Chris Hemsworth explains why he took on daredevil challenges and prepared for his own eventual death

In his latest show, "Limitless With Chris Hemsworth," Chris Hemsworth plunges into Arctic waters, dangles a thousand feet over a canyon while climbing a rope, fasts for four days, and prepares for his own death—all in pursuit to live longer.

The six-part National Geographic documentary streaming on Disney+ was not only physically straining but also challenged his mind and body. The "Thor" star told National Geographic that prior to taking on this gargantuan task, he had "always trained specifically for a movie" where the aim might have been "to have abs this summer or whatever." This, Hemsworth said, was "more superficial. I always felt better, but doing a deep dive into the science-backed evidence of why I felt better was a completely new experience."

In the series, Hemsworth undertakes complicated stunts, swims and surfs in a fjord's 36-degree water and plays underwater hockey during a four-day fast to understand the benefits of fasting. The show presents some insightful takeaways for viewers. The executive producer of the show, Jane Root, said that the show is less of a sci-fi vision of pursuing longevity and more about improving chances for a long "life that is fulfilled and happy and active."

Ross Edgey, who coached Hemsworth's fjord swim is also the person who helped him train for the movie "Thor: Love and Thunder." Edgey said: "People know Chris as the actor, but not a lot of people know him as the athlete." Hemsworth had been a hurdler in his school days and still surfs.

There is a moment in the show where Peter Attia, a preventative care physician, tells Hemsworth, then 37, that blood tests reveal he has 10 times the average risk of developing Alzheimer's disease because of genetic traits. Daily exercise, good sleep and stress reduction might help lower that vulnerability, Attia added. "It was initially pretty scary," Hemsworth said. "But now, because of this information, there's an opportunity to live an even better life."

Hemsworth also experiences aspects of old age in the series. He wears an MIT-designed suit that adds weight and restricts movement, hearing and vision, mimicking how he might feel in his late 80s. He spends time with people who are close to death and reflects on it. He also meets an apparently older woman, sitting with her back to him. The second he touches her shoulder he recognizes his wife, Elsa Pataky, who looks like an aged woman under extensive aging makeup.

She turns to him, and they hug each other. The showrunners hadn't warned Hemsworth about this encounter as they wanted to capture the actor's natural reaction. Suddenly, Hemsworth is faced with the challenge of reckoning with being near the end of his days, and it becomes evident why he'll sweat, freeze and starve. When asked whether it all come down to love, Hemsworth replied: "Absolutely. One of the first questions I had from Peter Attia was, 'What does your life look like in 20 years...  in 30? What does your death look like?' A good death for me would be having lived a good life."

The concept of the show came from a 2006 movie that producers Darren Aronofsky and Ari Handel had written: "The Fountain," which was about a man searching for everlasting youth. Aronofsky believes that the concept will be relatable to the audience due to an aging population and high-tech companies "trying to beat death and reaching for immortality in a lot of different ways."