"Hey, Mike! Give me a hand with this, will ya? It's heavy."

"Sure, Joe."

Apparently my name is Mike and I've decided to call Brad, Joe. We both crouch down and mime picking up a roughly 4-by-4 imaginary concrete block. We creep slowly, bent knees, our arms outstretched, taut. n "Let's put it down here," Brad/Joe says. Be careful of your back."

"I got it, I got it," I say, huffing.

I'm at the weekly practice of our improv troupe, The Improfessionals, and Brad and I are starting a three-person scene. The third member, Ann, stands on the sidelines waiting for a good time to enter.

In typical improv fashion, our fellow actors have set up the scene by giving us suggestions: Brad and I are brothers who run a concrete factory, and Ann is surprisingly free to be any character she likes. But to ramp up the challenge, they've endowed each of us with a phobia: mine is a fear of bold print, Brad's is a fear of aftershave lotion, and Ann's is condiments. Somehow we need to work these into the scene and our characters.

You probably know at least a bit about improv—a Second City show, Drew Carey's Whose Line Is It Anyway? on TV, unscripted movies like Waiting for Guffman or The Mighty Wind. Watching this type of comedic improv gives you the impression that the actors on stage are comic geniuses, on heavy doses of really good medication, or both. They're loose,…