An ultrasound shear wave elastography system (Aixplorer Supersonic Imagine, France) with a 40 mm linear array transducer (SL10-2, Supersonic Imagine, France) was used. The settings of the SWE system were set as follows: the instrument was set in the musculoskeletal mode. The frequency was 2~10 MHz. The SWE Opt was the penetration mode. The opacity was 85%. The elastic modulus range of the gastrocnemius was 0~200 kPa, while the elastic modulus range of the Achilles tendon was 0~800 kPa. The color scale used in the shear modulus (in kPa) showed the lowest values in blue to the highest values in red. The depth of the B-scan was 3.0 cm [30 (link)]. For the Achilles tendon, the size of the regions of interest (ROI) had to be set to 25∗12 mm and the Q-Box™ diameter was defined by the thickness of the tendon, which was the distance between the superior and inferior borders of the Achilles tendon [23 (link)]. For the MG and LG, the size of the ROI had to be set to 10∗10 mm and the diameter of the Q-Box™ is 5∗5 mm [31 (link)]. The transducer was positioned along the longitudinal axis of the AT, MG, and LG.
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