The New York Times has a great article on one of fitness' all time greatest exercises; the pushup.

The push-up is the ultimate barometer of fitness. It tests the whole body, engaging muscle groups in the arms, chest, abdomen, hips and legs. It requires the body to be taut like a plank with toes and palms on the floor. The act of lifting and lowering one’s entire weight is taxing even for the very fit.

There is definitely a great sense of pride felt as you achieve rep. after rep. of grueling pushup - and much soreness to be expected the next day.

They are important for people of all ages as they help to combat aging, muscle wasting, and bone loss. "Push-ups are important for older people, too. The ability to do them more than once and with proper form is an important indicator of the capacity to withstand the rigors of aging."

Mr. LaLanne, who once set a world record by doing 1,000 push-ups in 23 minutes, still does push-ups as part of his daily workout. Now he balances his feet and each hand on three chairs. “That way I can go way down, even lower than if I was on the floor,” he said. “That’s really tough.”

Enjoy this incredible video: