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High-intensity interval training (HIIT) is an emerging exercise strategy to improve health and fitness, but previous studies have evaluated HIIT interventions across different populations and outcomes. This review aimed to comprehensively synthesize published evidence on the effects of HIIT on key cardiometabolic health parameters in children and adolescents. We searched seven databases until February 2024. Systematic reviews were eligible if they 1) compared HIIT and active/non-active control conditions with meta-analysis, 2) examined cardiorespiratory fitness, body composition and cardiometabolic risk biomarkers, and 3) examined children and adolescents. We included 18 systematic reviews with meta-analysis, including 223 original studies and 13,900 unique participants. HIIT is effective for cardiorespiratory fitness in children and adolescents with diverse health and weight status (median standardized mean difference [SMD] = 0.75). Improvements in body composition and several cardiometabolic risk biomarkers, including systolic blood pressure (median SMD = -0.40), diastolic blood pressure (median SMD = -0.22), triglyceride (median SMD = -0.30), low-density lipoprotein cholesterol (median SMD = -0.90), and high-density lipoprotein cholesterol (median SMD = 0.34), have also been observed following HIIT, with a notably more pronounced effect in youth with overweight/obesity or metabolic disorders. Our umbrella review supports the effectiveness of HIIT in enhancing cardiometabolic health, suggesting its integration into physical activity promotion programmes in schools and communities.

Background: Although the efficacy of interval training for improving body composition has been summarized in an increasing number of systematic reviews in recent years, discrepancies in review findings and conclusions have been observed., Objective: This study aims to synthesize the available evidence on the efficacy of interval training compared with moderate-intensity continuous training (MICT) and nonexercise control (CON) in reducing body adiposity in apparently healthy adults., Methods: An umbrella review with meta-analysis was performed. A systematic search was conducted in seven databases (MEDLINE, EMBASE, Cochrane Database, CINAHL, Scopus, SPORTDiscus, and Web of Science) up to October 2023. Systematic reviews with meta-analyses of randomized controlled trials (RCTs) comparing interval training and MICT/CON were included. Literature selection, data extraction, and methodological quality assessment (AMSTAR-2) were conducted independently by two reviewers. Meta-analyses were performed using a random-effects model. Subgroup analyses were conducted based on the type of interval training [high-intensity interval training (HIIT) and sprint interval training (SIT)], intervention duration, body mass index, exercise modality, and volume of HIIT protocols., Results: Sixteen systematic reviews, including 79 RCTs and 2474 unique participants, met the inclusion criteria. Most systematic reviews had a critically low (n = 6) or low (n = 6) AMSTAR-2 score. Interval training demonstrated significantly greater reductions in total body fat percent (BF%) compared with MICT [weighted mean difference (WMD) of - 0.77%; 95% confidence interval (CI) - 1.12 to - 0.32%] and CON (WMD of - 1.50%; 95% CI - 2.40 to - 0.58%). Significant reductions in fat mass, visceral adipose tissue, subcutaneous abdominal fat, and android abdominal fat were also observed following interval training compared to CON. Subgroup analyses indicated that both HIIT and SIT resulted in superior BF% loss than MICT. These benefits appeared to be more prominent in individuals with overweight/obesity and longer duration interventions (≥ 12 weeks), as well as in protocols using cycling as a modality and low-volume HIIT (i.e., < 15 min of high-intensity exercise per session)., Conclusions: This novel umbrella review with large-scale meta-analysis provides an updated synthesis of evidence with implications for physical activity guideline recommendations. The findings support interval training as a viable exercise strategy for reducing adiposity in the general population., Competing Interests: Declarations Funding This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Conflict of interest All authors have no conflicts of interest to disclose. Availability of data and material The datasets analyzed in this review are available from the corresponding author on reasonable request. Code availability Not applicable. Author contributions E.P., J.L., S.W., and R.H. conceived the idea for the review. E.P., J.L., and R.H. conducted the search, study selection, data extraction, and quality assessment. E.P., J.L., and R.H. drafted the initial manuscript. E.P., J.L., and R.H. contributed to writing the manuscript. All authors reviewed and approved the final manuscript., (© 2024. The Author(s).)

Background: Time-restricted eating (TRE) is increasingly popular, but its benefits in combination with exercise still need to be determined., Objectives: This systematic review and meta-analysis aimed to evaluate the efficacy of TRE combined with exercise compared with control diet with exercise in improving the body composition and metabolic health of adults., Methods: Five electronic databases were searched for relevant studies. Randomized controlled trials (RCTs) examining the effect of TRE combined with exercise on body composition and metabolic health in adults were included. All results in the meta-analysis are reported as mean difference (MD) with 95% confidence interval (CI). Study quality was assessed using the revised Cochrane Risk of Bias Tool and Grading of Recommendations Assessment, Development, and Evaluation assessment., Results: In total, 19 RCTs comprising 568 participants were included in this systematic review and meta-analysis. TRE combined with exercise likely reduced the participants' body mass (MD: -1.86 kg; 95% CI: -2.75, -0.97 kg) and fat mass (MD: -1.52 kg; 95% CI: -2.07, -0.97 kg) when compared with the control diet with exercise. In terms of metabolic health, the TRE combined with exercise group likely reduced triglycerides (MD: -13.38 mg/dL, 95% CI: -21.22, -5.54 mg/dL) and may result in a reduction in low-density lipoprotein (MD: -8.52 mg/dL; 95% CI: -11.72, -5.33 mg/dL) and a large reduction in leptin (MD: -0.67 ng/mL; 95% CI: -1.02, -0.33 ng/mL). However, TRE plus exercise exhibited no additional benefit on the glucose profile, including fasting glucose and insulin, and other lipid profiles, including total cholesterol and high-density lipoprotein concentrations, compared with the control group., Conclusions: Combining TRE with exercise may be more effective in reducing body weight and fat mass and improving lipid profile than control diet with exercise. Implementing this approach may benefit individuals aiming to achieve weight loss and enhance their metabolic well-being. This study was registered in PROSPERO as CRD42022353834., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)