Objective：To investigate the lower limb skeletal muscle stiffness in healthy individuals.

Methods：Using ultrasonographic elastography, we measured the degree of stiffness of the rectus femoris and medial head of the gastrocnemius in healthy individuals and investigated the relationships between muscle stiffness and thickness, a quantitative measure of muscles, and between muscle stiffness and brightness, a qualitative measure of muscles. Furthermore, relationships between muscle stiffness and age, body weight, and body mass index (BMI) were also studied.

Results：Rectus femoris stiffness was positively correlated with muscle thickness. Rectus femoris stiffness had a weak negative correlation with muscle brightness and a weak positive correlation with body weight and BMI. Stiffness of the medial head of the gastrocnemius showed no correlation with any of the study variables. Muscle stiffness did not correlate with age in either of the muscles. No sex-related difference was found in the degree of muscle stiffness.

Conclusion：Although rectus femoris stiffness was associated with muscle thickness and brightness, these relationships were not observed for muscle stiffness of the medial head of the gastrocnemius. The data suggested that rectus femoris stiffness reflects the quantitative and qualitative states of the muscle, and the presence of such relationships may depend on the location of the muscle.