重要な仕事は1930年代にJ. H. Kellgren(ロンドン)とMichael Gutstein(ベルリン)、Michael Kelly(オーストラリア)らによってなされた。Kellgrenは食塩水を健常ボランティアに実験的に注入し、関連通が生じることを示した。今日、トリガーポイント療法はマッサージ師、理学療法士、整骨医、セラピスト、自然療法医、カイロプラクター、鍼灸師、ニューロマスキュラーセラピストによって扱われている。
❍ ジャネット.G.トラベル医師
アメリカの医師であるJanet G. Travellが最も詳細且つ重要な研究を行った。トラベルはジョン.F.ケネディー大統領の背部痛を治癒させた実績から、女性として初めて大統領の侍医に選ばれた。トラベルは1900年から1942年の間に40報以上の論文を発表し、1983年にトリガーポイントマニュアル第一巻を発刊した。トラベルは晩年、同僚であるディビット.シモンズと幅広く共同研究を行った。(トリガーポイントマニュアル第三版がシモンズにより間もなく発刊される)
トラベルとシモンズはThe Trigger Point Manual [1]の中でペインクリニックの患者の75%に、痛みの原因としてのトリガーポイントが見つかると報告している。彼女らはトリガーポイント由来の痛みが、手根管症候群、滑液包炎、腱炎、狭心症、坐骨神経痛などと誤診されていると指摘している。関節炎は痛みの原因として引き合いに出されるが、関節炎と痛みがいつも同伴するわけではない。真の痛みの原因は慢性的な不良姿勢や不良動作、下肢長の不均等などの構造的欠損等により活性化されたトリガーポイントである。
Paul Svacina(Engineer and bodyworker, in California)はこの理論が現代社会におけるストレスと運動不足が筋筋膜痛と筋筋膜トリガーポイントを増加させて来ていることを支持すると信じている。
(09.09.25 追加)
There are many ideas about how trigger points are formed and why they cause pain. It was once believed that trigger points were scars or inflammation in the muscle. This was disproved when biopsies showed no abnormalities.
More recently it has been proposed that trigger points are spasms or contractures of voluntary muscle, possibly caused by an abnormality at the neuromuscular junction where the nerves controlling muscles connect to the muscle fibers (Travell & Simons). This theory seems unlikely because no contractions of voluntary muscle have been identified by traditional EMG and because the trigger points are often not in the location of the neuromuscular junction.
The most recent proposed mechanism is that trigger points are muscle spindles, made over-active by adrenalin stimulation. These very short muscle fibers, only about 1 cm in length, are called intrafusal muscle fibers to distinguish them from the voluntary muscle fibers which are called extrafusal muscle fibers. Only the intrafusal muscle fibers inside the spindle are activated by adrenalin via the sympathetic nervous system which also controls heart rate, blood pressure and other internal regulatory functions. The “sympathetic spindle spasm” theory of trigger points proposes that when spindles are over-activated by adrenalin they become painful. A clinical research trial is being conducted and should be completed by the end on 2006 by David Hubbard in San Diego, California. Paul Svacina, Engineer and bodyworker also in California, believes that this theory supports the idea that stress and decrease of moderate physical activity in modern lives has increased the occurrence of myofascial pain and trigger points.
The most accepted theory for a trigger point mechanism is that an event of muscular overload causes a prolonged release of Ca2+ ion from the sarcoplasmic reticulum (storage unit for the muscle cell) which results in a sticking of the untrained or overloaded cells. This leads to a contracture with compression of capillaries and results in an increased local energy demand and local ischemia (loss of blood circulation) to the area. This "energy crisis" (as it is termed in the seminal work on trigger points) causes the release of chemicals that augment pain activity. Since an involved muscle is weakened by this theorised sustained shortening, surrounding muscles themselves may develop trigger points in a compensatory fashion.[11][15]
Current hypotheses include:
Travell’s Initial Trauma Theory Integrated Trigger Point Hypothesis Pain-Spasm-Pain Cycle Muscle Spindle Hypothesis Neuropathic Hypothesis Fibrotic Scar Tissue Hypothesis A 2008 review in Arch Phys Med Rehabil. of two recent studies, concludes they present groundbreaking findings that can reduce some of the controversy surrounding myofascial trigger points (MTrPs). The integrated hypothesis is the most credible and most complete proposed etiology of MTrPs. However, the feedback loop suggested in this hypothesis has a few weak links, and studies by Shah and colleagues in particular supply a solid link for one of them. The feedback loop connects the hypothesized energy crisis with the milieu changes responsible for noxious stimulation of local nociceptors that causes the local and referred pain of MTrPs. Shah's reports quantify the presence of not just 1 noxious stimulant but 11 of them with outstanding concentrations of immune system histochemicals. The results also strongly place a solid histochemical base under the important clinical distinction between active and latent MTrPs. [6] Subjects with active MTrPs in the muscle have a biochemical milieu of selected inflammatory mediators, neuropeptides, cytokines, and catecholamines different from subjects with latent or absent MTrPs. [8]