U.S. Navy Lt. Natalie Schibell was watching the competition television series “American Ninja Warrior,” which promotes itself as “the world’s most difficult obstacle course,” when a friend dared her to apply to be on the show.

“I never turn down a dare,” Schibell said by phone this week.

At the end of April, the environmental health officer at Naval Submarine Base New London in Groton found out that she would be one of about 800 contestants to compete in qualifying rounds in six cities across the country. City qualifying and city finals rounds are held in Venice Beach, Calif., Kansas City, Kan., Orlando, Fla., Houston and Pittsburgh. The show’s producers aim for only 20 percent of the contestants to reach the national final rounds in Las Vegas.

Schibell, 33, applied to the show in January, and after waiting for three months she said she was “feeling pretty disappointed, and all of a sudden out of nowhere someone called me. I was over the moon, so thrilled and excited.”

At the sub base, she ensures public health and safety on Navy vessels, facilities and installations for the 6,500 active duty members on base and the roughly 17,000 others that use the base facilities.

By competing on the show, Schibell said she hopes to “inspire sailors to support the Navy’s culture of fitness, and to inspire people to work out and be healthy.”

The show received a record 50,000-plus applications this year. To apply, prospective contestants have to create a 3- to 4-minute video and fill out a lengthy questionnaire. A lot of the questions were personal, Schibell said. She was asked to name people who inspire her, what type of athletic accomplishments she’s achieved, if she’s doing the course for anyone in particular, and to explain why she thinks she’ll be the next American Ninja Warrior, to which Schibell responded “versatility.” She has a varied athletic background — swimming, track, crew, field hockey and lifeguarding.

The most difficult question to answer, Schibell said, was one about her insecurities.

“I’m a female. I’m short. So a lot of people tend to judge a book by its cover and they really have no idea until they get to know me that I’m a lot tougher than I look,” she said, of her answer.

The West Long Beach, N.J., native is just shy of 5-foot-3 and weighs 125 pounds.

“I look like I’m a little younger than my real age and maybe unintimidating to people who don’t know me. But people who do, know better,” she said.

In the past few weeks, Schibell has had to “step up” her training to prepare her for the obstacle course. One of the biggest challenges has been finding American Ninja Warrior gyms, or gyms with similar obstacles, nearby. She’s traveled to Pennsylvania and New Jersey to train and get exposure to the obstacles she may face and plans to travel to a gym in Massachusetts for the same reason. At times she’s had to improvise her training.

Schibell said a lot of what she does involves using her own body weight as a workout tool: calisthenics, core body work, sprinting, swimming. She anticipates the obstacle called the Warped Wall will be the most challenging.

The wall, which Schibell said she’s seen twice now, is 14 feet high and is a staple in nearly every course in the show’s history. In a Youtube video about the Warped Wall, Evan Dollard, a previous competitor and American Ninja Warrior, compares it to “running up the side of a building and catching a window ledge on the second floor. 

“It’s a learned skill for anyone but especially for someone with my height and stature,” she said.

American Ninja Warrior, now in its seventh season, airs on Mondays at 8 p.m. on NBC. Repeats air on the Esquire Network. The San Pedro Regionals are expected to air on June 29. You can follow @NatalieSchibell on Twitter and tweet your support for #NavyNat.

j.bergman@theday.com

Twitter: @JuliaSBergman