The effect of hip flexion angle on muscle elongation of the hip adductor muscles during stretching.

In order to perform effective static stretching of the hip adductor muscles, it is necessary to clarify the position where the muscles are most stretched. However, the effective flexion angle in stretching for each adductor muscle remains unclear. The goal of this study was to investigate the effect of hip flexion angle on muscle elongation of hip adductor muscles during stretching. Sixteen healthy men were recruited for this study. Shear elastic modulus, an index of muscle elongation, of the adductor longus (AL), and both the anterior and posterior adductor magnus (anterior AM) were measured using ultrasonic shear wave elastography at rest (supine position) and at 5 stretching positions (maximal hip abduction at 90°, 60°, 30°, 0°, and -15° hip flexion). For the AL, the shear elastic modulus at rest was significantly lower than that in all stretching positions. However, there was no significant difference among stretching positions. For the anterior AM, there was no significant difference between stretching positions and at rest. For the posterior AM, the shear elastic modulus in 90°, 60°, and 30° hip flexion were significantly higher than that at rest. The shear elastic modulus in 90° hip flexion was significantly higher than that in 60° and 30° hip flexion. Our results suggest that the AL is elongated to the same extent by maximal hip abduction regardless of hip flexion angle, the anterior AM is not elongated regardless of the hip flexion angle; the posterior AM is elongated at all angles except at 0° and -15° hip flexion and is most extended at 90° hip flexion.