Your move: Use the 20-20 rule. “Trying to sit up perfectly straight all day is impractical and will only tire you out,” says Alan Hedge, Ph.D., an ergonomics professor at Cornell University. Instead, every 20 minutes, stand for 20 seconds and stretch or shake things out. “Just 20 seconds away from your computer screen reduces fatigue and increases blood circulation,” says Hedge. Better yet, take it to the next level: Eliminate sitting altogether and discover How to Upgrade to a Stand-up Desk.