en آسیب شناسی ورزشی و حرکات اصلاحی Sport injury and corrective exercises كاربردي Applicable <div style="text-align: justify;"><strong>Purpose</strong>: Ultrasonography (US) can be used to measure the dimensions and the cross-section of muscles. This study aims to investigate the intra- and inter-tester reproducibility of the US measures of the cross-section of the longus colli (LC) muscle at rest and in contraction states in patients with chronic non-specific neck pain (CNSNP) and healthy individuals.<br> <strong>Methods</strong>: This cross-sectional study was conducted on seven healthy individuals and seven patients with chronic non-specific pains. The cross-section of the LC muscle was measured at rest and in contraction states at the C5-6 vertebrae by two raters using the US on two consecutive days. The data were analyzed by the Pearson correlation coefficient (ICC).<br> <strong>Results</strong>: The intra-tester reproducibility was excellent in the healthy (ICC>0.97) and patient (ICC>0.95) groups at rest and in contraction. The inter-tester reproducibility was great in the healthy group (ICC>0.97) in both states and at rest (ICC=0.98) and in the contraction (ICC>0.95) in the patient group.<br> <strong>Conclusion</strong>: The results revealed that the US demonstrated higher agreement in measuring the cross-section of the LC in healthy subjects and patients with CNSNP. Thus, this method is reliable and can be used to measure the cross-section of the muscles.</div> Ultrasonography (US), Cross section area, Longus colli (LC) muscle, Reproducibility 253 260 http://ptj.uswr.ac.ir/browse.php?a_code=A-10-600-1&slc_lang=en&sid=1 Afsaneh Samiei afsanehsamiei72@yahoo.com 0009-0007-1001-6064 No Department of Physiotherapy, School of Rehabilitation, Zahedan University of Medical Sciences, Zahedan, Iran. Mohammad Hosseinifar fardash_s@yahoo.com 0000-0003-1866-8642 Yes Department of Physiotherapy, School of Rehabilitation, Zahedan University of Medical Sciences, Zahedan, Iran. Fateme Ghiasi fqiasi@gmail.com 0000-0001-9849-6670 No Department of Physiotherapy, School of Rehabilitation, Zahedan University of Medical Sciences, Zahedan, Iran. Hasan Namvar hassan_753@yahoo.com 0000-0002-1355-0007 No Department of Physiotherapy, School of Rehabilitation, Zahedan University of Medical Sciences, Zahedan, Iran. Ahmadreza Asgari Ashtiani ahmadaskary@@gmail.com 0000-0002-0210-9005 No Department of Physiotherapy, School of Rehabilitation, Zahedan University of Medical Sciences, Zahedan, Iran.