Reliability and Validity of a Low Load Endurance Strength Test for Upper and Lower Extremities in Patients With Fibromyalgia

Abstract Munguía-Izquierdo D, Legaz-Arrese A. Reliability and validity of a low load endurance strength test for upper and lower extremities in patients with fibromyalgia. Objective To evaluate the reliability, standard error of the mean (SEM), clinical significant change, and known group validity of 2 assessments of endurance strength to low loads in patients with fibromyalgia syndrome (FS). Design Cross-sectional reliability and comparative study. Setting University Pablo de Olavide, Seville, Spain. Participants Middle-aged women with FS (n=95) and healthy women (n=64) matched for age, weight, and body mass index (BMI) were recruited for the study. Interventions Not applicable. Main Outcome Measures The endurance strength to low loads tests of the upper and lower extremities and anthropometric measures (BMI) were used for the evaluations. The differences between the readings (tests 1 and 2) and the SDs of the differences, intraclass correlation coefficient (ICC) model (2,1), 95% confidence interval for the ICC, coefficient of repeatability, intrapatient SD, SEM, Wilcoxon signed-rank test, and Bland-Altman plots were used to examine reliability. A Mann-Whitney U test was used to analyze the differences in test values between the patient group and the control group. We hypothesized that patients with FS would have an endurance strength to low loads performance in lower and upper extremities at least twice as low as that of the healthy controls. Results Satisfactory test-retest reliability and SEMs were found for the lower extremity, dominant arm, and nondominant arm tests (ICC=.973–.979; P .05 for all). The Bland-Altman plots showed 95% limits of agreement for the lower extremity (4.7 to –4.5), dominant arm (3.8 to –4.4), and nondominant arm (3.9 to –4.1) tests. The endurance strength to low loads test scores for the patients with FS were 4-fold lower than for the controls in all performed tests ( P