The utility of the reperfusion rate of tissue oxygen saturation as a measure of vascular endothelial function in adolescents: reliability, validity and sensitivity.

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.

The effect of 4 weeks of high-intensity interval training and 2 weeks of detraining on cardiovascular disease risk factors in male adolescents.

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. ABSTRACT: High-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 > 0.14) or blood biomarkers (all P > 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.

Effects of High-Intensity Interval Training on the Vascular and Autonomic Components of the Baroreflex at Rest in Adolescents.

PURPOSE: In a sample of healthy adolescents, the authors aimed to investigate the effects of high-intensity interval exercise (HIIE) training and detraining on baroreflex sensitivity (BRS) and it's vascular and autonomic components at rest. METHODS: Nineteen volunteers were randomly allocated to (1) 4 weeks HIIE training performed 3 times per week or (2) a control condition with no intervention for the same duration as HIIE training. PRE, POST, and following 2 weeks of detraining resting supine heart rate and blood pressure were measured, and a cross-spectral method (integrated gain [gain in low frequency]) was used to determine BRS gain. Arterial compliance (AC) was assessed as the BRS vascular component. LFgain divided by AC (LFgain/AC) was used as the autonomic determinant of BRS. RESULTS: The HIIE training was completed with 100% compliance. HIIE did not change resting gain in low frequency (LFgain) (P = .66; effect size = 0.21), AC (P = .44; effect size = 0.36), or LFgain/AC (P = .68; effect size = 0.19) compared to control. CONCLUSION: Four weeks of HIIE training does not change BRS and its autonomic and vascular determinant in a sample of healthy adolescents at rest.

Highly Cushioned Shoes Improve Running Performance in Both the Absence and Presence of Muscle Damage.

PURPOSE: We tested the hypotheses that a highly cushioned running shoe (HCS) would 1) improve incremental exercise performance and reduce the oxygen cost (Oc) of submaximal running, and 2) attenuate the deterioration in Oc elicited by muscle damage consequent to a downhill run. METHODS: Thirty-two recreationally active participants completed an incremental treadmill test in an HCS and a control running shoe (CON) for the determination of Oc and maximal performance. Subsequently, participants were pair matched and randomly assigned to one of the two footwear conditions to perform a moderate-intensity running bout before and 48 h after a 30-min downhill run designed to elicit muscle damage. RESULTS: Incremental treadmill test performance was improved (+5.7%; +1:16 min:ss; P < 0.01) in the HCS when assessed in the nondamaged state, relative to CON. This coincided with a significantly lower Oc (-3.2%; -6 mL·kg-1·km-1; P < 0.001) at a range of running speeds and an increase in the speed corresponding to 3 mM blood lactate (+3.2%; +0.4 km·h-1; P < 0.05). As anticipated, the downhill run resulted in significant changes in biochemical, histological, and perceptual markers of muscle damage, and a significant increase in Oc (+5.2%; 10.1 mL·kg-1·km-1) was observed 48 h post. In the presence of muscle damage, Oc was significantly lower in HCS (-4.6%; -10 mL·kg-1·km-1) compared with CON. CONCLUSIONS: These results indicate that HCS improved incremental exercise performance and Oc in the absence of muscle damage and show, for the first time, that despite worsening of Oc consequent to muscle damage, improved Oc in HCS is maintained.

Steady-state [Formula: see text] above MLSS: evidence that critical speed better represents maximal metabolic steady state in well-trained runners.

The metabolic boundary separating the heavy-intensity and severe-intensity exercise domains is of scientific and practical interest but there is controversy concerning whether the maximal lactate steady state (MLSS) or critical power (synonymous with critical speed, CS) better represents this boundary. We measured the running speeds at MLSS and CS and investigated their ability to discriminate speeds at which [Formula: see text] was stable over time from speeds at which a steady-state [Formula: see text] could not be established. Ten well-trained male distance runners completed 9-12 constant-speed treadmill tests, including 3-5 runs of up to 30-min duration for the assessment of MLSS and at least 4 runs performed to the limit of tolerance for assessment of CS. The running speeds at CS and MLSS were significantly different (16.4 ± 1.3 vs. 15.2 ± 0.9 km/h, respectively; P < 0.001). Blood lactate concentration was higher and increased with time at a speed 0.5 km/h higher than MLSS compared to MLSS (P < 0.01); however, pulmonary [Formula: see text] did not change significantly between 10 and 30 min at either MLSS or MLSS + 0.5 km/h. In contrast, [Formula: see text] increased significantly over time and reached [Formula: see text] at end-exercise at a speed ~ 0.4 km/h above CS (P < 0.05) but remained stable at a speed ~ 0.5 km/h below CS. The stability of [Formula: see text] at a speed exceeding MLSS suggests that MLSS underestimates the maximal metabolic steady state. These results indicate that CS more closely represents the maximal metabolic steady state when the latter is appropriately defined according to the ability to stabilise pulmonary [Formula: see text].

The acute effect of high- and moderate-intensity interval exercise on vascular function before and after a glucose challenge in adolescents.

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. ABSTRACT: Interventions 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 < 0.01) with no changes in HIIR and MIIR (both P > 0.59). There was no change in PRH after the OGTT (all P > 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.

Effects of exercise intensity on vascular and autonomic components of the baroreflex following glucose ingestion in adolescents.

PURPOSE: To investigate the effects of an oral glucose tolerance test (OGTT) on baroreflex sensitivity (BRS) in a sample of healthy adolescents, and how acute exercise bouts of different intensities alter the effects of the OGTT on BRS. METHODS: Thirteen male adolescents (14.0 ± 0.5 years) completed three conditions on separate days in a counterbalanced order: (1) high-intensity interval exercise (HIIE); (2) moderate-intensity interval exercise (MIIE); and (3) resting control (CON). At ~ 90 min following the conditions, participants performed an OGTT. Supine heart rate and blood pressure were monitored continuously at baseline, 60 min following the conditions, and 60 min following the OGTT. A cross-spectral method (LFgain) was used to determine BRS gain. Arterial compliance (AC) was assessed as the BRS vascular component. LFgain divided by AC (LFgain/AC) was used as the autonomic component. RESULTS: Although non-significant, LFgain moderately decreased post-OGTT when no exercise was performed (pre-OGTT = 24.4 ± 8.2 ms mmHg- 1; post-OGTT = 19.9 ± 5.6 ms mmHg- 1; ES = 0.64, P > 0.05). This was attributed to the decrease in LFgain/AC (pre-OGTT = 1.19 ± 0.5 ms µm- 1; post-OGTT = 0.92 ± 0.24 ms µm- 1; ES = 0.69, P > 0.05). Compared to CON (Δ = - 4.4 ± 8.7 ms mmHg- 1), there were no differences for the pre-post-OGTT delta changes in LF/gain for HIIE (Δ = - 3.5 ± 8.2 ms mmHg- 1) and MIIE (Δ = 1.3 ± 9.9 ms mmHg- 1) had no effects on BRS following the OGTT (all ES < 0.5). Similarly, compared to CON (Δ = - 0.23 ± 0.40 ms µm- 1) there were no differences for the pre-post-OGTT delta changes in LF/gain for HIIE (Δ = - 0.22 ± 0.49 ms µm- 1) and MIIE (Δ = 0.13 ± 0.36 ms µm- 1). CONCLUSION: A moderate non-significant decrease in BRS was observed in adolescents following a glucose challenge with no apparent effects of exercise.

Reliability of low-flow vasoreactivity in the brachial artery of adolescents.

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.