Quantitative evaluation of passive muscle stiffness by shear wave elastography in healthy individuals of different ages.

Objectives: To investigate age-related changes on passive muscle stiffness in healthy individuals and measure the shear modulus in different age groups.
Methods: Shear wave elastography (SWE) movies of gastrocnemius medialis (GM) were collected during passive stretching induced by ankle rotation from plantarflexion (PF) to dorsiflexion (DF). A series of SWE images at ankle angles of PF 40°, PF 30°, PF 20°, PF 10°, 0°, DF 10°, DF 20°, and DF 30° were collected and shear moduli measured accordingly for analyses.
Results: Eighty-six healthy volunteers (27 children, 31 middle-aged adults, and 28 older people) were recruited. No significant difference was observed in the shear modulus between the three groups at ankle angles of PF 40°, PF 30°, PF 20°, PF 10°, and 0° (p > 0.05). The difference in the shear modulus among the three groups became significant as DF increased. At ankle angles of DF 10°, DF 20°, and DF 30°, the shear modulus was the greatest in the older group, followed by the middle-aged group and then the children group (p = 0.007, 0.000, and 0.000, respectively).
Conclusions: Passive muscle stiffness increases with age, and the difference between age groups was pronounced only after reaching a certain degree of stretching.
Key Points: • The influence of age on passive muscle stiffness becomes pronounced only after reaching a certain degree of stretching. • Age should be considered when evaluating passive muscle stiffness in muscular disorders.