Objectives. To examine the validity of self-reported flexibility with International Fitness Scale (IFIS) against upper and lower flexibility in fibromyalgia and healthy women. To study the test-retest reliability of the IFIS flexibility item in female fibromyalgia patients.
Methods. For validity purpose, the final sample comprised 413 fibromyalgia and 195 control women. For the test-retest (one-week interval) reliability purpose, 101 fibromyalgia women participated. Flexibility level was both self-reported (i.e. IFIS) and performance-based using standard fitness tests (i.e. “chair sit and reach” and “back scratch”). One-way analysis of variance (ANOVA) was used to examine the associations of self-reported flexibility (very poor, poor, average and good/very good) and performance-based flexibility. Post hoc group comparisons were used to assess the differences across categories of self-reported fitness. The test-retest reliability of the IFIS was tested with weighted Kappa (k) coefficients.
Results. Fibromyalgia women reporting a “poor”, “average” or “good/very good” flexibility on IFIS had better performance-based test results on flexibility compared with those reporting “very poor” flexibility level (all p < 0.05). Likewise, control women reporting a “good/very good” flexibility on IFIS obtained better performance-based test results on flexibility compared with those reporting “average”, “poor” or “very poor” flexibility level (all p < 0.05). The weighted Kappa was 0.63 which represent a substantial test-retest agreement.
Conclusions. The IFIS is a moderately valid and reliable tool for ranking fibromyalgia patients and controls according to their flexibility level. These results extend the current knowledge on the validity and reliability of the IFIS to measure flexibility in diverse populations.
Corresponding author. alvarezg@ugr.es
