Objective: The purpose of this study was to determine the relative and absolute reliability of the pressure pain threshold (PPT) in the shoulder muscles of participants with and without unilateral subacromial impingement syndrome.

Methods: Study of intraday intra- and interrater and interday intrarater reliability. Fifty-two participants symptomatic for unilateral subacromial impingement syndrome were divided into 2 groups (SG1 and SG2) of 26 participants each, and 26 participants asymptomatic for shoulder pain took part in the study. Two raters assessed the PPT in 4 shoulder muscles. Each rater assessed symptomatic (SG1) and asymptomatic participants twice on the same day, and one of the raters on 2 different days (SG2). The intraclass correlation coefficient, standard error of measurement (SEM_95% and SEM%), and minimum detectable change (MDC_95% and MDC%) were calculated.

Results: Relative reliability was good or excellent for all assessments, as well as for both groups and raters (intraclass correlation coefficient: 0.87-0.98). The SEM_95% values for intra- and interday intrarater measures were between 0.43 and 1.50 kgf/cm² and SEM% between 6.76 and 12.86%, whereas MDC_95% values ranged from 0.60 to 2.12 kgf/cm² and MDC% from 9.56 to 18.18%. In interrater measures, SEM_95% was between 0.58 and 0.77 kgf/cm² and SEM% between 10.10% and 13.71%, whereas MDC_95% varied from 0.82 to 1.08 kgf/cm² and MDC% from 14.29% to 19.39%.

Conclusion: Relative reliability was good or excellent. This study presents absolute reliability values that could be used as a reference in the clinical use of PPT.