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Objective: To determine whether true interindividual response differences (IIRD) exist with respect to changes in anxiety because of aerobic exercise training in adults with fibromyalgia (FM).

Data Sources: Data from a previous meta-analytical database of randomized controlled trials of exercise in adults with arthritis and other rheumatic diseases.

Study Selection: Randomized controlled trials limited to aerobic exercise training on anxiety in adults 18 years or older with FM were included.

Data Extraction: Change outcome SDs treated as point estimates for anxiety were used to calculate true IIRD from each study. In addition, treatment effect data were extracted.

Data Synthesis: The inverse variance heterogeneity model was used to pool all results. For the 5 studies and 321 participants in which results were pooled, statistically significant treatment effect reductions in anxiety were observed (mean, -0.77 points, 95% CI, -1.25 to -0.77). However, no significant IIRD were found (mean, 0.6 points, 95% CI, -1.2 to 1.5). The 95% prediction interval for true IIRD in a future study was -1.7 to 0.8. The percent chance, ie, probability, of a clinically meaningful difference in variability, was 61.5% (only possibly clinically important).

Conclusions: The results of the current study suggest that aerobic exercise is associated with reductions in anxiety among adults with fibromyalgia. However, there is currently a lack of convincing evidence to support the notion that true IIRD exist. Therefore, a search for potential mediators and moderators associated with aerobic exercise and changes in anxiety among adults with FM may not be warranted. However, additional research is needed before any true level of certainty can be established. This includes (1) the assessment of IIRD in future randomized controlled trials, (2) randomized controlled trials of longer duration, and (3) an increase in the proportion of men included in randomized controlled trials.