The present meta-analysis aimed to assess the effects of low-volume high-intensity interval training (LV-HIIT; i.e., ≤5 min high-intensity exercise within a ≤15 min session) on cardiometabolic health and body composition. A systematic search was performed in accordance with PRISMA guidelines to assess the effect of LV-HIIT on cardiometabolic health and body composition. Twenty-one studies (moderate to high quality) with a total of 849 participants were included in this meta-analysis. LV-HIIT increased cardiorespiratory fitness (CRF, SMD = 1.19 [0.87, 1.50]) while lowering systolic blood pressure (SMD = −1.44 [−1.68, −1.20]), diastolic blood pressure (SMD = −1.51 [−1.75, −1.27]), mean arterial pressure (SMD = −1.55 [−1.80, −1.30]), MetS z-score (SMD = −0.76 [−1.02, −0.49]), fat mass (kg) (SMD = −0.22 [−0.44, 0.00]), fat mass (%) (SMD = −0.22 [−0.41, −0.02]), and waist circumference (SMD = −0.53 [−0.75, −0.31]) compared to untrained control (CONTROL). Despite a total time-commitment of LV-HIIT of only 14%–47% and 45%–94% compared to moderate-intensity continuous training and HV-HIIT, respectively, there were no statistically significant differences observed for any outcomes in comparisons between LV-HIIT and moderate-intensity continuous training (MICT) or high-volume HIIT. Significant inverse dose–responses were observed between the change in CRF with LV-HIIT and sprint repetitions ( β = −0.52 [−0.76, −0.28]), high-intensity duration ( β = −0.21 [−0.39, −0.02]), and total duration ( β = −0.19 [−0.36, −0.02]), while higher intensity significantly improved CRF gains. LV-HIIT can improve cardiometabolic health and body composition and represent a time-efficient alternative to MICT and HV-HIIT. Performing LV-HIIT at a higher intensity drives higher CRF gains. More repetitions, longer time at high intensity, and total session duration did not augment gains in CRF.

The aims of this study were (1) to determine how stair-climbing-based exercise snacks (ES) compared to moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness (CRF), and (2) to explore whether ES could improve maximal fat oxidation rate (MFO) in inactive adults. Healthy, young, inactive adults ( n: 42, age: 21.6 ± 2.3 years, BMI: 22.5 ± 3.6 kg·m⁻², peak oxygen uptake (VO₂peak): 33.6 ± 6.3 mL·kg⁻¹·min⁻¹) were randomly assigned to ES, MICT, or Control. ES ( n = 14) and MICT ( n = 13) groups performed three sessions per week over 6 weeks, while the control group ( n = 15) maintained their habitual lifestyle. ES involved 3 × 30 s “all-out” stair-climbing (6 flight, 126 steps, and 18.9 m total height) bouts separated by >1 h rest, and MICT involved 40 min × 60%–70% HR_max stationary cycling. A significant group × time interaction was found for relative VO₂peak ( p < 0.05) with ES significantly increasing by 7% compared to baseline (MD = 2.5 mL·kg⁻¹·min⁻¹ (95% CI = 1.2, 3.7), Cohen’s d = 0.44), while MICT had no significant effects (MD = 1.0 mL·kg⁻¹·min⁻¹ (−1.1, 3.2), Cohen’s d = 0.17), and Control experienced a significant decrease (MD = −1.7 mL·kg⁻¹·min⁻¹ (−2.9, −0.4), Cohen’s d = 0.26). MFO was unchanged among the three groups (group × time interaction, p > 0.05 for all). Stair climbing-based ES are a time-efficient alternative to MICT for improving CRF among inactive adults, but the tested ES intervention appears to have limited potential to increase MFO.

To (1) systematically review the chronic effect of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on maximal fat oxidation (MFO) in overweight and obese adults, and (2) explore MFO influencing factors and its dose-response relationships with HIIT and MICT. Studies using a between-group design involving overweight and obese adults and assessing the effect of HIIT and MICT on MFO were included. A meta-analysis on MFO indices was conducted, and the observed heterogeneities were explored through subgroup, regression, and sensitivity analyses. Thirteen studies of moderate to high quality with a total of 519 overweight and obese subjects were included in this meta-analysis (HIIT, n = 136; MICT, n = 235; Control, n = 148). HIIT displayed a statistically significant favorable effect on MFO compared to no-training (MD = 0.07; 95%CI [0.03 to 0.11]; I² = 0%). Likewise, MICT displayed a statistically significant favorable effect on MFO compared to no-training (MD = 0.10; 95%CI [0.06 to 0.15]; I² = 95%). Subgroup and regression analyses revealed that exercise intensity (Fat_max vs. non-Fat_max; %VO₂peak), exercise mode, BMI, and VO₂peak all significantly moderated MICT on MFO. When analyzing studies that have directly compared HIIT and MCIT in obese people, it seems there is no difference in the MFO change (MD = 0.01; 95%CI [-0.02 to 0.04]; I² = 64%). No publication bias was found in any of the above meta-analyses (Egger's test p > 0.05 for all). Both HIIT and MICT are effective in improving MFO in overweight and obese adults, and they have similar effects. MCIT with an intensity of 65–70% VO₂peak, performed 3 times per week for 60 min per session, will optimize MFO increases in overweight and obese adults. Given the lack of studies examining the effect of HIIT on MFO in overweight and obese adults and the great diversity in the training protocols in the existing studies, we were unable to make sound recommendations for training.