Measurement of gastrocnemius muscle elasticity by shear wave elastography: association with passive ankle joint stiffness and sex differences

Passive joint stiffness is an important quantitative measure of flexibility, but is affected by muscle volume and all of the anatomical structures located within and over the joint. Shear wave elastography can assess muscle elasticity independent of the influences of muscle volume and the other nearby anatomical structures. We determined how muscle elasticity, as measured using shear wave elastography, is associated with passive joint stiffness and patient sex. Twenty-six healthy men (24.4 +/- A 5.9 years) and 26 healthy women (25.2 +/- A 4.8 years) participated in this study. The passive ankle joint stiffness and tissue elasticity of the medial gastrocnemius (MG) were quantified with the ankle in 30A degrees plantar flexion (PF), a neutral anatomical position (NE), and 20A degrees dorsiflexion (DF). No significant difference in passive joint stiffness by sex was observed with the ankle in PF, but significantly greater passive ankle joint stiffness in men than in women was observed in NE and DF. The MG elasticity was not significantly associated with joint stiffness in PF or NE, but it was significantly associated with joint stiffness in DF. There were no significant differences in MG elasticity by sex at any ankle position. Muscle elasticity, measured independent of the confounding effects of muscle volume and the other nearby anatomical structures, is associated with passive joint stiffness in the joint position where the muscle is sufficiently lengthened, but does not vary by sex in any joint position tested.