Actor Yim Si-wan plays the role of Suh Yun-bok in the new drama film, "Road to Boston." Courtesy of Lotte Entertainment

Playing a character based on a real-life person often poses more complex challenges to an actor, especially if that person is a legendary athlete.

Actor Yim Si-wan / Courtesy of Lotte Entertainment

That was what actor Yim Si-wan faced in his latest role as legendary marathoner, Suh Yun-bok, in the period drama film, "Road to Boston," propelling him to dedicate himself physically and mentally to portray the figure.

"I felt a great sense of responsibility in portraying such an impressive real-life figure. And after deciding to play the character, I took part with the mindset of a national athlete representing our country," the actor said during an interview with The Korea Times, at a cafe in Jongno District, Thursday.

Based on a true story, the upcoming film follows the inspiring journey of Suh and his coach, former Olympic medalist Sohn Kee-chung (Ha Jung-woo), to gear up for the 1947 Boston Marathon.

When former medalist and marathon coach Nam Seung-ryong (Bae Sung-woo) and Sohn spot Suh's talent, they convince him to compete in the international marathon with Korea's flag on his chest. Suh went on to make history, by not only winning the marathon, but also setting a world record.

This marked the first time a Korean athlete competed under the national flag since the country was liberated from Japanese colonial rule (1910-45).

"Road to Boston," set to hit theaters on Sept. 27, is led by famous filmmaker Kang Je-gyu, who helmed the 1999 action film, "Shiri," and the 2004 smash-hit war movie, "Taegukgi."

Preparing for the physically-demanding role was not easy, the actor said.

Yim shared that the overwhelming weight of playing the character, who set a historic milestone for the country, motivated him to put enormous effort into reaching the physical appearance of a professional athlete.

"I felt a sense of duty to attain the physical shape of a marathoner. And Suh had such a well-built and healthy physique. So during the three months I had to prepare for the film and the five months of filming, I lived like a semi-professional athlete to emulate that physique," he said, adding that his body fat content went down to six percent.

"In the morning, I received marathon training, followed by weight training during lunch, and supplementary training in the evening. I ate chicken breast for all three meals to cut down on fat. I know real athletes will have more rigorous routines, but I felt my life was closer to an athlete's life than an actor's … I told myself, ‘I'm a national athlete' for eight months."

A scene from the film "Road to Boston" / Courtesy of Lotte Entertainment

The actor fills most of the 108-minute film with scenes of running, from the process of qualifying for the international marathon to the final and emotional journey of competing in the match.

Despite the tough training he endured to create the character, Yim did not have much difficulty filming scenes that required physical strength.

"Surprisingly, my strength actually improved as I was training for the marathon. So I didn't find it as exhausting. But rather, it felt like a duty and a mission that I needed to compete," he said.

"I never actually interviewed athletes, but I just delved into the mindset one (an athlete) would have towards that goal. I also have a goal to complete a project every time I work on a piece. So I believed that their goals, passion, and mindset would be much stronger than what I experienced. And I aimed to maximize those aspects to portray the character."

Filming for the movie was completed three years ago, but the release was delayed because of COVID-19 and Bae's drunk driving scandal.

Yim expressed excitement over the film's long-awaited release.

"I realized that the success of a film doesn't end with successfully wrapping the filming. But it truly comes to life when you meet the audience, whether the feedback is positive or negative. So (the release) gave me a profound sense of purpose, like vitality, as an actor," he said.

The actor added that he hopes this film will give people a chance to learn more about Suh.

"Although I was familiar with Sohn, I only learned about Suh after reading the script. And I felt people like this deserve more recognition," he said. "I hope that people will learn more about not only Sohn, but also Suh and take pride in them after watching our film."