1. Post-isometric relaxation (PIR) PIR involves isometric contraction of the stretched muscle. This is thought to initiate a latency period within the muscle which then facilitates the use of other techniques. A key study in the development of PIR was that by Lewitt and Simons in 1984 (17). Their large study was on the role of PIR in myofascial pain relief in 244 patients diagnosed with musculoskeletal pain (in 351 muscles). PIR was applied both in the clinic and outside the clinic, through self-treatment, and the results showed immediate relief in 94% of muscle sites. In the follow-up period, 63% had lasting relief from pain. The authors considered muscle length as a secondary outcome measure and described a functional increase in ROM, however the detailed results were not unpublished. As the technique is highly specific, the efficacy of self-treatment twice daily should also be questioned, and the placebo effect of self-management should be considered too. The majority of the small number of studies on MET examine the role of PIR. They suggest that PIR improves ROM in various muscle groups, but these findings should be viewed cautiously because the studies were either pilot studies (18), case studies (15) or had poor methodology. For example, the prospective pilot study by Wilson et al (18) examined 19 patients with acute lower back pain and found an 83% mean change in the Oswestry Disability Index compared to 65% in the control group. However here they combined MET with an exercise program, so the specific effect of MET could not be evaluated. Joanson (15) found that PIR combined with both eye and breathing movements increased cervical lateral flexion and rotation by 200 to 300%, and the neck disability score of patients in that study improved from moderate to mild. However as a case study these results could not be generalised to the rest of the population.

The majority of research has focused on single joint motion in one plane, with a lack of research into “true PNF” which involves multiple planes (19). Although commonly encountered in the literature, there are frequent deviations among the terms and descriptions used to describe PNF. This lack of uniformity has resulted in a number of differences in its clinical application (20).

The literature supports PNF as an effective method to increase range of movement by way of stretching, particularly with respect to short-term gain. Many of the studies focus on the hamstrings, and commonly use static stretching as a comparison. Shrier and Gossal (21) reported that PNF stretching brings about greater increases in range of motion compared with conventional methods such as static and ballistic techniques. A study by Funk et al (22) investigated the efficacy of PNF stretching following exercise to optimise hamstring flexibility in young elite college athletes participating in baseball, field-hockey and rowing. The 40 subjects were randomly assigned to 5 minutes of PNF or static stretching. The findings indicated that PNF caused significant increases in range of motion after exercise, compared with both the baseline and static stretching. However significant differences were not found with static stretching, which may be due to the population that was studied. Young elite athletes

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MET

PNF

PIR

IR

Modified PNF

Contract relax

Hold relax

Figure 1: Classification of MET and PNF based on Chaitow 2001 and Sharman et al 2006 (9,19)

undertake demanding training programs for their respective sports and they may require additional strategies beyond that of static stretching to enhance their flexibility and range of motion. This suggests that positive responses may have been observed with static stretching in a less conditioned population and emphasises the need for a therapist's involvement to effectively perform PNF stretching. It should also be noted that PNF did not significantly increase range of movement when performed before exercise, which indicates that stretching following a warm-up may be beneficial for reducing muscle stiffness and the incidence of injury.

PHYSIOLOGICAL THEORY BEHIND MET AND PNF

Although much theory exists, the specific physiological principles of stretching are still not understood. Both neurophysiological and biomechanical theories have been proposed. Alter (10) believes that flexibility is developed when connective tissues and muscles are elongated through regular and proper stretching. The muscles may be protected by a protective mechanism called the "stretch reflex", a basic operation of the nervous system that is initiated when a muscle is stretched.

Muscle tension is regulated by two key sensory receptors (see Online extras for more details): 1. Muscle stretch receptors which lie among the muscle fibres in the belly of the muscle.

2. Golgi tendon body receptors which lie in the junction

between the muscle and the tendon. With respect to the neurophysiological theory, it is thought that MET and PNF initiate a refractory (or latency) period after isometric contraction of either the agonist or antagonist muscle. This refractory period stimulates a response from Golgi tendon organs which then causes reduced muscle tone and thus enables increased movement in the joint or muscle to a new position (7,9,17). Golgi tendon organs (see Figure 2) are: n proprioceptors that provide information about changes in muscle tension n located at the junction of skeletal muscles and their tendons n arranged in series with muscle fibres with sensory dendrites that interweave with collagen fibrils in the tendon activated by muscle contraction pulling the collagen fibrils tight.

sportEX dynamics 2010;25(Jul):12-16

Contract relax

antagonist relax