• Skeletal muscle accounts for 40% of body weight, and about 85% of human pain complaints. The most common muscles affected are those in the neck, shoulder girdle, low back and hip girdle.
• There are approximately 696 muscles in the body (347 paired and 2 unpaired).
• Muscles are sprained when they are placed under an excessive physical load. The sprain does not normally affect the whole muscle, but is usually confined to several small muscles fibres within the main body of the muscle.
• The sprain causes a rupture of a few muscle cells, producing initial pain and inflammation, and which usually settles within 1 -2 weeks. During this healing period it is possible to feel a painful taut band within the affected muscle where it has been sprained. This taut band is often referred to as an active trigger point (TrP).
• If the sprain is bad enough, sensitization of the dorsal horn at the appropriate level in the spinal cord occurs (see Pain Mechanisms and Simple Sprain), leading to a increase in resting tone within the whole muscle i.e. it appears hat the whole muscle has gone into spasm. When the resting tone of the whole muscle increases, it is much less willing to relax increasing the likelihood of further injury and cramps.
• In most people the sprain heals naturally, leading to resolution of the muscle tenderness, the trigger point, and also the dorsal horn changes in the spinal cord.
• In some people the pain resolves but the taut band remains, producing a latent trigger point (TrP). A latent TrP does not normally cause pain unless it is prodded, rolled around, or stretched. It may leave the muscle vulnerable to further injury in the future as the latent trigger point may make the muscle less willing to lengthen or relax.
• In a small proportion of people the TrP remains active long after the original injury. The reason for this is not fully understood, but it appears that a self-perpetuating loop operates making it possible for trigger points to remain active for decades.  There is often also a complex interactive between fear of the pain, excessive guarding of the part, and abnormal beliefs about the cause of the pain. Many patients are told that the cause of the pain is due to arthritis, especially when it has gone on for many months after the original injury.
• Active Trigger Points usually have the following characteristics:-
• • A history of sudden onset after an acute muscle overload, or a gradual onset with chronic overload.
  • A pattern of referred pain characteristic for the individual muscle.
  • Weakness and restricted range of movement appropriate for the muscle involved.
  • A taut palpable band within the muscle.
  • Focal tenderness on digital pressure.
  • A twitch response in the muscle on snapping the trigger point with the finger, or when needling the trigger point.
  • Reproduction of the patient's local and referred pain on examination and during injection treatment.
  • Resolution of the pain with specific treatment for the trigger point.

• The principles of treating trigger points are as follows:-
• • Reduce the pain generated by the TrP by using local methods.
  • Improve the suppleness of the muscle by using stretching techniques shortly after the treatment. These should also be continued at home regularly to maintain the improvement.
  • Strengthening the muscle afterwards to prevent vulnerability to further injury.
• Using one without the other often results in failure. It is extremely important for patients to fully understand and accept the cause of the pain, the patterns of referred pain, and to accept responsibility for their own recovery by complying with the necessary stretch routines.
• For Spinal Trigger Points, please look at Spinal Manipulation.
• The following treatments have been described for treating active trigger points:-
• Spray and Stretch
• A cool spray (vapo-coolant) is sprayed on the skin overlying the affected muscle, while the muscle itself is gently placed into it's maximum stretched position. The vapo-coolant spray helps to inhibit the dorsal horn mechanisms responsible for keeping the muscle in a contracted state, allowing the TP to be deactivated by the stretching techniques.
• Positional Release
• • TP's are deactivated by positioning the patient in such a way that the affected muscle is shortened as much as possible. This minimized position is then held and supported by the therapist (with the patient in a completely relaxed state) for at least 90 seconds, before being slowly released back to normal again.
  • At the heart of this technique is the supposition that muscles are sprained when placed under a physical load, usually when the muscle is at maximal stretch. The control system for that muscle (dorsal horn in the spinal cord, position or stretch receptors in the muscle) then exhibits a form of "memory" keeping the sprained part of the muscle in a contracted state. Minimizing the length of the muscle for 90 seconds helps to reset the control system by reducing the degree of dorsal horn sensitization and also by reducing the abnormal muscle position receptors activity.
• Muscle Energy Technique (also known as Post Isometric Relaxation)
• Ischemic Compression
  • TrP's are deactivated by the therapist applying firm pressure with a finger or thumb for at least 3 - 5 minutes. This renders the point temporarily short of oxygen (ischemic) allowing it relax.
• Dry Needling / Myofascial Acupuncture
• TrP's are deactivated by needling them with fine acupuncture type needles. Different needling techniques include:-
• Lift and thrust - where the needle is gently moved in and out of the TP
• Periosteal pecking - where the surface of the bone underneath the muscle is gently tapped or scraped with the needle tip
• Twizzelling - where the needle is gently rotated along its long axis until the muscle grips it, preventing it from being turned any further
• Trigger Point Injections (TPI's)
• • TrP's are deactivated by injecting them with local anaesthetic. The local anaesthetic immediately causes the TP to relax.
  • Deep TrP's sometimes require electromyogram (EMG) guidance to improve the accuracy of the TPI. Superficial easily palpable ones can be treated without such guidance.
  • Many patients will respond to a series of three TPI's. Botox A injections should be considered in resistant cases (see below).
  • Spinal Trigger Points are often treated with combination TPI's plus Spinal Manipulation.
• Trigger Point Injections with Botox
  • TrP's are deactivated by injecting them with Botulinum Toxin. Botox blocks motor nerve impulses from  reaching the injected muscle fibre, therefore producing pain relief because of intense relaxation. Botox binds irreversibly to specific receptors, producing muscle relaxation which lasts up to 3 months. Muscle tone slowly returns as new receptors are produced.

Pictures taken from Myofascial Pain and Dysfunction: The Trigger Point Manual, Volumes I + II by J.G. Travell and D.G. Simons (Illustrations B.D. Cummings)