Tough Mudder events are 10- to 12-mile obstacle course challenges that test all-around strength, stamina and mental grit.
More than half-a-million people have participated worldwide and raised more than $3 million for the Wounded Warrior Project.
On average, only 78 percent of participants complete a Tough Mudder challenge.
Participants leap off a platform in the Walk the Plank obstacle.
Racers crawl under live wires in the Electric Eel obstacle in Toronto.
Crawling through the dirt in Kiss of Mud.
Wetting down the course.
A team poses during Tough Mudder Toronto.
Climbing the Spider's Web.
Competitor Nicole Bahn.
Getting a haircut.
Jason Capiello, Tomas Molfino, Lucas Rooney, and Anson Felder rock the schoolboy punk look.
Read more about Tough Mudder and the other top obstacle courses in the November issue of Outside.
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