‘Brittany Runs a Marathon’ predictable but also funny

Jillian Bell gives title character quick-witted, improvisatory edge.

In “Brittany Runs a Marathon,” Jillian Bell plays the title character, a young woman approaching 30 whose life has stalled into a deadening cycle of partying, meaningless sex, shallow friendships and an off-off-Broadway theater gig that barely keeps her aflfloat.

As an archetype, Brittany resembles the characters Amy Schumer has played in such makeover comedies as “Trainwreck” and “I Feel Pretty”: the funny, resilient but wounded girl whose selfdeprecation masks deeper self-loathing, and whose selfsabotage veers precariously toward self-harm.

The title of “Brittany Runs a Marathon” is nothing if not literal: Here, the means of the heroine’s salvation is her discovery of running, but the twist is that even that healthy pastime — and the positive changes it engenders — invites new ways for Brittany to indulge her deepest weaknesses.

Wr i t t e n a n d d i re c t e d by newcomer Paul Downs Colaizzo, “Brittany Runs a Marathon” is an engaging, modestly amusing, sometimes laugh-out-loud hilarious comedy of manners in which the usual millennial excesses are skewered, from the invidious hellhole of social media to the mendacities of online dating.

The best part of “Brittany Runs a Marathon” is that is provides a showcase for Bell, who, before these two movies, has usually been relegated to scene-stealing but all-too-brief supporting roles. Right offff the bat, she gives Brittany a quick-witted, improvisatory edge, which eventually is shown to cover up for deep-seated social anxiety. Bell plays all the layers with admirable skill, managing to be tartly funny, abrasively offffffffffffputting and wrenchingly vulnerable within the space of just a few moments.

She also pulls offff the physical transformation that forms the somewhat contradictory climax of “Brittany Runs a Marathon.” This is a movie that is adamantly body-positive (“You totally missed the point of those Dove ads,” Brittany complains to a doctor who tells her she’s overweight), but it also revels in the fifit, lip-glossed, romantically fulfifilled butterflfly who emerges from her cocoon of red wine, Aderall and shame.

Not content to leave it there, Colaizzo pre-empts his foreordained happy ending just long enough to question how Brittany — and the audience — would precisely defifine that term. “Brittany Runs a Marathon” is perfunctory, idealized, sometimes awkwardly composed, almost always predictable. But it stays the course, with admirable grit and more than a few entertaining grins.

JON PACK, AMAZON STUDIOS Jillian Bell stars in the comedy “Brittany Runs a Marathon” as Brittany.