You could always go out and buy an anatomy book, and just do studies of that, that way you'll know the skeletal and muscle structure

Or yo could head down to the local subway or mall or whatever, and just do some quick gesture type sketches... bookstores and coffee lounges are the best because people sit still longer there XD
That way when you're drawing and make a ridiculously loud exasperated noise because the dum-dum moved while you were drawing them people won't look at you funny 8D Not that I've done that before...