Physical activity lowers future cardiovascular disease (CVD) risk; however, few children and adolescents achieve the recommended minimum amount of daily activity. Accordingly, there is virtue in identifying the efficacy of small volumes of high-intensity exercise for health benefits in children and adolescents for the primary prevention of CVD risk. The purpose of this narrative review is to provide a novel overview of the available literature concerning high-intensity interval-exercise (HIIE) interventions in children and adolescents. Specifically, the following areas are addressed: 1) outlining the health benefits observed following a single bout of HIIE, 2) reviewing the role of HIIE training in the management of pediatric obesity, and 3) discussing the effectiveness of school-based HIIE training. In total, 39 HIIE intervention studies were included in this review. Based upon the available data, a single bout of high-intensity exercise provides a potent stimulus for favorable, acute changes across a range of cardiometabolic outcomes that are often superior to a comparative bout of moderate-intensity exercise (14 studies reviewed). HIIE also promotes improvements in cardiorespiratory fitness and cardiometabolic health status in overweight and obese children and adolescents (10 studies reviewed) and when delivered in the school setting (15 studies reviewed). We thus conclude that high-intensity exercise is a feasible and potent method of improving a range of cardiometabolic outcomes in children and adolescents. However, further work is needed to optimize the delivery of HIIE interventions in terms of participant enjoyment and acceptability, to include a wider range of health outcomes, and to control for important confounding variables (eg, changes in diet and habitual physical activity). Finally, research into the application of HIIE training interventions to children and adolescents of different ages, sexes, pubertal status, and sociocultural backgrounds is required.

Background: Impairments in macrovascular, microvascular and autonomic function are present in asymptomatic youths with clustered cardiovascular disease risk factors. This study determines the within-day reliability and between-day reliability of a single protocol to non-invasively assess these outcomes in adolescents. Methods: Forty 12- to 15-year-old adolescents (20 boys) visited the laboratory in a fasted state on two occasions, approximately 1 week apart. One hour after a standardized cereal breakfast, macrovascular function was determined via flow-mediated dilation (FMD). Heart rate variability (root mean square of successive R-R intervals; RMSSD) was determined from the ECG-gated ultrasound images acquired during the FMD protocol prior to cuff occlusion. Microvascular function was simultaneously quantified as the peak (PRH) and total (TRH) hyperaemic response to occlusion in the cutaneous circulation of the forearm via laser Doppler imaging. To address within-day reliability, a subset of twenty adolescents (10 boys) repeated these measures 90 min afterwards on one occasion. Results: the within-day typical error and between-day typical error expressed as a coefficient of variation of these outcomes are as follows: ratio-scaled FMD, 5·1% and 10·6%; allometrically scaled FMD, 4·4% and 9·4%; PRH, 11% and 13·3%; TRH, 29·9% and 23·1%; and RMSSD, 17·6% and 17·6%. The within- and between-day test–retest correlation coefficients for these outcomes were all significant (r > 0·54 for all). Conclusion: Macrovascular, microvascular and autonomic functions can be simultaneously and non-invasively determined in adolescents using a single protocol with an appropriate degree of reproducibility. Determining these outcomes may provide greater understanding of the progression of cardiovascular disease and aid early intervention.

Purpose to examine the influence of exercise intensity on postprandial health outcomes in adolescents when exercise is accumulated throughout the day. Methods 19 adolescents (9 male, 13.7 ± 0.4 years old) completed three 1-day trials in a randomised order: (1) rest (CON); or four bouts of (2) 2 × 1 min cycling at 90% peak power with 75 s recovery (high-intensity interval exercise; HIIE); or (3) cycling at 90% of the gas exchange threshold (moderate-intensity exercise; MIE), which was work-matched to HIIE. Each bout was separated by 2 hours. Participants consumed a high fat milkshake for breakfast and lunch. Postprandial triacylglycerol (TAG), glucose, systolic blood pressure (SBP) and fat oxidation were assessed throughout the day. Results There was no effect of trial on total area under the curve (TAUC) for TAG (P = 0.87). TAUC-glucose was lower in HIIE compared to CON (P = 0.03, ES = 0.42) and MIE (P = 0.04, ES = 0.41), with no difference between MIE and CON (P = 0.89, ES = 0.04). Postprandial SBP was lower in HIIE compared to CON (P = 0.04, ES = 0.50) and MIE (P = 0.04, ES = 0.40), but not different between MIE and CON (P = 0.52, ES = 0.11). Resting fat oxidation was increased in HIIE compared to CON (P = 0.01, ES = 0.74) and MIE (P = 0.05, ES = 0.51), with no difference between MIE and CON (P = 0.37, ES = 0.24). Conclusion Neither exercise trial attenuated postprandial lipaemia. However, accumulating brief bouts of HIIE, but not MIE, reduced postprandial plasma glucose and SBP, and increased resting fat oxidation in adolescent boys and girls. The intensity of accumulated exercise may therefore have important implications for health outcomes in youth.

Method: Twenty adolescents (10 male, 14.3 ± 0.3 years) completed three 1-day trials: (1) rest (CON); (2) 8 × 1 min cycling at 90 % peak power with 75 s recovery (HIIE); (3) cycling at 90 % of the gas exchange threshold (MIE), 1 h before consuming a high-fat milkshake (1.50 g fat and 80 kJ kg−1). Postprandial TAG, SBP and fat oxidation were assessed over 4 h

Acute exercise transiently improves endothelial function and protects the vasculature from the deleterious effects of a high-fat meal (HFM). We sought to identify whether this response is dependent on exercise intensity in adolescents. Twenty adolescents (10 male, 14.3 ± 0.3 yr) completed three 1-day trials: 1) rest (CON); 2) 8 × 1 min cycling at 90% peak power with 75 s recovery [high-intensity interval exercise (HIIE)]; and 3) cycling at 90% of the gas exchange threshold [moderate-intensity exercise (MIE)] 1 h before consuming a HFM (1.50 g/kg fat). Macrovascular and microvascular endothelial function was assessed before and immediately after exercise and 3 h after the HFM by flow-mediated dilation (FMD) and laser Doppler imaging [peak reactive hyperemia (PRH)]. FMD and PRH increased 1 h after HIIE [P < 0.001, effect size (ES) = 1.20 and P = 0.048, ES = 0.56] but were unchanged after MIE. FMD and PRH were attenuated 3 h after the HFM in CON (P < 0.001, ES = 1.78 and P = 0.02, ES = 0.59). FMD remained greater 3 h after the HFM in HIIE compared with MIE (P < 0.001, ES = 1.47) and CON (P < 0.001, ES = 2.54), and in MIE compared with CON (P < 0.001, ES = 1.40). Compared with CON, PRH was greater 3 h after the HFM in HIIE (P = 0.02, ES = 0.71) and MIE (P = 0.02, ES = 0.84), with no differences between HIIE and MIE (P = 0.72, ES = 0.16). Plasma triacylglycerol concentration and total antioxidant status concentration were not different between trials. We conclude that exercise intensity plays an important role in protecting the vasculature from the deleterious effects of a HFM. Performing HIIE may provide superior vascular benefits than MIE in adolescent groups.

Introduction: Impairments in vascular function are present in asymptomatic youths with risk factors for cardiovascular disease. Exercise can promote vascular health in youth, but the effects of exercise intensity and the time course in response to acute exercise are unknown. Methods: Twenty adolescents (10 male, 14.1 ± 0.3 yr) performed the following on separate days in a counterbalanced order: 1) cycling at 90% of the gas exchange threshold (moderate-intensity exercise (MIE)) and 2) 8 × 1-min cycling at 90% peak power with 75-s recovery (high-intensity interval exercise (HIIE)). The duration of MIE (25.8 ± 2.1 min) was work-matched to HIIE (23.0 min). Macro- and microvascular functions were assessed before, immediately after, and 1 and 2 h after exercise by flow-mediated dilation (FMD) and laser Doppler imaging (total reactive hyperemia). Results: FMD was attenuated immediately after HIIE (P < 0.001, effect size (ES) = 1.20) but not after MIE (P = 0.28, ES = 0.26). Compared with that before exercise, FMD was elevated 1 and 2 h after HIIE (P < 0.001, ES = 1.33; P < 0.001, ES = 1.36) but unchanged in MIE (P = 0.67, ES = 0.10; P = 0.72, ES = 0.08). Changes in FMD were unrelated to shear or baseline arterial diameter. Compared with that in preexercise, total reactive hyperemia was always greater after MIE (P < 0.02, ES > 0.60 for all) and HIIE (P < 0.001, ES > 1.18 for all). Total reactive hyperemia was greater in HIIE compared with that in MIE immediately after (P = 0.03, ES = 0.67) and 1 h after (P = 0.01, ES = 0.62) exercise, with a trend to be greater 2 h after (P = 0.06, ES = 0.45). Conclusions: Exercise intensity is positively associated with macro- and microvascular function 1 and 2 h after exercise. Performing HIIE may provide superior vascular benefits than MIE in adolescents.

Background: the repeated act of heading has been implicated in the link between football participation and risk of neurodegenerative disease, and acutely alters cerebrovascular outcomes in men. This study assessed whether exposure to a realistic number of headers acutely influences indices of cerebral blood flow regulation in female footballers. Methods: Nineteen female players completed a heading trial and seated control trial on two separate days. The heading trial involved six headers in one hour (one every 10 minutes), with the ball travelling at 40 ± 5 km/h. Cerebrovascular reactivity to hypercapnia and hypocapnia was determined using serial breath holding and hyperventilation attempts. Dynamic cerebral autoregulation (dCA) was assessed by scrutinizing the relationship between cerebral blood flow and mean arterial blood pressure during 5 minutes of squat stand maneuvers at 0.05 Hz. Neurovascular coupling (NVC) was quantified as the posterior cerebral artery blood velocity response to a visual search task. These outcomes were assessed before and one hour after the heading or control trial. Results: No significant time by trial interaction was present for the hypercapnic (P=0.48, ηp2=0.05) and hypocapnic (P=0.47, ηp2=0.06) challenge. Similarly, no significant interaction effect was present for any metric of dCA (P>0.12, ηp20.14, ηp2

Background: Public health guidelines for children advocate physical activity (PA) and the restriction of continuous sedentary time. Schools offer an attractive setting for health promotion, however school-based interventions to increase PA typically fail, and primary school children may spend most of the school day sitting down. Classroom movement breaks have been identified as an attractive opportunity to address this concern and may positively influence behaviour, but little is known about the barriers to implementing movement within lessons from a multi stakeholder perspective. The purpose of this study was to explore 1) the perceptions of primary school pupils, staff members and governors regarding classroom movement breaks, and 2) their perceived barriers and facilitators to implementing PA into the classroom. Methods: Thirty-four pupils (Key Stages 1 and 2, ages 5-7 y) took part in a focus group discussion. Sixty-four staff members and twenty governors completed a questionnaire and an optional follow up semi-structured telephone interview. Qualitative data were analysed using thematic analysis. Results: Pupils, staff members and governors expressed an enthusiasm for movement breaks provided that they were short, simple, pupil-guided and performed at the discretion of the teacher. Time and concerns regarding transitioning back to work following a movement break were identified as key barriers by pupils and staff. Governors and some staff expressed that favourable evidence for movement breaks is needed to facilitate their adoption, particularly regarding the potential for improvements in cognitive functioning or classroom behaviour. Conclusion: There is a wide appeal for classroom-based activity breaks, when delivered in a manner that is not disruptive. Future research which examines the potential benefits of such activity breaks is warranted.

The effect of age and sex on intracranial and extracranial cerebrovascular function is poorly understood. We investigated the relationships between age, sex and cerebrovascular reactivity (CVR) to hypercapnia in 73 healthy adults (18-80 years, N=39 female). CVR to hypercapnia was assessed in the middle cerebral artery (MCA) using transcranial Doppler ultrasound and at the internal carotid artery (ICA) using duplex ultrasound. MCA CVR was characterised by peak MCA velocity (MCAv) response per mmHg increase in end-tidal CO2, and by using a mono-exponential model to characterize the kinetics (time-constant) of the MCAv response. ICA reactivity was assessed as the relative peak increase in artery diameter. Hierarchical multiple regression determined the relationships between age, sex, and the age by sex interaction on all baseline and CVR outcomes. There was no relationship between ICA reactivity (%) with age (P=0.07), sex (P=0.56) or a moderator effect of sex on the age effect (P=0.24). MCAv CVR showed no relationship with age (P=0.59), sex (P=0.09), or an age by sex moderator effect (P=0.90). We observed a positive relationship of MCAv CVR time-constant with age (P=0.013), such that the speed of the MCA response was slower with advancing age. The present study provides comprehensive data on age and sex specific relationships with intracranial and extracranial cerebrovascular responses to hypercapnia. Despite similar MCAv CVR and ICA reactivity between sexes, kinetic responses of the MCA revealed a slower rate of adjustment with advancing age.

Cerebrovascular reactivity of the middle cerebral artery velocity (CVR MCAv) to carbon dioxide (CO2) is a common method to assess cerebrovascular function. Yet, the approaches used to calculate CVR outcomes vary. The aim of this study was to explore the within and between-day reliability of traditional CVR outcomes. The second aim was to explore the reliability of novel kinetic-based analyses. Healthy adults (n=10, 22.3±3.4 years) completed assessments of CVR over four minutes using a fixed fraction of inspired CO2 (6%). This was repeated across four separate visits (between-day), and on one visit measures were repeated 2.5 hours later (within-day). No mean biases were present between assessments for traditional CVR metrics, expressed as absolute (cm/s/mmHg) or relative (%/mmHg) outcomes (minute-3, minute-4, peak 1 second, peak 30 second) (between-day: P>0.14, ηp20.22, d>0.27). Absolute, rather than relative CVR, yielded the most reproducible parameters (coefficient of variation: 8.1-13.2% versus 14-83% respectively). There were significant differences between CVR outcomes (P0.89) dependent on the time point used to determine CVR, as a steady state MCAv response was rarely observed. Furthermore, the MCAv response was not reproducible within an individual (kappa=0.15, P=0.09). No mean differences were present for novel kinetic outcomes (amplitude, time-delay, time constant) (between-day: P>0.05, d0.38, d

Abstract
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. Objective. To quantify the agreement between left and right middle cerebral artery blood velocity (MCAv) responses to incremental and constant work-rate exercise in adults. Approach Seventeen healthy adults (23.8 ± 2.4 years, 9 females) completed a ramp incremental test to exhaustion on a cycle ergometer, three 6-minute transitions at a moderate-intensity, and three at a heavy-intensity, all on separate days. Bilateral MCAv was measured throughout using transcranial Doppler ultrasonography, with left and right MCAv data analysed separately. Data were analysed at baseline, gas exchange threshold, respiratory compensation point and exhaustion during ramp incremental exercise. MCAv responses to constant work-rate exercise were analysed using a mono-exponential model, to determine time- and amplitude-based kinetic response parameters. Main Results Left and right MCAv responses to incremental and constant work-rate exercise were significantly, strongly and positively correlated (r ≥ 0.61, P &lt; 0.01). Coefficient of variation (left versus right) ranged from 7.3%–20.7%, 6.4%–26.2% and 5.9%–22.5% for ramp, moderate and heavy-intensity exercise, respectively. The relative change in MCAv from baseline was higher in the right compared to left MCAv during ramp, moderate and heavy-intensity exercise (all P &lt; 0.05), but the effect sizes were small (d ≤ 0.4). Small mean left–right differences were present during ramp incremental exercise at all time-points (&lt;6 cm s−1; &lt;4%), and for all kinetic parameters during moderate and heavy-intensity exercise (&lt;3 cm s−1, &lt;3%, &lt;4 s). Significance These findings demonstrate similarities between left and right MCAv responses to incremental and constant-work rate exercise in adults on a group-level, but also highlight individual variation in the agreement between left and right MCAv exercise responses.

The aim of this review was to understand the association between habitual physical activity (hPA) and carotid-femoral pulse wave velocity (cfPWV) in an ostensibly healthy adult population. Searches were performed in MEDLINE Web of Science, SPORTDiscus and CINAHL databases published up to 01/01/2022 (PROSPERO, Registration No: CRD42017067159). Observational English-language studies assessing the relationship between cfPWV and hPA (measured via self-report or device-based measures) were considered for inclusion in a narrative synthesis. Studies were excluded if studying specific disease. Studies were further included in pooled analyses where a standardised association statistic for continuous hPA and cfPWV was available. 29 studies were included in narrative synthesis, of which 18 studies provided sufficient data for pooled analyses, totalling 15,573 participants. A weak, significant, negative correlation between hPA and cfPWV was observed; partial r = -0.08 95%CI [-0.15, -0.01]; P = 0.045. Heterogeneity was high (I2 = 94.5% P

Background: Repeated heading has been associated with an increased risk of neurodegenerative disease and has been shown to acutely alter cerebrovascular outcomes and postural control. The majority of work investigating heading and these outcomes have utilised heading stimuli which lack ecological validity and recruited almost exclusively males despite suggestions women may suffer greater cerebral white matter alterations following head impacts. This study assessed whether a more ecologically valid heading stimulus alters indices of cerebral blood velocity regulation and postural control in women. Methods: on separate days, nineteen female footballers completed a heading and time-matched non-heading control trial wherein participants remained seated. The heading trial consisted of six headers performed in one hour (one every 10 minutes), with a ball travelling at 40 ± 5 km/h. Cerebrovascular reactivity to hypercapnia and hypocapnia were determined using five repetitions of breath holding and hyperventilation respectively. Dynamic cerebral autoregulation was assessed via analysing the relationship between middle cerebral artery blood velocity and mean arterial pressure during 5 minutes of repeated squat stands performed at 0.05 Hz. Postural control was analysed by the concurrent assessment of objective balance and centre of pressure displacement during double-leg stance. Outcomes were assessed before and one hour after the heading and control trial. Results: No significant time by trial interaction was present for the hypercapnic (P=0.48, ηp2=0.05) or hypocapnic (P=0.47, ηp2=0.06) challenge. Similarly, no interaction effect was present for any metric of dCA (P>0.12, ηp2 0.13 ηp2

Longitudinal, cross-sectional, and acute experimental research demonstrate that a short sleep duration is associated with an increased risk of both cardiovascular and cerebrovascular disease. Chronic habitual short sleep duration is associated with an increased dementia risk, however a quarter of the population fail to meet sleep duration guidelines. It is thought that alterations in cerebrovascular function precede symptoms of cognitive decline and dementia. Currently, no evidence exists on measures of cerebrovascular function, such as neurovascular coupling (NVC), and habitual sleep across the lifespan. The association of chronic poor sleep and dementia is likely due to the repeated exposure to a poor night’s sleep. Therefore, there is value in performing controlled, interventional work to understand the acute responses to a single night of sleep restriction. Furthermore, following a night of poor sleep, individuals commonly consume caffeine to increase alertness, but caffeine is known to simultaneously reduce brain blood flow. It is unknown how caffeine affects cerebrovascular function in a sleep restricted state. The purpose of this thesis was therefore to explore 1) the impact of one night of partial sleep restriction on NVC and, 2) whether caffeine ingestion affects NVC after partial sleep restriction in young healthy adults. NVC was determined using transcranial Doppler ultrasound (TCD) to measure blood velocity through the posterior cerebral artery (PCAv) during a visual search task. TCD was also used to measure blood velocity through the middle cerebral artery (MCAv) during cognitive function tests, both of which were assessed before and after normal sleep and partial sleep restriction, and following caffeine ingestion. This study found that NVC was unaltered following partial sleep restriction, and that the magnitude of the NVC response was unchanged after caffeine ingestion in both the rested and sleep restricted state. However, both absolute PCAv and MCAv were lower after caffeine, though this response did not differ between normal and restricted sleep. This study was the first to examine the effects of partial sleep restriction and subsequent caffeine ingestion on a measure of cerebrovascular function. However, sleep restriction was only studied in the form of a 50% sleep restriction, with sleep taking place in the second half of the night. Future research should explore whether the relationship between sleep and NVC is dependent on how sleep is accrued throughout the night, for example fragmented/broken sleep.

AbstractDynamic cerebral autoregulation (dCA) describes the regulation of cerebral blood flow (CBF) in response to fluctuations in systemic blood pressure (BP). Heavy resistance exercise is known to induce large transient elevations in BP, which are translated into perturbations of CBF, and may alter dCA in the immediate aftermath. This study aimed to better quantify the time course of any acute alterations in dCA after resistance exercise. Following familiarisation to all procedures, 22 (14 male) healthy young adults (22 ± 2 years) completed an experimental trial and resting control trial, in a counterbalanced order. Repeated squat‐stand manoeuvres (SSM) at 0.05 and 0.10 Hz were used to quantify dCA before, and 10 and 45 min after four sets of ten repetition back squats at 70% of one repetition maximum, or time matched seated rest (control). Diastolic, mean and systolic dCA were quantified by transfer function analysis of BP (finger plethysmography) and middle cerebral artery blood velocity (transcranial Doppler ultrasound). Mean gain (p = 0.02; d = 0.36) systolic gain (p = 0.01; d = 0.55), mean normalised gain (p = 0.02; d = 0.28) and systolic normalised gain (p = 0.01; d = 0.67) were significantly elevated above baseline during 0.10 Hz SSM 10‐min post resistance exercise. This alteration was not present 45 min post‐exercise, and dCA indices were never altered during SSM at 0.05 Hz. dCA metrics were acutely altered 10 min post resistance exercise at the 0.10 Hz frequency only, which indicate changes in the sympathetic regulation of CBF. These alterations recovered 45 min post‐exercise.

Neurovascular coupling (NVC) is the matching between local neuronal activity and regional cerebral blood flow (CBF), but little is known about the effects of age and sex on NVC. This study aimed to investigate the relationships and interaction between age and sex on NVC. Sixty-four healthy adults (18–85 years, N = 34 female) completed a visual stimulus evoked NVC assessment to a flashing checkerboard. NVC responses were measured in the posterior cerebral artery (PCAv) using transcranial Doppler ultrasound. A hierarchical multiple regression was used to determine the relationships between age, sex, and the age by sex interaction on NVC. There was a significant age by sex interaction for baseline (P = 0.001) and peak PCAv (P = 0.01), with a negative relationship with age in females (P &lt; 0.005), and no relationship in males (P ≥ 0.17). NVC responses as a percent increase from baseline showed a significant age by sex interaction (P = 0.014), with a positive relationship with age in females (P = 0.04) and no relationship in males (P = 0.17), even after adjusting for baseline PCAv. These data highlight important sex differences, with an association between age and NVC only apparent in females but not males, and thus a need to account for sex dependent effects of ageing when investigating cerebrovascular regulation.

Purpose: Retired male footballers are at 3.5 times greater risk of neurodegenerative disease, with repeated heading suggested to contribute to the increased risk. Currently, no such cohort data exist in women players. However, the women’s game is growing, so studies are needed to understand whether heading acutely alters outcomes potentially linked to neurodegenerative disease in this group. Alterations in neurovascular coupling (NVC) may precede the cognitive impairment associated with neurological disease, and evidence suggests that NVC is acutely altered following heading in men. Increased intracranial pressure (ICP) is linked with unfavourable patient outcomes following mild traumatic brain injury. This study assessed whether exposure to a realistic number of football headers acutely influenced NVC, ICP and cognitive function in women footballers. Methods: 19 women footballers completed a heading trial consisting of 6 headers at 40 ± 5 km/h, evenly spaced across an hour, and a time-matched seated control trial. Trials were performed on separate days, spaced a least 7 days apart. The posterior cerebral artery blood velocity response to a visual search task was measured via transcranial Doppler ultrasonography and used to quantify NVC. ICP was evaluated by measuring the optic nerve sheath diameter (ONSD). Finally, cognitive performance was determined using a modified version of the international shopping list test. Each outcome was assessed before and after the heading and control trials. Results: No significant time by trial interaction was present for any metric of NVC (P>0.14, ηp2

New Findings
What is the central question of this study?
What is the effect of 4 weeks of high‐intensity interval training (HIIT) and 2 weeks of detraining on vascular function and traditional cardiovascular disease (CVD) risk factors in male adolescents?

What is the main finding and its importance?
Four weeks of HIIT improved macrovascular function in adolescents. However, this training period did not measurably change microvascular function, body composition or blood biomarkers. Following 2 weeks of detraining, the improvement in flow‐mediated dilatation (FMD) was lost. This highlights the importance of the continuation of regular exercise for the primary prevention of CVD.

AbstractHigh‐intensity interval training (HIIT) represents an effective method to improve cardiometabolic health in adolescents. This study aimed to investigate the effect of 4 weeks of HIIT followed by 2 weeks of detraining on vascular function and traditional cardiovascular disease (CVD) risk factors in adolescent boys. Nineteen male adolescents (13.3 ± 0.5 years) were randomly allocated to either a training (TRAIN, n = 10) or control (CON, n = 9) group. Participants in TRAIN completed 4 weeks of HIIT running with three sessions per week. Macro‐ (flow‐mediated dilatation, FMD) and microvascular (peak reactive hyperaemia, PRH) function, body composition (fat mass, fat free mass, body fat percentage) and blood biomarkers (glucose, insulin, total cholesterol, high‐ and low‐density lipoprotein, triacylglycerol) were assessed pre‐, 48 h post‐ and 2 weeks post‐training for TRAIN and at equivalent time points for CON. Following training, FMD was significantly greater in TRAIN compared to CON (9.88 ± 2.40% and 8.64 ± 2.70%, respectively; P = 0.036) but this difference was lost 2 weeks after training cessation (8.22 ± 2.47% and 8.61 ± 1.99%, respectively; P = 0.062). No differences were detected between groups for PRH (P = 0.821), body composition (all P &gt; 0.14) or blood biomarkers (all P &gt; 0.18). In conclusion, 4 weeks of HIIT improved macrovascular function; however, this training period did not measurably change microvascular function, body composition or blood biomarkers. The reversal of the FMD improvement 2 weeks post‐training highlights the importance of the continuation of regular exercise for the primary prevention of CVD.

Introduction: the near-infrared spectroscopy (NIRS)-derived reperfusion rate of tissue oxygen saturation (slope 2 StO2) may provide a surrogate measure of vascular function, however, this has yet to be examined in a paediatric population. This study investigated in adolescents: 1) the between-day reliability of NIRS-derived measurements; 2) the relationship between slope 2 StO2 and macro- (flow-mediated dilation, FMD) and microvascular (peak reactive hyperaemia, PRH) function; and 3) the effect of high-intensity interval exercise (HIIE) on slope 2 StO2, FMD, and PRH. Methods: Nineteen boys (13.3 ± 0.5 y) visited the laboratory on two occasions, separated by ∼ 1 week. On visit 1, participants underwent simultaneous assessment of brachial artery FMD and slope 2 StO2 and PRH on the internal face of the forearm. On visit 2, participants completed a bout of HIIE with slope 2 StO2, FMD and PRH measured pre-, immediately post- and 1.5 h post-exercise. Results: Slope 2 StO2 showed no mean bias (p = 0.18) and an intraclass correlation coefficient of 0.67 (p = 0.003) between visits. No significant correlation between slope 2 StO2 and FMD or PRH was observed on visit 1 (r = -0.04, p = 0.89 and r = -0.30, p = 0.23, respectively) or visit 2 pre-exercise (r = -0.28, p = 0.25 and r = -0.31, p = 0.20, respectively). Compared to pre-exercise, FMD decreased immediately post-exercise (p < 0.001) and then increased 1.5 h post-exercise (p < 0.001). No significant change was detected for slope 2 StO2 (p = 0.30) or PRH (p = 0.55) following HIIE. Conclusion: in adolescents, slope 2 StO2 can be measured reliably, however, it is not correlated with FMD or PRH and does not follow the acute time course of changes in FMD post-exercise. Hence, the use of slope 2 StO2 as a surrogate measure of vascular function in youth must be refuted.

Introduction: Evidence for associations between physical activity (PA) or sedentary time (ST) and vascular health in paediatric populations is of low quality due to the predominance of self-report measures of PA time and intensities, small sample sizes, and a lack of control of confounding variables. This thesis examined associations between device-derived PA and ST with vascular outcomes and a clustered cardiometabolic risk (CMR) score in a population sample, with adjustment for covariates. Methods: Cross-sectional analysis of 4,277 children (2,226 girls) aged 10.6 ± 0.2 y from the Avon Longitudinal Study of Parents and Children. Clustered CMR was measured at age 9 y. Vascular outcomes (flow mediated dilation, distensibility coefficient, and pulse wave velocity) were measured age 10 y. Light and moderate to vigorous PA (MVPA) and ST were measured via accelerometers at age 11 y. Multiple linear regression analyses were used to examine associations between exposures and outcomes, with PA and ST entered as compositional exposure variables and non-compositional variables (min∙day-1). Results: Neither light PA, MVPA or ST were significantly associated with any of the vascular outcomes in the adjusted compositional and non-compositional models. The proportion of time spent in MVPA and ST (relative to the remaining activity behaviours) were inversely (b=-0.126; P=0.001) and positively (b=0.136; P=0.016) associated with CMR in the whole group analysis, respectively. MVPA was negatively associated with CMR in both boys (b=-0.144; P=0.011) and girls (b=-0.110; P=0.032), but only girls had a positive association between ST and CMR (b=0.199; P=0.005). In the non-compositional models, MVPA was inversely associated with CMR in the whole group analysis (b=-0.002; P=0.012). In the girls, ST was positively (b=0.001; P=0.035), and LPA was inversely (b=-0.001; P=0.035) associated with CMR. Conclusion: Longer exposure to CMR factors during adolescence may be needed to establish relationships between PA and ST with vascular outcomes. These findings support interventions that promote MVPA and minimise ST for reducing CMR in children. Prospective studies are required to understand the causal directions.

Understanding the contribution of the autonomic nervous system to cerebral blood flow (CBF) control is challenging, and interpretations are unclear. The identification of calcium channels and adrenoreceptors within cerebral vessels has led to common misconceptions that the function of these receptors and actions mirror those of the peripheral vasculature. This review outlines the fundamental differences and complex actions of cerebral autonomic activation compared with the peripheral circulation. Anatomical differences, including the closed nature of the cerebrovasculature, and differential adrenoreceptor subtypes, density, distribution and sensitivity, provide evidence that measures on peripheral sympathetic nerve activity cannot be extrapolated to the cerebrovasculature. Cerebral sympathetic nerve activity seems to act opposingly to the peripheral circulation, mediated at least in part by changes in intracranial pressure and cerebral blood volume. Additionally, heterogeneity in cerebral adrenoreceptor distribution highlights region-specific autonomic regulation of CBF. Compensatory chemo- and autoregulatory responses throughout the cerebral circulation, and interactions with parasympathetic nerve activity are unique features to the cerebral circulation. This crosstalk between sympathetic and parasympathetic reflexes acts to ensure adequate perfusion of CBF to rising and falling perfusion pressures, optimizing delivery of oxygen and nutrients to the brain, while attempting to maintain blood volume and intracranial pressure. Herein, we highlight the distinct similarities and differences between autonomic control of cerebral and peripheral blood flow, and the regional specificity of sympathetic and parasympathetic regulation within the cerebrovasculature. Future research directions are outlined with the goal to further our understanding of autonomic control of CBF in humans.

Purpose1) to investigate the effectiveness of school-based high-intensity interval training (HIIT) interventions in promoting health outcomes of children and adolescents compared with either a control group or other exercise modality; and 2) to explore the intervention characteristics and process outcomes of published school-based HIIT interventions.MethodsWe searched Medline, Embase, CINAHL, SPORTDiscus, and Web of Science from inception until 31 March 2021. Studies were eligible if 1) participants aged 5–17 years old; 2) a HIIT intervention within a school setting ≥ 2 weeks duration; 3) a control or comparative exercise group; 4) health-related, cognitive, physical activity, nutrition, or program evaluation outcomes; and 5) original research published in English. We conducted meta-analyses between HIIT and control groups for all outcomes with ≥ 4 studies and meta-regressions for all outcomes with ≥ 10 studies. We narratively synthesised results between HIIT and comparative exercise groups.ResultsFifty-four papers met eligibility criteria, encompassing 42 unique studies (35 randomised controlled trials; 36 with a high risk of bias). Meta-analyses indicated significant improvements in waist circumference (mean difference (MD) = -2.5cm), body fat percentage (MD = -1.7%), body mass index (standardised mean difference (SMD) = -1.0), cardiorespiratory fitness (SMD = +1.0), resting heart rate (MD = -5bpm), homeostatic model assessment–insulin resistance (MD = -0.7), and low-density lipoprotein cholesterol (SMD = -0.9) for HIIT compared to the control group. Our narrative synthesis indicated mixed findings between HIIT and other comparative exercise groups.ConclusionSchool-based HIIT is effective for improving several health outcomes. Future research should address the paucity of information on physical activity and nutrition outcomes and focus on the integration and long-term effectiveness of HIIT interventions within school settings.Trial registration numberPROSPEROCRD42018117567.

The acute effect of exercise intensity on cerebrovascular reactivity, and whether this mirrors changes in peripheral vascular function, has not been investigated. The aim of this study was to explore the acute effect of exercise intensity on cerebrovascular reactivity (CVR) and peripheral vascular function in healthy young adults (n=10, 6 females, 22.7 ± 3.5 years). Participants completed four experimental conditions on separate days: high intensity interval exercise (HIIE) with intervals performed at 75% maximal oxygen uptake (V̇O2max; HIIE1), HIIE with intervals performed at 90% V̇O2max (HIIE2), continuous moderate intensity exercise (MIE) at 60% V̇O2max and a sedentary control condition (CON). All exercise conditions were completed on a cycle ergometer and matched for time (30 min) and average intensity (60% V̇O2max). Brachial artery flow-mediated dilation (FMD) and CVR of the middle cerebral artery were measured before exercise, and one- and three hours post-exercise. CVR was assessed using transcranial Doppler ultrasonography to both hypercapnia (6% carbon dioxide breathing) and hypocapnia (hyperventilation). FMD was significantly elevated above baseline one and three hours following both HIIE conditions (P0.33). CVR to both hypercapnia and hypocapnia, and when expressed across the end-tidal CO2 range, was unchanged in all conditions, at all time points (all P>0.14). In conclusion, these novel findings show that the acute increases in peripheral vascular function following HIIE, compared to MIE, were not mirrored by changes in cerebrovascular reactivity, which was unaltered following all exercise conditions in healthy young adults.

The present thesis investigated the acute influence of amateur boxing on brain health parameters across two separate studies. The first study examined 20 university boxers visuomotor performance and neurocognitive function before and after 3 rounds of competitive amateur boxing. Visuomotor performance was assessed via a computer guided precision grip task, both with and without visual feedback, whilst neurocognitive function was assessed via a revised SCAT5 questionnaire and balance task. Boxers presented with no difference in average force or reaction time in both precision grip tasks, although performance error was greater after boxing when compared to pre boxing measures in the visual feedback precision grip task (P

New Findings
What is the central question of this study?
What is the effect of three repeated breath‐hold techniques routinely used by freedivers, thought to manipulate arterial partial pressures of O2 and CO2, on the cardiorespiratory and haematological response to breath‐holding during facial immersion?

What is the main finding and its importance?
All three techniques increased breath‐hold by a similar duration, probably owing to the similar marked increase in end‐tidal O2 and decrease in end‐tidal CO2 observed in all three trials before facial immersion. These were the only cardiorespiratory changes that were consistently manipulated before the maximal breath‐hold. This would suggest that pronounced bradycardia and vasoconstriction of selective vascular beds are probably not obligatory for prolonging breath‐hold duration.

AbstractRepeated maximal breath‐holds have been demonstrated to induce bradycardia, increase haematocrit and haemoglobin and prolong subsequent breath‐hold duration by 20%. Freedivers use non‐maximal breath‐hold techniques (BHTs) to improve breath‐hold duration. The aim of this study was to investigate the cardiorespiratory and haematological responses to various BHTs. Ten healthy men (34.5 ± 1.9 years) attended five randomized experimental trials and performed a 40 min period of quiet rest or one of three BHTs followed by a maximal breath‐hold challenge during facial immersion in water at 30 or 10°C. Cardiovascular and respiratory parameters were measured continuously using finger plethysmography and breath‐by‐breath gas analysis, respectively, and venous blood samples were collected throughout. Facial immersion in cold water caused marked bradycardia (74.1 vs. 50.2 beats/min after 40 s) but did not increase breath‐hold duration compared with warm water control conditions. Facial immersion breath‐hold duration was 30.8–43.3% greater than the control duration when preceded by BHTs that involved repeated breath‐holds of constant duration (P = 0.021), increasing duration (P &lt; 0.001) or increasing frequency (P &lt; 0.001), with no difference observed between BHTs. The increased duration of apnoea across all three BHT protocols was associated with a 6.8% increase in end‐tidal O2 and a 13.1% decrease in end‐tidal CO2 immediately before facial immersion. There were no differences in blood pressure, cardiac output, heart rate, haematocrit or haemoglobin between each BHT and control conditions (P &gt; 0.05). In conclusion, the duration of apnoea can be extended by manipulating blood gases through repeated prior breath‐holds, but changes in cardiac output and red blood cell mass do not appear essential.

Dynamic cerebral autoregulation (dCA) describes the active maintenance of cerebral blood flow (CBF) in response to rapid, systemic blood pressure (BP) fluctuations. dCA capacity has been linked to neurological pathologies such as dementia, stroke and traumatic brain injury and may be implicated as a target for therapeutic strategies. Resistance exercise is a common leisure activity with growing popularity and forms the basis for many strength sports as well as being recommended by public health institutions. Heavy resistance exercise is known to induce large transient increases in BP which are translated into elevations in CBF. dCA must act effectively to minimise the BP oscillations which are translated into the cerebrovasculature, however CBF is still significantly elevated which indicates that it is not entirely effective at maintaining a constant CBF. This begs the question: does resistance exercise lead to altered dCA capacity both acutely and/ or at baseline following years of training? This thesis is formed of two main sections. Firstly, the within- and between-day reliability of dCA metrics phase, gain and normalised gain at each phase of the cardiac cycle were determined using repeat squat-stand manoeuvres (SSM) to elicit orthostatic BP fluctuations. As dCA can be induced, measured and analysed with a variety of methods, understanding the reliability of the measures used is crucial when interpreting one’s results. SSM were utilised to elicit BP fluctuations at 0.05 and 0.10Hz due to the excellent signal-to-noise ratio which they produce. The novelty of this work is largely attributed to the exploration of dCA metrics during systole and diastole as well as mean values, both within- and between-day. Secondly, the acute effects of resistance exercise and long-term effects of regular resistance exercise on dCA are examined. Long-term effects were inferred by comparing phase, gain and normalised gain in resistance trained vs. recreationally active individuals by use of SSM in a rested condition. Acute effects were explored by comparing phase, gain and normalised gain pre-exercise to follow-up measures 10 and 45 minutes post-
3
exercise in both groups. The exercise protocol consisted of four sets of ten repetition back squats at 70% of the individuals one-repetition maximum. This work indicates that dCA induced by SSM at 0.05 and 0.10Hz produce excellent reproducibility of phase, gain and normalised gain within- and between-day when measured as the mean of the cardiac cycle. Diastolic and systolic outcomes were also largely reproducible, although notably less so than mean values. Cross-sectional analysis of baseline dCA between groups found no significant differences in phase, gain or normalised gain at any phase of the cardiac cycle. Furthermore, no group interaction effect was identified in response to an acute bout of resistance exercise, suggesting that the post-exercise effects on dCA were similar in both demographics. dCA was largely unaltered following resistance exercise; however, gain and normalised gain were significantly elevated when measured as the mean and systolic section of the cardiac cycle during 0.10Hz SSM only. This difference was only present 10, but not 45 minutes post-exercise which indicates rapid recovery towards baseline. Further research is warranted, but these preliminary findings suggest that resistance exercise may acutely impair sympathetic nervous activity responsible for CBF regulation, although this does not appear to lead to alterations at baseline.

Abstract
Purpose: the purpose of this study was: 1) to explore the perceptions of primary school staff members, pupils and governors in regard to classroom based physical activity (CBPA); 2) to understand the multiple levels of factors impacting these stakeholder’s acceptability of interventions and 3) to collaboratively design a successful classroom movement intervention that is accepted by the school governors, feasible for teachers and enjoyable for the pupils, with the main aim of breaking up continuous uninterrupted
classroom sedentary time.
Methods: Sixty-four staff members and twenty governors completed a questionnaire and 7 participants (n=5 staff and n=2 governors) took part in a further follow up semi structured telephone interview. Thirty-four Key Stage (KS) 1 and KS2 pupils from one federated village school in Somerset took part in a focus group discussion.
Results: all staff members, governors and pupils were aware of the value of PA and had similar barriers for implementation within the classroom environment. Two main barriers that were reported by the majority of staff members are time and transitioning back to work following movement. In addition, suggestions for increasing adoption and implementation were identified, for example, short and simple breaks, pupil guided choice and performed at the teacher’s discretion. Furthermore, the need for more sufficient evidence regarding pupil cognition following a movement break were requested by both governors and staff.
Key words: qualitative research, classroom, movement breaks, stakeholders, prolonged sedentary time
Abbreviations: Physical activity (PA), Key Stage 1 (KS1), Key Stage 2 (KS2)

New Findings

What is the central question of this study?
What is the effect of high‐intensity and moderate‐intensity interval running on macro‐ and microvascular function in a fasted state and following a glucose challenge in adolescents?


What is the main finding and its importance?
Both macro‐ and microvascular function were improved after interval running independent of intensity. This finding shows that the intermittent exercise pattern and its associated effect on shear are important for vascular benefits. In adolescents, macrovascular function was enhanced after an acute glucose load. However, the effect of chronic glucose consumption on vascular function remains to be elucidated.

AbstractInterventions targeting vascular function in youth are an important strategy for the primary prevention of cardiovascular diseases. This study examined, in adolescents, the effect of high‐intensity interval running (HIIR) and moderate‐intensity interval running (MIIR) on vascular function in a fasted state and postprandially after a glucose challenge. Fifteen adolescents (13 male, 13.9 ± 0.6 years) completed the following conditions on separate days in a counterbalanced order: (1) 8 × 1 min HIIR interspersed with 75 s recovery; (2) distance‐matched amount of 1 min MIIR interspersed with 75 s recovery; and (3) rest (CON). Macro‐ (flow‐mediated dilatation, FMD) and microvascular (peak reactive hyperaemia, PRH) function were assessed immediately before and 90 min after exercise/rest. Participants underwent an oral glucose tolerance test (OGTT) 2 h after exercise/rest before another assessment of vascular function 90 min after the OGTT. Following exercise, both HIIR and MIIR increased FMD (P = 0.02 and P = 0.03, respectively) and PRH (P = 0.04, and P = 0.01, respectively) with no change in CON (FMD: P = 0.51; PRH: P = 0.16) and no significant differences between exercise conditions. Following the OGTT, FMD increased in CON (P &lt; 0.01) with no changes in HIIR and MIIR (both P &gt; 0.59). There was no change in PRH after the OGTT (all P &gt; 0.40). In conclusion, vascular function is improved after interval running independent of intensity in adolescents. Acute hyperglycaemia increased FMD, but prior exercise did not change vascular function after the OGTT in youth.

Cardiovascular disease (CVD) is the leading global cause of mortality and the underlying atherosclerotic disease process which precedes overt CVD originates in youth. Consumption of sugar-sweetened beverages (SSB) are associated with CVD risk factors in youth and SSB intake is a key contributor to added dietary sugar intake in teenagers in the United Kingdom. Endothelial dysfunction is a prerequisite for atherosclerosis and previous research demonstrates that SSB consumption acutely impairs endothelial function. However, these studies have predominantly focused on adult populations, or have used a glucose bolus which is not representative of the sugar found in commercially available SSBs. The purpose of this thesis was to investigate the influence of different dietary sugars found in SSBs on macrovascular and microvascular outcomes and then observe whether the sugar type influences the cardiometabolic responses to a subsequent test meal challenge. This thesis also determined the reliability of measures for the assessment of macrovascular (flow-mediated dilation; FMD) and microvascular (laser Doppler flowmetry) function. Chapter 4: Assessed the within-day and between day reliability of the simultaneous assessment of macrovascular and microvascular function. The within-day and between-day typical error expressed as a coefficient of variation were as follows: FMD, 7.2% and 8.0%; peak reactive hyperaemia (PRH), 24.5% and 26.1%. These results determined that the reliability of outcomes in this study were consistent with existing paediatric data. Chapter 5: There was a large (ηp2=0.27) but not significant (P=0.06) interaction effect for FMD. There was a non-significant difference between the sucrose and control trials for FMD at 1 hour post drink consumption (P=0.06) and 3 hours post test meal consumption (P=0.09) but there was a medium effect at both times with effect sizes of 0.77 and 0.65, respectively, where FMD increased following sucrose consumption. PRH increased 1 hour post drink consumption in the fructose (P=0.01), glucose (P=0.04) and sucrose trials (P=0.04) when compared to control. PRH was greater in the fructose trial when compared to the control (P=0.03), glucose (P=0.01) and sucrose (P=0.02) trials. These findings suggest that SSB intake acutely improves macro- and micro- vascular function in adolescents. Overall, these findings provide important information in regards to the effects of SSBs on macrovascular and microvascular function in adolescents.

AbstractPurposeCerebrovascular reactivity (CVR) is impaired in adolescents with cardiovascular disease risk factors. A breath‐hold test is a noninvasive method of assessing CVR, yet there are no reliability data of this outcome in youth. This study aimed to assess the reliability of a breath‐hold protocol to measure CVR in adolescents.MethodsTwenty‐one 13 to 15 year old adolescents visited the laboratory on two separate occasions, to assess the within‐test, within‐day and between‐day reliability of a breath‐hold protocol, consisting of three breath‐hold attempts. CVR was defined as the relative increase from baseline in middle cerebral artery mean blood velocity following a maximal breath‐hold of up to 30 seconds, quantified via transcranial Doppler ultrasonography.ResultsMean breath‐hold duration and CVR were never significantly correlated (r &lt; .31, P &gt; .08). The within‐test coefficient of variation for CVR was 15.2%, with no significant differences across breath‐holds (P = .88), so the three breath‐hold attempts were averaged for subsequent analyses. The within‐ and between‐day coefficients of variation for CVR were 10.8% and 15.3%, respectively.ConclusionsCVR assessed via a three breath‐hold protocol can be reliably measured in adolescents, yielding similar within‐ and between‐day reliability. Analyses revealed that breath‐hold length and CVR were unrelated, indicating the commonly reported normalization of CVR to breath‐hold duration (breath‐hold index) may be unnecessary in youth.

Flavonoid supplementation improves brachial artery flow-mediated dilation (FMD), but it is not known whether flavonoids protect against vascular dysfunction induced by ischemia-reperfusion (IR) injury and associated respiratory burst. In a randomized, double-blind, placebo-controlled, crossover study, we investigated whether 4 wk supplementation with freeze-dried Montmorency cherry (MC) attenuated suppression of FMD after IR induced by prolonged forearm occlusion. Twelve physically inactive overweight, middle-aged men (52.8 ± 5.8 yr, BMI: 28.1 ± 5.3 kg/m2) consumed MC (235 mg/day anthocyanins) or placebo capsules for 4 wk, with supplementation blocks separated by 4 wk washout. Before and after each supplementation block, FMD responses and plasma nitrate and nitrite ([ NO2- ]) concentrations were measured at baseline and 15, 30, and 45 min after prolonged (20 min) forearm occlusion. FMD response was significantly depressed by the prolonged occlusion ( P < 0.001). After a 45-min reperfusion, FMD was restored to baseline levels after MC (ΔFMD presupplementation: -30.5 ± 8.4%, postsupplementation: -0.6 ± 9.5%) but not placebo supplementation (ΔFMD presupplementation: -11.6 ± 10.6, postsupplementation: -25.4 ± 4.0%; condition × supplement interaction: P = 0.038). Plasma [ NO2- ] decreased after prolonged occlusion but recovered faster after MC compared with placebo (Δ45 min to baseline; MC: presupplementation: -15.3 ± 9.6, postsupplementation: -6.2 ± 8.1; Placebo: presupplementation: -16.3 ± 5.9, postsupplementation: -27.7 ± 11.1 nmol/l; condition × supplement × time interaction: P = 0.033). Plasma peroxiredoxin concentration ([Prx2]) was significantly higher after MC (presupplementation: 22.8 ± 1.4, postsupplementation: 28.0 ± 2.4 ng/ml, P = 0.029) but not after placebo supplementation (presupplementation: 22.1 ± 2.2, postsupplementation: 23.7 ± 1.5 ng/ml). In conclusion, 4 wk MC supplementation enhanced recovery of endothelium-dependent vasodilatation after IR, in parallel with faster recovery of plasma [ NO2- ], suggesting NO dependency. These protective effects seem to be related to increased plasma [Prx2], presumably conferring protection against the respiratory burst during reperfusion. NEW & NOTEWORTHY This is the first study to demonstrate that 4 wk of Montmorency cherry powder supplementation exerted protective effects on endothelium-dependent vasodilation after transient ischemia-reperfusion injury in overweight, physically inactive, nonmedicated, hypertensive middle-aged men. These effects seem to be due to increased nitric oxide availability, as evidenced by higher plasma nitrite concentration and peak arterial diameter during the flow-mediated dilation measurement. This may be a consequence of increased concentration of peroxiredoxin and other antioxidant systems and, hence, reduced reactive oxygen species exposure.

Purpose: Macrovascular endothelial function is commonly assessed using flow-mediated dilation (FMD) and is nitric oxide (NO) dependent. However, the vasoreactivity to low flow during the FMD protocol may complement FMD interpretation. This study aimed to investigate in adolescents: (1) the day-to-day reliability of low-flow-mediated constriction (L-FMC) and composite vessel reactivity (CVR); and (2) the relationship between L-FMC and FMD. Methods: a retrospective analysis of data on 27 adolescents (14.3 ± 0.6 year, 12 males) was performed. Participants had two repeat measures, on separate days, of macrovascular function using high-resolution ultrasound for assessment of L-FMC, FMD, and CVR. Results: on average, the L-FMC response was vasoconstriction on both days (−0.59 ± 2.22% and −0.16 ± 1.50%, respectively). In contrast, an inconsistent response to low flow (vasoconstriction, dilation, or no change) was observed on an individual level. Cohen's Kappa revealed poor agreement for classifying the L-FMC measurement between visits (k = 0.04, P >.05). Assessment of the actual vessel diameter was robust with a coefficient of variation of 1.7% (baseline and peak) and 2.7% (low-flow). The between-day correlation coefficient between measures was r =.18, r =.96 and r =.52 for L-FMC, FMD, and CVR, respectively. No significant correlation between FMD and L-FMC was observed for either visit (r = −.06 and r = −.07, respectively; P >.05). Conclusion: in adolescents, the low-flow vasoreactivity is inconsistent between days. Whereas the actual vessel diameter is reproducible, the measurement of L-FMC and CVR has poor between-day reliability compared to FMD. Finally, L-FMC, and FMD are not significantly correlated.

Abstract
. Background
. Current evidence of metabolic health benefits of high-intensity interval training (HIIT) are limited to longer training periods or conducted in overweight youth. This study assessed 1) fasting and postprandial insulin and glucose before and after 2 weeks of HIIT in healthy adolescent boys, and 2) the relationship between pre intervention health outcomes and the effects of the HIIT intervention.
.
. Methods
. Seven healthy boys (age:14.3 ± 0.3 y, BMI: 21.6 ± 2.6, 3 participants classified as overweight) completed 6 sessions of HIIT over 2 weeks. Insulin resistance (IR) and blood glucose and insulin responses to a Mixed Meal Tolerance Test (MMTT) were assessed before (PRE), 20 h and 70 h after (POST) the final HIIT session.
.
. Results
. Two weeks of HIIT had no effect on fasting plasma glucose, insulin or IR at 20 h and 70 h POST HIIT, nor insulin and glucose response to MMTT (all P &gt; 0.05). There was a strong negative correlation between PRE training IR and change in IR after HIIT (r = − 0.96, P &lt; 0.05).
.
. Conclusion
. Two weeks of HIIT did not elicit improvements to fasting or postprandial glucose or insulin health outcomes in a group of adolescent boys. However the negative correlation between PRE IR and improvements after HIIT suggest that interventions of this type may be effective in adolescents with raised baseline IR.
.

Cardiovascular diseases (CVD) are the leading cause of non-communicable diseases worldwide, with the underlying atherosclerotic process originating in youth. Children and adolescents with CVD risk factors have impaired endothelial function, which is implicated in the process of atherosclerosis. Habitual sugar sweetened beverage (SSB) consumption is associated with the progression of CVD risk factors in youth, and adolescents consume the highest quantities of SSBs. Acute SSB consumption results in vascular dysfunction in adults, though the effects in youth are unknown. It is thought that exposure to CVD risk factors in youth may impair cerebrovascular reactivity (CVR), possibly having implications for future CVD risk. It is also unknown whether the types of sugar in SSBs have different consequences on vascular function. This thesis aimed to investigate the effect of sugar moiety on cerebrovascular function in adolescents, following consumption of a sugary drink and subsequent meal. Data on the reliability of CVR in a paediatric population was needed to first establish if this was a reliable measure of endothelial function. The purpose of this thesis was to: 1) examine the within and between-day reliability of a breath-hold protocol to assess CVR in adolescents. 2) examine the acute effect of sugar moiety (fructose, sucrose, glucose) on CVR and putative blood outcomes, and 3) examine the effects of SSB consumption on postprandial health in adolescents. Chapter 3 examined the reliability of a breath-hold protocol to assess CVR in youth, determined via transcranial Doppler ultrasonography of the middle cerebral artery (MCA). CVR was calculated as the percentage increase in MCAv mean following three breath-hold attempts. This outcome yielded acceptable levels of within and between-day reliability for use in multiple visit experiments to assess CVR in adolescents. Chapter 4 investigated the effect of sugar moiety on cerebrovascular function, measured through breath-hold induced CVR, in adolescents following SSB consumption and a subsequent challenge meal. This study found that the glucose and sucrose drinks resulted in elevated blood glucose levels compared to fructose and water. With consumption of fructose, elevations in uric acid were present, however the sugar moieties all presented similar increases in TAG concentrations following meal consumption. Despite these different metabolic responses, no significant impairments in CVR were present following the drink or challenge meal.
This thesis demonstrated that consumption of SSBs led to increases in glucose and uric acid concentrations, which have previously been shown to be atherogenic. This thesis also provided data on the reliability of CVR as a non-invasive and easy to administer tool for measurement of endothelial function in youth. This is the first study to demonstrate that breath-hold induced CVR can be reliably measured in youth, as a practical, affordable and non-invasive method. These findings provide valuable data that will inform the implementation and analysis of a breath-hold protocol for reliable CVR assessment in youth in future research. Having established that CVR was reliable within and between-day, it was not possible to determine if it was sensitive to change, with no effects seen on CVR following acute SSB consumption. To build on these findings, future research should explore the acute and chronic effects of SSB consumption, with consideration of measuring a range of different vascular outcomes such as changes in peripheral microvascular and macrovascular functions. As this thesis did not include another measure of peripheral endothelial function, it is not certain whether endothelial function was impaired, or if CVR was not sensitive to change in the present study. In order to determine if CVR is sensitive to change, future investigation is needed with established measures of peripheral endothelial function (i.e. flow mediated dilation) alongside measures of CVR.

Purpose: This study had 2 objectives: (1) to examine whether the validity of the supramaximal verification test for maximal oxygen uptake ( V˙O2max ) differs in children and adolescents when stratified for sex, body mass, and cardiorespiratory fitness and (2) to assess sensitivity and specificity of primary and secondary objective criteria from the incremental test to verify V˙O2max. Methods: in total, 128 children and adolescents (76 male and 52 females; age: 9.3-17.4 y) performed a ramp-incremental test to exhaustion on a cycle ergometer followed by a supramaximal test to verify V˙O2max. Results: Supramaximal tests verified V˙O2max in 88% of participants. Group incremental test peak V˙O2 was greater than the supramaximal test (2.27 [0.65] L·min-1 and 2.17 [0.63] L·min-1; P 

Purpose: Repeated cycles of endothelial ischemia–reperfusion injury and the resulting respiratory burst contribute to the irreversible pathophysiology of vascular diseases, and yet, the effects of ischemia reperfusion on vascular function, oxidative stress, and nitric oxide (NO) bioavailability have not been assessed simultaneously. Therefore, this study sought to examine the effects of prolonged forearm occlusion and subsequent reperfusion on NO-dependent brachial artery endothelial function. Methods: Flow-mediated dilatation was measured at baseline and 15, 30, and 45 min after 20-min forearm occlusion in 14 healthy, but physically inactive middle-aged men (53.7 ± 1.2 years, BMI: 28.1 ± 0.1 kg m−2). Venous blood samples collected from the occluded arm were analyzed for NO metabolites and markers of oxidative stress. Results: FMD was significantly depressed after the prolonged occlusion compared to baseline, with a significant reduction 15-min post-occlusion (6.6 ± 0.7 to 2.9 ± 0.4%, p < 0.001); FMD remained depressed after 30 min (4.1 ± 0.6%, p = 0.001), but was not significantly different to baseline after 45-min recovery (5.4 ± 0.7%, p = 0.079). Plasma nitrate (main time effect: p = 0.015) and nitrite (main time effect: p = 0.034) concentrations were significantly reduced after prolonged occlusion. Plasma catalase activity was significantly elevated at 4- (p = 0.016) and 45-min (p = 0.001) post-occlusion, but plasma peroxiredoxin 2 and protein carbonyl content did not change. Conclusions: Prolonged forearm occlusion resulted in acute impairment of endothelium-dependent vasodilatation of the brachial artery for at least 30 min after reperfusion. We demonstrate that this vascular dysfunction is associated with oxidative stress and reduced NO bioavailability following reperfusion.

Current physical activity guidelines for youth with type 1 diabetes (T1D) are poorly supported by empirical evidence and the optimal dose of physical activity to improve glycemic control is unknown. This case report documents the effect of acute high-intensity interval exercise (HIIE) and moderate-intensity exercise (MIE) on 24-h glycemic control in three adolescents with T1D using continuous glucose monitoring. Results highlight varied individual response to exercise across the participants. In two participants both MIE and HIIE resulted in a drop in blood glucose during exercise (-38 to -42% for MIE and -21-46% in HIIE) and in one participant both MIE and HIIE resulted in increased blood glucose (+19% and + 36%, respectively). Over the 24-h period average blood glucose was lower for all participants in the HIIE condition, and for two for the MIE condition, compared to no exercise. All three participants reported HIIE to be more enjoyable than MIE These data show both HIIE and MIE have the potential to improve short-term glycemic control in youth with T1D but HIIE was more enjoyable. Future work with a larger sample size is required to explore the potential for HIIE to improve health markers in youth with T1D.

Physical activity lowers future cardiovascular disease (CVD) risk; however, few children and adolescents achieve the recommended minimum amount of daily activity. Accordingly, there is virtue in identifying the efficacy of small volumes of high-intensity exercise for health benefits in children and adolescents for the primary prevention of CVD risk. The purpose of this narrative review is to provide a novel overview of the available literature concerning high-intensity interval-exercise (HIIE) interventions in children and adolescents. Specifically, the following areas are addressed: 1) outlining the health benefits observed following a single bout of HIIE, 2) reviewing the role of HIIE training in the management of pediatric obesity, and 3) discussing the effectiveness of school-based HIIE training. In total, 39 HIIE intervention studies were included in this review. Based upon the available data, a single bout of high-intensity exercise provides a potent stimulus for favorable, acute changes across a range of cardiometabolic outcomes that are often superior to a comparative bout of moderate-intensity exercise (14 studies reviewed). HIIE also promotes improvements in cardiorespiratory fitness and cardiometabolic health status in overweight and obese children and adolescents (10 studies reviewed) and when delivered in the school setting (15 studies reviewed). We thus conclude that high-intensity exercise is a feasible and potent method of improving a range of cardiometabolic outcomes in children and adolescents. However, further work is needed to optimize the delivery of HIIE interventions in terms of participant enjoyment and acceptability, to include a wider range of health outcomes, and to control for important confounding variables (eg, changes in diet and habitual physical activity). Finally, research into the application of HIIE training interventions to children and adolescents of different ages, sexes, pubertal status, and sociocultural backgrounds is required.

Background: Impairments in macrovascular, microvascular and autonomic function are present in asymptomatic youths with clustered cardiovascular disease risk factors. This study determines the within-day reliability and between-day reliability of a single protocol to non-invasively assess these outcomes in adolescents. Methods: Forty 12- to 15-year-old adolescents (20 boys) visited the laboratory in a fasted state on two occasions, approximately 1 week apart. One hour after a standardized cereal breakfast, macrovascular function was determined via flow-mediated dilation (FMD). Heart rate variability (root mean square of successive R-R intervals; RMSSD) was determined from the ECG-gated ultrasound images acquired during the FMD protocol prior to cuff occlusion. Microvascular function was simultaneously quantified as the peak (PRH) and total (TRH) hyperaemic response to occlusion in the cutaneous circulation of the forearm via laser Doppler imaging. To address within-day reliability, a subset of twenty adolescents (10 boys) repeated these measures 90 min afterwards on one occasion. Results: the within-day typical error and between-day typical error expressed as a coefficient of variation of these outcomes are as follows: ratio-scaled FMD, 5·1% and 10·6%; allometrically scaled FMD, 4·4% and 9·4%; PRH, 11% and 13·3%; TRH, 29·9% and 23·1%; and RMSSD, 17·6% and 17·6%. The within- and between-day test–retest correlation coefficients for these outcomes were all significant (r > 0·54 for all). Conclusion: Macrovascular, microvascular and autonomic functions can be simultaneously and non-invasively determined in adolescents using a single protocol with an appropriate degree of reproducibility. Determining these outcomes may provide greater understanding of the progression of cardiovascular disease and aid early intervention.

Purpose to examine the influence of exercise intensity on postprandial health outcomes in adolescents when exercise is accumulated throughout the day. Methods 19 adolescents (9 male, 13.7 ± 0.4 years old) completed three 1-day trials in a randomised order: (1) rest (CON); or four bouts of (2) 2 × 1 min cycling at 90% peak power with 75 s recovery (high-intensity interval exercise; HIIE); or (3) cycling at 90% of the gas exchange threshold (moderate-intensity exercise; MIE), which was work-matched to HIIE. Each bout was separated by 2 hours. Participants consumed a high fat milkshake for breakfast and lunch. Postprandial triacylglycerol (TAG), glucose, systolic blood pressure (SBP) and fat oxidation were assessed throughout the day. Results There was no effect of trial on total area under the curve (TAUC) for TAG (P = 0.87). TAUC-glucose was lower in HIIE compared to CON (P = 0.03, ES = 0.42) and MIE (P = 0.04, ES = 0.41), with no difference between MIE and CON (P = 0.89, ES = 0.04). Postprandial SBP was lower in HIIE compared to CON (P = 0.04, ES = 0.50) and MIE (P = 0.04, ES = 0.40), but not different between MIE and CON (P = 0.52, ES = 0.11). Resting fat oxidation was increased in HIIE compared to CON (P = 0.01, ES = 0.74) and MIE (P = 0.05, ES = 0.51), with no difference between MIE and CON (P = 0.37, ES = 0.24). Conclusion Neither exercise trial attenuated postprandial lipaemia. However, accumulating brief bouts of HIIE, but not MIE, reduced postprandial plasma glucose and SBP, and increased resting fat oxidation in adolescent boys and girls. The intensity of accumulated exercise may therefore have important implications for health outcomes in youth.

Method: Twenty adolescents (10 male, 14.3 ± 0.3 years) completed three 1-day trials: (1) rest (CON); (2) 8 × 1 min cycling at 90 % peak power with 75 s recovery (HIIE); (3) cycling at 90 % of the gas exchange threshold (MIE), 1 h before consuming a high-fat milkshake (1.50 g fat and 80 kJ kg−1). Postprandial TAG, SBP and fat oxidation were assessed over 4 h

Acute exercise transiently improves endothelial function and protects the vasculature from the deleterious effects of a high-fat meal (HFM). We sought to identify whether this response is dependent on exercise intensity in adolescents. Twenty adolescents (10 male, 14.3 ± 0.3 yr) completed three 1-day trials: 1) rest (CON); 2) 8 × 1 min cycling at 90% peak power with 75 s recovery [high-intensity interval exercise (HIIE)]; and 3) cycling at 90% of the gas exchange threshold [moderate-intensity exercise (MIE)] 1 h before consuming a HFM (1.50 g/kg fat). Macrovascular and microvascular endothelial function was assessed before and immediately after exercise and 3 h after the HFM by flow-mediated dilation (FMD) and laser Doppler imaging [peak reactive hyperemia (PRH)]. FMD and PRH increased 1 h after HIIE [P < 0.001, effect size (ES) = 1.20 and P = 0.048, ES = 0.56] but were unchanged after MIE. FMD and PRH were attenuated 3 h after the HFM in CON (P < 0.001, ES = 1.78 and P = 0.02, ES = 0.59). FMD remained greater 3 h after the HFM in HIIE compared with MIE (P < 0.001, ES = 1.47) and CON (P < 0.001, ES = 2.54), and in MIE compared with CON (P < 0.001, ES = 1.40). Compared with CON, PRH was greater 3 h after the HFM in HIIE (P = 0.02, ES = 0.71) and MIE (P = 0.02, ES = 0.84), with no differences between HIIE and MIE (P = 0.72, ES = 0.16). Plasma triacylglycerol concentration and total antioxidant status concentration were not different between trials. We conclude that exercise intensity plays an important role in protecting the vasculature from the deleterious effects of a HFM. Performing HIIE may provide superior vascular benefits than MIE in adolescent groups.

Introduction: Impairments in vascular function are present in asymptomatic youths with risk factors for cardiovascular disease. Exercise can promote vascular health in youth, but the effects of exercise intensity and the time course in response to acute exercise are unknown. Methods: Twenty adolescents (10 male, 14.1 ± 0.3 yr) performed the following on separate days in a counterbalanced order: 1) cycling at 90% of the gas exchange threshold (moderate-intensity exercise (MIE)) and 2) 8 × 1-min cycling at 90% peak power with 75-s recovery (high-intensity interval exercise (HIIE)). The duration of MIE (25.8 ± 2.1 min) was work-matched to HIIE (23.0 min). Macro- and microvascular functions were assessed before, immediately after, and 1 and 2 h after exercise by flow-mediated dilation (FMD) and laser Doppler imaging (total reactive hyperemia). Results: FMD was attenuated immediately after HIIE (P < 0.001, effect size (ES) = 1.20) but not after MIE (P = 0.28, ES = 0.26). Compared with that before exercise, FMD was elevated 1 and 2 h after HIIE (P < 0.001, ES = 1.33; P < 0.001, ES = 1.36) but unchanged in MIE (P = 0.67, ES = 0.10; P = 0.72, ES = 0.08). Changes in FMD were unrelated to shear or baseline arterial diameter. Compared with that in preexercise, total reactive hyperemia was always greater after MIE (P < 0.02, ES > 0.60 for all) and HIIE (P < 0.001, ES > 1.18 for all). Total reactive hyperemia was greater in HIIE compared with that in MIE immediately after (P = 0.03, ES = 0.67) and 1 h after (P = 0.01, ES = 0.62) exercise, with a trend to be greater 2 h after (P = 0.06, ES = 0.45). Conclusions: Exercise intensity is positively associated with macro- and microvascular function 1 and 2 h after exercise. Performing HIIE may provide superior vascular benefits than MIE in adolescents.

High-intensity interval training (HIIT) improves traditional cardiovascular disease (CVD) risk factors in adolescents, but no study has identified the influence of HIIT on endothelial and autonomic function in this group. Thirteen 13- to 14-yr-old adolescents (6 girls) completed six HIIT sessions over 2 wk. Each training session consisted of eight to ten 1-min repetitions of cycling at 90% peak power interspersed with 75 s of unloaded cycling. Traditional (triglycerides, cholesterol, glucose, insulin, and blood pressure) and novel [flow-mediated dilation (FMD), heart rate variability (HRV)] CVD risk factors were assessed in a fasted and postprandial state before (PRE), 1 day after (POST-1D), and 3 days after (POST-3D) training. Aerobic fitness was determined PRE and POST-3D. Two weeks of HIIT had no effect on aerobic fitness or traditional CVD risk factors determined in the fasted or postprandial state (P > 0.15). Compared with PRE, fasted FMD was improved POST-1D [P = 0.003, effect size (ES) = 0.70] but not POST-3D (P = 0.32, ES = 0.22). Fasted FMD was greater POST-1D compared with POST-3D (P < 0.04, ES = 0.48). Compared with PRE, postprandial FMD was greater POST-1D (P = 0.001, ES = 1.01) and POST-3D (P < 0.01, ES = 0.60). Fasted HRV was greater POST-1D (P = 0.001, ES = 0.71) and POST-3D (P = 0.02, ES = 0.44). The test meal lowered HRV in all laboratory visits (P < 0.001, ES = 0.59), but there were no differences in postprandial HRV between visits (P > 0.32 for all). Two weeks of HIIT enhanced endothelial function and HRV without improvements in traditional CVD risk factors. However, most of this favorable adaptation was lost POST- 3D, suggesting that regularly performing high-intensity exercise is needed to maintain these benefits.

The present study aimed to establish whether 2 weeks of high-intensity interval training would have a beneficial effect on aerobic fitness, fat oxidation, blood pressure and body mass index (BMI) in healthy adolescent boys. Ten adolescent boys (15.1 ± 0.3 years, 1.3 ± 0.2 years post-estimated peak height velocity) completed six sessions of Wingate-style high-intensity interval training over a 2-week period. The first session consisted of four sprints with training progressed to seven sprints in the final session. High-intensity interval training had a beneficial effect on maximal O2 uptake (mean change, ±90% confidence intervals: 0.19 L · min-1, ±0.19, respectively), on the O2 uptake at the gas exchange threshold (0.09 L · min-1, ±0.13) and on the O2 cost of sub-maximal exercise (-0.04 L · min-1, ±0.04). A beneficial effect on the contribution of lipid (0.06 g · min-1, ±0.06) and carbohydrate (-0.23 g · min-1, ±0.14) oxidation was observed during sub-maximal exercise, but not for the maximal rate of fat oxidation (0.04 g · min-1, ±0.08). Systolic blood pressure (1 mmHg, ±4) and BMI (0.1 kg · m2, ±0.1) were not altered following training. These data demonstrate that meaningful changes in health outcomes are possible in healthy adolescent boys after just six sessions of high-intensity interval training over a 2-week period. © 2013 © 2013 Taylor & Francis.

This study examined whether critical power (CP) in adolescents: (1) provides a landmark for maximal steady-state exercise; and (2) can be determined using 'all-out' exercise. Nine active 14-15 year olds (6 females, 3 males) performed five cycling tests: (1) a ramp test to determine VO 2peak; (2) up to four constant power output tests to determine CP; (3-4) constant power output exercise 10% above and 10% below CP; and (5) a 3 min all-out cycle test to establish the end power (EP) at 90 and 180 s of exercise. All participants completed 30 min of exercise below CP and were characterized by steady-state blood lactate and VO 2 profiles. In contrast, time to exhaustion during exercise above CP was 15.0 ± 7.0 min and characterized by an inexorable rise in blood lactate and a rise, stabilization (∼91% VO 2peak) and fall in VO 2 (∼82% VO 2peak) prior to exhaustion. Eight out of nine participants completed the 3 min test and their EPs at 90 s (148 ± 29 W) and 180 s (146 ± 30 W) were not different from CP (146 ± 27 W) (P = 0.98). The typical error of estimates for establishing CP using EP at 90 s or 180 s of the 3 min test were 25 W (19.7% CV) and 25 W (19.6% CV), respectively. CP in active adolescence provides a valid landmark for maximal steady-state exercise, although its estimation on an individual level using the 3 min all-out test may be of limited value. © Springer-Verlag 2011.