The Improvement in Exercise Performance during Reduced Muscle Mass Exercise is Associated with an Increase in Femoral Blood Flow in Older and Younger Endurance-Trained Athletes.

This study investigated whether the improved performance observed with maximal self-paced single-leg (SL), compared with double-leg (DL) cycling, is associated with enhanced femoral blood flow and/or altered tissue oxygenation. The hyperaemic response to exercise was assessed in younger and older athletes. Power output was measured in 12 older (65 ± 4 y) and 12 younger (35 ± 5 y) endurance-trained individuals performing 2 x 3 min maximal self-paced exercise using SL and DL cycling. Blood flow (BF) in the femoral artery was assessed using Doppler ultrasound and muscle oxygenation was measured using near-infrared spectroscopy on the vastus lateralis. SL cycling elicited a greater power output (295 ± 83 vs 265 ± 70 W, P < 0.001) and peak femoral BF (1749.1 ± 533.3 vs 1329.7 ± 391.7 ml/min, P < 0.001) compared with DL cycling. Older individuals had a lower peak BF in response to exercise (1355.4 ± 385.8 vs 1765.2 ± 559.6 ml/min, P = 0.019) compared with younger individuals. Peak BF in response to exercise was correlated with power output during SL (r = 0.655, P = 0.002) and DL (r = 0.666, P = 0.001) cycling. The greater exercise performance during SL compared with DL cycling may be partly explained by a greater hyperaemic response when reducing active muscle mass. Despite regular endurance training, older athletes had a lower femoral BF in response to maximal self-paced exercise compared with younger athletes.

Single- Versus Double-Leg Cycling: Small Muscle Mass Exercise Improves Exercise Capacity to a Greater Extent in Older Compared With Younger Population.

Manipulating the amount of muscle mass engaged during exercise can noninvasively inform the contribution of central cardiovascular and peripheral vascular-oxidative functions to endurance performance. To better understand the factors contributing to exercise limitation in older and younger individuals, exercise performance was assessed during single-leg and double-leg cycling. 16 older (67 ± 5 years) and 14 younger (35 ± 5 years) individuals performed a maximal exercise using single-leg and double-leg cycling. The ratio of single-leg to double-leg cycling power (RatioPower SL/DL) was compared between age groups. The association between fitness (peak oxygen consumption, peak power output, and physical activity levels) and RatioPower SL/DL was explored. The RatioPower SL/DL was greater in older compared with younger individuals (1.14 ± 0.11 vs. 1.06 ± 0.08, p = .041). The RatioPower SL/DL was correlated with peak oxygen consumption (r = .886, p < .001), peak power output relative to body mass (r = .854, p < .001), and levels of physical activity (r = .728, p = .003) in the younger but not older subgroup. Reducing the amount of muscle mass engaged during exercise improved exercise capacity to a greater extent in older versus younger population and may reflect a greater reduction in central cardiovascular function compared with peripheral vascular-oxidative function with aging.

Vascular adaptation to exercise: a systematic review and audit of female representation.

Biological sex is a salient factor in exercise-induced vascular adaptation. Although a male bias is apparent in the literature, the methodological quality of available studies in females is not yet known. This systematic review with narrative synthesis aimed to assess available evidence of exercise interventions on endothelial function, measured using flow-mediated dilation, in otherwise healthy individuals and athletes. A standardized audit framework was applied to quantify the representation of female participants. Using a tiered grading system, studies that met best-practice recommendations for conducting physiological research in females were identified. A total of 210 studies in 5,997 participants were included, with 18% classified as athletes. The primary exercise mode and duration were aerobic (49%) and acute (61%), respectively. Despite 53% of studies (n = 111) including at least one female, female participants accounted for only 39% of the total study population but 49% of the athlete population. Majority (49%) of studies in females were conducted in premenopausal participants. No studies in naturally menstruating, hormonal contraceptive-users or in participants experiencing menstrual irregularities met all best-practice recommendations. Very few studies (∼5%) achieved best-practice methodological guidelines for studying females and those that did were limited to menopause and pregnant cohorts. In addition to the underrepresentation of female participants in exercise-induced vascular adaptation research, there remains insufficient high-quality evidence with acceptable methodological control of ovarian hormones. To improve the overall methodological quality of evidence, adequate detail regarding menstrual status should be prioritized when including females in vascular and exercise research contexts.

Intraindividual variability in sleep among athletes: A systematic review of definitions, operationalizations, and key correlates.

Via systematic review with narrative synthesis of findings, we aimed to document the ways by which researchers have defined, operationalized, and examined sleep variability among athletes. We identified studies in which scholars examined intraperson variability in sleep among athletes via a search of six databases (Web of Science, Embase, Medline, PsycINFO, CINHAL Plus, and ProQuest Dissertations and Theses Global) using a protocol that included keywords for the target outcome (sleep*), population (athlet* OR sport*), and outcome operationalization (variability OR variation OR "standard deviation" OR fluctuate OR fluctuation OR stability OR instability OR reactivity OR IIV OR intraindividual). We complemented this primary search with citation searching of eligible articles. Assessments of study quality captured eight core elements, namely aims/hypotheses, sample size justification, sample representativeness, number of days sleep assessed, measures of sleep and its correlates, missing data, and inferences and conclusions. From a total of 1209 potentially relevant papers, we identified 16 studies as meeting our eligibility criteria. Concept definitions of variability were notably absent from this work and where available were vague. Quantitative deviations from one's typical level of target sleep metrics reflected the essence by which all but one of the research teams operationalized sleep variability. We assessed the overall quality of empirical work as moderate in nature. We propose a working definition of sleep variability that can inform knowledge generation on the temporal, day-to-day dynamics of sleep functioning that is required for personalized interventions for optimizing sleep health.

Questionnaires Measuring Physical Activity in Clinical Pediatric Populations: A Systematic Review.

PURPOSE: Regular physical activity (PA) is a cornerstone therapy for many childhood chronic health conditions, and questionnaires offer a simple method for monitoring PA and identifying children who do not meet clinical practice guidelines. The purpose of this systematic review is to determine which questionnaires are most efficacious for assessing PA in children with chronic health conditions. METHODS: Systematic literature searches were conducted through ProQuest, MEDLINE, Scopus, and SPORTDiscus from January 2010 to August 2020 to identify studies that measured PA with a validated questionnaire in children and adolescents aged 3-18 years old with chronic health conditions. In eligible studies, the validity and reliability of questionnaires were identified, and the modified COnsensus-based Standards for the selection of health status Measurement INstruments checklist and Grading of Recommendations, Assessment, Development, and Evaluations were used to assess the quality and strength of evidence and risk of bias. RESULTS: Four thousand four hundred and seventy-eight references were extracted, and 10 articles were included for review. From 10 eligible studies, 6 questionnaires were identified, none of which adequately measure PA in clinical pediatric populations. CONCLUSION: Questionnaires to adequately measure PA in children with chronic conditions are lacking. This compromises the identification of those who do not meet PA guidelines, limiting the opportunity to identify and address factors contributing to low PA levels.

Is there an athlete's artery? A comparison of brachial and femoral artery structure and function in male strength, power and endurance athletes.

OBJECTIVES: Exercise places physiological demands upon the cardiovascular system, subsequently leading to adaptations in structure and function. Different exercise modalities (endurance, strength and power) lead to distinct hemodynamic demands and, possibly, different patterns of adaptation. Our aim was to assess and compare brachial and femoral artery function and structure in elite level athletes engaged in endurance, strength and power sports. DESIGN: cross sectional comparison. METHODS: 30 male elite athletes (runners n=10, powerlifters n=11, weightlifters n=9) and 23 healthy controls were recruited. Brachial and femoral arterial diameters were assessed using ultrasound. Arterial function (brachial and femoral arteries) was determined using the flow mediated dilation (FMD) technique and body composition using body mass index (BMI) and body surface area (BSA). RESULTS: Weightlifters had significantly larger brachial arterial diameters compared to controls (4.39±0.34 vs 3.86±0.42mm, p<0.01). As weightlifter and power athletes had significantly higher body mass, BMI and BSA, we adjusted diameter for BSA. BSA-correction ameliorated differences in brachial artery resting diameters between athletes and controls. However, BSA-corrected femoral artery diameter was significantly larger in runners compared to controls (3.51±0.28 vs 3.25±0.34mm, p<0.05). There were no differences in brachial FMD between groups. Femoral artery FMD was significantly higher in runners and weightlifters compared to controls (p<0.05 for both groups). CONCLUSIONS: Heterogeneous, limb-specific structural and functional vascular adaptation is evident in athletes, which may be influenced by exercise modality. Further, vascular remodelling relates to differences in body shape, specifically body composition, which should be accounted for when comparing athletes.

eLearning in Physical Therapy: Lessons Learned From Transitioning a Professional Education Program to Full eLearning During the COVID-19 Pandemic.

OBJECTIVE: The objectives of this cross-sectional qualitative study were to explore the perspectives of students enrolled in one physical therapist undergraduate education program in Australia about their experience with transitioning to full eLearning and student recommendations to improve the learning experience during the COVID-19 pandemic. METHODS: Seven focus groups with 28 undergraduate physical therapist students were conducted following the transitioning to full eLearning as a result of strict physical distancing measures. Focus group questions explored the students' experiences of the transition from face-to-face to full eLearning approach and the students' recommendations for improving future eLearning experiences. Data were analyzed using inductive thematic analysis. RESULTS: The 3 themes identified were: (1) students presenting heightened negative feelings such as anxiety, stress, and reduced motivation to study; (2) students continuing to value the face-to-face learning, as it provided social support and facilitated feedback from peers and tutors; (3) student recommendations for eLearning included having online lectures and supplementary videos but face-to-face practical classes and developing healthy learning habits such as scheduled times for studying, exercise, and other activities that regulate stress. CONCLUSIONS: The transition to a full eLearning approach in an undergraduate physical therapist education program during the COVID-19 pandemic revealed that students had heightened negative emotions due to the pandemic. Students valued face-to-face practical classes to learn and receive social support from peers and tutors. Student recommendations to future eLearning suggested changes to curriculum development geared toward a greater blended approach to learning. Blended learning may include using online lectures instead of face-to-face lectures and online resources to supplement student learning of practical skills. IMPACT: As higher education moves toward a more blended approach, lessons learned from this study can help educators design future physical therapist education programs. The findings can also assist programs in delivering a full eLearning approach as the COVID-19 pandemic continues.

Effects of Land versus Water Walking Interventions on Vascular Function in Older Adults.

PURPOSE: Endothelial dysfunction is an early and integral atherogenic event. Interventions that improve endothelial function also reduce cardiovascular risk. Due largely to the direct hemodynamic effects of repetitive exercise on the artery wall, exercise training has shown to enhance endothelial function. Land walking (LW) and water walking (WW) induce distinct hemodynamic responses, so the comparison of their effects provides an approach to study shear stress effects on endothelial function. We hypothesized that LW and WW training would have different effects on peripheral artery endothelial function. METHODS: Fifty-one sedentary, older (age = 61.9 ± 6.6 yr, 23.5% male) individuals were randomized into one of three groups: control (n = 16), or one of two exercise groups consisting of 3 × 50 min supervised and individually tailored walking sessions per week for 24 consecutive weeks, performed either on LW (n = 17) or on WW (n = 18). Brachial artery endothelial function (flow-mediated dilation) and smooth muscle cell function (glyceryl trinitrate administration) were tested in all participants before (week 0) and after (week 24) the intervention. RESULTS: Differences were apparent in flow-mediated dilation change between the LW group (week 0, 5.39% ± 0.71%, to week 24, 7.77% ± 0.78%; P = 0.009) and the control group (week 0, 5.87% ± 0.73%, to week 24, 5.78% ± 0.78%). No differences in artery dilation response were found after glyceryl trinitrate administration (all P > 0.05). CONCLUSION: This study suggests that 6-month center-based LW may be superior to WW in terms of improvement in arterial endothelial function in older sedentary individuals.

High-intensity interval training in patients with left ventricular assist devices: A pilot randomized controlled trial.

BACKGROUND: Left ventricular assist device (LVAD) implantation is an established treatment for patients with advanced heart failure. To date, studies evaluating the impact of aerobic training in patients with LVADs have focused on moderate-intensity exercise. METHODS: This pilot randomized controlled trial compared the effects of high-intensity interval training (HIIT) with those of moderate-intensity continuous training (MICT) on peak oxygen consumption (V̇O2 peak) in patients with LVADs. Secondary outcomes included 6-minute walk test distance, flow-mediated dilation, and anthropometry. Assessments were conducted at baseline and after 12 weeks of supervised training performed 3 times weekly. Participants were randomized to HIIT (4 sets of 4 minutes at 80%-90% V̇O2 reserve, alternating with 3 minutes at 50%-60% V̇O2 reserve) or MICT groups (28 minutes continuously at 50%-60% V̇O2 reserve). Within and between-group differences were analyzed using linear mixed models. Data are expressed as marginal means with 95% confidence intervals or as mean ± SD. RESULTS: A total of 21 participants were randomized (HIIT: age 57.7 ± 13.1 years; n = 11 and MICT: age 55.6 ± 14.2 years; n = 10) (mean ± SD). No major adverse events occurred in response to training in either group. HIIT significantly improved V̇O2 peak (15.6 [13.2-17.8] to 18.4 [16.0-20.8] ml/kg/min) (marginal mean [95% CI]) compared with MICT (16.2 [13.8-18.7] to 17.2 [14.6-19.7] ml/kg/min; p < 0.05 between groups). No significant group differences were detected in secondary outcomes. CONCLUSION: In patients with LVADs, HIIT was well tolerated and increased aerobic capacity more than MICT. These preliminary findings support the prescription of high-intensity exercise in clinically stable patients with LVADs but warrant validation in a larger sample and across a broader range of physiologic and clinical outcomes. CLINICAL TRIAL REGISTRATION: URL: https://www.anzctr.org.au, unique identifier: ACTRN12616001596493.

Land-walking vs. water-walking interventions in older adults: Effects on aerobic fitness.

BACKGROUND: Low cardiorespiratory fitness is an independent predictor of all-cause and cardiovascular mortality, and interventions that increase fitness reduce risk. Water-walking decreases musculoskeletal impact and risk of falls in older individuals, but it is unclear whether water-walking improves aerobic fitness in the same way as weight-dependent land-walking. This randomized controlled trial involved 3 intervention groups-a no-exercise control group (CG), a land-walking (LW) group, and a water-walking (WW) group-to investigate the comparative impacts of LW and WW to CG on fitness. METHODS: Both exercise groups attended individually tailored, center-based, intensity-matched 3 × weekly sessions for 24 weeks, which progressed to 150 min of exercise per week. This was followed by a 24-week no-intervention period. Maximal graded exercise tests were performed on a treadmill at Weeks 0, 24, and 48. RESULTS: Maximal oxygen uptake increased from Week 0 to Week 24 in both exercise groups (0.57 ± 0.62 mL/kg/min, 0.03 ± 0.04 L/min for LW; 0.93 ± 0.75 mL/kg/min, 0.06 ± 0.06 L/min for WW, mean ± SE) compared to the CG (-1.75 ± 0.78 mL/kg/min, -0.16 ± 0.05 L/min) (group × time, p < 0.05). Time to exhaustion increased significantly following LW only (123.4 ± 25.5 s), which was significantly greater (p = 0.001) than the CG (24.3 ± 18.5 s). By Week 48, the training-induced adaptations in the exercise groups returned to near baseline levels. CONCLUSION: Our study supports current physical-activity recommendations that 150 min/week of moderate-intensity exercise produces improvements in fitness in previously sedentary older individuals. Also, LW and WW elicit similar improvements in fitness if conducted at the same relative intensities. Exercise-naïve older individuals can benefit from the lower impact forces and decreased risk of falls associated with WW without compromising improvements in cardiorespiratory fitness.

Land- versus water-walking interventions in older adults: Effects on body composition.

OBJECTIVES: Increasing physical activity is a priority worldwide, including for older adults who may have difficulty performing traditional forms of exercise, and for whom retention of muscle mass is an important consideration. Water-based exercise may provide an alternative if benefits are comparable. We compared the impact on body composition of 24-week water- versus land-walking interventions in healthy but inactive older adults. DESIGN: Randomised, controlled trial. METHODS: 72 participants (62.5±6.8yr) were randomised to a land-walking (LW), water-walking (WW) or control (C) group in a supervised centre-based program. The exercise groups trained 3 times/week at matched intensity (%HRR), increasing from 40-45% to 55-65% heart rate reserve (HRR). Height, weight, body mass index (BMI), waist and hip girths were recorded; dual X-ray absorptiometry (DXA) provided fat and lean tissue masses. Participants were re-assessed 24 weeks after completion of the intervention. RESULTS: There were no significant changes in body mass or BMI following either exercise protocol, however central adiposity was reduced in both exercise groups, and the WW group increased lower limb lean mass. These benefits did not persist over the follow-up period. CONCLUSIONS: Exercise can confer beneficial effects on body composition which are not evident when examining weight or BMI. Both WW and LW improved body composition. Water walking can be recommended as an exercise strategy for this age group due to its beneficial effects on body composition which are similar to, or exceed, those associated with land-walking. For benefits to persist, it appears that exercise needs to be maintained.

Differential impact of water immersion on arterial blood flow and shear stress in the carotid and brachial arteries of humans.

Arterial shear stress is a potent stimulus to vascular adaptation in humans. Typically, increases in retrograde shear have been found to acutely impair vascular function while increases in antegrade shear enhance function. We hypothesized that blood flow and shear stress through the brachial and carotid arteries would change in a similar manner in response to water immersion, an intervention which modifies hemodynamics. Nine healthy young male subjects were recruited to undergo controlled water immersion in a standing upright position to the level of the right atrium in 30°C water. Diameters were continuously and simultaneously recorded in the brachial and common carotid arteries along with mean arterial pressure (MAP), cardiac output (CO), and heart rate before, during, and after 10 min of immersion. MAP and CO increased during water immersion (baseline vs. 8-10 min; 80 ± 9 vs. 91 ± 12 mmHg; and 4.8 ± 0.7 vs. 5.1 ± 0.6 L/min, P < 0.01 and P < 0.05, respectively). We observed a differential regulation of flow and shear stress patterns in the brachial and carotid arteries in response to water immersion; brachial conductance decreased markedly in response to immersion (1.25 ± 0.56 vs. 0.57 ± 0.30 mL.min/mmHg, P < 0.05), whereas it was unaltered in the carotid artery (5.82 ± 2.14 vs. 5.60 ± 1.59). Our findings indicate that adaptations to systemic stimuli and arterial adaptation may be vessel bed specific in humans, highlighting the need to assess multiple vascular sites in future studies.

Left ventricular morphology and function in adolescents: Relations to fitness and fatness.

BACKGROUND: Obesity in childhood predisposes individuals to cardiovascular disease and increased risk of premature all-cause mortality. The aim of this study was to determine differences in LV morphology and function in obese and normal-weight adolescents. Furthermore, relationships between LV outcomes, cardiorespiratory fitness (CRF) and adiposity were explored. METHODS: LV morphology was assessed using magnetic resonance imaging (MRI) in 20 adolescents (11 normal-weight [BMI equivalent to 18kg/m2-25kg/m2] and 9 obese [BMI equivalent to ≥30kg/m2]); 13.3±1.1years, 45% female, Tanner puberty stage 3 [2-4]) using magnetic resonance imaging (MRI). Global longitudinal strain (GLS), strain rate (SR) and traditional echocardiographic indices were used to assess LV function. CRF (peak oxygen consumption), percent body fat (dual-energy x-ray absorptiometry), abdominal adipose tissue (MRI), and blood biochemistry markers were also evaluated. RESULTS: Adolescents with obesity showed significantly poorer LV function compared to normal-weight adolescents (P<0.05) indicated by higher GLS (+6.29%) and SR in systole (+0.17s-1), and lower SR in early diastole (-0.61s-1), and tissue Doppler velocities (S' -2.7cm/s; e' -2.3cm/s; A' -1.1cm/s). There were no group differences in LV morphology when indexed to fat free mass (P>0.05). Moderate to strong associations between myocardial contractility and relaxation, adiposity, arterial blood pressure and cardiorespiratory fitness were noted (r=0.49-0.71, P<0.05). CONCLUSION: Obesity in adolescence is associated with altered LV systolic and diastolic function. The notable relationship between LV function, CRF and adiposity highlights the potential utility of multidisciplinary lifestyle interventions to treat diminished LV function in this population. CLINICAL TRIAL REGISTRATION: NCT01991106.

The effect of water immersion during exercise on cerebral blood flow.

INTRODUCTION: Regular exercise induces recurrent increases in cerebrovascular perfusion. In peripheral arteries, such episodic increases in perfusion are responsible for improvement in arterial function and health. We examined the hypothesis that exercise during immersion augments cerebral blood flow velocity compared with intensity-matched land-based exercise. METHODS: Fifteen normotensive participants were recruited (26 ± 4 yr, 24.3 ± 1.9 kg·m). We continuously assessed mean arterial blood pressure, HR, stroke volume, oxygen consumption, and blood flow velocities through the middle and posterior cerebral arteries before, during, and after 20-min bouts of water- and land-based stepping exercise of matched intensity. The order in which the exercise conditions were performed was randomized between subjects. Water-based exercise was performed in 30°C water to the level of the right atrium. RESULTS: The water- and land-based exercise bouts were closely matched for oxygen consumption (13.3 mL·kg·min (95% confidence interval (CI), 12.2-14.6) vs 13.5 mL·kg·min (95% CI, 12.1-14.8), P = 0.89) and HR (95 bpm (95% CI, 90-101) vs 96 bpm (95% CI, 91-102), P = 0.65). Compared with land-based exercise, water-based exercise induced an increase in middle cerebral artery blood flow velocity (74 cm·s (95% CI, 66-81) vs 67 cm·s (95% CI, 60-74) P < 0.001), posterior cerebral artery blood flow velocity (47 cm·s (95% CI, 40-53) vs 43 cm·s (95% CI, 37-49), P < 0.001), mean arterial blood pressure (106 mm Hg (95% CI, 100-111) vs 101 mm Hg (95% CI, 95-106), P < 0.001), and partial pressure of expired CO2 (P ≤ 0.001). CONCLUSIONS: Our findings suggest that water-based exercise augments cerebral blood flow, relative to land-based exercise of similar intensity, in healthy humans.

Distinct effects of blood flow and temperature on cutaneous microvascular adaptation.

PURPOSE: We performed two experiments to determine whether cutaneous microvascular adaptations in response to repeated core temperature (Tc) elevation are mediated by increases in skin blood flow (SkBF) and/or skin temperature. METHODS: Healthy subjects participated for 8 wk in thrice-weekly bouts of 30-min lower limb heating (40°C). In study 1, both forearms were "clamped" at basal skin temperature throughout each heating bout (n = 9). Study 2 involved identical lower limb heating, with the forearms under ambient conditions (unclamped, n = 10). In both studies, a cuff was inflated around one forearm during the heating bouts to assess the contribution of SkBF and temperature responses. We assessed forearm SkBF responses to both lower limb (systemic reflex) heating and to local heating of the forearm skin, pre- and postintervention. RESULTS: Acutely, lower limb heating increased Tc (study 1, 0.63°C ± 0.15°C; study 2, 0.69°C ± 0.19°C; P < 0.001) and forearm SkBF (study 1, 0.13 ± 0.03 vs 1.52 ± 0.51; study 2, 0.14 ± 0.01 vs 1.17 ± 0.38 cutaneous vascular conductance (CVC); P < 0.001), with skin responses significantly attenuated in the cuffed forearm (P < 0.01). SkBF responses to local heating decreased in study 1 (clamped forearms; week 0 vs week 8, 1.46 ± 0.52 vs 0.99 ± 0.44 CVC; P < 0.05), whereas increases occurred in study 2 (unclamped; week 0 vs week 8, 1.89 ± 0.57 vs 2.27 ± 0.52 CVC; P < 0.05). Cuff placement abolished local adaptations in both studies. CONCLUSIONS: Our results indicate that repeated increases in SkBF and skin temperature result in increased skin flux responses to local heating, whereas repeated increases in SkBF in the absence of change in skin temperature induced the opposite response. Repeated increases in Tc induce intrinsic microvascular changes, the nature of which are dependent upon both SkBF and skin temperature.

Sympathetic nervous system activation, arterial shear rate, and flow-mediated dilation.

The aim of this study was to examine the contribution of arterial shear to changes in flow-mediated dilation (FMD) during sympathetic nervous system (SNS) activation in healthy humans. Ten healthy men reported to our laboratory four times. Bilateral FMD, shear rate (SR), and catecholamines were examined before/after 10-min of -35-mmHg lower body negative pressure (LBNP10). On day 1, localized forearm heating (LBNP10+heat) was applied in one limb to abolish the increase in retrograde SR associated with LBNP. Day 2 involved unilateral cuff inflation to 75 mmHg around one limb to exaggerate the LBNP-induced increase retrograde SR (LBNP10+cuff). Tests were repeated on days 3 and 4, using 30-min interventions (i.e., LBNP30+heat and LBNP30+cuff). LBNP10 significantly increased epinephrine levels and retrograde SR and decreased FMD (all P < 0.05). LBNP10+heat prevented the increase in retrograde SR, whereas LBNP10+cuff further increased retrograde SR (P < 0.05). Heating prevented the decrease in percent FMD (FMD%) after LBNP10 (interaction effect, P < 0.05), whereas cuffing did not significantly exaggerate the decrease in FMD% (interaction effect, P > 0.05). Prolongation of the LBNP stimulus for 30-min normalized retrograde SR, catecholamine levels, and FMD (all P > 0.05). Attenuation of retrograde SR during 30 min (LBNP30+heat) was associated with increased FMD% (interaction effects, P < 0.05), whereas increased retrograde SR (LBNP30+cuff) diminished FMD% (interaction effects, P < 0.05). These data suggest that LBNP-induced SNS stimulation decreases FMD, at least in part due to the impact of LBNP on arterial shear stress. Prolonged LBNP stimulation was not associated with changes in SR or FMD%. Our data support a role for changes in SR to the impact of SNS stimulation on FMD.

Cardiovascular responses to water immersion in humans: impact on cerebral perfusion.

Episodic increases in cerebrovascular perfusion and shear stress may have beneficial impacts on endothelial function that improve brain health. We hypothesized that water immersion to the level of the right atrium in humans would increase cerebral perfusion. We continuously measured, in 9 young (means ± SD, 24.6 ± 2.0 yr) healthy men, systemic hemodynamic variables along with blood flows in the common carotid and middle and posterior cerebral arteries during controlled filling and emptying of a water tank to the level of the right atrium. Mean arterial pressure (80 ± 9 vs. 91 ± 12 mmHg, P < 0.05), cardiac output (4.8 ± 0.7 vs. 5.1 ± 0.6 l/min, P < 0.05) and end-tidal carbon dioxide (PetCO2, 39.5 ± 2.0 vs. 44.4 ± 3.5 mmHg, P < 0.05) increased with water immersion, along with middle (59 ± 6 vs. 64 ± 6 cm/s, P < 0.05) and posterior cerebral artery blood flow velocities (41 ± 9 vs. 44 ± 10 cm/s, P < 0.05). These changes were reversed when the tank was emptied. Water immersion is associated with hemodynamic and PetCO2 changes, which increase cerebral blood velocities in humans. This study provides an evidence base for future studies to examine the potential additive effect of exercise in water on improving cerebrovascular health.

Repeated core temperature elevation induces conduit artery adaptation in humans.

PURPOSE: Shear stress is a known stimulus to vascular adaptation in humans. However, it is not known whether thermoregulatory reflex increases in blood flow and shear can induce conduit artery adaptation. METHODS: Ten healthy young volunteers therefore underwent 8 weeks of 3 × weekly bouts of 30 min lower limb heating (40 °C) during which the upper body was not directly heated. Throughout each leg heating session, a pneumatic cuff was placed on one forearm and inflated to unilaterally restrict reflex-mediated blood flow responses. RESULTS: Each bout of leg heating significantly increased brachial artery shear rate in the uncuffed arm (96 ± 97 vs 401 ± 96 l/s, P < 0.01), whereas no change was apparent in the cuffed arm (83 ± 69 vs 131 ± 76 l/s, P = 0.67). Repeated episodic exposure to leg heating enhanced brachial artery endothelial function (measured by flow-mediated dilation) in the uncuffed arm from week 0 (5.2 ± 1.9 %) to week 4 (7.7 ± 2.6 %, P < 0.05), before returning to baseline levels by week 8. No adaptation was evident in the cuffed arm. CONCLUSIONS: We conclude that repeated increases in core temperature, induced via lower limb heating, resulted in upper limb conduit artery vascular adaptation which was dependent upon increases in shear stress. To our knowledge this is the first study to establish a beneficial systemic impact of thermoregulatory reflexes on conduit artery function in humans.

The effect of exergaming on vascular function in children.

OBJECTIVES: To assess whether exergaming can induce measurable changes in heart rate (HR), energy expenditure (EE), and flow-mediated dilation (FMD) arterial function in healthy children. STUDY DESIGN: Fifteen children (8 males, 10.1 ± 0.7 years, body mass index 17.9 ± 2.4 kg.m(-2)) undertook a graded exercise test and 2 × 15 minute exergaming sessions (Xbox 360-Kinect); high intensity exergaming (HiE, Kinect Sports-200 m Hurdles) and low intensity exergaming (LoE, Kinect Sports-Ten Pin Bowling). Brachial artery FMD, a measure of endothelial function and arterial health, was measured before and immediately after each exergaming intervention. Actihearts were used to measure EE and HR during game play and a physical activity enjoyment scale assessed enjoyment. RESULTS: Average HR during HiE (146 ± 11 beats per minute) was greater than during LoE (104 ± 11 beats per minute, P < .05), a pattern reinforced by EE data (HiE 294.6 ± 75.2 J.min(-1).kg(-1), LoE 73.7 ± 44.0 J.min(-1).kg(-1), P < .05). FMD decreased after HiE (P < .05), whereas no change was observed following LoE. Subjects reported no differences in enjoyment between LoE and HiE. CONCLUSION: HiE, but not LoE, induced large HR and EE responses that were associated with effects on vascular function. This study suggests that an acute bout of HiE exergaming may provide a substrate for beneficial arterial adaptations in children.

A comparison of caffeine versus pseudoephedrine on cycling time-trial performance.

Both caffeine (CAF) and pseudoephedrine (PSE) are proposed to be central nervous system stimulants. However, during competition, CAF is a permitted substance, whereas PSE is a banned substance at urinary levels >150 µg · ml(-1). As a result, this study aimed to compare the effect of CAF versus PSE use on cycling time trial (TT) performance to explore whether the legal stimulant was any less ergogenic than the banned substance. Here, 10 well-trained male cyclists or triathletes were recruited for participation. All athletes were required to attend the laboratory on four separate occasions--including a familiarization trial and three experimental trials, which required participants to complete a simulated 40 km (1,200 kJ) cycling TT after the ingestion of either 200 mg CAF, 180 mg PSE or a nonnutritive placebo (PLA). The results showed that the total time taken and the mean power produced during each TT was not significantly different (p > .05) between trials, despite a 1.3% faster overall time (~57 s) after CAF consumption. Interestingly, the time taken to complete the second half of the TT was significantly faster (p < .05) in CAF as compared with PSE (by 99 s), with magnitude based inferences suggesting a 91% beneficial effect of CAF during the second half of the TT. This investigation further confirms the ergogenic benefits of CAF use during TT performances and further suggests this legal CNS stimulant has a better influence than a supra-therapeutic dose of PSE.