Kevin Hart Handles Front Desk of Philly Gym for New Mountain Dew Ad

Kevin Hart is taking over a gym in Philly for Mountain Dew in what appears to be a new ad for the green pop ... and a peek behind the scenes looks promising for laughs.

TMZ has obtained footage of Kevin at a Philadelphia Sports Clubs gym early Sunday morning, where cameras were rolling as he got a lesson from an employee on how to work the front desk. From the looks of it here, Kev's got it all under control.

He hilariously gives a blow-by-blow of what he plans to be doing behind the desk -- "I'ma get back here, and I'm gonna help people!" -- while the gym worker gives him a quick rundown on how to check first and last names. Simple enough ... go dew you, "Daniel."

Hard to tell if this is part of a bigger ad campaign by MD, but it wouldn't be surprising if it is. Kevin's done plenty of TV spots for Mountain Dew in the past ... most were pretty funny.