In order to understand correct stretching techniques it is beneficial to know a little about the biochemical and physiological properties of the soft tissues that are being stretched.
All soft tissues (muscles, tendons, joint capsules, fascia, skin) are more extensible when they are warm. This is because they are thermo-elastic. This is like a blacksmith working with a horseshoe; when the horseshoe is hot it can be stretched and manipulated, but when it is cooled it is rigid and inflexible. All stretching is ineffective if it is performed when the body is cold, and should therefore be preceded by a series of warm-up exercises to increase tissue temperature.
Muscles and tendons have a neural reflex arc that prevents excessive stretching, or tension developing. Receptor nerves within the muscle are sensitive to changes in muscle length and tension. When a muscle is stretched, the muscle spindles send a message to the central nervous system to cause a reflex contraction of the muscle in order to prevent stretch damage. However, if the stretch is maintained for more than 6 seconds the Golgi tendon organs respond to the change in muscle tension by sending a signal to the central nervous system which causes the muscle to relax. This means that stretching exercises should be done slowly with a gradual increase in the range of movement every few seconds. The total duration of the stretch should be about 20 seconds.