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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.

Low physical fitness in childhood is linked with poor health now and in later life. This study estimated temporal trends in physical fitness for Hong Kong children aged 6-12 years from 2003-04 to 2015-16. Objectively measured body size and physical fitness data for 27,513 children were obtained from four population-representative surveys of Hong Kong primary school students. Temporal trends in means were estimated by population-weighted linear regression. Trends in distributional characteristics were visually described. Overall, there was a small increase in mean height (effect size (ES) = 0.20 (95%CI: 0.13, 0.28)), with a negligible increase (ES < 0.2) in mean body mass. When adjusted for trends in age, gender, and body size, there was a small decline in sit-and-reach performance (ES = -0.43 (95%CI: -0.43, -0.42)), a small improvement in 9-min run/walk performance (9-to-12-year-olds, ES = 0.26 (95%CI: 0.26, 0.27)), with negligible declines in handgrip strength, 6-min run/walk (6-to 8-year-olds), and sit-ups performance. Temporal trends were not always uniform across the population distribution, with declines in run/walk, sit-ups, and sit-and-reach performance generally largest in children with low fitness. Increased national health promotion strategies that address culturally specific factors are encouraged to further improve the existing trends, especially for children with low fitness.

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.

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.

Weight-making practices have been shown to impair musculoskeletal and physiological function of jockeys. This study investigated the "in-race" heart rate (HR) responses and hydration status during competitive racing, as well as selected physiological and lifestyle parameters of professional jockeys based in Hong Kong. "In-race" HR responses and early morning hydration status of 20 male jockeys were examined in hot and moderate climactic occasions. Additionally, bone mineral density (BMD), dietary intake and lifestyle choices were assessed. Osteopenia was observed in the calcanei of jockeys (left: 0.51 ± 0.06; right: 0.46 ± 0.12 g · cm -2 ). Energy and protein intake were significantly lower on a race day compared to a non-race day (P < 0.05). "In-race" HR max values were similar to those from VO 2max laboratory tests (186 ± 14 vs. 185 ± 8 bpm). Hypohydration was observed on both racing days. (USG: 1.0247 ± 0.006 and 1.0256 ± 0.0258 mg · L -1 for hot and moderate conditions, respectively). Sauna usage (25.5%) and food restriction (20.4%) were the most common weight-making practices. Current lifestyle choices of jockeys result in suboptimal bone health, hydration status and nutritional intake, which can significantly enhance the fracture risk. Further research should develop exercise and nutrition guidelines for optimising their skeletal health.