The effect of hip rotation on shear elastic modulus of the medial and lateral hamstrings during stretching

Regarding hamstring stretching methods, many studies have investigated the effect of stretching duration or frequency on muscle stiffness. However, the most effective stretching positions for hamstrings are unclear because it is impossible to quantify muscle elongation directly and noninvasively in vivo. Recently, a new ultrasound technology, ultrasonic shear wave elastography, has permitted noninvasive and reliable measurement of muscle shear elastic modulus, which has a strong linear relationship to the amount of muscle elongation. This study aimed to investigate the effect of hip internal and external rotation on shear elasticmodulus of the lateral and medial hamstrings, respectively, during stretching in vivo using ultrasonic shearwave elastography. Twenty-three healthy men (age, 23.0 +/- 2.1 years) were recruited for this study. To investigate the effect of hip rotation on the elongation of the medial and lateral hamstrings, shear elastic modulus of the biceps femoris (BF) and semitendinosus (ST) was measured at rest (a supine position with 90 degrees knee flexion, 90 degrees hip flexion, and hip neutral rotation) and in seven stretching positions (with 45 degrees knee flexion and hip internal, external, and neutral rotation) using ultrasonic shearwave elastography. In both BF and ST, the shear elastic modulus in the rest position was significantly lower than that in all stretching positions. However, no significant differences were seen among stretching positions. Our results suggest that adding hip rotation at a stretching position for the hamstrings may not have a significant effect on muscle elongation of the medial and lateral hamstrings. (C) 2014 Elsevier Ltd. All rights reserved.