Here's one for the leg muscles...

... as you sit in front of your computer with your legs on the left side of the desk, and the kitty comes jumping up - move your legs to the edge of the desk to make room for your kitty - hold your legs there for a minute, before you gently push the kitty a tiny bit backwards - relax. A minute later, as the kitty is pushing your legs over the edge, repeat the excersise. This I assure you, will strenghten your leg muscles and keep your kitty entertained - until he's HAD ENOUGH and leaves!