A new experimental model of muscle pain in humans based on short-wave diathermy

Background: Experimental models of pain in humans are crucial for understanding pain mechanisms. The most often used muscle pain models involve the injection of algesic substances, such as hypertonic saline solution or nerve growth factor or the induction of delayed onset muscle soreness (DOMS) by an unaccustomed exercise routine. However, these models are either invasive or take substantial time to develop, and the elicited level of pain/soreness is difficult to control. To overcome these shortcomings, we propose to elicit muscle pain by a localized application of short-wave diathermy (SWD). Methods: In this crossover study, SWD was administered to 18 healthy volunteers to the wrist extensor muscle group, with a constant stimulation intensity and up to 4 min. Pressure pain threshold (PPT), pinprick sensitivity (PPS) and self-reported muscle soreness were assessed at baseline and at 0, 30 and 60 min after application of SWD. Results: SWD evoked localized muscle pain/soreness in the wrist extensor muscle group and a decrease of PPT in the treated arm compared with the control arm that lasted for at least 60 min, reflecting ongoing hyperalgesia after SWD application. PPS was not significantly altered 30–60 min following SWD, suggesting a minimal contribution from skin tissue to sustained hyperalgesia. Conclusions: SWD was able to elicit muscle soreness and hyperalgesia up to 60 min after its application. Thus, this new model represents a promising tool for investigating muscle pain in humans. Significance: This study presents an experimental model to elicit sustained muscle pain based on short-wave diathermy. The main advantages of the model are its noninvasiveness, the possibility to control stimulation parameters in a reliable way and the convenience of the time frame in which pain and hyperalgesia are developed.