Spatiotemporal characterization of an experimental model of muscle pain in humans based on short‐wave diathermy

Abstract

Background: Commonly used models for eliciting muscle pain involve the injectionof algesic substances or the induction of delayed onset muscle soreness. The formerrequire invasive procedures, and the time frame for pain induction and subsidencein the latter can be inconvenient. This study presents a detailed spatiotemporal characterization of a new experimental model of muscle pain based on short-wave diathermy (SWD), developed to overcome the limitations of existing models.Methods: The shoulder was selected as target site and the effects of the modelwere tested in two sessions to assess its reliability. Pain intensity profiles wererecorded during the application of SWD, and changes in pressure pain threshold(PPT) in the infraspinatus muscle, together with pain intensity, duration, andquality were assessed 30 min after induction.Results: SWD-induced pain intensity scores averaged 4 points on a visual analoguescale, whereas PPT showed a consistent decrease of about 25% relative to baselinevalues. Pain was localized in the shoulder area, and was described as continuous,dull, well-delimited, heavy, and bearable. Pain lasted for an average of 145 min without requiring reinduction and was reliably elicited in both experimental sessions.Conclusion: SWD can be used to elicit experimental muscle pain in a noninvasive, long-lasting, and reliable way and allows for repeated within- andbetween-session testing in the shoulder.Significance Statement: SWD produces deep heating in muscles by convertingelectromagnetic energy to thermal energy. It was previously shown that it can beused to elicit experimental pain in the forearm muscles, and the present studydemonstrates that this can be reliably generalized to other body sites, such as theshoulder. Furthermore, SWD application is non-invasive and presents a convenient time frame for pain induction and subsidence, thus overcoming limitationsassociated with traditional muscle pain models.