Myofascial trigger points are a muscular dysfunction at the level of the motor end-plate and the sarcoplasmic reticula that, in turn, cause a local contraction with ischemia -induced hypoxia. Along with the hypoxia, the resulting energy crisis leads to a sensation of the surrounding nociceptors . Extracorporeal shock wave therapy (ESWT) is recently considered an effective treatment for myofascial pain syndrome. It's been proved an effective in musculoskeletal disease fasciitis

. It is significant since it is a non-invasive and simple treatment, easy to apply at a large surface, and has fewer side effects with low intensity even if it requires relatively high cost, ESWT has been proved to be more effective than conventional ultrasound on MTrPs in the upper trapezius muscle and showed that ESWT is more effective

. It has been found that three sessions of ESWT significantly improved pain levels, neck disabilities, and the quality of life by reducing the number of MTrPs .

ESWT could reduce the pain of myofascial pain syndrome by pain signal alteration, promoting angiogenesis and increasing perfusion in ischemic tissues induced by sensitization of nociceptors and muscle ischemia.

Ultrasound with deep heat is used in treatment of myofascial trigger point due to the properties of achieving vasodilation, accelerating the metabolism, increasing viscoelasticity and reducing pain and muscle spasm

High power pain threshold ultrasound found to be effective in many literatures in treatment of myofascial trigger point

. Study was performed comparing effect of high power pain threshold ultrasound with conventional ultrasound proved that high power pain threshold is more effective in treating upper trapezius myofascial It was found in the treatment of MPS, HPPT US therapy could be considered as a reliable and more effective and has positive effect method than low-dose and conventional US therapies

This study will be presented as a part of ongoing study. The ongoing study investigates the effect of different intensities of ultrasound on upper trapezius trigger points. The current study will investigate the myoelectric activities of trigger points after application of high power pain threshold ultrasound

Myofascial pain is defined as pain that originates from myofascial trigger points in skeletal muscle. It is prevalent in regional musculoskeletal pain syndromes, either alone or in combination with other pain generators Myofascial pain syndrome is represented by many clinical symptoms such as pain, hyperirritable nodule of spot tenderness, referred pain, and muscle spasm by trigger points. The upper trapezius is probably the muscle most often beset by trigger points It was assumed that the muscle fibers are shortened and taut bands are made by calcium influx in damaged fibers or acetylcholine secretion in motor end plates. The trigger points are the hyperirritable nodules of spot tenderness in a palpable taut band of skeletal muscle that may cause pain to a distant point and also causes distant motor and autonomic effects Once myofascial trigger points are activated, changes in the structural characteristics and contraction function of the muscle will occur. The most distinctive changes are taut bands, tender nodules, referred pain, local twitch response, muscle weakness, and restricted range of motion Patients with unilateral pain of an upper trapezius muscle exposed to a fatiguing load analyzed with surface electromyography (sEMG) were found to have a difference in sEMG response between healthy and symptomatic muscle Surface electromyography (EMG) analyzes functional changes in muscle by measuring quantitative changes in motor unit action potential that is activated by muscle contraction

Surface EMG, which was used to evaluate the functionality of trigger points in this study, is nonintrusive and convenient; thus, it is widely used in studies on the functional characteristics of muscle, by analyzing the electrical activity of muscle Surface EMG recording fortrigger points shows changes in recruitment of fast-twitch muscle fibers and conduction velocity of motor unit action potential According to Gemmell and Bagust (2009) EMG recordings confirm increased spontaneous activity of motor units in patients with myofascial pain during the "resting state" of muscles.

The treatments of myofascial pain are divided into the invasive and the non-invasive therapy. The invasive therapy is about the injection of medications, dry needling and non-invasive therapy refers to massage, stretching and ultrasound Extracorporeal shock wave therapy (ESWT) is recently considered an effective treatment for myofascial pain

, It is a non-invasive and simple treatment, easy to apply at a large surface, and has fewer side effects with low intensity even if it requires relatively high cost.

ESWT could reduce the pain of myofascial pain syndrome by pain signal alteration, promoting angiogenesis and increasing perfusion in ischemic tissues induced by sensitization of nociceptors and muscle ischemia .

High power pain threshold ultrasound resolve acute active trigger points . High power-pain threshold ultrasound efficient method for relieving painand disability and increasing range of motion Although significant in decreasing tissue stiffness Previous study, which is the first to make a combined evaluation of the effectiveness of low-, moderate- and high dose (HPPT) US therapies in MPS, the results obtained considered significantly in that greater improvements in clinical parameters were generally determined going from low dose to high dose and that the effect was achieved in only four sessions of HPPT US therapy. the cycle of pain-spasm-ischemia-pain is more effectively resolved when the dosage of US, applied for the treatment of trigger points in MPS, is increased the cycle of pain-spasm-ischemia-pain is more effectively resolved when the dosage of US, applied for the treatment of trigger points in MPS, is increased. Therefore, HPPT US therapy can be considered as a more economical treatment than conventional US treatments due to less number of treatment sessions.

Inclusion Criteria:

• Both genders will be included with their age between

  . •Symptoms of active TrPs unilateral on at least one side of the upper fiber of trapezius muscle presence of at least one trigger point symptoms lasting from 0 to 2 weeks age

• Subjects have pain at rest, local twitch response, jump sign, limited range of motion and referred pain lies over the lateral aspect of the upper trapezius fiber and superiorly to the ipsilateral occiput .

Exclusion Criteria:

Exclusion Criteria:

• patients who had medication or other therapies for myofascial pain syndrome (Ji Hm et al., 2012) (2)
• patients who had neurological deficits involving the upper limbs, advance osteopathic or arthropathic disorders of the cervical spine or the shoulder of the investigated side
• contraindication of ESWT such as hypertension, coagulopathy, ulcer, recent severe hemorrhage, neoplasm, renal insufficiency, severe hepatic disease, epilepsy, cutaneous pathology, central pain, pregnancy and mental retardation
• The presence of previously diagnosed disease such as (diabetes mellitus, fibromyalgia, hormonal disorder hypothyroidism, hyperthyroidism and rheumatoid arthritis