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As an exercise device, the Wii Fit is intended for the most grossly obese or most embarrassingly inactive only. Jogging in place for four minutes is surely better than nothing, but it doesn't really substitute for the 30 minutes of activity a day that is reccommended.
One thing that the Wii Fit does to well, though, is give you some good advice. One of the first things the little machine asks you to do is take a "Fit Test." Again, this test has little actual bearing to one's fitness. The Fit Test essentially tests your balance and measures what it calls your "Center of Weight." When I first took the Fit Test, it gave me a Wii Fitness age of 48.
First, that's brutally unfair. The Fit Test works on the Body Mass Index (BMI). I'm a little overweight, but according to Wii Fit, my BMI
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Anyway, my Center of Weight seemed to be two inches behind the actual middle of my body. So the Wii Fit reccommended that I practice standing with more of my weight toward my toes. I can't say for sure that it's improved my posture, but I'm definitely more cognizant of how I stand.
I'm not going to become an evangelist for Wii Fit other than for fun (the Step game is particularly great). But I think that if a little piece of technology can convice you to stand differently, I think that's worthy of mention.