PURPOSE: Skeletal muscle stiffness is thought to be the result of increased tissue hardness, but measurement accuracy has been dependent on operator technique. We have proposed a novel shear wave real-time imaging method (color Doppler shear wave imaging: CD SWI) with continuous shear waves excited from the tissue surface by a mechanical vibrator. METHODS: Using the method, shear wave velocity was measured for the upper trapezius muscle. Adaptive shear wave velocity measurement by means of quality estimation of shear wave wavefront was adopted. We recruited 23 male volunteers with no history of orthopedic disease and recorded shear wave propagation to assess the intra- and inter-observer reliability. For intra-observer reliability, one observer took two measurements separated by a time delay, and the intra-class correlation coefficient (ICC) was calculated (1,1). For inter-observer reliability, ICC (2,1) was calculated from both observers' measurements. RESULTS: Mean propagation speed was 3.75 ± 0.47 (first) and 3.71 ± 0.49 m/s (second) for Observer A (ICC (1,1) = 0.91 [95% CI 0.76-0.96]) and 3.80 ± 0.53 m/s for Observer B (ICC (2,1) = 0.83 [95% CI 0.56-0.94]). CONCLUSIONS: This result suggests that our technique is satisfactorily reliable and has potential for future application in various fields, such as evaluation of muscle condition or the effects of rehabilitation.