Will Smith “fell to his knees” after a particularly brutal training session for a $87.7 million flick, according to the boxing trainer.

When you collaborate with Michael Mann on a movie, you will most likely establish yourself as an authority in the area of expertise of your character. So when Will Smith was cast to play the extraordinarily talented heavyweight champion, Muhammad Ali, the actor had him put on weight and enter boxing matches against famous opponents.

One could argue that a film’s emotional impact and ability to evoke strong feelings in the audience are what truly distinguish a good film. Actors must go through intense training in order to accomplish this, particularly when playing a historical figure who overcame significant physical challenges. This was the case for Smith during his 2001 performance as boxer Muhammad “the Greatest” Ali; he even reportedly “fell to his knees” amid the rigorous training required for the role.

Will Smith went through rigorous training for Ali

Will Smith’s Hard Road In Michael Mann’s Ali

Certain performances are so powerful that they leave a lasting impression on the viewers as well as the athletes. The life of the legendary boxer Muhammad Ali was brilliantly portrayed in the 2001 Michael Mann film Ali. But a secret story of rigorous training and commitment was being told behind the scenes. In an intriguing anecdote, Will Smith‘s boxing coach revealed how he took the actor to the edge of his comfort zone and eventually brought him to the ground “to his knees”.

The boxing coach for Ali revealed that at one point the Wild Wild West actor “fell to his knees and I made him write Muhammad Ali’s name in the snow” because of the intense training he underwent.

Will Smith in and as Ali

Speaking to NME, Darrell Foster—who has coached a number of Hollywood stars, such as Woody Harrelson, Antonio Banderas, and Eddie Murphy—discussed the rigorous regimen Smith had to go through to accurately portray the legendary fighter. He explained:

“I took Will up to 10,000 feet in Aspen, Colorado so he could understand what it felt like to experience oxygen deprivation in order to correlate it to how Ali felt in the 14th round with [former world heavyweight champion] Joe Frazier and how it feels to actually not be able to breathe and you’ve still gotta keep fighting,” Foster recalled. “I made Will run and throw punches. He fell to his knees and I made him write Ali’s name in the snow. And he said: ‘Now I get it’.”

The film centered on the ten years in the life of boxer Muhammad Ali, from 1964 to 1974. These years include his victory over Sonny Liston for the heavyweight title, his conversion to Islam, his criticism of the Vietnam War, his expulsion from the sport, and his comeback match against Joe Frazier in 1971.

Will Smith in Michael Mann’s Ali

Michael Mann: Will Smith Became a ‘Fighter’ in Ali

The actors are free to let their hair down and play their roles with elegance because Michael Mann‘s action scenes are typically meticulously planned and rehearsed. This is partly true for Ali, but to accurately capture the rough ballet of boxing, Mann let his leading man (Will Smith) spar with some very strong opponents. As he stated to Entertainment Weekly:

“First of all, Will became a fighter. He boxed every Thursday, and worked out six hours a day five days a week. He actually trained with [Ali trainer] Angelo Dundee. So Will hit and got hit. There was choreography where we knew certain things were coming, certain historical events that we knew we had to include, but in between it was all improvised sparring. In fact, everybody who plays a boxer in the film IS a boxer. We didn’t use stunt coordinators or stuntmen..”

Will Smith Became a ‘Fighter’ in Ali

Although Ali was well-received by critics, it was a box office bomb, earning only $87 million compared to an estimated $118 million production budget. Jon Voight and Smith were nominated for Best Supporting Actor and Best Actor, respectively, at the Academy Awards.

Stream Ali on DIRECTV.