The effect of exercise intensity on chronic inflammation: A systematic review and meta-analysis

Abstract

Objectives: Chronic inflammation is independently associated with the incidence and progression of chronic disease. Exercise has been found to reduce chronic inflammation, however the role of exercise intensity (work rate) is unknown. This review aimed to determine the pooled effect of higher- compared to lower-intensity aerobic and resistance exercise on chronic inflammation in adults. Design: Systematic review and meta-analysis. Methods: Five electronic databases were searched. Intervention trials that assessed the effect of ≥2 different exercise intensities on peripheral markers of chronic inflammation [c-reactive protein (CRP), interleukin (IL)-6, tumour necrosis factor (TNF)-α and IL-10] in adults were included. Random-effect meta-analyses were conducted to calculate the mean difference in change scores between groups [effect size (ES)]. Sub-group analyses were performed to explore the influence of age, chronic disease, body mass index and intervention duration on inflammation heterogeneity. Results: Of 3952 studies identified, 27 were included. There were no significant effects of exercise intensity on IL-6 (ES=-0.039, 95%CI=-0.353–0.275; p = 0.806), TNF-α (ES = 0.296, 95%CI=-0.184–0.777; p = 0.227) and IL-10 (ES = 0.007, 95%CI=-0.904–0.919; p = 0.987). A significant pooled ES was observed for higher- versus lower-intensity exercise on CRP concentrations, in studies of middle-aged adults (ES=-0.412, 95%CI=-0.821– -0.004, p = 0.048) or interventions >9 weeks in duration (ES=-0.520, 95%CI=-0.882–-0.159, p = 0.005). Conclusions: Exercise intensity did not influence chronic inflammatory response. However, sub-analyses suggest that higher-intensity training may be more efficacious than lower-intensity for middle-aged adults, or when longer duration interventions are implemented (>9 weeks), in the most commonly-reported analyte (CRP).