This weekend 2000 athletes will head to Chamonix in France to participate in the Ultra Trail du Mont Blanc.

Widely known as one of the toughest footraces in the world, its route takes athletes through 3 countries in a course of about 103 miles and an elevation of 30,000 ft.

The usual course starts in Chamonix, France and goes through Italy and Switzerland before returning to France via the Col des Montets, a mountain pass in the French Alps.

But the course is subject to change. Even on the day. In 2010, organisers famously cancelled the race 10 hours into it, after a mudslide changed conditions to dangerous levels of uncertainty. Last year the course was re-routed mid race after a vital aid station suffered damage in heavy snow. This added an extra 2 miles to the race. With thunderstorms and freezing temperature threatening this year’s event athletes must be prepared for anything.

Nevertheless, it is one of the most popular races in the world. Places fill up very quickly, and participants must have already earned enough points in regional races before they can apply.

Helen Cospolich, who is involved in the organisation and run the race three times herself describes the global appeal:

‘The scenery and support of the Ultra-Trail du Mont Blanc are unmatched anywhere in the world. Running up and over high peaks, through small villages, across three countries and all to the cheers of large crowds make this race a very special event’

Good luck to all the athletes participating!