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Myofascial syndrome is a muscular pain syndrome with regional symptoms, often in neck, limb girdle or back area.It is common and causes much disability and inability to work.Myofascial pain may be activated by precision work, repetitive strain and recent injury.Typical findings are taut bands and painful trigger points (TrPs) in symptomatic muscles.TrPs express inflammatory metabolites in microdialysis.Pressure of TrP often elicits a twitch response and a typical spreading of pain.When needle electromyography (EMG) of TrP is compared to a painless point of the same or other muscle there are some differences.TrPs show more spontaneous electrical activity (SEA) than control points.SEA consists of two types of activity, often arising together: miniature end plate potentials (MEPPs) and end plate spikes (EPSs).In addition, about 15% of patients show a third type of activity in taut bands: complex repetitive discharges (CRDs).The prevailing hypothesis explain SEA as activation of the motor nerve terminal and postsynaptic muscle fibre by injury caused by the needle electrode.CDRs are explained by ephaptically activated loops of muscle fibres.We conjecture that active sites with MEPPs and EPSs reflect activity of intrafusal muscle fibres, and in fact muscle spindles may have pain receptors and elicit the pain in TrPs of myofascial syndrome.CRDs may reflect beta and gamma motor efferent muscle potentials activated via a spinal reflex arch.The afferent part of this reflex arch consists of Ⅲ-and Ⅳ-afferent chemoreceptor activity, caused by inflammatory agents in TrPs.This hypothesis may also explain the effect of needling therapy in myofascial syndrome.