Sibling rivalry reaches near-Olympic levels in “The Do-Deca-Pentathlon,” a delightfully scrappy backburner passion project from Jay and Mark Duplass in which two sad-sack thirtysomething brothers rekindle the 25-event athletic competition that ended their relationship as teenagers. Delivering high-concept laughs on an ultra-low budget, the project feels like a throwback to the Duplasses’ early indie work; it was shot shortly after “Baghead” and then shelved until they had completed Hollywood pics “Cyrus” and “Jeff, Who Lives at Home.” The wait was worth it: Eccentric without succumbing to quirk, this amusing, niche-targeted portrait of ultra-competitive losers crosses the finish line a winner.

Back in 1990, Mark (Steve Zissis) and Jeremy (Mark Kelly) devised an elaborate series of physical tests in such amateur categories as arm wrestling and skeeball to determine, once and for all, who was the better brother. The marathon event ended in a highly contested tie, since which the sibs have barely spoken. Now Mark is married (to Duplass regular Jennifer Lafleur) with a kid (Reid Williams), and Jeremy enjoys a wild bachelor life as a professional poker player.

Though each deeply envies what the other has, they’re both willing to risk it all to settle their old score. When Jeremy shows up unannounced on Mark’s birthday and crashes a low-key 5k fun run, the game is on: Ignoring his doctor’s advice to avoid stressful situations while naively hoping his wife won’t find out, Mark agrees to reopen the “do-deca-pentathlon.” Just as its name mangles the Greek language, so, too, does the contest dishonor the tradition of professional sports, counting table tennis and laser tag among its ridiculous tests of skill.

Whereas many of the Duplasses’ DIY colleagues make pics in which relationship issues serve as the subject rather than the subtext, this clever premise illustrates how a good story, however mundane it may seem, can provide a far more entertaining way of absorbing the same insights. At the same time, what makes their style feel so much more genuine than most scripted studio comedies is the way the duo allows the cast to improvise within the carefully mapped confines of that concept. That approach pushes character to the front and encourages identification, earning big laughs as auds recognize what isn’t being articulated during awkward moments. For example, a scene in which a shirtless, schlubby-looking Zissis reflects on how fat his feet have gotten serves as an unexpectedly poignant apology to his wife.

Though d.p. Jas Shelton’s twitchy zooms and fly-on-the-wall lensing betray the directors’ mumblecore origins, it’s not hard to imagine how “The Do-Deca-Pentathlon” might work as a studio comedy. As it happens, this was one of the scripts the Duplass brothers sold to Fox when trying to transition into the industry, and though the pic might not reach a wide audience in this form, the indie approach serves the material well. By casting relative unknowns Zissis and Kelly, both far from conventionally handsome and yet instantly lovable in their own ways, the Duplasses suggest how the characters’ unhealthy rivalry has held them back in their life goals.

Rather than working together, as the co-helmers have, the brothers got in one another’s way. As the competition escalates before the eyes of their horrified family, including unconditionally supportive mom Alice (Julie Vorus), the brothers’ hilariously self-destructive antics give way to direct dramatic confrontations between characters who clearly have a lot to get off their chests.

Four years in the works since the film’s 2008 shoot, the deceptively casual editing reps a victory unto itself, especially given the pic’s improv-friendly style and the sheer ambition of mounting so many sub-sporting events on limited means, making for a riotous mid-movie montage once the guys really get into it. Julian Wass’ score goes a long way to embellish the modest effort, from its anthemic opening theme — a larger-than-life scene-setter perfectly suited to the brothers’ overblown contest — to the poignantly unobtrusive music that accompanies later emotional moments.

The Do-Deca-Pentathlon

  • Production: A Red Flag Releasing release presented with Fox Searchlight Pictures. Produced by Jay Duplass, Mark Duplass, Stephanie Langhoff. Co-producer, Ross Partridge. Directed, written by Jay Duplass, Mark Duplass.
  • Crew: Camera (color, HD), Jas Shelton; editors, Jay Deuby, Nat Sanders; music, Julian Wass; music supervisor, Marguerite Phillips; set designers/costume designers, Marguerite Phillips, Ross Partridge; sound, Alex Lipschultz; re-recording mixer, John M. Chalfant. Reviewed at SXSW Film Festival (Narrative Spotlight), March 11, 2012. Running time: 76 MIN.
  • With: With: Steve Zissis, Mark Kelly, Jennifer LaFleur, Julie Vorus, Reid Williams.
  • Music By: