By Nicholas DeRenzo
The Active Times

Hear the phrase "extreme sports" and you might immediately think of the X Games.

This twice-annual Olympic-style tournament, which comes in Winter and Summer editions, showcases the best and brightest in sports like skiing, snowmobiling, biking, and skateboarding. The events are understandably well-publicized, but they’re only the tip of the extreme sports iceberg.

Outside of these arenas, there’s quite literally a world of extreme challenges and championships, many of which you may never have heard of. In fact, many of these events take place in appropriately extreme destinations: Imagine running 135 miles in the hottest place on Earth -- in the middle of summer; or crossing an ocean using only human muscle.

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How about diving 400 feet on a single breath into the world’s deepest sinkhole, or surfing down the face of a 50-foot wave?

If these events sound death defying, that’s because they are. To take big wave surfing as an example, the sport has claimed the lives of several of its leading lights, and more are likely to follow.

If you think getting swallowed by a giant wall of water sounds scary, then imagine flying around a mountain -- literally -- in a wingsuit, or flying down one -- metaphorically -- on a skateboard.

But the risk of drowning or slamming into a mountainside isn’t the only thing that makes a sport extreme. We found one centuries-old precursor to football where brawling is encouraged, and another oddball competition where your worst likely fate is throwing your back out.

Far and wide, you’ll find athletes in peak physical condition battling the elements and testing their own limits as they compete to be named the fastest, strongest, bravest -- and perhaps the craziest.

More Stories from The Active Times:
-- 12 Crazy Man-Made Adventures
-- The World's Most Thrilling Cliff Diving Spots
-- 10 Outrageous Artificial Climbing Walls
-- 20 Most Epic American Day Hikes