the effects of arm movement on reaction time in patients with latent and active upper trapezius myofascial trigger point

background: myofascial pain syndrome is a significant source of mechanical pain. the aim of this study was to investigate the effects of arm movement on reaction time in females with latent and active upper trapezius myofascial trigger point. methods: in this interventional study, a convenience sample of fifteen women with one active mtp, fifteen women with one latent mtp in the upper trapezius, and fifteen normal healthy women were participated. participants were asked to stand for 10 seconds in an erect standing position. muscle reaction times were recorded including anterior deltoid (ad), cervical paraspinal (cp) lumbar paraspinal (lp), both of upper trapezius (ut), sternocleidomastoid (scm) and medial head of gastrocnemius(gcm). participants were asked to flex their arms in response to a sound stimulus preceded by a warning sound stimulus. data were analyzed using one-way anova test. results: there was significant differences in motor time and reaction time between active and control groups (p< 0.05) except for gcm. there was no significant difference in motor time between active and passive groups except for ut without mtp and scm (p< 0.05). also, there were no significant differences in motor times between latent mtp and control groups. furthermore, there was no significant difference in premotor times between the three groups. conclusion: the present study shows that patients with active mtp need more time to react to stimulus, but patients with latent mtp are similar to healthy subjects in the reaction time. patients with active mtp had less compatibility with environmental stimulations, and they responded to a specific stimulation with variability in surface electromyography (semg).