Physiology of Stretching

Muscle and connective tissue have two lines of defense against overstretching and injury.

1. The Stretch Reflex
Nerve receptors called muscle spindles lie within our muscles. These receptors detect the degree and speed of a stretch. They send this information to the spinal cord which then returns a message to contract the muscle preventing potential damage. This contraction response will last up to 6-8 seconds.

The harder a muscle is stretched, the stronger the reflex contraction. This means gentle stretching causes less resistance to the stretch and is therefore more effective.

As we hold a gentle static stretch, the muscle spindles reduce their rate of firing which decreased the amount of reflex contraction. This is why it is important to hold a stretch.

2. Inverse Stretch Reflex
Golgi tendon organs (GTO's) lie around muscle / tendon junction and detect tension in the muscle and tendon. Tendon tension occurs both during intense muscle contraction and stretching. When GTO's detect tendon tension they send a message to the spinal cord which returns a message back to relax the muscle fibres.

This reflex can be used to a stretchers advantage. When a stretch is held for a minimum of 7 seconds the muscle spindles decrease their firing and allow the muscle and connective tissue to stretch a bit further. Now the increased stretch places tension on the tendon activating the GTO's and therefore relaxing the muscle. A greater stretch can now be achieved.