Background: In patients with chronic tension-type headache (CTTH) changes in pressure pain in the cervical region are associated with peripheral or central sensitization. It is hypothesized that an increase of isometric strength of neck flexors would lead to a decrease of pressure pain in CTTH, as an expression of reduced peripheral or central sensitization Objective: In this study we aimed to analyze the correlation between change in isometric strength of the neck flexors and change in pressure pain scores (PPS) in patients with CTTH. Study Design: Comparative analysis of data from previous study. Setting: Primary healthcare center. Methods: Data from 145 patients with CTTH who underwent a manual therapy program including isometric strength training of the neck flexors were analyzed at 8 and 26 weeks posttreatment. PPS were measured as a total of pain scores on a numeric rating scale (score 0 to 10) on application of a pressure stimulus of 3kg/cm at 8 cervical- and suboccipital muscles. Isometric strength of the neck flexors was measured in seconds. Correlations were computed between changes in PPS and isometric neck flexor strength. Results: Isometric strength of neck flexors scored significantly different compared to baseline measurement (mean 30.0 seconds, sd:25.2), and increased with a mean difference of 17.33 seconds (95%CI: 20.61 to 14.05) at 8 weeks and 19.18 seconds (95%CI: 23.48 to 14.87) at 26 weeks. Similarly, compared to PPS baseline measurement (31.6 points, sd:18.6), mean difference in PPS was significantly decreased at 8 and 26 weeks: -11.3 points (95%CI: -8.77 to -13.83) and -11.15 points (95%CI: -8.31 to -13.99). There is a negative correlation between changes in PPS and changes in isometric strength of neck flexors which is weak at 8 weeks (r = -0.243, P = 0.004) and moderate at 26 weeks (r = -0.318, P < 0.000). Limitations: Correlational analysis. Conclusion: Decrease in PPS correlates with increases in isometric strength of neck flexors in patients with CTTH in short- and long-term Key words: Chronic tension-type headache, pressure pain, neck flexors, manual therapy, sensitization, isometric strength, cervical spine