Interval training has been promoted as a superior, time-efficient exercise strategy for enhancing cardiorespiratory fitness in the ageing population. This study assessed the effectiveness of interval training compared with that of moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness in middle-aged and older adults. Six databases were systematically searched for studies with exercise interventions (minimum 2-week duration). Meta-analyses were conducted for within-group and between-group comparisons of maximal oxygen uptake (VO_2max). Sub-group analysis was performed using the nature of interval training (high-intensity interval training [HIIT] and sprint interval training [SIT]). Of 3,257 studies, 14 were included (429 participants). Within–group analyses demonstrated significant VO_2max improvements (mL/kg/min) following interval training (mean difference: MD = 2.26; 95% confidence interval [CI] = 1.50–3.02) and MICT (MD = 1.34; 95% CI = 0.45–2.23]. When comparing the modes of training, the gain in VO_2max was significantly greater following interval training (MD = 1.10; CI = 0.55-1.64). Sub–group analysis showed that HIIT (MD = 1.04; CI = 0.21–1.88) and SIT (MD = 1.18; CI = 0.60-1.76) resulted in superior VO_2max gain than MICT. This study provides evidence synthesis for interval training as a viable exercise strategy to improve cardiorespiratory function in healthy ageing.

Background: High‐intensity interval training (HIIT) is characterized by repeated bouts of relatively intense exercise interspersed with recovery periods. Previous studies have evaluated this exercise strategy with various population subgroups, regimens, and comparator groups, limiting the generalizability of findings. We performed a novel umbrella review to generate an up‐to‐date synthesis of the available evidence regarding the effect of HIIT on cardiorespiratory fitness (CRF) in adults as compared to non‐exercise control and traditional continuous forms of exercise such as moderate‐intensity continuous training (MICT).Methods: An umbrella review was conducted in accordance with the Preferred Reporting Items for Overviews of Reviews guideline. Seven databases (MEDLINE, EMBASE, Cochrane Database, CINAHL, Scopus, SPORTDiscus, and Web of Science) were searched until February 2024. Systematic reviews with meta‐analyses comparing HIIT and active/non‐active control conditions were included. Literature search, data extraction, and methodological quality assessment (AMSTAR‐2) were conducted independently by two reviewers.Results: Twenty‐four systematic reviews with meta‐analyses, representing 429 primary studies and 12 967 unique participants, met the inclusion criteria. Most of the systematic reviews received moderate‐to‐critically low AMSTAR‐2 scores. The data showed that HIIT, including the particularly intense variant “sprint interval training” (SIT), significantly increases CRF in adults compared to non‐exercise control (standardized mean difference [SMD]: 0.28 to 4.31; weighted mean difference [WMD]: 3.25 to 5.5 mL/kg/min) and MICT (SMD: 0.18 to 0.99; WMD: 0.52 to 3.76 mL/kg/min). This effect was consistently observed across specific groups of individuals (e.g., apparently healthy adults, individuals with overweight/obesity, older adults, and high‐level athletes) and HIIT modalities (e.g., low‐volume HIIT, whole‐body HIIT, home‐based HIIT, aquatic HIIT, and short SIT).Conclusion: Existing evidence from systematic reviews consistently supports the effect of HIIT on enhancing CRF in adults when compared to non‐exercise control and MICT. Our findings offer a comprehensive basis that may potentially contribute to informing physical activity guidelines aimed at improving CRF in the general population.

Objective To assess the effectiveness of high-intensity interval training (HIIT) compared with traditional moderate-intensity continuous training (MICT) and/or non-exercise control (CON) for modification of metabolic syndrome (MetS) components and other cardiometabolic health outcomes in individuals with MetS. Design Systematic review and meta-analysis Data sources Five databases were searched from inception to March 2024. Study appraisal and synthesis Meta-analyses of randomised controlled trials (RCTs) comparing HIIT with MICT/CON were performed for components of MetS (waist circumference (WC), systolic blood pressure (SBP), diastolic blood pressure (DBP), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), and fasting blood glucose (BG)) and clinically relevant cardiometabolic health parameters. Subgroup moderator analyses were conducted based on the intervention duration and HIIT volume. Results Out of 4819 studies, 23 RCTs involving 1374 participants were included (mean age: 46.2–67.0 years, 55% male). HIIT significantly improved WC (weighted mean difference (WMD) –4.12 cm, 95% CI –4.71 to –3.53), SBP (WMD –6.05 mm Hg, 95% CI –8.11 to –4.00), DBP (WMD –3.68 mm Hg, 95% CI –5.70 to –1.65), HDL-C (WMD 0.12 mmol/L, 95% CI 0.04 to 0.20), TG (WMD –0.34 mmol/L, 95% CI –0.41 to –0.27) and BG (WMD –0.35 mmol/L, 95% CI –0.54 to –0.16) compared with CON (all p<0.01). HIIT approaches demonstrated comparable effects to MICT across all parameters. Subgroup analyses suggested that HIIT protocols with low volume (ie, <15 min of high-intensity exercise per session) were not inferior to higher volume protocols for improving MetS components. Conclusion This review supports HIIT as an efficacious exercise strategy for improving cardiometabolic health in individuals with MetS. Low-volume HIIT appears to be a viable alternative to traditional forms of aerobic exercise.

High-intensity interval training (HIIT) has been proposed as a time-efficient exercise protocol to improve metabolic health, but direct comparisons with higher-volume moderate-intensity continuous training (MICT) under unsupervised settings are limited. This study compared low-volume HIIT and higher-volume MICT interventions on cardiometabolic and psychological responses in overweight/obese middle-aged men. Twenty-four participants (age: 48.1±5.2yr; BMI: 25.8±2.3kg·m⁻²) were randomly assigned to undertake either HIIT (10 X 1-min bouts of running at 80–90% HR_max separated by 1-min active recovery) or MICT (50-min continuous jogging/brisk walking at 65–70% HR_max) for 3 sessions/week for 8 weeks (2-week supervised + 6-week unsupervised training). Both groups showed similar cardiovascular fitness (VO_2max) improvement (HIIT: 32.5±5.6 to 36.0±6.2; MICT: 34.3±6.0 to 38.2±5.1mL kg⁻¹ min⁻¹, p < 0.05) and %fat loss (HIIT: 24.5±3.4 to 23.2±3.5%; MICT: 23.0±4.3 to 21.5±4.1%, p< 0.05) over the 8-week intervention. Compared to baseline, MICT significantly decreased weight and waist circumference. No significant group differences were observed for blood pressure and cardiometabolic blood markers such as lipid profiles, fasting glucose and glycated haemoglobin. Both groups showed similar enjoyment levels and high unsupervised adherence rates (>90%). Our findings suggest that low-volume HIIT can elicit a similar improvement of cardiovascular fitness as traditional higher-volume MICT in overweight/obese middle-aged men.

High-intensity interval training (HIIT) or moderate-intensity continuous training (MICT) alone has been shown to improve metabolic health, but the effects of alternating the two training approaches as often practiced in real life remained unclear. To examine the effects of HIIT or MICT alone or alternating HIIT-MICT on cardiometabolic responses in inactive obese middle-aged men. Forty-two participants (age: 42 ± 5 y; BMI: 26.3 ± 2.1 kg m⁻²) were randomly assigned to four groups: HIIT (12 x 1-min running bouts at 80–90% HR_max interspersed with 1-min active recovery at 50% HR_max), MICT (40-min brisk walk at 65–70% HR_max), alternating HIIT-MICT or a non-exercise control group (CON). Exercise sessions were conducted three times per week for 16 weeks. Maximal oxygen uptake (VO_2max), body composition (by bioelectrical impedance analysis), blood pressure, fasting blood glucose, insulin resistance (HOMA-IR) and lipid profile were assessed at baseline and after the 16-week intervention. Enjoyment and self-efficacy were also assessed at the end of intervention. All exercise groups showed a similar VO_2max increase of ∼15% (HIIT: 34.3 ± 4.4 vs 39.1 ± 5.4; MICT: 34.9 ± 5.0 vs 39.4 ± 7.2; and alternating HIIT-MICT: 34.4 ± 5.0 vs 40.3 ± 4.6 mL kg⁻¹min⁻¹) compared to baseline and CON (all p < 0.05). Weight, BMI, % fat and waist circumference also showed similar reductions in all exercise groups compared to baseline and CON (all p < 0.05). No significant group difference was observed for all blood markers. Compared to baseline, total cholesterol decreased after HIIT-MICT, while HIIT significantly decreased fasting insulin level and improved insulin resistance (p < 0.05). Enjoyment, self-efficacy and adherence were similar among all exercise groups. HIIT or MICT alone or alternating HIIT-MICT similarly improve cardiovascular fitness and body composition in obese middle-aged men despite differences in total training volume and time commitment.

High‐intensity interval training (HIIT) has gained attention as a potentially effective alternative to traditional exercise modalities for individuals with type 2 diabetes mellitus (T2DM). Previous studies have evaluated this exercise strategy with various regimens, comparator groups and outcomes, limiting the generalisability of findings. We performed a novel umbrella review to generate an up‐to‐date synthesis of the available evidence regarding the effect of HIIT on glycaemic control and other clinically relevant cardiometabolic health outcomes in individuals with T2DM, as compared with traditional moderate‐intensity continuous training (MICT) and/or non‐exercise control (CON). This umbrella review followed the Preferred Reporting Items for Overviews of Reviews guideline. Seven databases were searched until August 2024. Systematic reviews with meta‐analyses comparing HIIT with MICT and/or CON were included. Literature search, data extraction and methodological quality assessment (A MeaSurement Tool to Assess systematic Reviews 2 [AMSTAR‐2]) were conducted independently by two reviewers. Ten systematic reviews with meta‐analyses, encompassing 76 primary studies and 2954 unique participants, met the inclusion criteria. The data indicated that HIIT significantly improves glycosylated haemoglobin and cardiorespiratory fitness compared with CON (weighted mean difference [WMD]: −0.83% to −0.39% and 3.35–6.38 mL/kg/min) and MICT (WMD: −0.37% to −0.07% and 1.68–4.12 mL/kg/min) in individuals with T2DM. HIIT is also effective in improving other glycaemic parameters, including fasting blood glucose, fasting blood insulin and HOMA‐IR. Improvement in body composition, lipid profiles and blood pressure has also been observed following HIIT. Most systematic reviews received moderate to low AMSTAR‐2 score. This umbrella review supports HIIT as an efficacious exercise strategy for improving glycaemic control and certain relevant cardiometabolic health outcomes in individuals with T2DM. Our findings offer a comprehensive basis that may potentially contribute to informing physical activity recommendations for incorporating HIIT into T2DM management strategies.