Acute effects of static stretching on the hamstrings using shear elastic modulus determined by ultrasound shear wave...

Static stretching (SS) with hip flexion and knee extension is often used to stretch the hamstrings. However, it is unclear whether there are the differences in the acute effect of this SS maneuver on flexibility between each component of the hamstrings, namely the semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF) muscles.

The aims of this study were to investigate the acute effects of SS on the flexibility of the individual muscle components of the hamstrings, and to examine the difference in the acute effect of SS between these components using shear elastic modulus as the index of muscle flexibility.

Twenty healthy men (age, 23.4 ± 2.3 years) volunteered for this study. The shear elastic modulus of the ST, SM and BF muscles were measured using ultrasound shear wave elastography before (PRE) and immediately after (POST) 5 min of SS. Measurements of shear elastic modulus were taken with the knee at 90° (slack position) and 45° (extension position) of flexion.

In all muscles, the shear elastic modulus at both knee angles decreased significantly after SS. The percentage change in the shear elastic modulus from PRE to POST in the muscles at 45° of knee flexion was greatest in the SM.

These results suggest that SS with hip flexion and knee extension has acute effects on increasing flexibility of the hamstring muscle components, especially the SM muscle.