Kato, E. (2009). A 6-week stretching program alters mechanical and architectural properties of the gastrocnemius muscle-tendon unit. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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This study investigated changes in the mechanical and architectural properties of the human gastrocnemius muscle-tendon unit by a 6-week stretching program. Healthy men were divided into a stretching group (N = 8) and a control group (N = 8). The stretching program consisted of static stretching (one minute of passive dorsiflexion performed five times) everyday for six weeks. Before the intervention and 1, 2, 4, and 6 weeks after the onset of the stretching program, the passive dorsiflexion range of motion was measured by goniometry as well as muscle and tendon elongation by ultrasonography. To measure muscle and tendon elongation, an ultrasound probe mounted with a water bag was attached over the distal end of the medial gastrocnemius at the muscle-tendon junction, so that longitudinal scanning was made along the length of the muscle. The change in total muscle-tendon unit length was estimated from the change in ankle angle. The Achilles tendon elongation was calculated as the difference between elongations of the muscle-tendon unit and muscle belly. Negligible muscle activity during the stretching was confirmed through surface electromyograms taken from the medial and lateral gastrocnemii, soleus, and tibialis anterior muscles during stretching. The fascicle length was also measured in the mid-belly of the medial gastrocnemius using ultrasonography.

The passive dorsiflexion range of motion increased significantly at week 4 and later from the onset of the stretching program, which was accompanied by a significant increase in Achilles tendon elongation, especially in the dorsiflexed position. There was no further increase in muscle belly elongation in the dorsiflexed position. The plantar flexion torque passively attained at rest (0 degree of ankle joint) decreased significantly, while the fascicle length increased significantly at week 4 and later. This result indicates that the Achilles tendon elongation became smaller after the stretching program due to elongated fascicles and the muscle belly at rest at 0 degree of ankle joint. However, an increase in tendon elongation in the dorsiflexed position after the stretching program suggests a decrease in tendon stiffness, especially under higher passive tension.

Implication. A six-week static stretching program affects both mechanical and architectural properties of the gastrocnemius muscle-tendon unit, with different changes of muscular and tendinous components being joint angle dependent. Such stretching reduces the elastic properties of the muscle which could account for a significant portion of performance loss due to this type of stretching.

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