As if running a marathon wasn't hard enough, 27 hardy souls recently braved sub zero temperatures and polar bears to run one at the North Pole.
One of the world's toughest races, the North Pole Marathon sees competitors from across the world race 26.2 mile across the ice and snow in temperatures of -32C.
The endurance feat, known as the world's coolest marathon, is organised by Irishman Richard Donovan, who won the first ever South Pole Marathon in Antarctica in 2002.
A dedicated runner he has also completed the Everest Challenge Marathon, the Himalayan 100-Mile Stage and the gruelling Trans 333 across the Sahara Desert.
Before launching the North Pole contest he ran a solo marathon there himself to see if it could be done - becoming the first person to complete marathons at both poles.
To complete the full distance competitors in the race run around a 5km circuit, pounding across six to 12 feet of ice covering the Arctic Ocean.
Uneven terrain makes it difficult to get up a rhythm, with the surface changing between soft, hard and loose snow.
And the extreme cold makes it difficult to regulate body temperatures with runners too cold at the start, but too hot once they hit their stride.
With a time of 4hrs 54mins 3secs Istvan Toth of Hungary proved the eventual winner, with Australian Richelle Turner the fastest woman in 6hrs 3mins and 6secs.
British runners included married couple Peter and Aly Van Den Berg, who had never run a marathon before. Mr Van Den Berg was the fastest Brit with a time of 5:23:55 while his wife crossed the line in 8:52:04.