Muscle shear elastic modulus in hamstrings: effect of intensity, contraction type, and relationship with muscle anatomy

We used shear wave elastography (SWE) to examine changes in hamstrings muscle shear elastic modulus with contraction type and intensity. Also, we examined the relationships between hamstrings muscle size/architecture and shear modulus. Shear modulus increased curvilinearly with increasing contraction intensity in all muscles and contraction types, although it plateaued at a lower intensity in biceps femoris long head (BFlh) and semimembranosus (SM) compared to semitendinosus (ST). ST anatomical cross-sectional area (ACSA) and BFlh pennation angle (PA) explained >50% of the inter-individual differences in their respective peak isometric shear modulus. The greater change in ST shear modulus with contraction intensity compared to BFlh and SM, indicate an increased load borne by ST during knee flexion. Influence of muscle anatomy on shear modulus is muscle- and contraction-type specific.