Running up stairs is a time-honored way to improve aerobic conditioning. Take them 2 at a time if you're athletic and consider them to be part of your interval training. Even if you're new to exercise, you can benefit from walking up stairs whenever you get a chance. The calories burned will add up, and your conditioning will improve. If you have trouble finding time to exercise, take 10 minutes once or twice a day and walk up and down stairs at work (or before or after). Hold on to the rail if you need to.