The new movie “Brittany Runs a Marathon” is an almost ideal example of the troubles Hollywood gets into trying to base films on “true stories.” Without that problem, viewers who can’t stand pop psychology and its language might be the only moviegoers naysaying the film.

It has the “Rocky” story. Brittany (Jillian Bell, a familiar face) has come to New York City to work in advertising, but she has suffered some reverses. Now she has a job as an usher at a theater and she lives in a sublet room with an ego-maniacal video-blogger who takes B. out drinking in uninspiring nightclubs.

One might not call Brittany a heroine. It becomes increasingly obvious that she is self-destructive. She overeats, drinks, allows others to direct her and takes odd recreational drugs. In fact, she goes to a doctor asking for a prescription for Adderall.

But he’s one of the film story’s good guys. He tells her she needs to get some exercise and maybe lose a little weight. Perhaps surprisingly, she accepts his advice and begins doing a little jogging. She meets two other runners.

Just to be in the zeitgeist, one of them is a homosexual and the other is in the middle of a rancorous divorce. The three decide they are going to run in the NYC Marathon 11 months from then. And we have titles on the screen telling us when each new season has arrived.

Brittany trains, we see in a montage of brief shots reminiscent of Rocky’s training in that movie. Brittany does not draw a pass into the race, so she has to raise money to pay for a slot. Perhaps this is why she looks for another job.

Her second is a glorified dog walker. During the day she visits a large dog whose owner family is out of town. Their apartment or house is pretty plush. And the night man on the job, Jern (a South Asian — the zeitgeist again), has moved in. Soon she fights with her insensitive roommate, moves into the dog’s home herself, and then moves into Jern’s bed.

All the while she is losing weight. Then one day she gains a little. She redoubles her jogging and injures herself. No running in the marathon now.

So when the dog’s owners come home, she is bereft. She and Jern split. And she can’t even stand following her old running pals’ training. She returns to her sister’s house in Philadelphia, disgraces herself with a difficult-to-believe attack on a hefty stranger, and gets the talk from her brother-in-law.

For some reason she begins to jog again when she is well, and the narrative arc starts all over again. But there are only 15 minutes of film time remaining to show what happens to her this time.

Like the unbelievable attack, the strange assumption of a second job, and the murky mystery of the donation for running slot, this ungainly restructuring of the viewer’s idea of the story only happens because writer and director Paul Downs Colaizzo is working from what the movie insists is a true story.

If the plot of “Brittany Runs a Marathon” were generated rather than borrowed, the viewer wouldn’t be distracted by these and other minor problems. And Bell gives a pretty creditable performance. So our only complaint with the film would be that every motivation any character in this movie feels is going to get a pop-psychology analysis.

But, then, maybe that would be enough to keep most of us from getting into the story.

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