Effect of high frequency electromagnetic wave stimulation on muscle injury in a rat model

The aim of this study was to investigate biological changes in tissues with muscle contusion after the application of high frequency (HF) electromagnetic wave. An acrylic pipe was placed on the right hind limb and a metallic ball was dropped inside the pipe, which resulted in a muscle contusion. After acquiring the optimal condition for muscle contusion, 20 Sprague-Dawley rats were allocated to the HF treatment (N = 10) and sham groups (N = 10), which then underwent muscle contusion injury at their right thigh. The thickness and circumference of the right thigh and the left thigh (negative control groups) were measured (day 0). HF electromagnetic wave stimulation for three days was performed on the contusion area in the HF group after one day. Thickness was measured at the thickest area of both hind limbs and the circumference was measured every day for three days. The sham group received no treatment, and the circumference and thickness were measured using the same method. After three days, Hematoxylin and eosin and immunohistochemical (IHC) staining for IL-1β were performed and TUNEL assay was conducted for apoptosis in the skin and muscle layers. The thigh muscle thickness at day 1 was significantly different between groups (P = 0.018) and this difference was observed between both sham and control groups (corrected P = 0.007), and between sham and HF groups (corrected P = 0.043). Thigh circumference was significantly different at day 3 (P = 0.047) and this difference was found between sham and control groups (corrected P = 0.018), and between sham and HF groups (corrected P = 0.032). In the HF group, the inflammatory response was reduced to almost the same level as the control group. Evaluation of IL-1β level, the inflammatory cytokine, through IHC showed marked localization of IL-1β in muscle fibers of the sham group. However, significantly less IL-1β was observed in the muscle of the HF treatment group. There was neither injury nor apoptosis after HF stimulation. Application of the HF showed therapeutic effect on muscle contusion by reducing muscle swelling. This effect might be caused by the anti-inflammatory action of the HF, which evoked energy into the injured muscle.