Tender or not tender: test-retest repeatability of pressure pain thresholds in the trapezius and deltoid muscles of healthy women.

OBJECTIVE To examine the test-retest repeatability of pressure pain thresholds in the shoulder muscles of healthy women. DESIGN Four experimental sessions (days 1, 3, 28, 30), each including 4 consecutive pressure pain threshold measurements at 10-minute intervals. SUBJECTS Twenty-four healthy female volunteers, mean age 42 years. METHODS Two examiners measured pressure pain thresholds bilaterally over the trapezius and deltoid muscles with an electronic algometer. Student's paired t-test, intraclass correlation coefficient, ANOVA repeated measures, 95% confidence interval and mean maximal absolute measurement error, were used for statistics. RESULTS Reliability for each point in all sessions was high; ICC range 0.70-0.94, mean maximal differences; 53-102 kPa (all 4 muscles), and between points in each muscle: ICC right trapezius 0.59-0.77, left 0.67-0.84, right deltoid 0.66-0.83, left 0.70-0.90. Mean maximal differences were 69-101 kPa and 65-111 kPa for the trapezius and deltoid muscles, respectively. The inter-individual variation was 5-fold (trapezius 88-574 kPa; deltoid 91-529 kPa). At the group level, the variation was limited when the first measurement was excluded. Inter-rater and intra-rater repeatability was high without significant differences. Only small side-to-side differences were seen. CONCLUSION Repeated measurements show stable intra-individual values. The method can be recommended when used by trained and experienced examiners.