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. ObjectiveTo 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). DesignCross-sectional reliability and comparative study. SettingUniversity Pablo de Olavide, Seville, Spain. ParticipantsMiddle-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. InterventionsNot applicable. Main Outcome MeasuresThe 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. ResultsSatisfactory test-retest reliability and SEMs were found for the lower extremity, dominant arm, and nondominant arm tests (ICC=.973–.979; P<.001; SEMs=1.44–1.66 repetitions). The differences in the mean between the test and retest were lower than the SEM for all performed tests, varying from −.10 to .29 repetitions. No significant differences were found between the test and retest (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<.001 for all). ConclusionsThe endurance strength to low loads tests showed good reliability and known group validity and can be recommended for evaluating endurance strength to low loads in patients with FS. For individual evaluation, however, an improved score of at least 4 and 5 repetitions for the upper and lower extremities, respectively, was required for the differences to be considered as substantial clinical change. Patients with FS showed impaired endurance strength to low loads performance when compared with the general population.