Jake Gyllenhaal, Jeff Bauman discuss ‘Stronger,’ based on Boston Marathon bombing book

Jeff Bauman awoke in a Boston hospital bed. His legs were gone. He had barely escaped death when twin explosions near the finish line of the Boston Marathon left three others dead and dozens more horribly injured.

He was unable to speak, but with a pen he scribbled a note: Had anyone seen his estranged girlfriend, Erin Hurley, whom he had come to Boylston Street to see cross the finish line.

“I was worried because she was on the course. I heard the second bomb but didn’t know how far [away] it was,” Mr. Bauman said during a recent press tour stop in the District. “I had no idea what was going on.”

Knowing he had lost his lower limbs, he also scribbled another note: “Lt. Dan.”

“I saw my friend who was in the [hospital], and he’s trying to explain to me that I didn’t have any legs, and I couldn’t really tell him, ’Bro, I already know,’” Mr. Bauman said. “So I had to joke with him.”

And yet even while humorously comparing himself to Forrest Gump’s platoon leader, who lost both legs in the jungles of Vietnam, Mr. Bauman had the presence of mind to scribble a third, even more important note.

He had seen one of the men who had done it.

Mr. Bauman wrote a book about his experiences helping authorities to identify one of the Tsarnaev brothers, which was but prologue to the long physical and emotional recovery he faced ahead.

“There was a huge responsibility in trying to get his journey right, and by right I mean what he went through emotionally, physically, sort of recalibrating his entire life after the event,” the actor Jake Gyllenhaal, seated next to Mr. Bauman, said of portraying the Bostonian in “Stronger,” the film adaptation of Mr. Bauman’s book that comes out Friday in the capital.

“My first impression of Jeff was I was nervous to meet him,” Mr. Gyllenhaal said. “I guess I was surprised at how well we got along as two people.”

Mr. Gyllenhaal said that it was not only Mr. Bauman’s strength that came through in the book “Stronger,” but also the author’s fierce sense of humor.

“I expected I think what you’d expect a guy going through all the things he goes through. But his sense of humor was really unexpected,” Mr. Gyllenhaal said, “which is what I think made it great.”

“I knew that as soon as Jake jumped on that it was going to happen because Jake doesn’t mess around,” Mr. Bauman said.

The film “Stronger” doesn’t shy from either the pain or the humiliation Mr. Bauman endured in the weeks and months following the terror attack. In the family home with flights of stairs, he falls often, frequently injuring himself, and has to ask for help with such menial tasks as using the toilet or turning on a shower.

In his anger he often strikes out at Erin (Tatiana Maslany) and his mother, Patty (Miranda Richardson).

He drinks often, and won’t let even his wheelchair prevent him from picking bar fights.

Unlike his subject, Mr. Gyllenhaal is blessed to have legs. (Mr. Bauman now walks using metal prostheses.) So Mr. Bauman coached the Oscar-nominated actor in the finer points of two-limbed mobility while prepping the film.

“The first thing that we did work on was just going over how I transferred out of my chair into cars,” Mr. Bauman said. “How I got up from the ground. How I got up from a seat. He watched all those things and did a lot of research on it.

“I was really concerned about that,” Mr. Bauman said. “How far are you going to go with this? And he went all the way with it, which was amazing and makes me proud.”

The film’s props department fashioned Mr. Gyllenhaal with prostheses to wear over his actual legs, which he could then tuck out of view of the camera.

“One of the things you realize is your center of gravity completely changes” using your arms for everything, Mr. Gyllenhaal said. “My brain would try to center where I was and know that I didn’t have” the ability to use his legs at all, a crucial step into inhabiting Mr. Bauman’s new world.

“I’ve seen my younger brothers in the military try to get around in my wheelchair and they’re ’gassed’ after like five minutes,” Mr. Bauman said. “It just works different muscles.

“It was fun to watch [the actors] cheating and using their legs. ’You can’t do that!’” Mr. Bauman said.

As much as getting across the physicality was the need to portray the psychological damage done unto Mr. Bauman by the bombings.

“In terms of understanding him, I was more interested in the guy who was ’the guy before this event,’” Mr. Gyllenhaal said. “This isn’t a movie really about the end at all, it’s about this human being getting through a really tough time. And I think that’s where we all can relate. We all know someone who is struggling with something.”

The two men have traveled together for weeks promoting “Stronger.” Mr. Gyllenhaal calls Mr. Bauman a friend and, with a knowing smile, said he is now able to pick up on the Bostonian’s particular quirks.

“He’s not always the most” talkative, Mr. Gyllenhaal said of his friend. “You [sometimes] can’t get a lot of information out of him.

“It was just spending lots and lots of time observing him — watching how he got up every day, and watching him interact with his family and all the people who took care of him.”

If Mr. Bauman is sometimes quiet, it could be from revisiting the most difficult point of his life when watching Mr. Gyllenhaal portray him on set. Much of the film centers on Jeff’s relationship with Erin, and how issues that were present before the bombing become magnified.

“The hardest thing I had to go through was [watching] the relationship between Erin and I. I had to relive watching me get into the shower and telling her to leave — pushing her away,” Mr. Bauman said of one of the film’s more difficult scenes. “As a guy, I wanted to be the strong one. I definitely want her to see me as strong.

“That was really the toughest thing to relive through the film because Tatiana Maslany did it so well,” he said of the actress portraying Erin. “It still hurts but it’s real. I’m starting to find it lovely, and [the film] shows me what we went through together and how hard it was for us.”

Both subject and actor hope “Stronger” will inspire those who are dealing with tough times to know they are more durable than they ever dared believe.

“There are people dealing with pain and struggle and maybe feeling like you won’t ever get through it. And I think that Jeff shows you that you really can,” Mr. Gyllenhaal said. “If he can get through it, you can get through it.”