Reckon you could run up and down an old railway tunnel non stop for 55 hours?

Well if you feel up to the challenge you can send Mark Cockbain a message and see if you're not too late to join the forty runners lining up in front the Combe Down Tunnel, near Bath when the race kicks off.

The Tunnel is a disarmingly simple race really, runners have 55 hours to run up and down the dank and dingy 1 mile long tunnel 100 times (for a total of 200 miles). No support runners, no poles and no headphones. Sounds like hell right, well it probably is. In the year we went to this the DNF rate was about 95% meaning that out of the 40 who started only 2 crossed that finish line.

Brutal yes but is it the toughest out there?

This question got us talking at the Chia Charge office, just what makes a race tough. Here's what we came up with -

1. Duration 

"The longer you're out there the harder it's going to get" is a pretty fair rule of thumb when it comes to ultra marathons. It's not just the fitness demands either, the more time you have to spend on the course, the more the wear and tear gets  you down. Skin starts to chafe, stomachs start to rebel and feet start to disintegrate. 

2. Conditions

It doesn't matter whether the weather is forecast for arctic blizzards or scorching heat waves. Brutal conditions can turn even the flatest, most gentle course into a nightmare really quick.

This is a big part of the reason why races like the Yukon Artic Ultra, the Spine and the Marathon De Sables are so feared.   

3. Boredom

What a race like the Tunnel might lack in things like weather and elevation it certainly makes up for in sheer mindnumbingess. Without scenery or navigation to distract you there is absolutely nothing to take your mind off how tired your legs are or the blisters slowly consuming your feet. It's not just the Tunnel that can test your mental fortitude either, there are hundreds of races out there that will destroy your soul from 6 hour track runs to the 3100 mile The Self-Transcendence race.

4. Elevation & Terrain

Snow capped mountains might be beautiful to look at, but in races these rocky giants make things a whole lot tougher. Getting up and down them in one piece requires more than just a good pair of legs, the higher you get the fiercer and more unpredictable the weather can be, climb higher still and the effects altitude can put a dampener on your race really quick.

It's not just mountains either than can make a race tough, sand dunes, ice and miles and miles of undulating rocky trails can all make a mile seem like 8.

5. The Unknown 

It's a lot easier to push yourself when you know what's ahead of you and know that everything is fixed. But as soon as someone says run until I say stop or takes away some of those comforts, your mind will start playing tricks. There aren't too many of these unknowable races out there but one you may have heard of is the infamous Barkley Marathon.     

What have we got right and what have we missed? Let us know what you dread in a race and what makes you sign up on the spot.