1. Proprioceptive Neuromuscular Facilitation

2. Pre Task
Proprioceptive neuromuscular facilitation is an advanced stretching technique. It is also considered to be one of the most effective forms of flexibility training for increasing range of motion. There are a few different PNF techniques but the most practical is the CRAG technique (contract – relax – antagonist – contract)

3. Key Terms You Should Know Before we start this section
Muscle spindles
These detect how far and how fast a muscle is being stretched and produce the stretch reflex
Golgi tendon organs
These are activated when there is tension in a muscle

4. The role of muscle spindles and Golgi Tendon Organs in PNF
In PNF, motor action has to be controlled in order for movement to be effective.
There are several internal regulatory mechanisms that make this possible.
Muscle Spindles & Golgi Tendon Organs are types of proprioceptors
(remember these are sensory organs in the muscles tendons and joints in the body that measure movement)

5. Muscle Spindles
These are very sensitive proprioceptors that lie between skeletal muscle fibres.
They are often called stretch receptors as they provide information (excitory signals) to the central nervous system about how fast and how far a muscle is being stretched.
The central nervous system then sends an impulse back to the muscle telling it to contract, which triggers the stretch reflex.
This reflex action that causes the muscle to contract to prevent overstretching reduces the risk of injury.

6. Golgi Tendon Organs
These are found between the muscle fibre and tendon. They detect levels of tension in a muscle. When the muscle is contracted isometrically in PNF, they sense the increase in muscle tension and send inhibitory signals to the brain which allows the antagonist muscle to relax and lengthen. This is known as autogenic inhibition.

8. Key Terms You Should Know
Isometric Contraction
Where there is tension in a muscle but no visible movement.
Autogenic inhibition
Where there is a sudden relaxation of the muscle in response to high tension. The receptors involved in this process are golgi tendon organs.

9. A practical example can be seen below
PNF in Practice
A practical example can be seen below
Here, the individual performs a passive stretch with the help of a partner and extends the leg until tension is felt. This stretch is detected by the muscle spindles. If the muscle is being stretched too far, then a stretch reflex should occur.
The individual then isometrically contracts the muscle for at least ten seconds by pushing their leg against their partner who supplies just enough resistance to hold the leg in a stationary position. Remember Golgi tendon organs are sensitive to tension developed in a muscle, and during an isometric contraction they are activated and inhibitory signals they send override the excitory signals from the muscle spindles, therefore delaying the stretch reflex.
As the leg is lifted again, the Golgi tendon organs are responsible for the antagonist muscle relaxing, which means the leg stretches further. This process can be repeated until no more gains are possible

10. Practice Questions
The training that elite performers undertake may include proprioceptive neuromuscular facilitation (PNF) stretching. Explain the role of the muscle spindles and Golgi Tendon Organs in PNF stretching?
Contraction of different types of muscle fibres involves the use of motor units. What do you understand by the term ‘motor unit’?
How are motor units involved in the process of spatial summation?
Describe the characteristics of the main muscle fibre type used by marathon runners?