Temporal Summation of Activity-related Pain (TSAP): A Novel Approach to Assessing Repetitive Movement-evoked Pain in Chronic Shoulder Pain

This study aimed to evaluate the clinical usefulness of TSAP by examining its relationship with conventional assessments of movement-evoked pain and other clinical outcomes, and to assess its impact on shoulder dysfunction.

Thirty individuals (mean age 66.0 ± 10.4 years, 14 females) with chronic shoulder pain participated in this study. TSAP was assessed in two steps. First, the minimum load that induced pain during 90° abduction in the scapular plane (task movement) was identified. Next, participants performed 10 repetitions of the task movement, and the pain intensity was measured at both the first and tenth repetitions. The pain intensity at the first repetition was recorded as initial-TSAP, and the difference between the pain intensity at the tenth and first repetitions was used as the TSAP score. Participants were also assessed for movement-evoked pain through interview (i-MEP), Temporal Summation of Pain (TSP) on the bilateral deltoid using pinprick stimuli, the Central Sensitization Inventory-9 (CSI-9), and Quick DASH. We conducted correlation analysis to examine the relationships between TSAP and these measures. Multiple linear regression analyses were also conducted, with Quick DASH as the dependent variable, and TSAP, initial-TSAP, and i-MEP as independent variables in the unadjusted model. An adjusted model was also developed, incorporating sociodemographic factors as potential confounders.

TSAP showed a significant correlation with bilateral TSP (ρ = 0.70 [affected] and 0.66 [control], P  0.001) and Quick DASH (ρ = 0.44, P =0.02), but not with initial-TSAP (ρ = 0.04) and CSI-9 (ρ = 0.07). In the unadjusted model, a significant regression equation was found [F (3, 26) = 7.18, P 0.001, adjusted R² = 0.39], with TSAP score (t = 3.11, P 0.01) and initial-TSAP (t = 2.13, P = 0.04) as significant predictors of Quick DASH. In the adjusted model, a significant regression equation was also found [F (10, 19) = 3.28, P 0.05, adjusted R² = 0.44], with TSAP score (t = 2.66, P = 0.02) as the only significant predictor.

TSAP reflects sensitivity to mechanical stimuli, the wind-up phenomenon. In addition, TSAP may potentially capturing aspects that cannot be assessed by conventional methods for evaluating central sensitization-related symptoms. Moreover, TSAP may be superior to conventional assessments of movement-evoked pain, which often rely solely on patient interviews or single-task evaluations, in evaluating the impact of pain during daily activities.

TSAP helps to provide a valuable approach for assessing activity-related pain in individuals with shoulder pain, offering insights that could improve clinical management and patient outcomes.