Effects of Posture Change during Static Stretching of the Gastrocnemius on the Muscle Viscoelasticity

To evaluate how muscle tone decreases during static stretching, we have proposed a method that involves using a wearable indentation tester. In a previous study on the rectus femoris, we sometimes observed change of posture during self-static stretching. We did not consider the degree of elongation of the muscle due to change of posture; however, this does actually affect muscle viscoelasticity measured by the indentation tester. In this paper, we investigate the effect of joint angle on muscle viscoelasticity in self-static stretching of the gastrocnemius. We measured the muscle reaction force of the gastrocnemius as a viscoelastic index and the ankle joint angle. We found that relations between the reaction force and the ankle joint angle changed are classified in several patterns. This suggests that we can evaluate the decrease of muscle tone by only the muscle reaction force even if muscle elongation changes during static stretching.