I don’t think I’ve ever identified more with a movie than with the crowd-pleasing “Brittany Runs a Marathon.” Yes, it’s “Rocky” in running shoes, but first-time writer-director Paul Downs Colaizzo manages to apply a glorious new spin by sticking with what he knows, or more precisely, who he knows.

That would be his roommate, Brittany O’Neil. Like her movie doppelganger, played splendidly by major-star-in-the-making Jillian Bell, she found herself fat, out of shape and directionless; a hard-partying boozehound ordered by her doctor to straighten up and lose 50 pounds or face major health problems. Big shock, she starts running, a block at a time. And before you know it, those blocks become New York miles. But more importantly, she stops hating herself, begins taking chances and in turn acquiring possibilities.

The movie’s Brittany does the same, with Colaizzo laying down all his “Rocky” cards early; everything but her punching a side of beef and charging up the museum steps. It’s 30 minutes in, and you’ve figured out how all aspects of her untidy life will burst into a rainbow of enlightenment, as she finds her Adrien and stumbles across the finish line in star-spangled shorts claiming moral victory. Not so fast.

Colaizzo thankfully doesn’t run that way. He digs deeper, and so does Bell in delving into more than just inspiration and personal bests. In most movies, Brittany’s predictable weight loss and the boost in self-confidence would easily fill the allotted 106 minutes. But this is real life and as such, shedding pounds and wearing down running shoes might be terrific for you physically, but it does little for you mentally. And Brittany is toting baggage far outweighing her original 197 pounds. Running does nothing to dispel the anger and resentment rooted in a childhood shattered by her parents’ bitter divorce.

It’s cost her the ability to trust, believe and allow herself to be happy around a host of new-found friends in the equally insecure gay dad, Seth (Micah Stock); divorcee neighbor, Catherine (Bell’s “Sword of Trust” co-star, Michaela Watkins), and freeloading house-sitter, Jern (a perfectly impish Utkarsh Ambudkar).

An existential crisis would seem an odd thing to dump on one of Hollywood’s funniest women, but Bell accepts the challenge and literally runs with it. Her Brittany may be a riot to hang around, quick with a quip and armed with stinging one-liners (many of them ad-libbed), but she’s also mean and self-loathing. It’s not an easy fix and the movie doesn’t allow her one.

I know, because Brittany’s life was my life. Like her, I was dangerously overweight (me in my late teens; she in her mid-20s), had an epiphany and started running. I began with one lap around the tractor-testing track at the University of Nebraska ag school. One lap became 10, 20, 30 … I started entering 5Ks and 10Ks. And like Brittany, I joined a running club, which led to wanting to do the ultimate: the 26-mile marathon. Not only did I do one, I did seven, two in fewer than 2 hours and 50 minutes.

Ultimately, I wanted to run Boston as badly as Brittany wants to run her hometown New York City Marathon. And again like her, I wound up with a stress fracture in my shin just weeks before the starting gun sounded. I ran the race anyway; slow as hell, but still a respectable 3 hours and 30 minutes. That was 35 years ago, but “Brittany” and Bell brought it all vividly back. It was like deja vu all over again. It amazed me how a film could dive so deep into my head and mine my thoughts so perfectly down to the fact that a thin body and fast feet don’t make you a better person or erase your peccadillos. But it does give you the initiative to change, and sometimes that’s all you need.

That’s where the truth in “Brittany Runs a Marathon” lies. It puts Bell through an emotional ringer, proving yet again that when it comes to drama, there are few better at misery than comedians. Thank you, Jack Lemmon, Robin Williams, Tom Hanks and Adam Sandler. Her performance reminded me a lot of Amy Schumer in “Trainwreck,” but Bell goes her one better by daring to squelch the funny after the first 30 minutes and spend the next 75 going into dark, fascinating places. It’s a bravura turn that should break the “22 Jump Street” scene-stealer out of character-actor hell.

Mile for mile, it’s one of the year’s best performances. It starts slow, finishes strong, leaving us all cheering as she breaks the mold - losing the race but winning many a heart.

Al Alexander may be reached at alexandercritica@aol.com.

“Brittany Runs a Marathon”
Cast includes Jillian Bell, Michaela Watkins, Utkarsh Ambudkar, Micah Stock and Alice Lee.
(R for language throughout, sexuality and some drug material)
Grade: A-