What is it that makes a race tough? To our mind, there are four main criteria: distance, cut-off times, terrain and weather conditions. When several – or all – of these are challenging, then you have the ingredients for a truly tough race. As a veteran of the Spartathlon and James Poole Speed Project solo and unsupported, James Poole knows more than most about the extreme end of running. Here is his six-strong list of the world’s toughest races.

Iditarod Trail Invitational

1,000 miles across some of the most inhospitable terrain on earth. ‘It’s in Alaska, goes down to something like -40C at night, and it’s incredibly long’ says Poole. The winner of the most recent event completed it 22 days 22 hours. You’re pulling a sled the whole way and the qualifying criteria is extremely stringent. But don’t worry, if it all sounds just a bit much, there’s a shorter version, which is a mere 350 miles in length. Where do we sign?

Hong Kong 4 Trails

Off the grid, unsanctioned and extremely difficult, the Hong Kong 4 Trails might just be the greatest race you’ve never heard of. Masterminded by Andre Blumberg, a German expat living in Hong Kong, it involves completing the four trails of Hong Kong in 60 hours. ‘What’s brilliant about this race is that not only do you have to complete the trails, but you then have to get to the next one – and the final one is accessible only by ferry. And if you miss the connection, you won’t complete the challenge before the cut-off.’ It’s 300km, extremely humid and hilly, and requires both physical fitness and mental sharpness to complete. Should you get to the finish, you get to kiss a blue-green postbox – a little like how finishers of the Spartathlon get to kiss King Leonidas’ foot.

Barkley Marathons, US

Only 17 runners have ever completed this ridiculously tough race in Tennessee. The Barkley is hugely challenging both physically and mentally, and has a punchy cut-off of 60 hours, so you can’t bag much sleep. On top of the running, all of which happens on unmarked trails, competitors have to collect pages from various books strewn across the forest. It’s roughly 100 miles in distance and extremely hilly. This year, three people managed to complete it, but most years, the Barkley wins.

The Spine

Single-stage race along the entirety of the Pennine Way. In January. It’s a hugely long way – 268 miles – the weather is reliably horrendous. There’s an element of navigation required and sleep deprivation is guaranteed. ‘It’s a legendary race but I never want to do it,’ says Poole. ‘You look at the footage of it and think, “Why the hell would you put yourself through it?”’ As the race is non-stop, Poole thinks this makes it even harder: ‘The impetus is on you not to stop, to keep moving at all costs, as the clock is always ticking.’

The Red Bull X Alp

This is a bit of a cheat as it’s a hike, run, fly event. Competitors cover 1200km point to point. The flying part happens via a small parachute, packed into a bag. A typical day might see you run and hike 40km, crack open the parachute and fly for 50km. When the weather’s bad, competitors will run more than they fly, and you’re not allowed to fly at night (for obvious reasons). ‘It’s totally mad and totally brilliant,’ says Poole. ‘It’s actually made me want to learn how to use one of these parachutes.’ After you, James. After you.

The Last Annual Vol State

A 314-mile road race from Doraner Landing in Missouri to “The Rock” atop the Sand Mountain in Georgia. Organised by Gary Cantrell (aka Lazarus Lake), evil genius behind Your 50 mile ultramarathon training plan, it’s a brute of a race, made even more difficult by the heat and humidity. Runners can be “crewed” (supported by a team) or “screwed” (unsupported). ‘This race goes through some of the hottest parts of the deep south. If you’re self-supported, you’ll be sleeping rough on the side of the road. I don’t think it has anything of any note; it’s just very hot and pointless,’ says Poole. ‘When you get to the finish, you just get a handshake.’