Exercise and Therapeutic Ultrasound in Skeletal Muscle Regeneration

Abstract

0125 Following skeletal muscle contusion injury, ultrasound (US) is a commonly utilized treatment modality among sports medicine practitioners. There is evidence that the mechanical effects of non-thermal US elicit changes in membrane permeability, which over several days purportedly hastens the post-contusion-injury muscle regenerative process. However, how US influences both satellite cell proliferation and ultimately muscle contractile proteins is poorly understood, and the interaction between US and low-intensity exercise following contusion injury has not been investigated. PURPOSE: To gain enhanced insight into the biological markers underlying the potential rehabilitative process associated with US, and determine if low-intensity exercise (EX) enhances the effect of US treatment. METHODS: Twenty male Wistar rats (8–9 mo) were studied and were randomly assigned to either an EX or NoEX group. Following anesthesia, each rat received a bilateral contusion injury to the gastrocnemius (GTN) muscles. The reproducible injury was generated using a validated drop-mass technique. To visualize satellite cell proliferation, immediately following the contusion injury a pellet of the thymidine analog, bromodeoxyuridine, was implanted subcutaneously in the scruff of the neck. In both groups the right leg received US while the left received no US. The design lead to the generation of 4 groups of 10 GTN muscles: 1) EX + US; 2) EX + NoUS; 3) NoEX + US; and 4) NoEX + NoUS. An additional 5 animals served as a non-injured, − US treated, and− exercised control group. Both exercise and US treatments were administered for four consecutive days, and began 24h post-contusion-injury. Exercise treatment consisted of 20 minutes/day of low-intensity treadmill walking (14m/min), and the US treatments (settings = 0.1 W/cm2 and 3 MHz) were 5 minutes in duration. Left non-US treated legs received sham US treatments. Following all treatment protocols (96h) GTN muscles were surgically removed and rats were sacrificed. GTN muscles were weighed, frozen, and stored at−80°C for analysis of fiber cross-sectional area (CSAf), myofibrillar protein concentration, and satellite cell number. A two way (exercise × treatment) MANOVA was performed. RESULTS: Preliminary results from 5 rats in the NoEx group demonstrate no statistically significant (p<0.05) differences between US-treated and sham-treated muscles in mass (3.25 ± 0.22 g and 3.34 ± 0.23 g, respectively) nor in CSAf (1,600 ± 455.43 square microns and 1,549 ± 1,109.74 square microns, respectively). CONCLUSIONS: The US treatment protocol used appears to have no effect on the measured markers of skeletal muscle regeneration.