who has spent the past year smashing the records of the The Three Peaks Challenge, The Otter Challenge and The Puffer – says that Labs are the perfect breed for this blitz workout. “If you can outrun a dog in intervals, then I don’t want to run against you,” he says.

It’s the not just the dog’s speed but his ability to maintain it which makes Monty Calitz’s only training buddy. “They are innately able to keep an amazing, constant pace.”

“Generally what happens in intervals is you almost start too fast and then you start relaxing – that’s not what you want. You want to start out fast and you want to remain there. I start out, he’ll run with me and then if I drop down a little bit, I’ll lose ground on him and I’ll realise I need to speed up to catch up with him.”

By always being the chaser, Calitz is forced to keep his heart rate as high as possible. “Because my dog tends to run in front of me instead of next to me, as soon as I start catching up he speeds up a little bit – it’s that little cat and mouse thing.”

“This mimics the feeling of running on a trail where you run uphill for an extended amount of time and you only have a short recovery period where you go again.”