RATING |

Paul Downs Colaizzo, writer and director of Brittany Runs a Marathon, spent only a few years of his formative years in Voorhees, but local legends left a mark, and you can feel the imprint of Rocky on his new movie.

It is, at its core, the story of a woman who wants to prove something mainly to herself, and though there is a competition involved, it’s not about winning — it’s just about going 15 rounds, or in this case, 26.22 miles.

What the two movies also have in common is a performance by an actor making a big jump in class — in this case Jillian Bell, who’s been making us laugh for years with vivid supporting turns in comedies like 22 Jump Street. Here, she gets a formidable starring role (she’s in every scene) that calls for a daunting array of emotions, and an impressive summoning of craft and instinct — it’s really up to Bell (who lost 40 pounds for the transformative part) to help guide the audience through the perilous territory that comes with the story of a woman who wants to change her life, and with it her body.

For party-girl Brittany, it starts with trip to the doctor’s office — she wants some pep pills but what she gets is some bad news about her blood work. She’s just 28, but tests show problems with her blood pressure and liver, likely related to her weight and couch-centered lifestyle.

“I think you totally missed the point of those Dove ads,” pleads Brittany, in a line that is typical of the way the movie uses comedy to approach touchy material, a mode that suits Bell — she’s reaching for a joke, and getting a laugh, but she shows us the panic in her character’s eyes.

Brittany makes the decision to take up jogging, joins a running club, is urged on by new running pals (Micah Stock and Michaela Watkins), adopts the goal of training for the New York City Marathon, and you think you see where the movie is going.

Not so fast — a phrase that also describes Brittany’s time in the 5K. Colaizzo has a much more ambitious movie in mind — one that looks penetratingly at the loneliness and unhappiness at the core of Brittany’s life (there are some rock-bottom moments that left a preview audience gasping), and these are things that no amount of running or weight loss can cure.

So the movie takes interesting turns — Brittany does lose a lot of weight, and she does start to notice being noticed. Yet when a handsome chap in a suit holds the subway door for her (pointedly reversing the trajectory and outcome of an earlier scene) what’s at work in the scene is not elation, but a kind of melancholy — Brittany still carries with her all those years of invisibility, and this informs her reaction.

Bell registers all of this beautifully, and manages to keep us laughing while also exploring the prickly riddle of the character’s psyche. Brittany’s opinion of herself lags behind her physical transformation, and she is often hard on people who are in her corner — her running partners, her potential boyfriend (Utkarsh Ambudkar). She clashes with her social media-obsessed roommate (Alice Lee), who doesn’t seem to know how to react to Brittany as anything other than her chubby sidekick. Was Brittany always an Instragram accessory, there to provide contrast?

But the estrangement is Brittany’s fault, too — she can’t accept help from people. Not from the new friends trying to encourage her, not even from the brother-in-law (Lil Rel Howery) who takes her in (in his Philly home) when she hits a bumpy road in Brooklyn.

For years, the world told her she wasn’t worth paying attention to, and she started to believe it. Brittany’s road to a different kind of belief is itself a bit of a marathon, and the movie sometimes seems (like its title character) to drag its feet. It’s messy, but with the untidiness of real life.

RATING |

Brittany Runs a Marathon. Directed by Paul Downs Colaizzo. With Jillian Bell, Utkarsh Ambudkar, Michaela Watkins, Micah Stock and Lil Rel Howery. Distributed by Amazon.

Running time: 1 hour, 44 mins.

Parents guide: R (language, drugs, sex)

Playing at: Ritz 5