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PubMed2026

Optimising Exercise Prescription: A Meta-Analysis Examining the Dose Response of Exercise Duration on Cardiorespiratory Fitness Following HIIT and MICT.

BACKGROUND: High-intensity interval training (HIIT) is often promoted as a time-efficient alternative to moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness, yet the duration of HIIT sessions varies considerably across studies. OBJECTIVE: We aimed to characterise the dose-response relationship between exercise session duration and the improvement in cardiorespiratory fitness for HIIT and MICT. METHODS: A dose-response meta-analysis of randomised controlled trials comparing exercise duration in HIIT and MICT, following Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and registered in PROSPERO (CRD42022335590). Effect sizes were calculated using a random-effects meta-analysis. The primary outcome was maximal oxygen uptake (VO2max). Secondary outcomes included blood pressure, lipid profiles, glucose metabolism markers and body composition measures. A one-stage random-effects dose-response meta-analysis was performed to examine the relationship between exercise duration and adaptations. We searched PubMed and Google Scholar; eligibility criteria for selecting studies were randomised controlled trials in humans, published in English and exercise interventions lasting at least 4 weeks. RESULTS: We identified 69 randomised controlled trials (2387 participants). High-intensity interval training elicited greater improvements in VO2max than MICT (d = 0.38, 95% confidence interval 0.27-0.49, p < 0.001). High-intensity interval training demonstrated a non-linear dose-response relationship between exercise session duration and VO2max, with 80% of maximal effect (changes in VO2max = 3.45 mL/kg/min) achieved with only ~11 min/session (95% confidence interval 9.5-40.2). Moderate-intensity interval training showed a linear dose-response relationship between exercise session duration and VO2max, requiring ~52 min/session to achieve 80% of the maximal observed effect (95% confidence interval 30.4-55.8). The dose-response relationship was consistent across populations. High-intensity interval training and MICT had comparable effects in improving cardiometabolic risk factors. CONCLUSIONS: High-intensity interval training demonstrated a non-linear dose response, with 80% of maximal effect on VO2max in ~11 min/session, whilst MICT required four to five times longer to reach similar responses. The different types of training had comparable effects on cardiometabolic risk factors.

Journal Article↗

PubMed2026

All eyes on gas exchange: impact of controlled arterial hypertension on cardiopulmonary function and the effects of high-intensity interval training.

INTRODUCTION: Arterial hypertension (AH) impairs vascular function which, in turn, may reduce cardiopulmonary function. However, the impact of AH on cardiorespiratory fitness (CRF) and its potential mechanisms remains insufficiently investigated. We compared cardiopulmonary function during exercise testing (CPET) between adults with and without AH (part 1) and evaluated the effects of high-intensity interval training (HIIT) in adults with AH on submaximal cardiopulmonary CPET parameters (part 2). METHODS: Thirty-eight adults with AH and 19 controls without AH partook in the study. Adults with AH were randomized into either HIIT or a control group. CPET assessed CRF and submaximal exercise parameters, including the oxygen uptake efficiency slope (OUES), V̇E/V̇CO 2 slope, PETCO 2 , V̇O 2 /work rate (WR) slope, and O 2 pulse. The HIIT intervention consisted of triweekly sessions over 8 weeks. RESULTS: Adults with AH had a 6.5 ml kg -1  min -1 (95% confidence interval: 1.7-11.3) lower CRF, a steeper V̇E/V̇CO 2 slope (moderate-large effect size), lower PETCO 2 (large effect size), flatter V̇O 2 /WR slope (moderate effect size), and lower O 2 pulse (small-moderate effect size) than adults without AH. HIIT improved CRF and altered certain cardio-circulatory parameters in AH, including OUES (small-large effect size), V̇O 2 /WR slope (small-moderate effect size, low precision) and O 2 pulse (small-moderate effect size). However, effects of HIIT on pulmonary-vascular parameters were inconclusive, with large variability observed in the V̇E/V̇CO 2 slope and PETCO 2 . CONCLUSION: Adults with controlled AH might have lower CRF, indicating limitations in pulmonary-vascular and cardio-circulatory organ systems. A short-term 8-week HIIT enhances CRF and cardio-circulatory function, however, evidence is limited for improvements in pulmonary-vascular function.

Humans↗

PubMed2026

Application of 13C MRS demonstrates carbohydrate feeding spares muscle but not liver glycogen utilization during high-intensity interval exercise.

We examined liver and muscle glycogen utilization during high-intensity interval cycling, and the impact of carbohydrate (CHO) feeding, using noninvasive 13C magnetic resonance spectroscopy (MRS). Following 24 h of standardized dietary intake, nine male cyclists completed 8 × 5-min intervals (1-min recovery), ingesting either placebo (PLA), 60 g maltodextrin (CHO), or 60 g maltodextrin plus caffeine, taurine, l-theanine, l-citrulline, and citicoline (CHO+) in a randomized crossover design. 13C MRS and 1H imaging were performed pre- and postexercise to determine liver and muscle glycogen and liver volume, respectively. Liver glycogen utilization was not significantly different between trials (P = 0.101) despite lower postexercise plasma glucagon concentrations in CHO and CHO+ (P = 0.001). In contrast, muscle glycogen utilization was significantly lower (∼40%) with CHO feeding compared with PLA (P = 0.006), yet this sparing effect was not evident with CHO+ (P = 0.073) in accordance with a higher mean power output during the late intervals (+2.8%, P = 0.046). Plasma glucose was comparable between trials (P = 0.175), whereas plasma lactate was higher in CHO+ versus CHO (P = 0.003), alongside lower blood bicarbonate (P = 0.005), base excess (P < 0.001), and total CO2 (P = 0.004). These findings demonstrate preferential use of skeletal muscle glycogen during high-intensity interval training (HIIT), which is attenuated under conditions of CHO feeding. This sparing effect is, however, not evident with the coingestion of a caffeine-containing multi-ingredient blend, potentially due to an increased capacity to sustain higher power outputs resulting in greater glycogen utilization.NEW & NOTEWORTHY Using 13C MRS, we provide data demonstrating preferential use of skeletal muscle glycogen during HIIT. Furthermore, data show muscle glycogen utilization is attenuated with CHO feeding, yet sparing is not evident when coingesting a caffeine-containing formulation, potentially reflecting increased capacity to perform more total work rather than a direct metabolic effect of caffeine. In contrast, liver glycogen utilization was not significantly different with CHO feeding despite a modest reduction of ∼5 g versus placebo.

Male↗

PubMed2026

Optimal dose and exercise modality to improve HbA1c in older adults with type 2 diabetes mellitus: a systematic review with pairwise, network, and dose-response meta-analyses.

We aimed to compare exercise modalities and evaluate dose-response relationships with glycemic control including continuous aerobic exercise (CAE), resistance training (RT), combined exercise (CE), mind-body exercise (MBE), and high-intensity interval training (HIIT) in older adults with type 2 diabetes mellitus (T2DM). Three databases were searched for randomized controlled trials of exercise interventions in older adults with T2DM reporting glycated hemoglobin (HbA1c). Pairwise, Bayesian network, and dose-response meta-analyses were conducted. Compared with control, HIIT demonstrated the largest estimated reduction (MD = -0.95%; 95% CrI -1.45, -0.49), followed by CE (MD = -0.59%; 95% CrI -0.93, -0.25), CAE (MD = -0.46%; 95% CrI -0.69, -0.24), MBE (MD = -0.42%; 95% CrI -0.76, -0.10), and RT (MD = -0.29%; 95% CrI -0.51, -0.08). Dose-response network meta-analyses suggested a non-linear association between overall exercise dose and HbA1c reduction, with maximal estimated benefits at approximately 704 METs-min/week with the 95% CrI excluding zero between 241 and 920 METs-min/week. HIIT demonstrated the steepest estimated dose-response relationship, but with wider credible intervals. Other exercise modalities showed more gradual dose-response patterns across their estimated effective ranges. Our findings suggest that exercise prescription for older adults with T2DM should be individualized according to exercise modality, dose, and health status.

Humans↗

PubMed2026

Exploring the role of successful exercise-induced body weight loss on cardiometabolic health in individuals with metabolic syndrome.

BACKGROUND AND AIM: High-intensity interval training (HIIT) is known to improve cardiorespiratory fitness (i.e., VO2MAX), a key marker of cardiometabolic health in individuals with metabolic syndrome (MetS). Nonetheless, body weight loss is widely recognized as a crucial factor in reducing insulin resistance and improving metabolic risk factors. Thus, we aimed to determine the importance of body weight loss following exercise training on improving MetS. METHODS AND RESULTS: Two hundred and twenty-eight adults (55.3 ± 7.9 yr) with overweight/obesity (32.5 ± 4.6 kg·m-2) and MetS were randomized to: a) standard health care non-exercise group (CONTROL group, N=58) or b) standard health care plus 16 weeks of HIIT (EXER group, N=170). MetS (MetS z-score), insulin resistance (HOMA-IR), cardiorespiratory fitness (VO2PEAK), maximal cycling power (WPEAK), and body weight/composition were assessed. After intervention, EXER group participants were divided according to their weight loss response to training: i) those achieving the weight loss predicted from estimated exercise energy expenditure (-BW group, n=78; -3.3 ± 2.2 kg); ii) those not reaching the expected weight loss (=BW group, n=38; -0.7 ± 0.5 kg); iii) and those who gained weight (+BW group, n=54; 1.1 ± 1.0 kg). VO2PEAK significantly improved regardless of body weight loss response (-BW, 0.3 ± 0.3; =BW, 0.2 ± 0.3; +BW, 0.3 ± 0.2 L·min-1; all p < 0.001) compared to CONTROL group (0.0 ± 0.3 L·min-1). However, significant improvements in MetS z-score (-0.31 ± 0.41) and HOMA-IR (-0.7 ± 1.6) were observed only in the -BW group (both p < 0.001). CONCLUSIONS: Exercise recommendations should consider that greater improvements in MetS are observed when interventions are accompanied by successful body weight loss. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05120778.

Humans↗