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

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).

The influence of training characteristics on the effect of exercise training in patients with coronary artery disease: Systematic review and meta-regression analysis

BACKGROUND

Although exercise-based cardiac rehabilitation improves exercise capacity of coronary artery disease patients, it is unclear which training characteristic determines this improvement. Total energy expenditure and its constituent training characteristics (training intensity, session frequency, session duration and programme length) vary considerably among clinical trials, making it hard to compare studies directly. Therefore, we performed a systematic review and meta-regression analysis to assess the effect of total energy expenditure and its constituent training characteristics on exercise capacity.

METHODS

We identified randomised controlled trials comparing continuous aerobic exercise training with usual care for patients with coronary artery disease. Studies were included when training intensity, session frequency, session duration and programme length was described, and exercise capacity was reported in peakVO₂. Energy expenditure was calculated from the four training characteristics. The effect of training characteristics on exercise capacity was determined using mixed effects linear regression analyses. The analyses were performed with and without total energy expenditure as covariate.

RESULTS

Twenty studies were included in the analyses. The mean difference in peakVO₂ between the intervention group and control group was 3.97ml·min^-1·kg^-1 (p<0.01, 95% CI 2.86 to 5.07). Total energy expenditure was significantly related to improvement of exercise capacity (effect size 0.91ml·min^-1·kg^-1 per 100J·kg, p<0.01, 95% CI 0.77 to 1.06), no effect was found for its constituent training characteristics after adjustment for total energy expenditure.

CONCLUSIONS

We conclude that the design of an exercise programme should primarily be aimed at optimising total energy expenditure rather than on one specific training characteristic.