Coach Note - Understanding Stretching
 

When a muscle is being stretched, the central nervous system uses a protective mechanism called the stretch reflex to limit the muscle's ability to go farther in fear of danger. The stretch reflex continues to become more sensitive when muscles are not lengthened (creating a strong feeling of stiffness).

The stretch reflex becomes less sensitive the more the muscles are exposed to the stretching stimulus (creating more flexibility). So the goal of stretching is to decrease the sensitivity of the stretch reflex (improving our tolerance to the stretched position) and therefore improve flexibility. The majority of improvement in "flexibility" comes from a change to the central nervous system, not a change of the muscle length.