The Stretch Reflex

Your muscles are protected by a mechanism called the stretch reflex. Any time you stretch the muscle fibers (muscles) to far (either by bouncing or overstretching), a nerve reflex responds by sending a signal to the muscles to contract; this keeps the muscles from being injured. Therefore, when you stretch too far you're actually tightening the very muscles you are trying to stretch! ( You get a similar involuntary muscle reaction when you accidentally touch something hot; before you can think about it, your body quickly moves away from the heat.)