Pain and fear avoidance partially mediate change in muscle strength during resistance exercise in women with fibromyalgia.

OBJECTIVES Resistance exercise results in health benefits in fibromyalgia. The aim of this study was to determine the factors that mediate change in muscle strength in women with fibromyalgia as a result of resistance exercise. METHODS Sixty-seven women with fibromyalgia (age range 25-64 years) were included. Tests of muscle strength and questionnaires related to pain, fear avoidance and physical activity were carried out. Multivariable stepwise regression was used to analyse explanatory factors for change and predictors for final values of knee-extension force, elbow-flexion force and hand-grip force. RESULTS Change in knee-extension force was explained by fear avoidance beliefs about physical activity at baseline, together with change in pain intensity, knee-extension force at baseline, age and body mass index (BMI) (R2=0.40, p = 0.013). Change in elbow-flexion force was explained by pain intensity at baseline, together with baseline fear avoidance beliefs about physical activity, BMI and elbow-flexion force at baseline (R2 = 0.32, p = 0.043). Change in hand-grip force was explained by hand-grip force at baseline, change in pain intensity and baseline fear avoidance (R2 = 0.37, p = 0.009). Final muscle strength was predicted by the same variables as change, except pain. CONCLUSION Pain and fear avoidance are important factors to consider in rehabilitation using resistance exercise for women with fibromyalgia.