A solid way to asses your fitness level is to calculate your VO2max, which is your maximum oxygen consumption during an exercise that gradually increases in intensity, New Scientist reports. The higher your number, the fitter you are. A VO2max test is usually done on a treadmill with you breathing into a face mask, but you can do this test yourself without such gadgetry. Use a watch to measure how quickly you can walk a mile, then measure your heart rate. With your time, heart rate, age, gender, and weight, you can figure out your VO2 max by plugging the numbers into a ready-made calculator.
--Aileen TorresPhotograph by filtran via Flickr