Effects of High-Intensity Interval Training on Cardiorespiratory Fitness in Adults with Type 2 Diabetes

Abstract

Abstract Background and Objective: High-intensity interval training (HIIT) has emerged as a time-efficient exercise modality with potential cardiometabolic benefits in clinical populations. However, the magnitude of its effects on cardiorespiratory fitness, as measured by peak oxygen uptake (VO2peak), in adults with type 2 diabetes mellitus (T2DM) remains incompletely characterized. This systematic review and meta-analysis aimed to quantify the effects of HIIT on VO2peak in adults with T2DM and to identify moderating variables associated with training response. Review Methods: A systematic search of PubMed, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials was conducted from database inception to December 2025. Randomized controlled trials (RCTs) comparing HIIT to a control condition (no exercise, usual care, or moderate-intensity continuous training) in adults with T2DM and reporting VO2peak as an outcome were eligible for inclusion. Study selection, data extraction, and risk of bias assessment using the Cochrane Risk of Bias tool (RoB 2) were conducted independently by two reviewers. A random-effects meta-analysis was performed, with heterogeneity assessed using the I² statistic. Subgroup analyses were conducted by control condition, HIIT protocol, and intervention duration. Results: Fourteen RCTs involving 521 participants met the inclusion criteria. HIIT was associated with a significant improvement in VO2peak compared to control conditions (standardized mean difference [SMD] = 0.68, 95% CI: 0.45–0.91, p < 0.001), with moderate heterogeneity (I² = 52%). Subgroup analyses indicated that HIIT produced greater improvements in VO2peak compared to no-exercise controls (SMD = 0.84) than compared to moderate-intensity continuous training (SMD = 0.41). Intervention duration of twelve weeks or longer was associated with larger effect sizes. No serious adverse events related to HIIT were reported across included studies. Conclusions: HIIT produces clinically meaningful improvements in cardiorespiratory fitness in adults with T2DM and appears to be safe in this population. These findings support the inclusion of HIIT as a component of exercise programming for individuals with T2DM, particularly when time efficiency is a priority. Future research should examine the long-term sustainability of HIIT adherence and its effects on glycaemic control and cardiovascular outcomes in larger, more diverse samples.