PNF stretching is considered to be the most effective way to increase static flexibility and is a combination of static passive stretching and isometric stretching. PNF stands for Proprioceptive Neuromuscular Facilitation and was first developed as a treatment for paralysis patients.
PNF stretching is usually carried out with a partner who provides the resistance for the isometric contraction although it can be done without a partner (but generally will be less effective). If using a partner, then it is important that the partner be attentive and focused.
The most commonly used PNF technique is the “Hold-Relax” which is sometimes referred to as the “Contract-Relax”. The muscle is stretched passively towards the limit of its range of motion and then the muscle being stretched is isometrically contracted for 5-15 seconds after which the muscle is relaxed for a couple of seconds before being subjected to a passive stretch which should be greater than the initial passive stretch. This stretch is held for around 10-15 seconds before repeating the PNF stretch one or two more times.
PNF Stretching Examples: Hamstring Stretch
For an example of a PNF stretch, then the person being stretched lies flat on their back with one leg bent at 45 degrees and the other leg extended straight. The partner lifts the straight leg until a comfortable stretch is felt through the hamstring (nb partner just supports the stretched leg and does not push). This stretch is held for 15 seconds.
The stretchee should then isometrically contract the hamstring against partner’s resistance for 5-15 seconds, relaxes and the partner gently guides the hamstring to a deeper stretch. This is repeated a few more times until there is no further increase in range of motion.
Brief PNF Physiology of Stretching
Muscles spindles cells located within the muscles, protect the muscle from injury. They sense how far and fast a muscle is being stretched and when activated produce a stretch reflex. This reflex causes the muscles to contract to prevent overstretching the muscle.
Located within the muscle tendon is another sensor called the golgi tendon which senses how much tension is being put upon the tendon. When the golgi tendon is activated then it relaxes the muscles (unlike the muscle spindle).
A voluntary contraction during a stretch increases the tension on the muscle, activating the golgi tendon organs more than the stretch alone. So when the voluntary contraction is stopped the muscle is inhibited from contracting against a subsequent stretch. PNF stretches uses this to take advantage of the sudden vulnerability of the muscle and its increased range of motion by using the period immediately following the isometric contraction to train the stretch receptors to get used to this new, increased, muscle length. This is accomplished by the final passive stretch.
Some General Recommendations for PNF Stretching
•Leave 48 hours between PNF stretching routines
•For each muscle group complete 2-5 sets of the chosen exercise
•Each set should consist of one stretch held for 10-15 seconds after the contracting and relaxing phases
•PNF is not recommended for anyone under 18 years old
•A 5-10 minute thorough warm up is recommended before performing PNF stretching as a separate exercise session.
While most of us could obtain benefit from the improvement in flexbility that PNF stretching can bring, there is some conjecture amongst sports professionals about the effective of stretching in general to reduce the risk of injuries and to improve performance. Although there is some conflicting evidence reported, on balance research literature reviews such as reported by Thacker et al (1) support the hypothesis that routine stretching has little impact on reducing total injuries amongst competitive or recreational athletes.
As with all stretches, only take a PNF to the limit of what feels comfortable. Pain is an indication that you are overstretching.
In addition, there are advantages and disadvantages of PNF stretching and it may be worthwhile discussing these with a suitably qualified sports therapist.
(1) Thacker SB, Gilchrist J, Stroup DF, Kimsey CD., Jr. “The impact of stretching on sports injury risk: a systematic review of the literature”. Med Sci Sports Exerc. 2004;36:371-378
(2) Caplan N, Roggers R, Parr MK, Hayes PR. “The effect of proprioceptive neuromuscular facilitation and static stretch training on running mechanics.” J Strength Cond Res, 2009, 23: 1175-1180