Nonthermal ultrasound and exercise in skeletal muscle regeneration.

Abstract

To determine whether continuous nonthermal therapeutic ultrasound (US) and low-intensity exercise (Ex) influence skeletal muscle regeneration after a standardized contusion injury in an animal model. Randomized controlled trial with blinded comparisons in a 2 x 2 factorial (US by Ex) design. Animal care facility and exercise physiology biochemistry laboratory. Twenty male Wistar rats (age, 8 mo) received a reproducible bilateral contusion injury to the gastrocnemius muscles. Ten gastrocnemius muscles from 5 noninjured, nontreated rats provided baseline control data. US (continuous duty cycle, 3 MHz; intensity, 0.1 W/cm2 ; transducer, 1cm2 ; duration, 5 min/d; duty cycle, 100%) and exercise (20 min/d of low-intensity treadmill walking at 14 m/min). Gastrocnemius muscles from injured rats received exercise treatment alone (Ex + NoUS), exercise and US treatment (Ex + US), US treatment alone (NoEx + US), and no treatment (NoEx + NoUS). Ninety-six-hour postinjury muscle mass, contractile protein concentration, fiber cross-sectional area, number of nuclei per fiber, and myonuclear density. Myonuclei per fiber were statistically greater in injured than in noninjured gastrocnemius muscle (P < .05). There were no statistical differences (P > .01) among the 4 injured treatment groups for any of the outcome measures chosen as biomarkers of skeletal muscle regeneration. There is no evidence that the specific continuous US and Ex protocols investigated enhanced skeletal muscle regeneration after contusion injury.