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 to control conditions (CON) or continuous training (CT). Databases were searched for HIIT interventions based on 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 to both CON & CT, (HIIT vs. CON: standardised mean difference (SMD)=-0.49, confidence intervals (CI) -0.87 to -0.12, p=0.009; CT: SMD=-0.35, -0.68 to -0.02, p=0.036). Compared to 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 with or at risk of Type 2 diabetes experienced reductions in fasting glucose (-0.92mmol.L-1, -1.22 to -0.62, p<0.001) compared to CON. HIIT appears effective at improving metabolic health, particularly in those at risk of or with Type 2 diabetes. Larger randomised controlled trials of longer duration than those included in this meta-analysis are required to confirm these results.