Runners pass a heat danger warning sign during the AdventurCORPS Badwater 135 ultra-marathon race. Photo / Getty

Athletes are constantly trying to take things further and push themselves to the extreme. As a result, there are some seriously tough events out there all designed to test your limits.

Here are 10 of the toughest sporting events in the world.

1. Ironman World Champs - Kona

The Hawaiian Iron Man Triathlon came about in 1977 to challenge athletes competent at endurance swimming, running and biathlon. Honolulu-based couple Judy and John Collins decided to combine the three toughest endurance races in Hawaii - a 3.8km roughwater swim, 180km bike race and 42.16km marathon.

The following year, 15 people took part in the Ironman challenge. The athletes were given three sheets of paper with rules and a course description. On the final page was written; "Swim 2.4 miles! Bike 112 miles! Run 26.2 miles! Brag for the rest of your life!"

This year, more than 2000 athletes will embark on the 226.2km journey (now taking place along the Kona Coast) to test their bodies, minds and spirits.

2. Marathon des Sables - Sahara Desert

This ultramarathon is ranked by the Discovery Channel as the toughest footrace on earth. The MdS takes place in the Sahara Desert and athletes are required to carry all they need, except for a tent and water, on their backs.

MdS was started in 1986 by Patrick Bauer and places are much sought after.

3. Badwater Ultramarathon - Death Valley, California

This 217km course starts 86m below sea level in the Badwater Basin, Death Valley, California and ends at an elevation of 2548m. Gruelling as this sounds, the event also takes place in mid-July when temperatures climb to over 49C.

According to AdventureCORPS®, Inc. who now host the event:

• 743 people have entered the Badwater 135 since 1987, for a total of 1396 entries.
• Of those 1396 entries, 1142 have been men.
• Of those 1396 entries, 254 have been women.
• Of the 743 unique individuals who have begun the event, 652 finished officially (88 percent).
• The youngest female finisher ever was Claire Heid, 23, USA, in 2012.
• The youngest male finisher ever was Nickademus Hollon, 19, USA, in 2009.
• The oldest female finisher ever was Sigrid Eichner, 64, Germany, in 2005.
• The oldest male finisher ever was Jack Denness, 75, UK, in 2010.
• The average age is 46.

In February this year, the National Park Service put a moratorium on sporting events in Death Valley National Park to complete a safety assessment.

4. Comrades Marathon - South Africa

The world's oldest and largest ultramarathon run covers around 90km and takes place between Pietermarizburg in KwaZulu-Natal, and Durban.

The first Comrades Marathon took place on 24 May 1921, with 34 runners. It has taken place every year since then with the exception of the war years (1941 - 1945). The direction alternates each year.

5. Antarctic Ice Marathon

This 42.2km, five-day race takes place a few hundred kilometres from the South Pole at the foot of the Ellsworth Mountains.

Athletes will have to compete in snow, ice and a windchill temperature of -20C, all at an altitude of 700m.

This is the southernmost marathon on earth.

6. Norseman xtreme triathlon - Norway

This course runs from fjord to peak, starting at sea level, and finishing 1850m above - 220km away.

For safety reasons, only 250 athletes can compete, and of those, only 160 are allowed to finish at the peak of the mountain. The remainder complete their iron-distance on the plateau below the peak. Those who finish on top receive a black t-shirt, and those who finish on the plateau receive a white t-shirt.

7. Tour de France

The race is an annual multiple stage bicycle race primarily held in France. It was first organised in 1903 by a journalist of the magazine L'Auto. The race has taken place each year, except during the two World Wars. These days, the Tour de France consists of 21 day-long stages, over a 23 day period, and covers around 3500km.

8. Iditarod Trail Invitational - Alaska

Contenders run, bike, sled or ski across 1600km of Alaskan snow, carrying their own supplies. There is a maximum time limit of 30 days to complete the race. Temperatures can drop to minus 100C, frostbite is common.

9. The Barkley Marathons - Tennessee

This ultramarathon takes place in Tennessee's Frozen Head State Park. Athletes need to run 160km in 60 hours through thorns and mud. Every 32km contestants loop back to a campsite where there is food, sleeping bags and beer. There they decide if they will continue the race, or not. Very few athletes finish.

10. Race Across America

This 4800km bike race takes place from the Pacific coast of the US to the Atlantic. Participants can race in teams, or solo. All riders have 12 days to finish the race - solo participants can sleep as little as 90 minutes per day, and spend around 20 hours each day on their bikes. Riders have to be monitored at all times.

- nzherald.co.nz