Stability of behavioral estimates of activity-dependent modulation of pain

Temporal sensory summation of pain (TSSP) is a proxy measure of windup in humans and results in increased ratings of pain caused by a repetitive, low-frequency noxious stimulus. Aftersensations (ASs) are pain sensations that remain after TSSP has been induced. We examined the within-session and across-session variability in TSSP and AS estimation in healthy participants and in participants with exercise-induced muscle pain in order to determine whether the presence of pain affected the stability of TSSP and ASs. TSSP was estimated by application of 10 repetitive, low-frequency (<0.33 Hz) thermal pulses and measured by the simple slope of pain ratings between the first and fifth pulses. ASs were measured by the presence of any remaining pain sensations up to 1 minute after TSSP was induced. TSSP estimation remained moderately stable in pain-free participants and in participants with pain within a single testing session but demonstrated low stability across sessions in pain-free participants. AS estimation was stable for all groups. Estimation of TSSP and ASs using these protocols appears to be a reliable single-session outcome measure in studies of interventions for acute muscle pain and in experimental studies with healthy participants. This article evaluates the reliability of a commonly used method of estimating TSSP and ASs in both healthy participants and in a clinically relevant model of acute pain. These protocols have the potential to be used as single-session outcome measures for interventional studies and in experimental studies.