Effects of therapeutic ultrasound on the mechanical properties of skeletal muscles after contusion Efeitos do ultra-som terapêutico nas propriedades mecânicas do músculo esquelético após contusão

Background: Therapeutic ultrasound is a resource commonly applied to speed up tissue repair in muscle injuries. The absorption of the ultrasound waves is determined by their frequency and intensity. For a given intensity, the depth reached by 1MHz is greater than the depth reached by 3MHz. Objective: To analyze the mechanical properties of muscles subjected to acute impact injury treated with therapeutic ultrasound at the frequencies of 1 and 3MHz. Methods: Forty female Wistar rats (200.1±17.8g) were used, divided into four groups: (1) control; (2) muscle injury without treatment; (3) muscle injury treated with therapeutic ultrasound at the frequency of 1MHz (0.5W/cm 2 ); and (4) muscle injury treated with therapeutic ultrasound at the frequency of 3MHz (0.5W/cm 2 ). The injury was produced in the gastrocnemius muscle by means of an impact mechanism. The treatment consisted of a single five-minute session per day, for six consecutive days. The muscles were subjected to mechanical traction tests in a universal test machine. Results: Means and standard deviations for the mechanical properties of the injured groups that received therapeutic ultrasound were significantly greater than those of the injured group without treatment (p<0.05). The property of stiffness should be highlighted: the application of therapeutic ultrasound increased muscle stiffness by approximately 38%. Conclusions: Therapeutic ultrasound increased the mechanical properties of the injured muscles, and brought them to a level close to the control group. However, no significant difference in mechanical properties was observed between the groups treated with ultrasound at the frequencies of 1MHz and 3MHz.