Article compliments of Personal Training on the Net. PNF stretching techniques have been widely used by physicians, physical therapists and athletic trainers. The theory behind PNF stretching is that it quickens neuromuscular responses by stimulating neural proprioceptors. Proprioceptors are nerve endings found in muscles, tendons, and joints which are sensitive to changes in tension. One of these proprioceptors, the Golgi Tendon Organ (GTO) is sensitive to an increase in tension within muscles. When activated the GTO causes the muscle to relax. If this occurs in the same muscle experiencing the increased tension, the result is what we call autogenic inhibition. PNF stretching is very advanced stretching technique and involves a variety of strategies to provide many results. It can be done alone, however it is typically performed with a partner who provides resistance and helps increase the range of motion. The most common form of PNF stretching is the contract-relax method. This method uses a muscle contraction followed by passive stretching. It is usually repeated several times. It is also recommended to mildly stimulate the opposing muscle group in order to return to neuromuscular balance. PNF stretching can be slightly uncomfortable for your clients when compared to static stretching, and should be performed with a knowledgeable and experienced professional (1,2).When describing PNF stretches, the antagonist muscle refers to the muscle that is being stretched and the agonist muscle refers to the muscle that is opposite the antagonist. For example, during knee flexion the leg extensors (quadriceps) will be stretched; they are the antagonist muscle group and the leg flexors (hamstrings), which cause the movement, are the agonist muscle group (1,2).
During PNF stretches, three techniques are used to increase the range of motion. The three PNF stretching techniques are: (1) hold-relax, (2) hold-relax with agonist muscle contraction, and (3) contract-relax. It is recommended that these stretching techniques are completed in three phases. To begin, a passive stretch lasting 10-seconds is recommended. This “pre-stretch” establishes the client’s current flexibility limits. The stretching techniques differ based on the muscle contractions used in the second and third phases (1,2). Both isometric and concentric muscle contractions of the antagonist are used before applying a passive stretch of the antagonist to bring about autogenic inhibition. The isometric muscle contraction is termed “hold” and the concentric muscle contraction is termed “contract.” A concentric muscle contraction of the agonist is used during passive stretching of the antagonist muscle group to cause reciprocal inhibition. The concentric muscle contraction of the agonist muscle group is termed “agonist contraction.” Each PNF stretching technique also involves passive static stretches called “relax.” (1,2).
So what does the research say about PNF stretching? The original theory that PNF stretching techniques increase range of motion through reciprocal muscle inhibition, which decreases electromyographic activity, was disproved in 1979 (3) and again in 1980 and 1990 (4,5). Electromyographic activity shows that muscles are silent during normal stretches until end range of motion nears (2). PNF techniques, however increase electrical activity and muscle stiffness during the stretch (3,4,5,6), despite the increase in range of motion. This suggests that the muscle undergoing PNF stretching eccentrically contracts, which some clinicians consider potentially more dangerous than having no electrical activity in the muscle (2). Both PNF and ballistic stretching cause the muscle to eccentricly contract. However, PNF stretching appears to have a more pronounced analgesic effect than ballistic stretching. The benefits of the greater increase in range of motion should be balanced against a theoretical increase in the risk of injury. There is currently no data on risk of injury due to PNF stretching. For those personal trainers who want to use static stretching, one study (7) reported that static stretching (continuous stretching without rest) is superior to cyclic stretching (applying a stretch, relaxing, and reapplying the stretch), whereas two studies (8,9) suggested no difference. Since the results of these studies are mixed more research is needed to make a sound decision.
In general, PNF stretching has resulted in larger increases in range of motion when compared to static or ballistic stretching (10,11-17), though some study results have not shown statistical significance the trend is still present (16-20). When comparing the three different types of PNF techniques, the agonist-contract-relax method appears to produce the best results followed by the contract-relax method (10,15-17), and lastly the hold-relax technique (10,15-17,21). If you happen to be working with a female client who is looking for an increased vertical jump, research done by Church et al (22) suggests that performing PNF stretching just prior to the activity actually had a detrimental effect on vertical jump performance.
In regards to the middle aged and elderly clients, the effects of PNF stretching techniques are unknown and the physiological changes associated with aging may lead to differential responses to PNF stretching. Ferber et al (23) conducted a study to look at the response of PNF stretching on the elderly aged 50-75. They found that PNF stretching using agonist contract-relax can increase ROM in the elderly; however it was observed that PNF stretching may not help muscular relaxation despite the increased joint ROM. Therefore, Ferber et al (23) suggest caution be used when contemplating whether to use PNF stretching on aged clients due to potential age induced changes in muscle elasticity. Cornelius et al (24) found that PNF stretching was effective for increasing ROM, however, if a non-hypertensive person completed one or two trials of PNF stretching, systolic blood pressure was not increased. But if a participant completed three trials they experienced a statistically significant increase in systolic blood pressure.
In conclusion, there are many research studies that suggest PNF stretching techniques increase the ROM of their participants; however there are other potential dangers and lingering individual factors that are associated with detrimental effects of PNF stretching. Therefore, it is prudent for personal trainers to weigh the potential risks and benefits of performing PNF stretching techniques on your clients. More research is needed for us to make more informed conclusions on PNF stretching for different populations.
© Copyright Personal Training on the Net 1998 - All rights reservedReferences
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