The effects of high-intensity interval training on glucose regulation and insulin resistance: A meta-analysis

The aim of this meta-analysis was to quantify the effects of high-intensity interval training (HIIT) on markers of glucose regulation and insulin resistance compared with control conditions (CON) or continuous training (CT). Databases were searched for HIIT interventions based upon the inclusion criteria: training ≥2 weeks, adult participants and outcome measurements that included insulin resistance, fasting glucose, HbA1c or fasting insulin. Dual interventions and participants with type 1 diabetes were excluded. Fifty studies were included. There was a reduction in insulin resistance following HIIT compared with both CON and CT (HIIT vs. CON: standardized mean difference [SMD]=-0.49, confidence intervals [CIs] -0.87 to -0.12, P=0.009; CT: SMD=-0.35, -0.68 to -0.02, P=0.036). Compared with CON, HbA1c decreased by 0.19% (-0.36 to -0.03, P=0.021) and body weight decreased by 1.3kg (-1.9 to -0.7, P<0.001). There were no statistically significant differences between groups in other outcomes overall. However, participants at risk of or with type 2 diabetes experienced reductions in fasting glucose (-0.92mmolL^-1, -1.22 to -0.62, P<0.001) compared with CON. HIIT appears effective at improving metabolic health, particularly in those at risk of or with type 2 diabetes. Larger randomized controlled trials of longer duration than those included in this meta-analysis are required to confirm these results.