Viscoelasticity of the muscle-tendon unit is returned more rapidly than range of motion after stretching

The purpose of this study was to clarify the time course of the viscoelasticity of gastrocnemius medialis muscle and tendon after stretching. In 11 male participants, displacement of the myotendinous junction on the gastrocnemius medialis muscle was measured ultrasonographically during the passive dorsiflexion test, in which the ankle was passively dorsiflexed at a speed of 1°/s to the end of the range of motion (ROM). Passive torque, representing resistance to stretch, was also measured using an isokinetic dynamometer. On five different days, passive dorsiflexion tests were performed before and 0, 15, 30, 60 or 90 min after stretching, which consisted of dorsiflexion to end ROM and holding that position for 1 min, five times. As a result, end ROM was significantly increased at 0, 15 and 30 min (P<0.05 each) after stretching as compared with each previous value. Passive torque at end ROM was also significantly increased after stretching. Although the stiffness of the muscle-tendon unit was significantly decreased immediately after stretching (P<0.05), this shift recovered within 15 min. These results showed that the retention time of the effect of stretching on viscoelasticity of the muscle-tendon unit was shorter than the retention time of the effect of stretching on end ROM.