There are two types of Duplass Brothers completists. If you don’t know the Duplass brothers, Mark and Jay, they are often credited as key players in the ‘mumblecore’ movement of filmmaking. If you don’t know ‘mumblecore,’ watch the Duplass’ Sundance-selected debut feature, The Puffy Chair, and any film directed by Andrew Buljaski or Joe Swanberg. I’ll wait.

Anyway, as I was saying, there are two types of Duplass Brothers completists. You could see every movie starring a Duplass brother – Mark has developed quite an acting career of his own – or you can see every movie they have written and directed (always together). The SXSW 2012-selected Do-Deca-Pentathlon falls into the latter category.

It stars relatively unknown actors Steve Zissis and Mark Kelly as two grown brothers who still maintain a strong sibling rivalry. Zissis plays a depressed family man who wants to have a nice birthday weekend at his mom’s without his brother’s interference. Kelly plays an untamed professional poker player who can’t resist crashing the birthday weekend.

As with many Duplass brothers movies (of both types), the relationship between the brothers is well-developed. We see the jealousy they each have for the lives of the other as well as a certain begrudging love. I bought these two as brothers more than I did the pair in Jeff Who Lives at Home, the other recent Duplass-written and Duplass-directed film, starring Jason Segel and Ed Helms.

As the brothers in Do-Deca-Pentathlon re-ignite the titular sibling sports competition, the mom (Julie Vorus) and the wife (Jennifer Lafleur) raise objections. But the movie makes them smart enough to see right through the childish gambits the brothers use to disguise their epic sports challenge. The movie walks a fine line between dramatic sports movie, silly comedy and laid-back slice of life. I wouldn’t always say it makes it work, but the heart is in the right place.

So, back to the Duplass completists of the second type. This movie is for them, mostly, as I see it. The Duplass charm is present, but the film isn’t particularly ambitious or affecting. Apparently this movie was developed pre-Puffy Chair, which might explain why it feels like a step backwards from Jeff (as much as I disliked the gooey spiritual message Jeff dispenses) in terms of assuredness.

The concept of grown men clashing childishly in an epic sports competition is a promising one, (and true, apparently based on two real brothers the Duplasses knew growing up). But the potential is barely exploited. While the stakes are high for the Zissis character, they are unclear for the Kelly character. And the sporting competitions are mostly shown in montage, with only one laser tag sequence that seems to advance the plot and develop the characters at the same time as building suspense about who will win.

With Girls on HBO, and the Duplasses and Greta Gerwig working in Hollywood, it seems like mumblecore has gone mainstream. I’d like to hope that movies like Do-Deca, which are more fundamentalist (mumble-hard-core?), will still be made and enjoyed. But watching this film, I fear that the zeitgeist is ready to move on from twenty-somethings and their non-problems. Now that the mumblers are turning 30, is it time to put away childish things and make films about bigger issues? Jeff Who Lives At Home was dealing with this, and so is Do-Deca, in its own way. But the answers provided (rely on mystical coincidences, lose some weight) are still juvenile.