Exercise for Geeks?

An anonymous reader asks: "A bunch of friends and I have been wondering for a while how to stay fit (and additionally, how to bulk up). While common suggestions include team sports, few of us are able to get together and play something outdoors since the weather here is abysmal. We would like to know how you geeks stay fit individually in your homes, and are there any ways to do so (while building up muscle) that don't involve expensive equipment? Thanks."