Abstract Objective To investigate the applicability and reliability of isokinetic strength measurements during concentric and eccentric actions of the shoulder muscles in fibromyalgia (FM) patients. Design Test-retest reliability study. Setting University laboratory. Participants Women with FM (N=25) aged 37 to 69. Interventions Not applicable. Main Outcome Measures Two isokinetic tests of the shoulder were repeated after an interval of 7 days. Each test involved 3 repetitions of abduction and adduction performed at a rate of 60°/s. The first test involved 2 concentric muscle actions (concentric/concentric test). The second test involved concentric abduction followed by eccentric adduction (concentric/eccentric test). Unilateral peak torque (Nm) and average work (J) were measured. Applicability was calculated as the proportion of participants who were able to complete every test. Reliability was analyzed by intraclass coefficient (ICC), standard error of measurement, and smallest real difference (SRD). Results Applicability was 84% for the concentric/concentric test and 52% for the concentric/eccentric test. The main factor influencing applicability was age. In the concentric/eccentric test, measurement of peak torque showed high reliability for the abduction (ICC=.88; standard error of measurement=1.82; SRD=5.05) and adduction (ICC=.89; standard error of measurement=3.83; SRD=10.62) phases. In the concentric/concentric test, measurement of peak torque showed low reliability in the abduction phase (ICC=.29; standard error of measurement=6.45; SRD=17.87) and excellent reliability in the adduction phase (ICC=.92; standard error of measurement=5.95; SRD=16.50). Conclusions The applicability of shoulder isokinetic tests in FM patients who are women may be affected by age. In comparison, the concentric/concentric test was more applicable and less reliable than the concentric/eccentric test during abduction and adduction. These findings will facilitate the clinical interpretation of changes in isometric and isokinetic shoulder adduction and abduction tests in women with FM.