Having entered the K-pop scene as a teenager, Rain, whose real name is Jung Ji-hoon, has shown no lack of stamina so far while staging physically challenging pop performances on the K-pop scene.
Even given Jung's unusually well-built physique, filming "Uhm Bok-dong," a new drama film where he plays the main role, was a consuming physical challenge like never before.
"Uhm Bok-dong" is an entertaining history film based on a colonial-era Korean cycle champion of the same name. Jung brought Uhm's character alive on the screen to shed light on the life of the little-known historic cyclist.
Uhm won a series of national cycling competitions against powerful Japanese rivals during Japan's brutal colonial control of the Korean Peninsula from 1910-45.
The film casts Uhm's winning streak as boosting the morale of Koreans under the brutal colonial rule and inspiring the spirit of fighting for independence.
These images from the film "Uhm Bok-dong" was provided by Celltrion Entertainment.
As he took up the role without a body double, Jung was subjected to an intense regime of training which required him to cycle around a 420-meter track for nearly 10 hours for more than six months.
The total distance he has cycled for training and shooting may equal the distance around the globe, he said in an interview with Yonhap News Agency and other media outlets on Wednesday ahead of the film's release on Feb. 27.
"As I circled the track, I was thrown into the thought of, 'Who am I? And where am I?,'" the 37-year-old said.
"After repeating the routine endlessly, I felt like I had fallen into the pit of hell," Jung recalled. "The job was really demanding even for relatively healthy men like me, and for other supporting actors it caused complete exhaustion and some of them even threw up."
The intense muscle exercise forced him to opt for a larger pants size as his thighs dramatically grew in girth. Through diet and exercise, he has nearly recovered his original size, according to Jung.
"Uhm Bok-dong" is his first appearance in a Korean film in seven years since his last in the 2012 film "R2B: Return to Base."
Veteran actor Lee Beom-su, who produced "Uhm Bok-dong" and played the role of an independence fighter and cycling trainer in the film, first handed the film's script to Jung, and he was instantly intrigued.
"I found something dynamic in the script ... and I also thought that I could contribute to promoting the athlete Uhm Bok-dong who has not been well-known," Jung noted.
The K-pop star also recently entered into much celebrated marriage life with prominent actress Kim Tae-hee. The two top stars wed in early 2017 and have one daughter.
"After getting married and running toward the age of 40, I need to be more grown-up," he said.
"But musicians tend to retain aspects of a child. Without it, they cannot catch up with the latest trends. It's an irony that I need to grow up, but at the same time I have to listen to the music of young people," Jung said.
But he stopped short of mentioning his daughter, saying, "I want to draw a clear line between my family and career ... It seems that it will come back to me as a sword and arrow if I boast of my lovely daughter."
He plans to maintain both of the two long-established pillars of his career as long as his capability allows.
"As I have two occupations, I sometimes get confused myself. The time may come for me to have to give up one of them because a dance singer has an expiration date," Jung said.
"Still, I will continue to dance as long as my body is capable of movement and want to extend that expiration date by carefully managing my fitness."
Jung also said he is willing to act for indie films by student director.
"As I am in the course of building my career as an actor, I hope I could work for a various range of films even in a small role," he said, voicing his hope to build a long acting career.
Currently, he is in discussions over new roles in a TV drama series and a movie. Toward the end of the year, he will also release a new music album and go on a concert tour.