BARRIERS & MET: "FEATHER-EDGE" OR STRETCHED"?

Palpating end-of-range barrier of the hip adductor muscles 
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The essence of Muscle Energy Technique (MET) is that it harnesses the energy of the patient (in the form of muscular effort) to achieve a therapeutic effect.  Goodridge (in Goodridge & Kuchera 1997) summarises the essential as follows: 

"Good results [with MET] depend on accurate diagnosis, appropriate levels of force, and sufficient localisation. Poor results are most often caused by inaccurate diagnosis, improperly localized forces, or forces that are too strong"

In order to achieve those requirements of accuracy and appropriate focusing of effort, the ideal barrier from which to commence the sequence needs to be identified.

Kappler & Jones (2003) suggest that we consider joint restrictions from a soft tissue perspective. They suggest that, as the barrier is engaged, increasing amounts of force are necessary, as the degree of free movement decreases. They note that the word barrier may be misleading, if it is interpreted as a wall or rigid obstacle to be overcome with a push:

“As the joint reaches the barrier, restraints in the form of tight muscles and fascia, serve to inhibit further motion. We are pulling against restraints rather than pushing against some anatomic structure.”

If this is indeed the case, then methods such as MET - that address the soft tissue restraints – should help to achieve free joint motion. And it is at the moment that a‘ restraint’ to free movement is noted, that the barrier has actually been passed, also described as moving from ‘ease’ towards ‘bind’. The ‘feather-edge’ of resistance is a point that lies a fraction before that sense of ’bind’ or restriction is first noted, and it is suggested that it is from this point that any MET contraction effort should commence. (Stiles 2009)

Different barriers of resistance

An example

Stiles (2009) has described the following approach when preparing spinal articulation restrictions for MET application: 

“In spinal regions, identify the segment(s) of greatest restriction by palpation, observation, motion evaluation etc. With the patient seated, use flexion or extension, together with side flexion, rotation and translation, to maintain the most dysfunctional segment, at the apex of the curve, at the restriction barrier (‘feather-edge’). Establish a counterforce, and instruct the direction for the patient to move towards, using minimal effort.”

Stiles reports that a brief (3 to 5 seconds) firmly resisted patient effort, might involve – as examples - either lateral translation of the head/neck, or shoulder, or anterior or posterior translation of the abdomen or upper trunk. The contraction (resisted effort) usually needs to be maintained for a few seconds only, or (gently) for longer, before a brief – few seconds only- rest-period. After this relaxation moment, the new range/barrier in  previously restricted directions should be tested, with a new barrier engaged, and the process repeated, possibly using a different direction for the contraction effort. Stiles confirms his experience of what is a common clinical observation: 

“Only a 30-40% improvement in mechanical function is required with MET because the corrective process will continue for several days.”

Palpating for lumbar segmental restriction

Soft tissue tension determines the barrier

Parsons & Marcer (2005) note that active movement stops at the ‘physiological barrier.’ determined by the tension (‘bind’) in the soft tissues around the joint (e.g. muscles, ligaments, joint capsule), with normal ranges of movement of a joint (‘ease’) taking place within these physiological barriers. Factors such as exercise, stretching and age – as well as pathology or dysfunction - can modify the normal physiological range, however it is usually possible to passively ease a joint’s range beyond the physiological barrier, by stretching the supporting soft tissues until the anatomical limit of tension is reached.

Any movement beyond the anatomical barrier is likely to cause damage to the local soft tissues or joint surface. Joint restrictions, defined as ‘somatic dysfunction’ occur when normal ranges of movement are restricted, either due to compensatory, adaptive responses, to overuse for example, or to trauma.

Bolin (2010) describes identification of a barrier when using MET in a pediatric setting:

“[If when] evaluating the motion at the 3rd lumbar vertebra in neutral, flexion, and extension, a specific motion restriction can be identified for that particular structure (if dysfunction is present). If the evaluator finds the 3^rd lumbar transverse process deeper on the right and more easily rotated on the left, the segment can further be tested in flexion and extension and a positional diagnosis (eg, L3 ERSL) can be established.” 

The barrier would be engaged by having the patient: 

“positioned seated, lumbar spine flexed to the L3 level, then rotated and side-bent to the right (See figure).The treatment is performed using a patient’s muscle energy (approximately 5 pounds [2 kilos] of force) to sit upright (extension, side bending, and rotation to left) from that position while an examiner resists. This force is held for 5 seconds, then the patient briefly relaxes; during the relaxation, the slack is taken up and a new barrier in FLEXION, right rotation, and right side bending is engaged. This process is typically performed 3 times.”

Note: No hint is given of forced engagement of the barrier.

Should restriction barriers always be ‘released’?

Clinically, it is worth considering whether restriction barriers ought to be released, in case they might be offering some protective benefit.

As an example, van Wingerden (1997) reported that both intrinsic and extrinsic support for the sacroiliac joint derive in part from hamstring (biceps femoris) status. Intrinsically, the influence is via the close anatomical and physiological relationship between biceps femoris and the sacrotuberous ligament. He states that: 

"Force from the biceps femoris muscle can lead to increased tension of the sacrotuberous ligament in various ways. Since increased tension of the sacrotuberous ligament diminishes the range of sacroiliac joint motion, the biceps femoris can play a role in stabilization of the sacroiliac joint" (Vleeming et al 1989).

Van Wingerden also notes that in low-back patients, forward flexion is often painful, as the load on the spine increases. This happens whether flexion occurs in the spine or via the hip joints (tilting of the pelvis). If the hamstrings are tight and short they effectively prevent pelvic tilting. ‘

"In this respect, an increase in hamstring tension might well be part of a defensive arthrokinematic reflex mechanism of the body to diminish spinal load."

If such a state of affairs is longstanding, the hamstrings will have shortened, influencing both the sacroiliac joint and the lumbar spine. The decision to treat tight (‘tethered’) hamstring should therefore take account of why it is tight, and consider that in some circumstances it might be offering beneficial support to the SIJ, or reducing low-back stress.

Contrary views regarding the appropriate barrier for MET commencement

The ‘feather-edge’ principle of barrier identification has been emphasized in the notes above. In some MET descriptions however a different approach is suggested.

Shoup (2006) describes MET - as used in treatment of hypertonic or shortened muscular structures – as follows:

“The [practitioner] treats the hypertonic muscle by stretching the patient’s muscle to the restrictive barrier. Then the patient is asked to exert an isometric counterforce (contraction of a muscle against resistance while maintaining constant muscle length) away from the barrier, while the [practitioner] holds the patient in the stretched position. Immediately after the contraction, the neuromuscular unit is in a refractory or inhibited state, during which a passive stretch of the muscle may occur to a new restrictive barrier.

This model of MET usage mirrors that of van Buskirk (1990) who explains: 

“In [patient] indirect ‘muscle energy’ the skeletal muscles in the shortened area are initially stretched to the maximum extent allowed by the somatic dysfunction. With the tissues held in this position the patient is instructed to contract the affected muscle voluntarily. This isometric activation of the muscle will stretch the internal connective tissues. Voluntary activation of the motor neurons to the same muscles also blocks transmission in spinal nociceptive pathways. Immediately following the isometric phase, passive extrinsic stretch is imposed, further lengthening the tissues towards the normal easy neutral position.”

More than two approaches

We have now seen descriptions of MET where the barrier commences from an easy ‘feather-edge’ position, as well as from a position in which the restraining soft tissues are actually stretched (a ‘bind’ barrier) at the start of the isometric contraction. This latter approach raises several clinical questions:

1.   If, as may be the case, the soft tissues held in a stretched position before being required to contract, are already hypertonic, and possibly ischemic, is there a risk that the contraction effort might provoke cramp? This would appear to be a possibility, or even a likelihood, in muscles such as the hamstrings. Would it not be a safer option to employ light contractions, starting with the muscle group at an easy end-of-range barrier, rather than at stretch?

2.   Would the requested contraction effort from the patient be more easily initiated and achieved, if the muscle (group) is in a mid-range or easy end-of-range position, rather than at an end-of-range involving stretch, at the start?

Both comfort and safety issues would appear to support the ‘ease’ barrier rather than a firmer ‘bind’ barrier – provided the outcomes were not compromised -  and clinical experience as well as numerous studies, offer support for the ‘ease’ option.

Both Janda (1990, 1993), and Lewit (1999) have described protocols for the use of MET that support the lighter-barrier approach. In the end each practitioner’s clinical experience will guide therapeutic decision making, supported by research evidence where this is available, or by the clinical experience of others. 

I have opted for the lighter-barrier option.

References

Bolin D 2010  The application of osteopathic treatments to pediatric sports injuries. Pediatric clinics of North America, 57 (3):775-794

Goodridge J, Kuchera W 1997 Muscle energy treatment techniques. In: Ward R (ed) Foundations of osteopathic medicine. Williams and Wilkins, Baltimore

Janda V 1990 Differential diagnosis of muscle tone in respect of inhibitory techniques. In: Paterson J K, Burn L (eds) Back pain, an international review. Kluwer, New York, pp 196–199

Kappler RE, Jones JM. 2003 Thrust (High-Velocity/Low-Amplitude) techniques. In Ward RC (Ed) Foundations for osteopathic medicine, 2/e. Philadelphia, Lippincott, Williams & Wilkins pp852-880

Lewit K 1999 Manipulation in Rehabilitation of the Locomotor System. 3rd edition. Butterworths, London

Parsons J Marcer N 2005 (Eds) Osteopathy: Models for diagnosis, treatment an practice. Churchill Livingston Edinburgh

Shoup D DO An Osteopathic Approach to Performing Arts MedicinePhys Med Rehabil Clin N Am 17 (2006) 853–864

Stiles E 2009 Muscle Energy Techniques IN: Franke H ED. The History of MET In: Muscle Energy Technique History-Model-Research . Verband der Osteopathen Deutschland, Wiesbaden

Van Buskirk R 1990 Nociceptive reflexes and the somatic dysfunction. Journal of the American Osteopathic Association 90(9): 792–809

van Wingerden J-P 1997 The role of the hamstrings in pelvic and spinal function. In: Vleeming A, Mooney V, Dorman T, Snijders C, Stoekart R (eds) Movement, stability and low back pain. Churchill Livingstone, New York

Vleeming A, Mooney A, Dorman T, Snijders C, Stoekart R 1989 Load application to the sacrotuberous ligament: influences on sacroiliac joint mechanics. Clinical Biomechanics 4: 204–209