Knee Extensor Strength Is Associated with Pressure Pain Thresholds in Adults with Fibromyalgia

OBJECTIVE Individuals with fibromyalgia (FM) have lower muscle strength and lower pressure pain thresholds (PPT). The primary aim of this study was to determine the associations between muscle strength and PPT in adults with FM to test the hypothesis that greater measures of muscle strength would be associated with greater values of PPT. Secondary aims included determining the effects of pain severity and the peak uptake of oxygen (VO2) on the associations between muscle strength and PPT. METHODS Knee extensor and flexor strength (N = 69) was measured in the dominant leg using a dynamometer, and PPT was assessed using an electronic algometer. Pain severity was determined using the Multidimensional Pain Inventory, and peak VO2 uptake was quantified using an electronically braked cycle ergometer. RESULTS Univariable linear regression analysis demonstrated a significant association between PPT (dependent variable) and isometric knee extensor (P<.001), isokinetic (60°/s) knee extensor (P = .002), and isokinetic (60°/s) knee flexor strength (P = .043). In a multiple variable linear regression analysis adjusted for age, sex, pain severity, body mass index and peak VO2 uptake, a significant association was found between PPT and isometric knee extensor strength (P = .008). In a similar multiple variable analysis, a significant association was found between PPT and isokinetic knee extensor strength (P = .044). CONCLUSION Greater measures of isometric and isokinetic knee extensor strength were significantly associated with greater values of PPT in both univariable and multiple variable linear regression models. TRIAL REGISTRATION ClinicalTrials.gov NCT01253395.