If you’re not already among the 21 million with a Wii Fit video system, odds are you’re starting to hear the steady drumbeat from your kids as the holidays rev up: “We just absolutely have to have a Wii Fit! It’ll make us healthy!”

Since it’s introduction in 2007, the Wii Fit has been touted as the antidote to the typical video game that straps a kid to the couch for hours on end. With the Wii Fit you’re up and doing just about every activity you can think of, from snowboarding and tennis to skateboarding and yoga. But how vigorously are you doing them?

That’s what the American Council on Exercise and researchers at the University of Wisconsin La Crosse Exercise and Health Program wanted to know. So they recruited 16 volunteers ages 20 to 24, established a baseline fitness for each, then tested them on the game’s six most aerobically challenging activities: Free Run, Island Run, Free Step, Advanced Step, Super Hula Hoop and Rhythm Boxing.

I won’t get into the specifics of the study – you can read them here. But the end result was this: While an hour on the Wii Fit certainly beats a session of Grand Theft Walrus, the study found that it’s no substitute for the real thing. In fact, the two games found to be the most physically taxing – Island Run and Free Run – still failed to “maintain or improve cardiorespiratory endurance as defined by the

American College of Sports Medicine.”

Further, the study found that the number of calories burned for the Wii Fit activities was significantly less than for the real McCoy.

“I guess anything is better than nothing, but we were a little bit underwhelmed with the exercise intensity of some of the exercises,” said John Porcari, one of the researchers. “The Wii Fit is a very, very mild workout.”

In short, better than nothing but no substitute for actually doing a thing.

Sorry, kids.