LONDON (AP) — For many, just the thought of running 12 miles (19 kilometers) over mounds of mud and through pools of ice water is enough to make them cry.

Now comes something that will really make them weep.

Tough Mudder, one of several obstacle course-style distance running events gaining in popularity, announced Tuesday it is adding a tear gas-experience to its repertoire this year with a stop labeled "Cry Baby." It's not dangerous, according to the company's CEO, but it can pose quite a challenge for participants.

"The idea of doing something that sounds painful, disorientating, is definitely something that's a little scary," said Will Dean, who came up with the business plan for Tough Mudder while studying for a master's degree at Harvard. "It definitely will make your eyes sting while you're in the smoke, but ultimately it's safe.

"The reason we have it is because it's intimidating."

Dean was not the first to come up with the idea of asking people to pay money for the chance to challenge themselves in a military-style obstacle course. Tough Guy, for one, has been around for nearly 30 years and bills itself as "The Original since 1987." Many others have followed in a similar vein, including Spartan Race and True Grit.

"I reinvent every year. Well, two or three times a year," said Tough Guy organizer Billy Wilson, who took Tough Mudder to court in its early days but eventually settled. "I create a new obstacle for each event, sometimes two."

Tough Mudder is a New York-based company that started in 2009 and this year is planning to stage 55 events in eight countries around the world. In addition to the main 10-12-mile (16-19-kilometer) challenge with about 20 obstacles for both men and women, the company also has Mudderella events for women and Mini Mudder runs for kids between 8 and 12.

Crawling over logs and under wooden beams through an enclosed area filled with tear gas is the most eye-catching of the new obstacles on the slate for this year's Tough Mudder events. There is also "Ring of Fire," where people slide down a fireman's pole through a ring set alight and into a tub of muddy water, and "Birth Canal," where participants crawl under a water-filled tarpaulin that creates a sense of claustrophobia.

The well-known "Electroshock Therapy" will also be in the mix, with participants running through wires charged with 10,000 volts of electricity.

"It's as much about the mental challenge as it is the physical component," said Dean, a 34-year-old British transplant who worked in counterterrorism for the U.K.'s Foreign Office before heading to Boston and then New York.

The first chance for runners to face the new Tough Mudder challenges, including the tear gas, will be at the Gulf Coast event near Pensacola, Florida, on March 7 at a cost of nearly $200 for a standard entry. Dean said he is expecting "Cry Baby" to be in place for all 55 editions in 2015.

The tear gas that will be used was created by the people at Tough Mudder to give runners a sense of what it's like to be faced with the chemical weapon often employed by police to disperse crowds, but the burning sensation will wear off quickly.

"It's best described as a tear gas-like substance," said Lucas Barclay, the vice president of event delivery for Tough Mudder. "It has no lasting effects."

Tough Guy also tries to stay fresh and ahead of the competition, and Wilson is planning to commemorate a famous World War I battle at his next event near Birmingham in central England on Feb. 1.

"I recreated Gallipoli beach for the 100th anniversary this year," Wilson said of the battle that started in April 1915 in which more than 46,000 allied soldiers were killed among 250,000 casualties. "Gallipoli has become a sacred place. I've recreated that."

The quest to give paying customers an exciting and challenging experience can come with complications and catastrophes. In April 2013, 28-year-old Avishek Sengupta died at a Tough Mudder event in West Virginia.

"We treat, first and foremost, safety as the most important part of our event," Barclay said. "We are always reviewing our safety features."

The prospect of being injured certainly keeps some people on the sidelines, but Dean said Tough Mudder is expecting its 2 millionth competitor this year.

And, as he is quick to point out, it's not a race against the clock. It's a test of one's inner strength.

"We spend so much of our lives competing with one another," Dean said. "In the long run, the race is only within yourself."

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