The event offered four distance categories of 20km, 50km, 185km, and the toughest, 500km. Vũ was among just 19 participants at the start line for the 500km category. She successfully crossed the finish line more than nine days later.

"Like many ultras, Montane Lapland Arctic Ultra (MLAU) is an emotional roller coaster. The stark difference between the days and nights, sunshine and no sunshine, means you can be singing and loving it in the forest but once the disorienting darkness descends, you're in the abyss, struggling to put one foot in front of the other," Vũ posted on Facebook after completing the competition.

"There were many moments when I was worried if I would ever see the finish line. MLAU is very different in the sense that the checkpoints can be 39-77km apart, which make timing for water, sleep and small rests very difficult.

"All things considered, the weather during the later days of the race was extremely cooperative which made the course much more runnable and I was able to push hard for some mileage gains.

"The race is so extremely difficult. But even when it was really tough and I felt depleted, what made it enjoyable was the loveliest crew of volunteers and staff at check points. They become a lovely physical and mental refuge where I could piece myself back together."

Starting on March 3 in Overkalix, participants could run, cycle or sky their chosen distance.

Thanh Vũ completed her race on foot on the night of March 13, covering 503.1km of trail in 9 days, 9 hours and 18 minutes. Her moving time was 7 days 19.31 hours with a total rest time of 1 day, 13.47 hours, and an average speed of 3.2km/h.

She placed No 15, while the winner was German Florian Reiterberger who competed with a fat bike and wrapped up his race on March 8. Four racers of this tough class did not finish the course.

Thanh Vũ, 34, earned many people's respect when she took top place in the triathlon Swiss Ultra 2022, where she swam 38km, cycled 1,800km and ran 422km in 328hr 27.55min.

Previously, she was the first Asian woman to complete the 4 Desert Grand Slam of 250km Namibia, 250km Gobi March, 250km Atacama Crossing and The Last Desert of 250km in the Antarctic.

She also took part in other ultramarathons such as running 522km through Australian desert in 2017, 230km in the Arctic in 2018, and 273km at the Grand Canyon in Arizona in 2018.

“I always set the goal of becoming the most resilient Vietnamese person in the world. When I conquer new milestones and return to everyday life, I want to be a better version of myself, so life will be meaningful," Vũ said during an event in 2022. "When I push myself, I feel more valuable to myself and those around me. I also want to inspire people, so that everyone can find challenges and overcome them." VNS