These notes summarise some of the many ways in which isometric contractions can be used in clinical practice
Isometric contractions and trigger points.
• Trigger points appear to be self-perpetuating, unless treated correctly.
• Whatever method is used to deactivate a trigger point – manual therapy, injection such as novocaine or xylocaine, coolant spray, dry needling, laser, acupuncture techniques – the muscle housing the trigger point always needs to be restored to its normal resting length
• If this is not achieved, reactivation of the trigger point is more likely (Simons et al 1999). Failure to restore the muscle containing the trigger point to its normal resting length is likely to lead to only short-term relief
• Whatever stretching methods are used it is important that the process should be gradual, gentle and painless
• The recommendation of Lewit (1999) and Simons et al (1999) is that muscle energy technique (MET) be used to achieve safe and (relatively) painless stretching
• This calls for gentle isometric contractions followed by stretch
• An isometric contraction, alone, produces a stretch of part of muscle (series elastic component) while the other part (parallel elastic component/actin-myosin) shortens (see illustrations above)
• Lewit suggests that, in many instances, simply stretching a muscle – with no other treatment – may be sufficient to deactivate trigger point activity
What happens during an isometric contraction?
As mentioned above – isometric contractions introduce a lengthening of the series elastic component (fascial, tendinous), while the parallel elastic (actin/myosin) component shortens – so that the muscle does not change length during the contraction.
Repetitions of isometric contractions effectively lengthen these structures overall – particularly if additional active or passive stretching is added. (Lederman 1997)
Simons (2002) suggests that mild, voluntary, isometric contractions therefore allow lengthened sarcomeres (contractile unit of a myofibril) to exert an effective elongation force on the shortened sarcomeres of the contraction knot of a myofascial trigger point (MTrP). Individual sarcomeres, like balloons are constant-volume structures (see illustrations above).
Adding pressure
The effects of simultaneous application of trigger point pressure release and voluntary isometric contraction are additive (Simons 2002)
Compressing them in the vertical dimension causes an increase in the horizontal dimension.
Thus, finger pressure applied downward onto a MTrP, tends to lengthen sarcomeres that are shortened, for any reason, and that may be responsible for the palpable taut band which is characteristic of MTrPs
Analgesic effects of isometric contractions
Studies show that both high and low-intensity isometric contractions have analgesic effects in healthy adults (Bement et al 2008)
A recent study (Bemant 2011) compared pain ratings and thresholds in men and women with Fibromyalgia syndrome (FMS), before and after isometric contractions, of varying intensity and duration, performed with the elbow flexor muscles:
1/ Maximal voluntary contractions (MVC)
2/ 25% MVC sustained until task failure,
3/ 25% MVC- for 2 minutes
4/ 80% MVC sustained until task failure
RESULTS:
Significant analgesic responses were noted in some FMS patients, with the greatest change noted after the long-duration, low-intensity contraction sustained until failure
Most benefit was experienced by younger women (average age 39) who had the lowest pain thresholds at outset
Staud et al (2005) showed evidence of negative effect following strong sustained isometric contractions in all FMS patients.
The message that emerges is that low intensity, sustained, isometric contractions produce a reduction in pain in most people, including those with fibromyalgia
Possible ‘hydraulic’ effects on fascia of isometric contractions ?
•Klingler & Schleip (2004) examined fresh human fascia, and noted that during light stretching, water is extruded, refilling afterwards.
•As water extrudes, temporary relaxation occurs in the longitudinal arrangement of collagen fibers.
During the reduced hydration period the tissues become far less stiff, more pliable, allowing increased range of movement
•If the stretch is moderate, and there are no micro-injuries, water subsequently soaks back into the tissue until it becomes stiff again
Many effects of manual therapy may relate to sponge-like squeezing and refilling effects in the semi-liquid ground substance, with its water-binding glycosaminoglycans and proteoglycans.
Isometric contractions and muscle energy technique (MET)
MET uses isometric contractions of varying durations and intensities (Chaitow 2006) to facilitate subsequent stretching procedures.
Fryer and Fossum (2009) have formulated a two possible models to explain the usefulness of these contractions:
1/ During the contraction fluid flow is stimulated on a cellular level, at the same time that fibroblasts are being stretched (as discussed above). This increases drainage from interstitial spaces, reducing concentrations of pro-inflammatory cytokines, so reducing the sensitization of peripheral nociceptors.
2/ As a contraction is initiated both muscle and joint mechano-receptors are activated.
This:
a/ , Evokes sympatho-excitation via somatic afferents that produces localized activation of the epriaqueductal grey that plays a role in descending modulation of pain
While:
b/ Encourages gating of nociceptive impulses in the dorsal horn through mechanoreceptor stimulation
These two processes (a & b) encourage nociceptive inhibition “stimulation produced analgesia:
As a result, following isometric contractions, stretching and range of motion are increased, making MET one of the siplest and most effective modalities.
And finally….
Isometric contractions, as well as most manual therapy methods result in upregulation of endogenous pain relieving substances, including endocannabinoids (Degenhardt 2007)
• The endocannabinoid (eCB) system offers ‘resilience to allostatic load’ – dampening nociception and pain. It is anxiolytic, decreases inflammation, and plays a role in fibroblast reorganization.
• Two cannabinoid receptors have been identified: CB1 in the nervous system, and CB2 associated with the immune system (and gut)
There are several tools to upregulate eCB activity, including manual therapy, exercise, acupuncture, and diet– increasing a sense of wellbeing and euphoria
McPartland et al (2005) measured Anandamide (AEA) levels pre- and post-osteopathic manipulative treatment (OMT) including Myofascial Release, Muscle Energy Technique, and HVLA – all of which involve fascial load.
It seems that shear and stretching load upregulates AEA, producing analgesic/euphoric cannabimimetic effects.
Pulsed MET
…..and then there is pulsed MET, the use of rhythmic mini-isometric contractions, which deserves a separate discussion……watch this space……..
REFERENCES
Bement M et al 2011 Pain Perception After Isometric Exercise in Women With Fibromyalgia Arch Phys Med Rehabil 92:89-95
Bement M et al 2008 Dose response of isometric contractions on pain perception in healthy adults Med Sci Sports Exerc. 40(11):1880-1889
Chaitow L 2006 Muscle Energy Techniques (3rd edition) Churchill Livingstone, Edinburgh
Degenhardt, B et al 2007. Role of osteopathic manipulative treatment in altering pain biomarkers: a pilot study. Jnl. American Osteopathic Association 107:387–394
Fryer G Fossum C 2009 Therapeutic Mechanisms Underlying Muscle Energy Approaches. In: Physical Therapy for tension type and cervicogenic headache: physical examination, muscle and joint management Fernández de las Peñas C Arendt-Nielsen L Gerwin R (eds): Jones & Bartlett, Boston.
Klingler W Schleip R Zorn A 2004 European Fascia Research Project Report. 5th World Congress Low Back and Pelvic Pain, Melbourne, November 2004
Lederman E. Fundamentals of manual therapy. London: Churchill Livingstone 1997. p34
Lewit K 1999 Manipulative therapy in rehabilitation of the locomotor system, 3rd edn. Butterworths, London
Simons D 2002 Understanding effective treatments of myofascial trigger points. Journal of Bodywork and Movement Therapies 6(2):81-88
Simons D Travell J Simons L 1999 Myofascial pain and dysfunction: the trigger point manual. Vol. 1, 2nd edition: The upper extremities. Williams and Wilkins, Baltimore, Maryland
Staud R et al 2005 Isometric exercise has opposite effects on central pain mechanisms in fibromyalgia patients compared to normal controls. Pain 118:1-2:176-184