Trigger point: an area of lactic acid build up and motor nerve irritation located in the belly of the muscle. The presence of a trigger point will restrict muscle action. It is also known as an “energy crisis” within the muscle.
The term trigger point originates from the fact that when pressure is applied to a particular point, a pain signal will be sent to other parts of the body. It can be identified when the muscle is palpated perpendicular to the affected muscle fibres.
Clinical signs of a trigger point include:
- referred pain.
- Referred pain occurs as a result of the link between the sensitive loci located in the trigger point region and how they are integrated with the spinal cord. Trigger point can also be viewed as a “pathogenic pathway of muscle pain from different causes” (Hong, 1996).
- a localised twitch response.
- a localised twitch response is an involuntary spinal cord reflex.
An example of a clinical sign may be an adversion to girthing up, especially if a trigger point is located in the pectorals. Horses with an owner-reported history of girth-aversion behaviour had higher severity trigger point scores than horses without a history of girth-aversion behaviour. Based on this, a knowledge of the presence and location of trigger points could assist in the development of prevention and management strategies to improve comfort, optimise performance, and reduce girth-aversion behaviour (Bowen et al., 2017).
They can be located through palpation, but also through electromyographic needling. In a study by Macgregor and von Schweinitz (2006) all equid subjects demonstrated objective signs of spontaneous electrical activity, spike activity and local twitch responses at the myofascial trigger point sites within taut bands. The frequency of these signs was significantly greater at myofascial trigger points than at control sites (P<0.05).
Trigger points occur mostly in response to:
- muscular tension/overuse
- not enough stretching
- not enough rest (leading to fatigue)
- nervous system overexertion/stress
- poor circulation — muscles of hypertonicity and hypotonicity most commonly can have decreased circulation and therefore decreased oxygen supply. This will result in a build up of toxins which can irritate the nerves.
- compensatory movement patterns resulting from osteoarthritis
- acute or chronic injury to a muscle, tendon, ligament, joint or nerve (Hong, 1996)
Trigger points vary in size and can feel like nodules. They are usually very tender, give easily under pressure and release fairly quickly. The surrounding muscle may remain supple, where the trigger point will feel like an intensely contracted sarcomere.
Different Types of Trigger Point
SILENT (LATENT) TRIGGER POINTS – triggered pain is of low intensity.
ACTIVE TRIGGER POINTS – triggered pain is of high intensity; very sensitive to palpation. A deep, dull, aching pain.
SPILLOVER TRIGGER POINT AREA – one trigger point that affects more than one area.
Types of Trigger Point Therapy
Trigger Point Technique
This technique is used to:
- release trigger points
- drain trigger points
(1) Hot hydrotherapy — application of heat to the trigger point will contribute to the effectiveness of TPRT. This is because it relaxes the muscle fibres by boosting microcirculation. This is most useful in cases of chronic trigger points.
(2) Effleurage — massage techniques to warm up the muscle and encourage muscle fibre relaxation longitudinally from origin to insertion.
(3) Pressure — light pressure at the location of maximum tenderness or over the nodule palpated. This should be held until you can feel the muscle relaxing and softening underneath your fingers. This may take a few seconds for acute trigger points, or 2-3 minutes for chronic trigger points. Every 30 seconds, intersperse the pressure with effleurage to boost circulation to the area and therefore promote toxin removal from the trigger point. When dealing with a silent trigger point, pressure may be increased with tolerance; depending on the muscle mass and horses reaction. When the trigger point begins to release, pressure should be gently released but maintained for a few seconds.
(3b) Pressure modifications — if pressure is not suitable for the location (ie. along venous or nervous tracks like in the brachiocephalic muscle), squeezing or pinching the trigger point between the thumb and first finger is an alternative. Depending on the horses tolerance, pressure may be continuous or varying.
(4) Observe — throughout treatment, continuously monitor the animals expression in order to determine the right amount of pressure. It should be a balance between pleasure and pain. Watch the eyes for softness, closing and slow blinking.
(5) Drainage — once the trigger point has been released, the area should be drained thoroughly with plenty of effleurage followed by light friction massage along the length of the muscle. This will aid in the long standing break up of toxins into the blood stream; this movement from the muscle into the circulation and thus lymphatic system is paramount for improved muscle health. As well as encouraging drainage, effleurage will also promote circulation to the area which will improve oxygen and nutrient supply essential for healing.
(6) Light movement — following TPRT, lightly exercising the animal in hand in walk can boost circulation and muscle movement further.
Trigger points can also be treated using dry needling by a veterinary surgeon only.
Cautions to the TPRT
- Do not use more pressure than is necessary; trigger points can be over-treated!
- Be gentle and do not rush; some trigger points may need up to 3 minutes to be released.
- Avoid deep palpation or muscular exertion following TPRT. The area where the trigger point was located may be sore for a few hours to a day. Incases of chronic TPRT, avoiding intensive exercise to the area for a few days should be recommended in order to avoid a vicious cycle of the trigger point returning. However, the animal should not be isolated.
- If there is inflammation present (indicative of heat and swelling), cold hydrotherapy applications can be useful post-treatment to calm nerve endings and stimulate circulation.
The Vicious Circle
Trigger points, if not treated or identified correctly, can either build up or return. It has been proposed that sustained low-level contractions (due to a trigger point spasm) cause a decrease in perfusion, hypoxia, and ischemia and that cellular responses occur due to stimulation of activating chemical substances, which affect neuropeptides. Specific neuropeptides, including calcitonin gene-related peptide and substance P, may facilitate an increased release of regulatory compounds, resulting in excessive acetylcholine (ACh). It is hypothesized that the excessive ACh release, sarcomere shortening, and inappropriate changes in receptor activity lead to development of a taut band and subsequent MTrPs. (ref)
The Link Between TP and Acupuncture Points
It has previously been claimed that there is a 71% correspondence between the location of trigger points and acupuncture points. A research article investigating the potential correlation between the location of trigger points and acupuncture points found that this was “conceptually not possible”. Only approximately 18%-19% correlate rather than the 71% that was previously claimed. However, this study found a probable correspondence of trigger points to a different class of acupuncture points, the a shi points, which appears to be an important finding (Birch, 2004).
Passive Stretching and TP
Jaeger and Reeves (1986) conducted research into effect of passive stretching on trigger point sensitivity and the referred symptoms of myofascial pain. The results showed that myofascial trigger point sensitivity decreases in response to passive stretch as assessed by the pressure algometer, and that trigger point sensitivity and intensity of referred pain are related.
Is Ischemic Pressure the Best?
Hou et al. (2002) – Ischemic compression therapy provides an alternative treatment to using either low pressure (within or at the pain threshold) and a long duration (90s) or high pressure (the average of pain threshold and pain tolerance) and short duration (30s) for immediate pain relief and trigger point sensitivity suppression. Results suggest that therapeutic combinations such as hot pack plus active ROM and stretch with spray, hot pack plus active ROM and stretch with spray as well as TENS, and hot pack plus active ROM and interferential current as well as myofascial release technique, are most effective for easing trigger point pain
Graff-Radford et al. (1989) No pain reductions were found in the 2 Hz, 250 msec TENS or the control. No significant alteration in myofascial trigger point sensitivity, assessed with the pressure algometer, was found between the groups. The results suggest that high frequency, high intensity TENS is effective in reducing myofascial pain, and that these pain reductions do not reflect changes in local trigger point sensitivity.
Hong, C. (1996) Pathophysiology of myofascial trigger point, Journal of the Formosan Medical Association, 95 (2), pp. 93-104
Hourdebaight, J. (2007) Equine Massage: A Practical Guide, Wiley Publishing Inc.