Two octogenarian climbers are facing off once again to earn the title of the oldest man to reach the summit of Mount Everest.
Yuichiro Miura, of Japan, is ascending the mountain in hopes of taking home the Guinness World Record that slipped away from him in May 2008, when he was just 75 years and 227 days.
Miura was beaten to the peak by Nepalese climber Min Bahadur Sherchan, who successfully made the climb one day before him, at the age of 76 and 340 days, according to the Guinness World Records website.
Five years later, both men meet again at Everest to test what is perceived to be possible when it comes to one of the greatest physical challenges a climber can endure.
Miura's daughter, Emili Miura, told ABC News in an email that her father is "scheduled to make [the] final attempt toward summit today."
"Anybody functioning in their 70s and 80s is going to be an elite athlete if they're there," RMI Expeditions mountain guide Alex Van Steen told ABC News. "I think the myth to bust might be the fact that if an 80-year-old can do it, Everest must be easy. It's not that way."
"There's a significant health risk [in climbing Everest]," Van Steen said. "It doesn't matter if you're 40 or if you're 80."
Van Steen, who has attempted Everest's North Ridge twice but never reached the summit, said that once a climber reaches a certain altitude, it becomes difficult to perform at a high physical level in the oxygen-limited area.
"I always paint a picture, it's as if you had just come off a nasty cold and have a hundred-pound bag of concrete on your back and you have to run a marathon," Van Steen said. "It feels oppressive. Maybe not to everyone, but it makes it difficult to function."
According to his Facebook page, Miura, 80, had reached the 8500-meter mark on Wednesday, close to the 8,850-meter summit. He posted a photo of himself and a fellow climber enjoying tea.
Meanwhile, 81-year-old Sherchan's journey to the mountain's apex has just begun. He posted a photo of himself at Everest base camp on Tuesday to his Facebook.
If Miura reaches the summit, his record will only hold if Sherchan is not successful in his expedition.
While Miura is the only man to summit Everest twice after turning 70 years old, according to his website, he set a goal for himself to revisit the climb at the age of 80.
"It is to challenge [my] own ultimate limit. It is to honor the great Mother Nature," he stated on his expedition's website. "If the limit of age 80 is at the summit of Mt. Everest, the highest place on earth, one can never be happier."
But Miura's journey has not been without limitations.
He fractured his pelvis in 2009, just one year after his second Everest Summit, his expedition's website stated. He was told a full recovery would be unlikely at the age of 76, but just six months after the injury, he was back in training to attain his goal.
He also suffered from arrhythmia and metabolic issues.
Sherchan has also faced setbacks. According to the Associated Press, his team has not received the financial help that the Nepal government promised to them.
Despite the health and safety risks that await climbers regardless of age, these men would not be attempting the summit if they were not extreme athletes.
"Climbing Everest requires an enormous amount of training, fitness, and willpower," said Van Steen. "That probably offsets however many issues they have."