Effects of a Four-week Static Stretch Training Program on Passive Stiffness of Human

1 gastrocnemius muscle-tendon unit in vivo. Abstract 9 Static stretch is commonly used to prevent contracture and to improve joint mobility. 10 However, it is unclear whether the components of the muscle-tendon unit are affected 11 by a static stretch training program. This study investigated the effect of a four-week 12 static stretch training program on the viscoelastic properties of the muscle-tendon unit 13 and muscle. The subjects comprised eighteen male participants (mean age: 21.4 years ± 14 1.7). The range of motion (ROM), passive torque, muscle-tendon junction (MTJ) 15 displacement and muscle fascicle length of the gastrocnemius muscle were assessed 16 using both ultrasonography and a dynamometer whilst the ankle was passively 17 dorsiflexed. After the initial test, the participants were assigned either to a group that 18 stretched for four-week (N = 9) or to a control group (N = 9). The tests were repeated 19 after the static stretch training program. 20 ROM and MTJ displacement significantly increased, and the passive torque at 30 deg 21 significantly decreased, in the stretching group after the study period. However, there 22 was no significant increase in muscle fascicle length. These results suggest that a 23 four-week static stretch training program changes the flexibility of the overall MTU 24 without causing concomitant changes in muscle fascicle length.