The human skeleton moves at its more than 230 joints, which are the places where bones connect. Those joints give you a basic range of motion. For example, everyone’s shoulder joints can rotate 360 degrees, and elbows can open and close to just under a 180 degree arc. The pull of ligaments—ropelike connective tissues that anchor one bone to the next around a joint—lengthen a bit to allow a joint to move, but keep the range of motion limited so that you don’t hurt yourself. So, the next time you are tempted to do a backbend or stretch your leg up to your ear, think of your joints and ligaments!