Pnfvsmet - PNF stretching vs MET similarities/differences techniques methods PDF

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PNF stretching vs MET
similarities/differences techniques methods...

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MET VERSUS PNF WHAT, WHEN AND HOW? Both MET (muscle energy technique) and PNF (proprioceptive neuromuscular facilitation) are perceived as effective manual techniques, but for many therapists there is still some confusion about them. This article aims to clarify the theory behind both, explaining what they involve, when they should be used, and how they should be carried out. Stretching is a primary tool for preventing injury, but it is vital for clinicians to understand how stretches are correctly applied. The outcome to improve flexibility is the same with MET and PNF, but there are a number of important differences in their clinical application. The lack of consensus among studies, combined with the development of both techniques at a similar time, has resulted in a blurring of their definitions and an overlap between the two in many studies. As well as comparing the techniques of MET and PNF, this article will examine the current evidence base for each.

BY CLAIRE FARQUHARSON, CHARTERED PHYSIOTHERAPIST AND SENIOR LECTURER IN SPORTS THERAPY

INTRODUCTION Muscle flexibility is an important aspect of human function, therefore limited flexibility predisposes a person to a variety of injuries, from muscle strains to more serious injuries such as a stress fracture (1). Many clinicians advocate a variety of stretching techniques as a primary tool to prevent impairment of functional activities, by regaining or maintaining muscle flexibility and avoiding a decrease in the range of movement (ROM) (2,3). Although the majority of authors specify different stretching techniques, such as static, dynamic, ballistic, active, passive, isometric, proprioceptive neuromuscular facilitation (PNF) or muscle energy technique (MET), no single technique has been advocated as being more effective (2–6). Within the field of manual therapy, MET and PNF are key areas taught in many educational programmes as an effective technique, as through a single procedure many therapeutic outcomes can be achieved (7). However as both techniques have become more widespread in both teaching and clinical practice it is vital that we as clinicians understand the techniques involved, to ensure that they are applied effectively.

WHAT IS MET? Generally there is a lack of consensus on the definition of MET. Many researchers adopt the preferred modern definition (8), namely that it involves“the voluntary contraction of the muscle in a precisely controlled direction, at varying levels of intensity, against a distinctly executed counterforce applied by the operator”. Research suggests that MET not only lengthens the contracted or spastic muscle, but it also strengthens physiologically weakened muscles. In addition to this, it also reduces localised oedema by acting as a lymphatic or venous pump to aid the drainage of fluid or blood, and mobilising the range of movement of a joint with restricted mobility. With respect to altering muscle length, MET is based on the recruitment of postural muscles which are more susceptible to shortening and require stretching (9).

WHAT IS PNF? PNF is a manual resistance technique which works by simulating fundamental patterns of movement to oppose motion in multiple planes concurrently. Initially used for stroke victims and children with cerebral palsy, it is now commonly used to treat a broad range of orthopaedic conditions (10). The goal of PNF is to promote functional movement through facilitation, inhibition, strengthening and relaxation of muscle groups. The technique uses concentric, eccentric and static muscle contractions. These muscle contractions with properly graded resistance are combined and adjusted to fit the needs of each patient.

HISTORY OF MET AND PNF Although the outcome of improved flexibility is the same in both MET and PNF, there are a number of differences

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KEy FEaTurEs oF MET aNd PNF MET n Lengthens contracted or spastic muscle n Strengthens physiologically weakened muscles n Reduces localised oedema n Mobilises ROM of joints with restricted mobility n Based on recruitment of postural muscles that are more susceptible to shortening and require stretching. PNF n Manual resistance technique n Simulates patterns of movement to oppose motion in multiple planes at same time n Useful for stroke victims, children with cerebral palsy, and various orthopaedic conditions n Promotes functional movement through facilitation, inhibition, strengthening and relaxation of muscle groups n Uses patient-specific concentric, eccentric and static muscle contractions in their clinical application. To date there is little research comparing them, and the lack of consensus and consistency among studies, combined with the development of both techniques at similar times, has resulted in an overlap between MET and PNF in many studies (10).

The rationale behind MET The initial definition of MET involved “resistive duction”, involving the application of pulsed contractions emerging from osteopathic traditions (11). However this is now termed as “pulsed MET” because it contradicts the modern approach that involves the application of slow controlled stretches in a specif ic direction. At about the same time the technique of PNF was being developed, at which point a number of inconsistencies in terminology arose within studies of the two approaches. To date there are few articles on the topic of MET, and only limited published research. There are few randomised controlled trials or peer-reviewed papers that substantiate the theory and support or validate its clinical use. Most

RESEARCH SUGGESTS THAT MET NOT ONLy LENGTHENS THE CONTRACTEd OR SPASTIC MUSCLE, BUT IT ALSO STRENGTHENS PHySIOLOGICALLy WEAKENEd MUSCLES previous research considered the effect of MET on the range of movement (ROM) of the hamstrings, finding that ROM improved with this method (5,7,12). The hamstrings may be particularly good muscles to examine because they exhibit both postural and phasic muscle components, and are prone to shorten not only through pathological conditions but also under normal circumstances (10,13). Other studies focused on the ankle (14–16 ) and cervical spine (15,16) and found that MET improved either the ROM or the pain level in both symptomatic and asymptomatic patients (but there were some methodological errors that must be taken into account). MET prefers the 25% contraction of available force to recruit the postural muscles that have shortened and require stretching. The theory is that increased contraction will lead to contraction of the phasic muscles, and decreased contraction is less likely to provoke cramp, tissue damage, or pain.

The rationale behind PNF

PNF was a philosophy as well as a treatment method. It was developed in the 1940s to rehabilitate patients with paralysis. In the 1900s, Sherrington had considered the neuromuscular system in terms of maximal muscle contraction and recruitment of additional muscles for promoting strength and flexibility (cited in Chaitow (9)). From this original concept, Kabat (cited in Chaitow (9)) looked at the patterns of natural movement in rehabilitating the muscles of polio patients. PNF was seen as an integrated approach because each treatment was directed at a “total human being” rather than a specific problem or body segment (10). The treatment approach was always positive, reinforcing and making use Glossary oF TErMs of things that the patient was able to do, on a physical or Based on adler 2003 (cited in Chaitow 2001), Chaitow 2001 (9), sharman psychological level, through the concept of applying spiral et al 2006 (19) and diagonal patterns with stronger contractions. PNF has, Contract relax Contraction (approximately 75%) of the muscle being therefore, been commonly used in both musculoskeletal and stretched neurological environments. hold relax Contraction (approximately 75%) of the opposing muscle to the Knott and Voss (citied in Chaitow (9)) developed one being stretched "modified PNF" that relates to the stretch concepts and Modified PNF Immediate isometric contraction (approximately 75%) of principles in athletes regarding flexibility, muscle recruitment specified muscle and rehabilitation patterns. It is often used to assist flexibility Muscle energy technique (MET) Contraction (approximately 25%) to recruit and coordination throughout the limbs' entire range of postural muscles that are more susceptible to shortening and require movement, helping the efficiency of recruitment of muscle stretching fibres and ultimately biomechanics, thus preventing undue Post-isometric relaxation (Pir) Slow isometric contraction (approximately stress on other structures. 25%) of the muscle being stretched Proprioceptive neuromuscular facilitation (PNF) Manual resistance technique TyPEs oF MET simulating fundamental patterns of movement to oppose motion in multiple planes As MET has progressed as a technique, two types evolved, reciprocal inhibition (ri) Slow isometric contraction (approximately 25%) of namely post-isometric relaxation (PIR) and reciprocal the opposing muscle of the one being stretched inhibition (RI) (9) (see Figure 1).

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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

Pir

PNF

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)

Contract relax antagonist relax

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.

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Box 1: CliNiCal aPPliCaTioN oF MET aNd PNF BasEd oN ChaiToW 2001, GoodridGE aNd KuChEra 1997, lEWiT aNd siMoNs 1984 (8,9,17)

Golgi organ capsule Muscle fibres Collagen fibrils running lengthwise

Tendon bundle sensory nerve and branches interweaving with collagen fibrils

Figure 2: Golgi tendon organ

The biomechanical theory involves a viscoelastic response of the muscle tendon unit (3,23).

Clinical considerations of MET and PNF Box 1 describes the main steps in conducting MET and PEF. Note that the patient must breathe normally throughout this procedure. In "acute" conditions, the isometric contraction should start at the resistance barrier, but in chronic conditions it starts short of the barrier. In acute conditions MET is applied to the new resistance barrier but in chronic conditions it is applied to the previous resistance barrier with a sustained stretch. In this setting, "acute" means a strain or injury that occurred in the last 3 weeks. If there are symptoms of pain or active inflammation, activation of the antagonist would be more appropriate. There are a number of common errors met during application of MET and PNF and these are summarised in Box 2. These errors usually result from inadequate instruction or proprioceptive feedback from the clinician.

MET 1. Target muscle is stretched to a position until resistance barrier is met Held for 15 seconds

PNF 1. Target muscle is stretched to a position until resistance barrier is met Held for 15 seconds

2. Patient SLOWLy resists 20–25% of maximum strength of either target muscle (PIR) or opposing muscle (IR) which is matched by the clinician to produce isometric contraction with no movement Held for 7–10 seconds

2. Patient IMMEdIATELy resists 75% or more of maximal strength of either target muscle (CR) or opposing muscle (HR) Held for 7–15 seconds

3. Patient relaxes completely while clinician finds new resistance barrier Relaxed for about 5 seconds 4. New barrier is found Held for 15 seconds

3. Patient relaxes completely Relaxed for 2–3 seconds 4. Patient IMMEdIATELy places limb into passive stretch further than initial barrier Held for 10–15 seconds 5. Patient relaxes completely Relaxed for 20 seconds 6. Procedure repeated three times

5. Whole procedure repeated three times

THERE IS A LACK OF CONSENSUS ON A dEFINITION OF MET.

CoNClusioN The lack of consensus on the classification and application of MET and PNF results in equivocal research for both techniques. On the whole, it seems MET is slower to apply than PNF, using just 25% contraction of muscle to decrease the risk of tissue provocation. True PNF is used for work on movement patterns and recruitment of muscle fibres. As with any manual therapy techniques, the effectiveness of each of them depends on accurate diagnosis, using an appropriate level of force and sufficient localisation of the targeted muscle. Box 3 contains a number of valuable tips for your work with MET and PNF. references 1. davis Sd, Ashby PE, McCale KL, McQuain JA, Wine JM. The effectiveness of three stretching techniques on hamstring flexibility using consistent stretching parameters. Journal of

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Box 2: CoMMoN Errors iN aPPliCaTioN oF PNF aNd MET BasEd oN GrEENMaN 1989 aNd ChaiToW 2001 (7,9) Patient-related errors

Clinician-related errors

n Contraction is incorrect, in the wrong direction or not sustained for long enough n The patient does not relax completely after the contraction n The patient starts or finishes the contraction too quickly (rather than a slow build up)

n Inaccurate positioning of joint or muscle in relation to resistance barrier n Inadequate application of counter-force n Movement of muscle to new position too quick (prevents latency in the muscle tone) n Patient given inadequate instructions n Muscle not maintained in stretch position for long enough

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strength Conditioning Research 2005;19(1):27–32 2. Handel M, Horstmann T, dickhuth H, Gulch RW. Effects of contract– relax stretch training in muscle performance in athletes. european Journal of Applied Physiology 1997;76:400–408 3. Magnusson SP, Simonsen EB, Aagard P, Glein GW, McHugh MP, Kjaer M. Viscoelastic response to repeated static stretching in the human hamstring muscle. scandinavian Journal of Medicine and science in sports 1995;5:342–347 4. Moore M, Hutton R. Electromyographic investigation of musclestretching techniques. Medicine and science in sports and exercise 1980;12:322–329 5. Bonnar B, deivert R,Gould T. The relationship between isometric contraction durations during hold–relax stretching and improvement of hamstring flexibility. Journal of sports Medicine and Physical fitness 2004; 44:258–261 6. Wallin d, Ekbolm B, Grahn R, Nordenborg T. Improvement of muscle flexibility: A comparison between two techniques. American Journal of sports Medicine 1985;13(4):263–268 7. Greenman P. Principles of...