Subjects

A total of 22 healthy female college students (mean age: 20.4 ± 0.8 years old, height: 160.05 ± 2.47 cm, and weight: 51.20 ± 4.04 kg) were recruited. The dominant leg was defined as the leg used more for kicking. Only triceps surae muscles of the right calf were measured. All subjects were identified as right leg–dominant. Because the instrumentation has a small threshold for musculoskeletal patterns that make it difficult to monitor larger muscle stiffness in male subjects, only female subjects were recruited for this study. Inclusion criteria were as follows: all subjects were healthy and able to follow the operator’s instructions. Exclusion criteria were as follows: anybody with a lower limb neuroskeletal muscle injury, such as Achilles tendon injury, heel discomfort, plantar fasciitis, or an anterior cruciate ligament (ACL) injury, and individuals taking corticosteroid medication.