Objective:To explore the influence of age on the passive stiffness of women′s quadriceps muscles and the relationship between stiffness and muscle functioning.Methods:Twenty healthy elderly women formed the senior-aged group, while 20 young, healthy women were selected as the young group. The passive stiffness of the subjects′ vastus medialis, rectus femoris and vastus lateralis muscles was measured using ultrasound shear wave imaging with the knee flexed to 30°, 60°, 90° and 105°. Both groups completed the 6-minute walk test (6MWT) and the five times sit-to-stand test (FTSST). Maximum voluntary isometric contraction (MIVC) strength during knee extension was also measured.Results:The passive muscle stiffness of the rectus femoris and vastus lateralis muscles was significantly greater in the senior-aged group when the knee was flexed at 60°, 90° or 105°. The 6MWT and FTSST times of the young group were of course significantly better, and their MIVC at 60° and 90° of knee flexion was also significantly stronger. Rectus femoris stiffness among the senior-aged group was negatively correlated with MIVC when the knee was flexed at 60°.Conclusions:The passive stiffness of the muscles studied increases with age, especially in stretching. When the knee joint is flexed at 60° there tends to be a negative correlation between the MIVC of the quadriceps femoris and the stiffness of the rectus femoris among elderly females.