Originally Posted by cyccommute

Notice how the rider is up off the saddle, his feet are parallel to the ground and his legs...specifically his thighs...are supporting his weight and acting like springs. Your legs and arms absorb more road shock than any bicycle suspension possibly can...short of a 9" travel downhiller.

What this position does is allows your bike to move up and down under you while your body follows a relatively flat line. The bike takes less punishment and your legs can handle the bending and flexing.