Participants were positioned prone on an exam table with their hips and knees supported in neutral position and then asked to remain relaxed with no muscular contraction. In an effort to standardize imaging locations between participants, thigh length from the ischial tuberosity to the midpoint between the femoral condyles was measured and recorded. Skin marks were then made on the participant at 33%, 50%, and 67% of the thigh length from the ischial tuberosity, which corresponded to approximately proximal, mid-belly, and distal regions of the hamstring muscle, respectively. These locations were determined based upon pilot testing to ensure that images were collected at these different regions with minimal tendon infiltration, and are consistent with previous investigations [19 (link)–22 (link)].
All images were obtained using the same machine (Aixplorer, Supersonic Imaging, Weston, FL) and sonographer with over 18 years of US experience (5+ years in MSK US). A linear array transducer (2–10 MHz) was used with the following parameters: imaging depth of 5 cm, dual transmit foci depth of 2 and 3 cm (corresponding to approximately the center of the muscle [23 (link)]), and gain of 38%, as this was determined from preliminary image acquisitions to result in clear images without image saturation. All ultrasound settings were kept constant for all image acquisitions [6 (link),24 (link)].
Ultrasound gel was liberally applied at each imaging site. To ensure that the targeted HS muscle was imaged, a transverse view was first visualized after ensuring the ultrasound probe was placed at the appropriate location with respect to the ischial tuberosity. Longitudinal B-mode images were then captured for each hamstring muscle (biceps femoris long head, BFlh; semitendinosus, ST; semimembranosus, SM) at each of the three locations along both thighs. Biceps femoris short head (BFsh) was excluded from the analysis primarily because BFsh is deep to BFlh, thereby making imaging difficult [25 (link)]. After image acquisitions were completed at all locations from both limbs, the participant sat on the exam table for 60 seconds, before laying back down. The same imaging procedure was then repeated for each limb.
All images were obtained using the same machine (Aixplorer, Supersonic Imaging, Weston, FL) and sonographer with over 18 years of US experience (5+ years in MSK US). A linear array transducer (2–10 MHz) was used with the following parameters: imaging depth of 5 cm, dual transmit foci depth of 2 and 3 cm (corresponding to approximately the center of the muscle [23 (link)]), and gain of 38%, as this was determined from preliminary image acquisitions to result in clear images without image saturation. All ultrasound settings were kept constant for all image acquisitions [6 (link),24 (link)].
Ultrasound gel was liberally applied at each imaging site. To ensure that the targeted HS muscle was imaged, a transverse view was first visualized after ensuring the ultrasound probe was placed at the appropriate location with respect to the ischial tuberosity. Longitudinal B-mode images were then captured for each hamstring muscle (biceps femoris long head, BFlh; semitendinosus, ST; semimembranosus, SM) at each of the three locations along both thighs. Biceps femoris short head (BFsh) was excluded from the analysis primarily because BFsh is deep to BFlh, thereby making imaging difficult [25 (link)]. After image acquisitions were completed at all locations from both limbs, the participant sat on the exam table for 60 seconds, before laying back down. The same imaging procedure was then repeated for each limb.
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