The Influence of Thermotherapy on Muscle Elasticity: Measurement of Pennation Angle with the Use of Ultrasound Images

The purpose of this study was to visualize the changes of muscle architecture by measuring pennation angle on ultrasound (US) images, and to examine the influence of thermotherapy on the elasticity of muscles which were stretched passively. Ten healthy male subjects positioned with the ankle joint planterflexed or dorsiflexed were continuously stretched in the dorsiflexion direction for 3 minutes in both positions, and the pennation angle and muscle extensibility were measured. Each subject received the following thermotherapy interventions randomly: Group 1 received continuous US wave (1 MHz, 1.5 W/cm2, 5 minutes); Group 2 underwent the same intervention as Group 1 but with no ultrasound output. Subjects of Group 3 were given 20 minutes of moist hot pack; Group 4 stayed still for 20 minutes. All interventions were practiced on the medial gastrocnemius muscle belly. Stretching was given after each intervention. Our study results showed that muscle extensibility did not differ significantly in any group, except for neutral positioning in groups 1 and 4. However, while groups 2 and 4 showed reduction in the pennation angle, it did not change in groups 1 and 3. These results support the hypothesis that thermotherapy is one of the factors which contributes to muscle relaxation. In other words, the measurements of pennation angle enables us to see in vivo effects of thermotherapy on muscle elasticity.