How old are you? Got that number in your head? Good. Remember it.
1) Do your age in pushups. If you're unprepared for that, do as many as you can, and THEN switch to your knees to finish off.
2) Do your age in SITUPS. Hook your toes under the couch, and get it done.
3) Do your age in JUMP SQUATS. Feet wide, land softly--like a ninja. Don't stop until you've done your age, though, no matter how badly it hurts. And it WILL hurt.
"But I'm 60!" Quit whining--that just means you've had longer to practice! Don't blame me for squandering the past 30 years, but don't try to get out of it, either, because when the zombies come knockin', they won't ask if you're too old to eat. They just eat.
Besides--the older we get, the more exercise we need. You may need to take a little break in there somewhere, especially on the jump squats, but make sure you're really pushing yourself.
Russ Craber, MBA, CSCS, has always been concerned about a post-apocalyptic zombie scenario, and can train you for optimal living after the inevitable occurs. You would be well-advised to heed his advice.