en Physiotherapy Physiotherapy Original Research Original Research <strong>Background: </strong>Myofascial pain syndrome is one of the most common complaints in patients referring to orthopedic treatment centers. The present study aimed to examine the effects of instrument-assisted soft tissue mobilization (IASTM) and dry needling (DN) on active myofascial trigger points (AMTrP) of the upper trapezius muscle (UTM).<br> &nbsp;&nbsp; <strong>Methods:</strong> The current study was designed as a randomized clinical trial and a total of 81 patients, aged 18-40 years, with active myofascial trigger points in the upper trapezius muscle were randomly divided into 3 groups: group 1 (n = 30) received DN treatment, group 2 (n = 26) received IASTM treatment, and group 3 (n = 25) was considered as the control group (no intervention). The numeric pain scale (NPS), pain pressure threshold (PPT), active cervical contra-lateral flexion (ACLF), neck disability index (NDI), and muscle thickness (MT), according to rehabilitative ultrasonic imaging (RUSI), were measured at baseline, immediately after the last session (session 4 in week 2), and 1 month after the last session. The statistical analysis was conducted at a 95% confidence level. The P values less than .05 were considered as statistically significant.<br> &nbsp;&nbsp; <strong>Results: </strong>Both techniques were effective in treating active trigger point of the upper trapezius (p<0.05), but there was no significant difference between the treatment groups in terms of any of the above variables except for ACLF (p>0.05)<br> <strong>Conclusion:</strong> Both IASTM and DN were determined to improve NPS, PPT, ROM, and NDI in participants with active trigger points in the upper trapezius, although IASTM was more effective in increasing ACLF in these patients. Instrument Assisted Soft Tissue Mobilization Technique, Dry Needling, Active Myofascial Trigger Points, Trapezius Muscle, Myofascial Pain Syndrome 448 456 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-5926-1&slc_lang=en&sid=1 Zeinab Ahmadpour Emshi zeinab.ahmadpour1372@gmail.com 200319475328460063258 200319475328460063258 No Physiotherapy Research Center, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran Farshad Okhovatian farshadokhovatian1965@gmail.com 200319475328460063259 200319475328460063259 Yes Physiotherapy Research Center, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran Marzieh Mohammadi kojidi Marzieh68mohammadi@gmail.com 200319475328460063260 200319475328460063260 No Physiotherapy Research Center, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran Alireza Akbarzadeh Baghban akbarzad@gmail.com 200319475328460063261 200319475328460063261 No Proteomics Research Center, Department of Biostatistics, School of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Hadi Azimi azimi.hz@gmail.com 200319475328460063262 200319475328460063262 No Department of English Language Teaching, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran