BACKGROUND Imaging of the Achilles tendon using ultrasound tissue characterization (UTC) involves taking up the slack of the tendon by including dorsiflexion of the ankle. This pilot study aimed to determine whether different longitudinal tension applied to the Achilles tendon during imaging affected the reliability of UTC. MATERIAL AND METHODS Nine asymptomatic active volunteers, aged between 23-49 years underwent imaging of 17 Achilles tendons. Three positions of tension included plantar grade, 50%, and 100% of maximal dorsiflexion, with a range of 18-32°. Ranges were established and standardized using an isokinetic dynamometer. A test and re-test process was conducted at each position to determine the intraclass correlation coefficients (ICCs) and minimum detectable change (MDC) per echotype. Images were analyzed using UTC software. RESULTS Plantar grade positioning images could not be obtained. ICCs for each echotype I-IV between test 1 and test 2 were 0.965, 0.962, 0.858, 0.739 at 100% dorsiflexion (95% CI, 0.86-0.99, 0.84-0.99, 0.51-0.97, and 0.2-0.94), and 0.771, 0.551, 0.569, 0.429 at 50% dorsiflexion (95% CI, 0.29-0.94, -0.09-0.88, -0.01-0.88, and -0.15-0.82). The MDC per echotype I-IV ranged between 4.1-1.0% of echotype data at 100% dorsiflexion, and 17.2-6.3% at 50% dorsiflexion. CONCLUSIONS Testing at maximum dorsiflexion provided improved reliability when using UTC in healthy individuals. The ICC at 100% dorsiflexion was increased, and the MDC was reduced for all echotypes. Therefore, standardizing test positions when using UTC is advisable for reliable comparison of results between studies.