Continuous therapeutic ultrasound accelerates repair of contraction-induced skeletal muscle damage in rats

Objective: To examine the effect of ultrasonography on the repair of muscle injured through repeated eccentric contractions. Design: Randomized, case-control study. Setting: Laboratory animal facility. Animals: Thirty-three Sprague-Dawley rats. Interventions: Specimens were anesthetized and each foot strapped, in turn, onto a motorized foot pedal, which moved the ankle repeatedly through a range of 110°. Extensor digitorum longus muscles were injured by stimulating the peroneal nerve during foot plantarflexion. Continuous 1.0MHz ultrasound treatments at 0.5W/cm²were applied through water submersion technique to 1 limb daily for 3, 5, or 7 days postinjury. The contralateral limb served as an injured control. Main Outcome Measures: Extensor digitorum longus maximum isometric tetanic force (P_o) was measured in vitro from all extensor digitorum longus muscles and used as a functional index of muscle injury. Results: Analysis of variance and Tukey post hoc analysis showed no significant differences in P_obetween treated and untreated limbs at 3 and 5 days, but at 7 days postinjury, P_oof ultrasound-treated muscle was significantly higher than was untreated muscle. Conclusion: Seven days of continuous therapeutic ultrasound improved force production after contraction-induced muscle injury.