To determine the elastic modulus of the upper trapezius muscle during the cervical flexion by shear wave elastography (SWE).

Twenty healthy male individuals were recruited from Luoyang Orthopedic-Traumatological Hospital in this study. During the cervical flexion at 0° and 30°, upper trapezius muscle elasticity was assessed by operators A and B. Five days later, the muscle was evaluated again by operator A. In addition, the upper trapezius muscle on the dominant and non-dominant side was assessed during the cervical flexion. The reliability was evaluated using the intraclass correlation coefficient (ICC) and a paired t-test was performed to compare the difference in the elastic modulus of the upper trapezius muscle during the cervical flexion between the two sides.

During the cervical flexion at 0° and 30°, the intra-operator reliabilities of assessing upper trapezius elastic properties by SWE were good (ICC=0.77~0.86) and inter-operator reliabilities (ICC=0.86~0.98) were excellent. The upper trapezius stiffness was (40.47±11.37) kPa during the cervical flexion at 0° and (49.52±14.46) kPa at 30°, with an increase of 22.36% and the minimal detectable change (MDC) was 7.04 kPa. In addition, the upper trapezius elastic modulus on the dominant side was significantly stiffer than that on the non-dominant side during the cervical flexion at 0° and 30° [(40.47±11.37) kPa vs (35.25±9.46) kPa, t=4.64, P＜0.001; (49.52±14.46) kPa vs (43.87±10.61) kPa, t=3.27, P=0.001)].

SWE is an effective technique for evaluating the elastic modulus of the upper trapezius muscle with high reliability and repeatability. Therefore, SWE has the advantage of assessing the elasticity of the musculoskeletal system.