Pain severity is associated with muscle strength and peak oxygen uptake in adults with fibromyalgia

W Michael Hooten,^1,2 Jolene M Smith,³ Jason S Eldrige,¹ David A Olsen,³ W David Mauck,¹ Susan M Moeschler<sup>1

1</sup>Department of Anesthesiology, ²Department of Psychiatry and Psychology, Mayo Clinic College of Medicine, ³Mayo School of Graduate Medical Education, Rochester, MN, USA

Background: The associations between pain, lower extremity strength, and aerobic conditioning have not been widely investigated in adults with fibromyalgia (FM). The principle objective of this study was to investigate the relationship between pain severity and knee strength in patients seeking treatment for FM. A secondary objective was to investigate the relationship between pain scores and aerobic conditioning.
Methods: Three measures of knee strength (isokinetic extensor, isokinetic flexor, isometric extensor) were quantified in the dominant leg of 69 adults with FM using a dynamometer at speeds of 60 degrees per second (60°/s) and 180°/s. Peak oxygen uptake (VO₂) was assessed using a cycle ergometer, and pain was assessed using the pain severity subscale of the Multidimensional Pain Inventory.
Results: In univariable linear regression analyses using pain severity as the dependent variable, lesser values of isokinetic knee extensor strength at 60°/s (P=0.041) and 180°/s (P=0.010), isokinetic knee flexor strength at 60°/s (P=0.028) and 180°/s (P=0.003), and peak VO₂ uptake (P=0.031) were predictive of greater pain severity scores. In multiple variable linear regression models adjusted for age, sex, body mass index, and opioid use, the following associations retained statistical significance; isokinetic knee extensor strength at 60°/s (P=0.020) and 180°/s (P=0.003), isokinetic knee flexor strength at 60°/s (P=0.015) and 180°/s (P=0.001), and peak VO₂ uptake (P=0.014). However, no significant associations were found between pain severity and isometric knee extensor strength.
Conclusion: The main findings from this study were that lesser values of isokinetic knee strength and peak VO₂ uptake were predictive of greater pain severity scores. These results build on the findings of previous investigations, but ongoing research is needed to further characterize the effects of strength and peak VO₂ uptake on the pathophysiology of FM.

Keywords: fibromyalgia, knee extensor strength, knee flexor strength, isokinetic, peak oxygen uptake