Influence of transducer pressure and examiner experience on muscle active shear modulus measured by shear wave elastography

Introduction: This study examined the effects of ultrasound transducer pressure and examiner experience on the biceps femoris long head and semitendinosus muscle active shear modulus in healthy individuals (n = 28). Methods: Active shear modulus was assessed using shear wave elastography at 20% of knee flexor maximal voluntary isometric contraction. Examiners with different experience levels measured the muscles' shear modulus with three pressure levels: mild, moderate, and hard. Results: A main effect of transducer pressure was found for both biceps femoris long head (p < 0.001; η²_p = 0.314) and semitendinosus muscles (p < 0.001; η²_p = 0.280), whereas differences were found between mild-moderate (biceps femoris long head: p = 0.013, d = 0.23; semitendinosus: p = 0.024, d = 0.25), and mild-hard pressures (biceps femoris long head: p = 0.001, d = 0.47; semitendinosus: p = 0.002, d = 0.47). Examiners performed similar shear modulus measurements in the biceps femoris long head (p = 0.299; η²_p = 0.041) and semitendinosus (p = 0.177; η²_p = 0.066), although the experienced examiner showed a higher measurement repeatability (biceps femoris long head: ICC = 0.86–0.95, semitendinosus: ICC = 0.89–0.96; vs. biceps femoris long head: ICC = 0.78–0.87, semitendinosus: ICC = 0.66–0.87). Conclusion: Transducer pressure influences the active shear modulus measurement between mild and moderate or hard pressures. Additionally, examiner experience seems to have no influence on muscle active shear modulus measurement when assessed at the same site (using casts). Implications for practice: Future studies assessing active muscle shear modulus should use mild transducer pressure and having experienced examiners in order to improve measurement reliability.