Wii actually had the opposite effect on me. I gained weaight. From around 145 lbs last January (I'm 5'10" btw) when I got the thing to around 160 lbs in late May when I sprained my ankle - and to answer your question, yes I sprained it playing Wii (but everyone except my wife believes I sprained it "jogging").
I started out boxing 30 mins every other day with 2.5 lbs wrist weights on each arm. By the end of May when, like a massive tool I sprained my ankle trying to jump over an object in my living room in between rounds, I was up to 8.5 lbs on each arm (which looked absurd). I suppose I gained weight because I built muscle and my appetite increased dramatically from all the activity.
In any case, I haven't been able to get back on my routine since the injury
