How can you tell if a dog has a trigger point?

In humans, we can identify a trigger point (also referred to as a myofascial trigger point) by regionalised aching and more intense pain when we move or reposition ourselves. The onset of the aching and pain may be directly related to an acute injury, chronic condition or repetitive muscle overload.

As dogs can’t tell us if they have an aching muscle, palpation or feeling the muscles can help identify a trigger point. When palpating a dog, the following may indicate the presence of a trigger point:

• A taut band of muscle with a very tender nodule, typically in the muscle belly.

A characteristic of a trigger point is a taut band of muscle. Muscles are comprised of bundles of tubular muscles fibres. Muscle fibres contain tubular myofibrils and myofibrils are comprised of sacromeres. Sacromeres are long, fibrous proteins that slide over each other when the muscle contracts and relaxes. The taut band that is characteristic of trigger points is caused by the sacromeres of the involved muscle fibres being hyper-contracted or shortened. The remaining fibres in the muscle are maximally stretched to compensate for the missing length of the shortened sacromeres.

Contracted sacromeres remain contracted because the molecule titin holds myosin in place and contributes to increased resting tension of the remaining stretched sacromeres. Titin’s role in muscle contraction is to limit the range of motion of sacromeres by preventing overstretch and recoiling the sarcomere after it is stretched. While myosin generates the force of muscle contraction through its interaction with the molecule actin.

• Pain

Another typical characteristic of a trigger point is pain particularly when gentle pressure is applied on the tender nodule. Gentle pressure can elicit a pain response like a sudden movement away or even a snap. Further, depending on the location of the trigger point and the level of sensitisation of local nocioceptors, pain can be referred to a distant location.

The pain cycle associated with trigger points starts with an abnormal release of acetycholine (ACh) from the motor neuron to active muscle contraction. As the energy supply to maintain the contraction is exhausted, the muscle remains contracted leading to the formation of contraction knots. An energy crisis develops based on the increased energy consumption (to keep some muscle fibres contracted) and loss of energy from the compromised muscle function. The outcome of the energy imbalance is the release of neurovasoreactive sensitising substances that sensitize local pain receptors (nocioceptors) leading to pain.

The degree to which the sensitising substances actually sensitise the nocioceptors depends on the location of the nocioceptor in relation to the affected motor end plate. For this reason, there is only a general correlation between a trigger point and pain.

• Painful limit when stretching the muscle

Another indicator of a trigger point is a painful end point in a stretch. Pain is caused by increased tension on the muscle attachments. The taut band of muscle applies tension on the myotendinous junctions of the muscle. These junctions are not designed to tolerate constant tension. When sustained tension and contraction is applied at the myotendinous junction inflammatory changes including possible development of oedema, release of pain inducing substances and degenerative changes can occur.

• Local twitch response.

A local twitch response is typically only observed in active trigger points. There is no motor response for latent trigger points.

What causes trigger points?

Trigger points are formed by acute or chronic muscle overload. Muscle overload results in the excessive release of ACh which causes the contraction knot and release of nocioceptor sensitising substances.

Muscular overload may be due to an injury or accident (slip, misstep, or fall), poor co-ordination when fatigued, a sudden, awkward movement or chronic overload caused by sustained muscle contraction and repetitive movement.

Occasionally trigger points serve as a stabilising mechanism to counteract instability elsewhere in the body. The best approach to such trigger points is to treat the underlying cause of the instability and then the trigger point may resolve spontaneously.

How to treat trigger points?

The goal of any treatment of trigger points is to restore the affected sacromeres to a uniform length. This will resolve the energy crisis and stop the release of neurovasoreactive substances which cause pain. It will also relieve tension on the musculotendinous junction which so the dog’s range of motion will be restored.

Contraction – release technique

This technique involves gently contracting the affected muscle, either passively or actively. This technique is effective as there are relatively few hyper-contracted muscle fibres in a muscle (1 in 50) that are involved in the taut band. These muscle fibres are unable to exert any force because they are already maximally contracted. The remaining stretched sacromeres are still able to exert optimal forces and in so doing when contracted (passively or actively) can overpower the shortened weak sacromeres. Gentle contractions allow the lengthened sacromeres to exert an elongation force on the shortened sacromeres. Gentle contractions are followed by relaxation or release. When these technique is performed slowly it allows the muscle fibres to reset the sarcomere length.

Release can be achieved actively or passively. Typically with dogs, passive release is used. With this technique, the practitioner gently manipulates the muscle without the dog engaging the muscle.

For this technique to be effective, the practitioner needs to sense the point of muscle resistance to facilitate the release. Too little contraction will have no effect and too great a contraction will cause pain and inhibit the release.

Trigger point pressure release technique

Trigger point massage is a deep massage technique to elongate contracted sacromeres. When the muscle is extended to eliminate slack, the practitioner applies gentle, persistent digital pressure at the trigger point while “sliding” their fingers along the length of the muscle away from the trigger point to elongate the fibres.

When the contracted sacromeres are compressed by the pressure of the practitioner’s fingers then the sacromeres become wider. The pressure reduces their height and in so doing makes them longer and normalises their length.

Sustained gentle pressure is required until a release is felt. Compression for too short a period will have little effect and the contracted sacromeres will return to their shortened state. When the contracted sacromeres are released and return to their normal length the muscle’s range of motion will be restored and tension in the muscle reduced.

Hot hydrotherapy

Due to the tenderness of trigger points, initial hot hydrotherapy may increase the effectiveness of trigger point release massage techniques. Hot hydrotherapy such as a warm towel or heat pack over the trigger point will stimulate the circulatory system to draw nutrients and oxygen to the site and remove the accumulation of sensitising substances.

How to prevent trigger points in dogs?

So, just like humans, dogs can get trigger points when they injure themselves or their muscles are overloaded. Here are some tips for preventing trigger points developing:

• Train and condition your dog for the activities you want them to perform – Injuries can result from poor co-ordination when a dog becomes fatigued. Ensure your dog’s body is sufficiently well conditioned and nourished before asking them to perform. This applies to sporting and pet dogs alike. Imagine expecting a dog to run next to your bike on Saturday mornings without conditioning them throughout the week. The dog will quickly fatigue which will change their gait and lead to changes in muscle recruitment.

• Rest – Ensure dogs have sufficient time to recover from strenuous exercise and activity. Strenuous exercise results in micro-tears in muscle fibres, giving the dog time to rest allows these tears to heal, making the muscles stronger.

• Repetitive strain – Eliminate repetitive actions that your dog may perform. Repetitive actions overloads specific muscle groups and can lead to the development of trigger points. Examples of repetitive actions include:

Ball chasing
Jumping up and down on furniture
Racing up and down stairs
Pulling on a lead or harness
Dog sport activities – jumping and turning, heeling on one side of the handler

Where possible, eliminate repetitive actions such as ball chasing or pulling on lead / harness or train your dog to perform repetitive actions on both sides e.g. heeling – teach the dog to heel on both sides of the handler to prevent overloading one side of their body.

• Treat early – If a dog incurs an injury or shows signs of muscular pain, seek treatment immediately to prevent further injury and compensation. Full Stride provides remedial massage treatments for dogs with muscle pain and mobility issues. Treatments are provided in the dog’s home in the Brisbane area or at the north Brisbane clinic.

Until next time, enjoy your dogs.

Sources:

Hourdebaight, Jean-Pierre 2004, Canine Massage: A complete reference manual 2nd edition, Dogwise Publishing, Wenatchee WA, USA

Simons, D.G. 2002 “Understanding effective treatment of myofascial trigger points” Journal of Bodywork and Movement Therapies, April 2002, 6 (2): 81 – 88.