Zac Efron, Robert De Niro go shirtless on 'Dirty Grandpa' set

TYBEE ISLAND, Ga., May 1 (UPI) -- Zac Efron and Robert De Niro showed off their muscles this week on set.

The 27-year-old actor and his 71-year-old co-star stripped down for a spring break scene in Dirty Grandpa. Efron stars as an uptight groom-to-be whose perverted, former Army general grandfather (De Niro) tricks him into driving to Florida days before his wedding.

Efron and De Niro were photographed as they engaged in what appeared to be a shirtless body competition. The elder actor was spotted doing one-handed pushups and picking up or supporting Efron in a variety of positions.

Dirty Grandpa is directed by Da Ali G Show writer Dan Mazer, and opens in theaters Aug. 12, 2016. The movie also stars Zoey Deutch as Efron's character's fiancée, with appearances by Aubrey Plaza, Dermot Mulroney and Julianne Hough.