Interaction of obesity and systemic inflammation with knee extensor strength in knee osteoarthritis

BACKGROUND: Knee osteoarthritis is accompanied by reduced muscle strength and a greater body mass index (BMI). Large BMI from accumulated fat mass is linked with greater systemic inflammation. Separate studies show inflammation is associated with reduced muscle strength in healthy adults. The purpose of this study was to investigate whether systemic inflammatory biomarkers interact with BMI to relate with knee extensor strength, and if the relationship differs based on sex. METHODS: 93 participants with clinical knee osteoarthritis (n = 59 females, n = 34 males) were included. Knee extensor strength (Nm) was an average of 5 maximum voluntary isometric knee extension efforts. BMI was measured while barefoot, wearing a t-shirt and shorts. Serum cytokines were obtained from venous blood samples from the antecubital fossae following a 30-min rest period. Linear regressions tested the interaction effect of each CRP and IL-10 on the relationship between knee extensor strength (dependent variable) and BMI (independent variable), for both males and females. FINDINGS: Among females with a large BMI, higher levels of IL-10 related to greater knee extensor strength (t = 2.18, p = 0.03). For males, the interaction of IL-10 (t = 0.61, p = 0.55) with CRP (t = -1.75, p = 0.09) with BMI was not significant. INTERPRETATION: Anti-inflammatory properties of IL-10 may serve to balance the effect of an increased BMI in females by counteracting inflammation-induced muscle damage. Understanding this association provides insight into biological factors that may contribute to disease progression, serving as a potential target for therapeutic interventions.