Funny you should ask this question lol as today I had my 1st time on my DD's Wii Fit
It is fun! I did push ups, planks, jackknives for abs, some very basic yoga poses etc.
It starts out very basic and as you go along the game opens up more options to workout to.
I don't think it will take the place of a Cathe or gym workout but for a rest day or for just hanging around at home to play is good.
All the teens in my area have been talking tons about this thing and for once it got my son who is on the HS Track Team off his XBOX 360 and he run with this thing and did some strength workouts.
It actually makes exercise for these kids fun as they are games but do work the body
After all this time I have been encouraging my oldest DD who does use Cathe sporadically and my son who wants to build strength I give him my old weights
Now they actually look forward to exercising.
Go figure!
I know I will be using it as much as the kids do ... it's good family fun
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I just saw this over at videofitness it may be something to look at :
http://forum.videofitness.com/showthread.php?t=118482