For many people, sprinting through dangling wires with 10,000 volts of electricity and then crawling through a pit of mud would be an absolute nightmare.

For a small but significant group of fitness enthusiasts, these tasks are par for the obstacle course in a growing number of "Tough Mudder" races.

Started in 2010 by a Harvard Business School student named Will Dean, these extreme races have exploded in popularity recently. In 2012 there were 36 Tough Mudder across the United States and Canada. In 2013, there will be 52 races.

"I was surrounded by supercompetitive alpha males at Harvard," Dean recently told the New York Times. "I thought if I could bring that to fitness, I’d be successful."

The races have been enormously profitable. Ben Kaplan of the National Post writes that Tough Mudder started with a $20 advertisement on Facebook. Now it is a $70 million company.

Some of the most passionate participants are Wall Street types who are looking for outlets to let go of some pent-up energy.

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"Finance people are in a weird juxtaposition,” Dean told the Times. "They may make 100 times more than their fathers, but their hands are soft. We designed Tough Mudder to fill that void."

The architect behind the 10-to-12 mile courses is Nolan Kombol. The 27-year-old Kombol told the National Post that he and his team spend up to six weeks designing a course, and for their design they draw on training programs used in the military. The courses test physical as well as mental ruggedness.

In this way, Tough Mudder offers a sort of cross-fit that the traditional marathon or even triathalon lacks.

"People say I must be some sort of masochist, but all I want to do is push people through new experiences," Kombol told the National Post. "You can run into some guy in a bar and find out you both did one of these and it’s like a badge of honour — it’s not running 10 miles or doing a bunch of push-ups and pull-ups, but using your mental grit."

Dean got the idea for the races from a series of similar competitions in Europe. Dean wasn't the first to bring this style across the pond, and two other major obstacle course companies exist: Warrior Dash and the Spartan Race series. Warrior Dash had the most events (49) in 2012, but Tough Mudder made the most money ($70 million). The fiery competition between the three companies was profiled in a recent feature in Outside magazine.

While sometimes overlooked in fitness, the team-building nature of these competitions has added significantly to the lore of the obstacle courses. Men and women complete the courses in groups, and they are reliant on their teammates in order to finish certain tasks.

"A part of me always wanted to join the army, but I never did," Evan Lotzof, a New Yorker who participated in a race in October, told the New York Times. "Tough Mudder gives me a sense of band of brothers."