If you are stuck inside, you can always resort to the good ol' treadmill to get a work out:
If you can't afford the super delux model, well, there's always the do it yourself version:
If all that walking and running isn't for you, perhaps you should consider aerobic dancing. This is a great work out for all the lady cats!
And don't forget that a good rest is important too:
Wow! All that activity wore me out! I think I need to take a nap now! Later!