(Shakespeare Theatre) (Shakespeare Theatre)

Bruce Dow has a weight loss plan for you! Play Pseudolus, the main character in “A Funny Thing Happened on the Way to the Forum,” now at the Shakespeare Theatre. A slave who longs to be free, Pseudolus spends most of the musical comedy onstage, and most of that onstage time running and/or jumping and/or singing and/or dancing.

“By the end of the show the leather belt they have for me is too loose,” Dow says. “I feel so bad for Jennifer Frankel, who plays Gymnasia, who at the end of the show is my girlfriend. She gets this fat sweaty ball of nightmare.”

In addition to the physical challenges of the role, Dow, who played Bottom in the theater’s recent production of “A Midsummer Night’s Dream,” says that musical theater poses some problems you don’t find in straight plays. “The scenes in a musical are abbreviated — the songs are where you get to explore the moment,” he says.

“In a Shakespeare play you can take all of a soliloquy to work your way through and find a moment where your character makes a decision,” he adds. “With a song, you have to accomplish the same thing, but you have to do it on beat four of bar 17.”

Even in the farce that is “Forum,” “there are huge moments for all the characters when danger enters into it,” Dow says. Pseudolus and another slave “start to tell lies and make up stories and try to finagle things, and there are big points where we could all die.”

That’s where the comedy comes from, Dow says. The characters have believable wants and take believable risks, but do it in a world where bursting into song is acceptable.

“It will be surprising to the audience how much heart [the show] has,” he says. “Everybody in the play has a deep want we can all relate to — for personal freedom, for emotional freedom, for love. My job is to base [my performance] in truth.”

The Story

In this Stephen Sondheim farce, Roman slave Pseudolus attempts to earn his freedom by bringing his master, Hero, together with the virginal courtesan Philia, who lives next door and is already promised to a very stabby general. There’s singing, dancing, mistaken identities and a song called “Everybody Ought to Have a Maid” that will stay lodged in your brain FOREVER.

Shakespeare Theatre’s Sidney Harman Hall, 610 F St. NW; through Jan. 5, $20-$115; 202-547-1122. (Gallery Place)