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During extended heat exposure, humans can experience three phases of heat adaptation. These start with the cardiovascular, sudomotor and neuroendocrine reactions induced by an acute heat exposure, progressing to an amplification of these responses (Phase two: positive adaptation), and possibly ending with the more efficient negative adaptation (Phase three) seen in indigenes from hot climates, where skin blood flow and sweating are reduced. This review briefly describes these physiological changes and provides a theoretical background underpinning adaptation strategies. Gender differences in the acute and adaptation responses are not discussed. Using simple modelling, there is a development of the key principles that are essential to evaluating the need for heat adaptation in various sports, and there is discussion of the disadvantages of heat adaptation. Several adaptation practices are described and evaluated relative to the needs of the athlete. From these, it is concluded that living and training under hot conditions may best improve performance in the heat. However, since high-intensity training is invariably hard to sustain in the heat, it is recommended that athletes live in the heat, experience heat under the pressure of competition, acclimate for a specific climate and then undertake high-quality training in the cool. Athletes must not ignore the psychological aspects of preparing for competition in the heat, since inappropriate choices can undo years of physiological preparation. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Strenuous exercise induces a marked reduction in renal hemodynamics. Prostaglandins (PG) play an important role in maintaining renal integrity in the face of hemodynamic changes. Inhibition of cyclooxygenase (COX) and thus PG formation can further compromise renal perfusion. The role of selective COX-2 inhibition on renal hemodynamics during exercise has not been investigated. METHODS: Twelve healthy males (22-47 yr) took part in a randomized placebo controlled study investigating the effects of nonselective COX inhibition (indomethacin) and COX-2 selective inhibition (celecoxib) on renal hemodynamics during exercise. Renal blood flow (RBF), glomerular filtration rate (GFR), and free water clearance were measured using standard clearance techniques. Each experimental session was performed at least a week apart. The medications were taken for 36 h before study with the last dose at 0700 h on the day of study. Following baseline studies, each participant exercised for 30 min at 80% of their maximal aerobic power. Renal function was monitored for 2 h post-recovery. RESULTS: RBF and GFR fell by 40% after exercise with no significant difference between placebo, indomethacin, or celecoxib. Indomethacin (-2.43 +/- 0.95 mL x min(-1), P < 0.007) and celecoxib (-3.88 +/- 0.94 mL x min(-1), P < 0.0001) significantly reduced free water clearance compared with placebo during recovery. CONCLUSION: This study has confirmed that selective and nonselective COX inhibition can induce significant inhibition of free water clearance, indicating that these acute changes are regulated predominantly via COX-2. Acute cerebral edema with hyponatremia has been reported after major endurance sporting events. Identifiable risk factors include excessive hydration and use of NSAID. Impaired free water clearance during exercise potentiated by COX inhibition provides a pathophysiological explanation for these observations. [ABSTRACT FROM AUTHOR]

Introduction: Climate change is raising global temperatures, leading to more extreme heat events, even in temperate climates like Aotearoa|New Zealand (A|NZ). The impact of rising temperatures and the adequacy of planning measures remain underexplored. This paper highlights A|NZ's anticipated heat-health challenges by analyzing vulnerable populations and assessing current response systems, thereby reinforcing the need for system-level redress, mitigation and adaptation., Content: A scoping review examined the impact of heat and existing mitigation and adaptation responses for vulnerable populations in temperate regions, with a focus on A|NZ. Additionally, temperature trend analysis was conducted for current and projected trends using Climate CHIP for six major heat-affected cities in A|NZ to assess the recognition of heat as a societal concern., Summary and Outlook: The review identified mitigation and adaptation strategies for existing vulnerable groups and discovered other potential vulnerable groups in A|NZ, including Indigenous people (Māori), Pacific communities, low-income groups, migrants, and visitors. Temperature trends show an increasing pattern, suggesting heightened future heat-related impacts on these populations. This review reveals A|NZ's growing vulnerability to rising temperatures, particularly among high-risk groups, and calls for stronger mitigation and adaptation strategies to address future heat-health risks., (© 2024 Walter de Gruyter GmbH, Berlin/Boston.)

Postexercise reduction in blood pressure, termed postexercise hypotension (PEH), is relevant for both acute and chronic health reasons and potentially for peripheral cardiovascular adaptations. We investigated the interactive effects of exercise intensity and recovery postures (seated, supine, and standing) on PEH. Thirteen normotensive men underwent a V̇o 2max test on a cycle ergometer and five exhaustive constant load trials to determine critical power (CP) and the gas exchange threshold (GET). Subsequently, work-matched exercise trials were performed at two discrete exercise intensities (10% > CP and 10% < GET), with 1 h of recovery in each of the three postures. For both exercise intensities, standing posture resulted in a more substantial PEH (all P < 0.01). For both standing and seated recovery postures, the higher exercise intensity led to larger reductions in systolic [standing: -33 (11) vs. -21 (8) mmHg; seated: -34 (32) vs. -17 (37) mmHg, P < 0.01], diastolic [standing: -18 (7) vs. -8 (5) mmHg; seated: -10 (10) vs. -1 (4) mmHg, P < 0.01], and mean arterial pressures [-13 (8) vs. -2 (4) mmHg, P < 0.01], whereas in the supine recovery posture, the reduction in diastolic [-9 (9) vs. -4 (3) mmHg, P = 0.08) and mean arterial pressures [-7 (5) vs. -3 (4) mmHg, P = 0.06] was not consistently affected by prior exercise intensity. PEH is more pronounced during recovery from exercise performed above CP versus below GET. However, the effect of exercise intensity on PEH is largely abolished when recovery is performed in the supine posture. NEW & NOTEWORTHY The magnitude of postexercise hypotension is greater following the intensity above the critical power in a standing position.

We evaluated changes in hyperhydration and beverage hydration index (BHI, a composite measure of fluid balance after consuming a test beverage relative to water) during resting, induced by the consumption of beverages containing glycerol and sodium supplemented with fast-absorbing sucrose or slow-absorbing isomaltulose. In a randomized crossover, single-blinded protocol (clinical trials registry: UMIN000042644), 14 young physically active adults (three women) consumed 1 L of beverage containing either 7% glycerol + 0.5% sodium (Gly + Na), Gly + Na plus 7% sucrose (Gly + Na + Suc), Gly + Na plus 7% isomaltulose (Gly + Na + Iso), or water (CON) over a 40 min period. We assessed the change in plasma volume (ΔPV), BHI (calculated from cumulative urine output following consumption of water relative to that of the beverage), and blood glucose and sodium for 180 min after initiating ingestion. Total urine volume was reduced in all beverages containing glycerol and sodium compared to CON (all P  ≤ 0.002). The addition of isomaltulose increased BHI by ∼45% (3.43 ± 1.0 vs. 2.50 ± 0.7 for Gly + Na, P  = 0.011) whereas sucrose did not (2.6 ± 0.6, P  = 0.826). The PV expansion was earliest for Gly + Na (30 min), slower for Gly + Na + Suc (90 min), and slowest for Gly + Na + Iso (120 min) with a concomitant lag in the increase of blood glucose and sodium concentrations. Supplementation of beverages containing glycerol and sodium with isomaltulose but not sucrose enhances BHI from those of glycerol and sodium only under a resting state, likely due to the slow absorption of isomaltulose-derived monosaccharides (i.e., glucose and fructose).

Objective: Preoperative exercise training, or prehabilitation, aims to optimize cardiorespiratory fitness before surgery to reduce the risk of adverse perioperative events and delayed recovery. However, traditional exercise such as walking and cycling can be difficult for people with degenerative joint diseases of the lower limbs, such as osteoarthritis. The purpose of this study was to compare the effect of three low-impact interventions on cardiorespiratory fitness, physical function, and subjective health before total hip or knee arthroplasty., Methods: This was a randomized controlled trial involving 93 participants with severe knee or hip osteoarthritis awaiting joint replacement surgery. Participants underwent cardiopulmonary exercise testing (to measure peak oxygen consumption [ V ̇ $$ \dot{V} $$ O 2 ]), then were randomized to heat therapy (Heat; 20-30 min immersed in 40°C water followed by ~15 min light-resistance exercise), high-intensity interval training (HIIT; 6-8 × 60 s intervals on a cross-trainer or arm ergometer at ~90%-100% peak V ̇ $$ \dot{V} $$ O 2 ), or home-based exercise (Home; ~15 min light-resistance exercise); for up to 36 sessions (3 sessions per week for 12 weeks)., Results: Peak V ̇ $$ \dot{V} $$ O 2 increased by 16% across HIIT and to a greater extent than Heat (+2.5 mL × min -1 × kg -1 [95% CI: 0.5-4.4], P = 0.009) and Home (+3.2 mL × min -1 × kg -1 [1.2-5.2], P = 0.001). The anaerobic threshold increased across HIIT (+1.5 mL × min -1 × kg -1 [0.7-2.3], P < 0.001) and Heat (+1.2 mL × min -1 × kg -1 [0.4-1.9], P = 0.004), but not Home (-0.5 mL × min -1 × kg -1 [-1.3 to 0.3], P = 0.248). Subjective severity of osteoarthritis was unchanged with any intervention (P ≥ 0.250)., Conclusion: Heat therapy and HIIT improved indices of cardiorespiratory fitness preoperatively in patients who have difficulty performing lower-limb exercise., (© 2023 The Authors. Arthritis Care & Research published by Wiley Periodicals LLC on behalf of American College of Rheumatology.)

To date, the thermoregulatory response between continuous and intermittent exercises has been investigated whilst limited studies are available to examine the thermoregulatory responses between different modes of intermittent exercises. We sought to determine the effect of two patterns of short duration intermittent exercises (180:180 (3-min) and 30:30 s (30-s) work: rest) on thermoregulatory responses in a temperate environment (25 °C, 50% RH, vapor pressure: 1.6 kPa) with low airflow (0.2 m/s). Twelve male participants (Age:24.0(5.0) year; VO 2 max: 53(8) mL.kg -1 .min -1 ; BSA:1.7(0.1) m 2 ) cycled at 50% VO 2 max for 60 min in 3-min and 30-s intervals to result in the same 30-min net exercise duration. Core and skin temperatures, the percent increase of skin blood flow (forearm and chest) from baseline and local sweat rate (forearm and chest) were not different between 3-min and 30-s (all P > 0.35) from the onset of exercise to the end of the exercise. Similarly, the mean body temperature onsets of skin blood flow (forearm and chest) and local sweat rates (forearm and chest) were not different between different mode of intermittent exercises (all P > 0.1). Furthermore, thermal sensitivities of skin blood flow (forearm and chest) and local sweat rate (forearm and chest) with increasing mean body temperature were not different between different mode of intermittent exercises (all P > 0.1). We conclude that intermittent exercises with different work periods at moderate exercise intensity did not alter core temperature and thermoeffector responses in a temperate environment. (241/250)., Competing Interests: Declaration of competing interest None., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Being able to tread water effectively can improve the likelihood of survival following accidental immersion. People tread water in various ways, ranging from rudimentary 'doggy-paddle' to more elaborate techniques like the eggbeater, but little is known about the energetic and cognitive requirements of treading water. We therefore aimed to measure the demands of treading water techniques for people of different experience levels. Three cohorts, comprising 21 adult water treading experts (water polo players), 15 intermediate swimmers and 16 inexperienced swimmers, treaded water for 3 min each using four different techniques while cognitive and energetic economy measures were taken. For inexperienced swimmers, the flutter kick and breaststroke patterns produced the lowest self-reported physical and task load (rating of perceived exertion, NASA task load index), while cognitive (probe reaction time), cardiac (heart rate) and metabolic (oxygen consumption) load did not differ between techniques. In contrast, for expert water treaders, both breaststroke and eggbeater patterns produced lower cognitive, cardiac and metabolic loads. For intermediate swimmers, breaststroke resulted in the lowest cardiac and metabolic loads, as well as self-reported task load. Probe reaction time was highest while performing the eggbeater technique, indicating that this technique was challenging to coordinate and cognitively demanding. While the energetic demands of antiphase kicking patterns (such as eggbeater in experts or flutter kick in beginners) may be similarly low, the symmetric coordination of upright breaststroke may explain why this pattern's cognitive economy was favourable for all groups. As the eggbeater can be challenging to perform for many people, an upright breaststroke technique is an adequate alternative to adopt in survival situations., (© Journal of Sports Science and Medicine.)

Endurance exercise induces cardiovascular adaptations; the athletic phenotypes of the heart and arteries are well characterized, but few studies have investigated the effects of chronic exercise on the venous system. The aim of this study was to describe the anatomy and function of lower-limb deep and superficial veins in athletes compared with controls. Endurance-trained athletes and untrained controls (13 males, 7 females per group) were examined using ultrasound to measure vein diameter and flow, and air plethysmography to assess calf venous volume dynamics and muscle pump function at rest, during a single step, ambulation (10 steps) and after acute treadmill exercise (30 min ∼80% age-predicted heart rate maximum). Diameters of three of the seven deep veins assessed were larger in athletes ( P ≤ 0.0167) and more medial calf perforators were detectable (5 vs. 3, P = 0.0039). Calf venous volume was 22% larger in athletes ( P = 0.0057), and calf muscle pump ejection volume and ambulatory venous volume after 10 steps were both greater in athletes (20 and 46% respectively, P ≤ 0.0482). Following acute exercise, flow recovery profiles in deep and superficial veins draining the leg were not different between groups, despite athletes performing approximately four times more work. After exercise, venous volume and ejection volume were reduced by ∼20% in athletes with no change in controls (interaction, P ≤ 0.0372) and although ambulatory venous volume reduced, this remained greater in athletes. These findings highlight venous adaptations that compensate for the demands of regular endurance exercise, all of which are suited to enhance flow through the lower-limb venous system. NEW & NOTEWORTHY Although much literature exists describing adaptations to the heart and arteries in response to endurance exercise training, less is known about the effects on the venous system. Characteristics of "the athlete's vein" described here include deep and perforator vein remodeling, improved drainage, and greater calf venous volume at rest and on calf muscle pump activation. Following exercise, athletes demonstrated prompt flow recovery and appropriate volume reductions, and veins beneficially adapt to better tolerate the demands of regular physical activity.

Exercise is painful and difficult to perform for patients with severe lower-limb osteoarthritis; consequently, reduced physical activity contributes to increased cardiometabolic disease risk. The aim of this study was to characterize the acute and adaptive cardiovascular and metabolic effects of two low or no impact therapies in patients with severe lower-limb osteoarthritis: passive heat therapy (Heat) and high-intensity interval training (HIIT) utilizing primarily the unaffected limbs, compared to a control intervention of home-based exercise (Home). Participants completed up to 12 weeks of either Heat (20-30 min immersed in 40°C water followed by ~15-min light resistance exercise), HIIT (6-8 × 60-s intervals on a cross-trainer or arm ergometer at ~90-100% peak V ̇ $$ \dot{V} $$ O 2 ) or Home (~15-min light resistance exercise); all 3 sessions/week. Reductions in systolic (12 & 10 mm Hg), diastolic (7 & 4 mm Hg), and mean arterial (8 & 6 mm Hg) blood pressure (BP) were observed following one bout of Heat or HIIT exposure, lasting for the duration of the 20-min monitoring period. Across the interventions (i.e., 12 weeks), resting systolic BP and diastolic BP decreased with Heat (-9 & -4 mm Hg; p < 0.001) and HIIT (-7 & -3 mm Hg; p ≤ 0.011), but not Home (0 & 0 mm Hg; p ≥ 0.785). The systolic and diastolic BP responses to an acute exposure of Heat or HIIT in the first intervention session were moderately correlated with adaptive responses across the intervention (r ≥ 0.54, p ≤ 0.005). Neither intervention improved indices of glycemic control (p = 0.310). In summary, both Heat and HIIT induced potent immediate and adaptive hypotensive effects, and the acute response was moderately predictive of the long-term response., (© 2023 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

The physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced dehydration, and the kinetics of ad libitum rehydration following each method. Twelve fit participants (five females and seven males) completed four trials in randomised order: DEHydration to -3% change in body mass (∆BM) under passive or active heat stress, and EUHydration to prevent ∆BM under passive or active heat stress. In all trials, participants then sat in a temperate-controlled environment, ate a standard snack and had free access to water and sports drink during their two-hour recovery. During mild dehydration (≤2% ∆BM), active and passive heating caused comparable increases in plasma osmolality (P osm : ~4 mOsmol/kg, interaction: p = 0.138) and reductions in plasma volume (PV: ~10%, interaction: p = 0.718), but heat stress per se was the main driver of hypovolaemia. Thirst in DEHydration was comparably stimulated by active than passive heat stress ( p < 0.161) and shared the same relation to P osm (r ≥ 0.744) and ∆BM (r ≥ 0.882). Following heat exposures, at 3% gross ∆BM, PV reduction was approximately twice as large from passive versus active heating ( p = 0.003), whereas P osm perturbations were approximately twice as large from EUHydration versus DEHydration ( p < 0.001). Rehydrating ad libitum resulted in a similar net fluid balance between passive versus active heat stress and restored PV despite the incomplete replacement of ∆BM. In conclusion, dehydrating by 2% ∆BM via passive heat stress generally did not cause larger changes to PV or P osm than via active heat stress. The heat stressors themselves caused a greater reduction in PV than dehydration did, whereas ingesting water to maintain euhydration produced large reductions in P osm in recovery and therefore appears to be of more physiological significance.

Epidemiological evidence has highlighted a strong relationship between cardiorespiratory fitness and surgical outcomes; specifically, fitter patients possess heightened resilience to withstand the surgical stress response. This narrative review draws on exercise and surgical physiology research to discuss and hypothesise the potential mechanisms by which higher fitness affords perioperative benefit. A higher fitness, as indicated by higher peak rate of oxygen consumption and ability to sustain metabolic homeostasis (i.e. higher anaerobic threshold) is beneficial postoperatively when metabolic demands are increased. However, the associated adaptations with higher fitness, and the related participation in regular exercise or physical activity, might also underpin the observed perioperative benefit through a process of hormesis, a protective adaptive response to the moderate and intermittent stress of exercise. Potential mediators discussed include greater antioxidant capacity, metabolic flexibility, glycaemic control, lean body mass, and improved mood., (Copyright © 2022 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.)

Purpose: This study assessed whether increasing sodium in a sports drink above that typical (~ 20 mmol L -1 ) affects plasma sodium and volume responses during prolonged exercise in the heat., Methods: Endurance trained males (N = 11, 36 ± 14 y, 75.36 ± 5.30 kg, [Formula: see text]O 2max 60 ± 3 mL min -1  kg -1 ) fulfilled requirements of the study including one 1-h exercise pre-trial, to estimate fluid losses (to prescribe fluid intake), and two, experimental trials (3-h or until tolerance), in random order, cycling (55% [Formula: see text]O 2max , 34 °C, 65% RH). Beverages contained 6% carbohydrate and either 21 mmol L -1 (Low Na + ) or 60 mmol L -1 sodium (High Na + ). Analyses included linear mixed models and t-tests., Results: Cycling time was similar 176 ± 9 min (Low Na + ); 176 ± 7 min (High Na + ). Fluid intake was 1.12 ± 0.19 L h -1 ; 1.14 ± 0.21 L h -1 , resp. Body mass change was - 0.53 ± 0.40%;  - 0.30 ± 0.45%, resp. Sodium intake was 69 ± 12 mmol; 201 ± 40 mmol, resp. Plasma sodium concentration was greater in High Na + than Low Na + (p < 0.001); decreasing in Low Na + (- 1.5 ± 2.2 mmol L -1 ), increasing in High Na + (0.8 ± 2.4 mmol L -1 ) (p = 0.048, 95% CI [- 4.52, - 0.02], d = 0.99). Plasma volume decreased in Low Na + (- 2 ± 2%) but remained unchanged in High Na + (0 ± 3%) (p = 0.01, 95% CI [- 3.2, - 0.5], d = 0.80)., Conclusions: When conducting prolonged exercise in the heat, those who fully hydrate would benefit by increased sodium content of the beverage by improved plasma volume and sodium maintenance. Australian New Zealand Clinical Trials Registry (ACTRN12616000239460) 22/02/16., (© 2022. The Author(s).)

Physical activity is the most common source of heat strain for humans. The thermal strain of physical activity causes overbreathing (hyperventilation) and this has adverse physiological repercussions. The mechanisms underlying heat-induced hyperventilation during exercise are unknown, but recent evidence supports a primary role of carotid body hyperexcitability (increased tonic activity and sensitivity) underpinning hyperventilation in passively heated humans. In a repeated-measures crossover design, 12 healthy participants (6 female) completed two low-intensity cycling exercise conditions (25% maximal aerobic power) in randomized order, one with core temperature (T C ) kept relatively stable near thermoneutrality, and the other with progressive heat strain to +2°C T C . To provide a complete examination of carotid body function under graded heat strain, carotid body tonic activity was assessed indirectly by transient hyperoxia, and its sensitivity estimated by responses to both isocapnic and poikilocapnic hypoxia. Carotid body tonic activity was increased by 220 ± 110% during cycling alone, and by 400 ± 290% with supplemental thermal strain to +1°C T C , and 600 ± 290% at +2°C T C (interaction, P = 0.0031). During exercise with heat stress at both +1°C and +2°C T C , carotid body suppression by hyperoxia decreased ventilation below the rates observed during exercise without heat stress ( P < 0.0147). Carotid body sensitivity was increased by up to 230 ± 190% with exercise alone, and by 290 ± 250% with supplemental heating to +1°C T C and 510 ± 470% at +2°C T C (interaction, P = 0.0012). These data indicate that the carotid body is further activated and sensitized by heat strain during exercise and this largely explains the added drive to breathe. NEW & NOTEWORTHY Physical activity is the most common way humans increase their core temperature, and excess breathing in the heat can limit heat tolerance and performance, and may increase the risk of heat-related injury. Dose-dependent increases in carotid body tonic activity and sensitivity with core heating provide compelling evidence that carotid body hyperexcitability is the primary cause of heat-induced hyperventilation during exercise.

Humans hyperventilate under heat and cold strain. This hyperventilatory response has detrimental consequences including acid-base dysregulation, dyspnoea, decreased cerebral blood flow and accelerated brain heating. The ventilatory response to hypoxia is exaggerated under whole-body heating and cooling, indicating that altered carotid body function might contribute to thermally mediated hyperventilation. To address whether the carotid body might contribute to heat- and cold-induced hyperventilation, we indirectly measured carotid body tonic activity via hyperoxia, and carotid body sensitivity via hypoxia, under graded heat and cold strain in 13 healthy participants in a repeated-measures design. We hypothesised that carotid body tonic activity and sensitivity would be elevated in a dose-dependent manner under graded heat and cold strain, thereby supporting its role in driving thermally mediated hyperventilation. Carotid body tonic activity was increased in a dose-dependent manner with heating, reaching 175% above baseline (P < 0.0005), and carotid body suppression with hyperoxia removed all of the heat-induced increase in ventilation (P = 0.9297). Core cooling increased carotid body activity by up to 250% (P < 0.0001), but maximal values were reached with mild cooling and thereafter plateaued. Carotid body sensitivity to hypoxia was profoundly increased by up to 180% with heat stress (P = 0.0097), whereas cooling had no detectable effect on hypoxic sensitivity. In summary, cold stress increased carotid body tonic activity and this effect was saturated with mild cooling, whereas heating had clear dose-dependent effects on carotid body tonic activity and sensitivity. These dose-dependent effects with heat strain indicate that the carotid body probably plays a primary role in driving heat-induced hyperventilation. KEY POINTS: Humans over-breathe (hyperventilate) when under heat and cold stress, and though this has detrimental physiological repercussions, the mechanisms underlying this response are unknown. The carotid body, a small organ that is responsible for driving hyperventilation in hypoxia, was assessed under incremental heat and cold strain. The carotid body drive to breathe, as indirectly assessed by transient hyperoxia, increased in a dose-dependent manner with heating, reaching 175% above baseline; cold stress similarly increased the carotid body drive to breathe, but did not show dose-dependency. Carotid body sensitivity, as indirectly assessed by hypoxic ventilatory responses, was profoundly increased by 70-180% with mild and severe heat strain, whereas cooling had no detectable effect. Carotid body hyperactivity and hypersensitivity are two interrelated mechanisms that probably underlie the increased drive to breathe with heat strain, whereas carotid body hyperactivity during mild cooling may play a subsidiary role in cold-induced hyperventilation., (© 2022 The Authors. The Journal of Physiology © 2022 The Physiological Society.)

Teaching traditionally asserts that the arterial pressure pulse is dampened across the capillary bed to the extent that pulsatility is nonexistent in the venous circulation of the lower limbs. Herein, we present evidence of transmission of arterial pulsations across the capillary network into perforator veins in the lower limbs of healthy, heat-stressed humans. Perforator veins are connections from the superficial veins that drain into the deep veins. When assessed using ultrasound at rest, they infrequently demonstrate flow, and a pulsatile flow waveform is not described. We investigated perforator vein pulsatility in 10 young, healthy volunteers who underwent passive heating by +2°C core body temperature via a hot-water-perfused suit, and 5 who also underwent active heating by +2°C via low-intensity cycling while wearing the hot-water-perfused suit. At +0.5°C increments in temperature, blood velocity in an ankle perforator vein was measured using duplex ultrasound. In all perforators with heating, sustained flow was demonstrated, with a pulsatile waveform that was synchronous with the cardiac cycle. The maximum velocity was 30 ± 13 cm/s with passive heating and approximately half with active heating ( P = 0.04). The small veins of the skin at the ankle also demonstrated increased perfusion with pulsatility, seen with low-velocity microvascular imaging technology. We consider explanations for this pulsatility and conclude that it is propagated from the arterial inflow through the skin microcirculation as a result of increased dilatation and flow volume and that this is a normal response to increased skin blood flow.

New Findings: What is the central question of this study? What are the profiles of acute physiological and psychophysical strain during and in recovery from different modes of heating, and to what extent do these diminish after repeated exposure? What is the main finding and its importance? Mode of heating affects the strain profiles during heat stress and recovery. Exercise in the heat incurred the greatest cardiovascular strain during heating and recovery. Humid heat was poorly tolerated despite heat strain being no greater than in other heating modes, and tolerance did not improve with multiple exposures., Abstract: Heat stress is common and arises endogenously and exogenously. It can be acutely hazardous while also increasingly advocated to drive health and performance-related adaptations. Yet, the nature of strain (deviation in regulated variables) imposed by different heating modes is not well established, despite the potential for important differences. We, therefore, compared three modes of heat stress for thermal, cardiovascular and perceptual strain profiles during exposure and recovery when experienced as a novel stimulus and an accustomed stimulus. In a crossover design, 13 physically active participants (five females) underwent 5 days of 60-min exposures to hot water immersion (40°C), sauna (55°C, 54% relative humidity) and exercise in the heat (40°C, 52% relative humidity), and a thermoneutral water immersion control (36.5°C), each separated by ≥4 weeks. Physiological (thermal, cardiovascular, haemodynamic) and psychophysical strain responses were assessed on days 1 and 5. Sauna evoked the warmest skin (40°C; P < 0.001) but exercise in the heat caused the largest increase in core temperature, sweat rate, heart rate (post hoc comparisons all P < 0.001) and systolic blood pressure (P ≤ 0.002), and possibly decrease in diastolic blood pressures (P ≤ 0.130), regardless of day. Thermal sensation and feeling state were more favourable on day 5 than on day 1 (P ≤ 0.021), with all modes of heat being equivalently uncomfortable (P ≥ 0.215). Plasma volume expanded the largest extent during immersions (P < 0.001). The current data highlight that exercising in the heat generates a more complex strain profile, while passive heat stress in humid heat has lower tolerance and more cardiovascular strain than hot water immersion., (© 2022 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

New Findings: What is the central question to the study? Are primary indices of heat adaptation (e.g., expansion of plasma volume and reduction in resting core temperature) differentially affected by the three major modes of short-term heat acclimation, that is, exercise in the heat, hot water immersion and sauna? What it the main finding and its importance? The three modes elicited typical adaptations expected with short-term heat acclimation, but these were not significantly different between modes. This comparison has not previously been made and highlights that individuals can expect similar adaptation to heat regardless of the mode used., Abstract: Heat acclimation (HA) can improve heat tolerance and cardiovascular health. The mode of HA potentially impacts the magnitude and time course of adaptations, but almost no comparative data exist. We therefore investigated adaptive responses to three common modes of HA, particularly with respect to plasma volume. Within a crossover repeated-measures design, 13 physically active participants (five female) undertook four, 5-day HA regimes (60 min/day) in randomised order, separated by ≥4 weeks. Rectal temperature (T re ) was clamped at neutrality via 36.6°C (thermoneutral) water immersion (TWI; i.e., control condition), or raised by 1.5°C via heat stress in 40°C water, sauna (55°C, 52% relative humidity), or exercise in humid heat (40°C, 52% relative humidity; ExH). Adaptation magnitude was assessed as the pooled response across days 4-6, while kinetics was assessed via the 6-day time series. Plasma volume expansion was similar in all heated conditions but only higher than TWI in exercise in the heat (ExH) (by 4%, P = 0.036). Approximately two-thirds of the expansion was attained within the initial 24 h and was moderately related to that present on day 6, regardless of HA mode (r = 0.560-0.887). Expansion was mediated by conservation of both sodium and albumin content, with little evidence for these having differential roles between modes (P = 0.706 and 0.320, respectively). Resting T re decreased by 0.1-0.3°C in all heated conditions, and systolic blood pressure decreased by 4 mmHg, but not differentially between conditions (P ≥ 0.137). In conclusion, HA mode did not substantially affect the magnitude or rate of adaptation in key resting markers of short-term HA., (© 2021 The Authors. Experimental Physiology © 2021 The Physiological Society.)

We investigated whether substituting the final half within 60-min bouts of exercise with passive warm or cold water immersion would provide similar or greater benefits for cardiometabolic health. Thirty healthy participants were randomized to two of three short-term training interventions in a partial crossover (12 sessions over 14-16 days, 4 week washout): (i) EXS: 60 min cycling 70% maximum heart rate (HRmax), (ii) WWI: 30 min cycling then 30 min warm water (38-40°C) immersion, and/or (iii) CWI: 30 min cycling then 30 min cold water (10-12°C) immersion. Before and after, participants completed a 20 min cycle work trial, V . O 2 max test, and an Oral Glucose Tolerance Test during which indirect calorimetry was used to measure substrate oxidation and metabolic flexibility (slope of fasting to post-prandial carbohydrate oxidation). Data from twenty two participants (25 ± 5 year, BMI 23 ± 3 kg/m 2 , Female = 11) were analyzed using a fixed-effects linear mixed model. V . O 2 max increased more in EXS (interaction p = 0.004) than CWI (95% CI: 1.1, 5.3 mL/kg/min, Cohen's d = 1.35), but not WWI (CI: -0.4, 3.9 mL/kg/min, d = 0.72). Work trial distance and power increased 383 ± 223 m and 20 ± 6 W, respectively, without differences between interventions (interaction both p > 0.68). WWI lowered post-prandial glucose ∼9% (CI -1.9, -0.5 mmol/L; d = 0.63), with no difference between interventions (interaction p = 0.469). Substituting the second half of exercise with WWI provides similar cardiometabolic health benefits to time matched exercise, however, substituting with CWI does not., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Russell, Chang, Hill, Cotter and Francois.)

Ultrasound is an appealing tool to assess body composition, combining the portability of a field method with the accuracy of a laboratory method. However, unlike other body composition methods, the effect of hydration status on validity is unknown. This study evaluated the impact of acute hydration changes on ultrasound measurements of subcutaneous fat thickness and estimates of body fat percentage. In a crossover design, 11 adults (27.1 ± 10.5 years) completed dehydration and hyperhydration trials to alter body mass by approximately ±2%. Dehydration was achieved via humid heat (40 °C, 60% relative humidity) with exercise, whereas hyperhydration was via ingestion of lightly salted water. Ultrasound measurements were taken at 11 body sites before and after each treatment. Participants lost 1.56 ± 0.58 kg (-2.0 ± 0.6%) during the dehydration trial and gained 0.90 ± 0.21 kg (1.2 ± 0.2%) during the hyperhydration trial even after urination. The sum of fat thicknesses as measured by ultrasound differed by <0.90 mm across trials (p = .588), and ultrasound estimates of body fat percentage differed by <0.5% body fat. Ultrasound measures of subcutaneous adipose tissue were unaffected by acute changes in hydration status by extents beyond which are rare and overtly self-correcting, suggesting that this method provides reliable and robust body composition results even when subjects are not euhydrated.

Key Points: The human brain is particularly vulnerable to heat stress; this manifests as impaired cognition, orthostatic tolerance, work capacity and eventually, brain death. The brain's limitation in the heat is often ascribed to inadequate cerebral blood flow (CBF), but elevated intracranial pressure is commonly observed in mammalian models of heat stroke and can on its own cause functional impairment. The CBF response to incremental heat strain was dependent on the mode of heating, decreasing by 30% when exposed passively to hot, humid air (sauna), while remaining unchanged or increasing with passive hot-water immersion (spa) and exercising in a hot environment. Non-invasive intracranial pressure estimates (nICP) were increased universally by 18% at volitional thermal tolerance across all modes of heat stress, and therefore may play a contributing role in eliciting thermal tolerance. The sauna, more so than the spa or exercise, poses a greater challenge to the brain under mild to severe heating due to lower blood flow but similarly increased nICP., Abstract: The human brain is particularly vulnerable to heat stress; this manifests as impaired cognitive function, orthostatic tolerance, work capacity, and eventually, brain death. This vulnerability is often ascribed to inadequate cerebral blood flow (CBF); however, elevated intracranial pressure (ICP) is also observed in mammalian models of heat stroke. We investigated the changes in CBF with incremental heat strain under three fundamentally different modes of heating, and assessed whether heating per se increased ICP. Fourteen fit participants (seven female) were heated to thermal tolerance or 40°C core temperature (T c ; oesophageal) via passive hot-water immersion (spa), passive hot, humid air exposure (sauna), cycling exercise, and cycling exercise with CO 2 inhalation to prevent heat-induced hypocapnia. CBF was measured with duplex ultrasound at each 0.5°C increment in T c and ICP was estimated non-invasively (nICP) from optic nerve sheath diameter at thermal tolerance. At thermal tolerance, CBF was decreased by 30% in the sauna (P < 0.001), but was unchanged in the spa or with exercise (P ≥ 0.140). CBF increased by 17% when end-tidal P C O 2 was clamped at eupnoeic pressure (P < 0.001). On the contrary, nICP increased universally by 18% with all modes of heating (P < 0.001). The maximum T c was achieved with passive heating, and preventing hypocapnia during exercise did not improve exercise or thermal tolerance (P ≥ 0.146). Therefore, the regulation of CBF is dramatically different depending on the mode and dose of heating, whereas nICP responses are not. The sauna, more so than the spa or exercise, poses a greater challenge to the brain under equivalent heat strain., (© 2021 The Authors. The Journal of Physiology © 2021 The Physiological Society.)

Purpose: Cognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition., Methods: Eight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory., Results: No differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO 2 Hb-deO 2 Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions., Conclusion: Moderately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.

Key Points: Cognitive function depends on adequate cerebrovascular perfusion and control. However, it is unknown whether acutely-reduced cerebral blood flow (CBF) impairs cognition in healthy adults. In the present study, we used a placebo-controlled, single-blinded, randomized cross-over design to test the hypothesis that acutely-reduced CBF (using a pharmacological aid; indomethacin) would impair cognition in young and older healthy adults. At baseline, older adults had lower cognitive performance and CBF, but similar cerebrovascular reactivity to CO 2 and dynamic cerebral autoregulation compared to young adults. In both young and older adults, cognitive performance on a mental switching task was slightly (7%) reduced after indomethacin, but not significantly associated with reductions in CBF (∼31%). These results indicate that cognitive performance is broadly resilient against a ∼31% reduction in CBF per se in healthy young and older adults., Abstract: Cognitive function depends on adequate cerebrovascular perfusion and control. However, it is unknown whether acutely-reduced cerebral blood flow (CBF) impairs cognition in healthy adults. Using a placebo-controlled, single-blinded, randomized cross-over design, we tested the hypothesis that acutely-reduced CBF (using indomethacin [1.2 mg kg -1 oral dose]) would impair cognition in young (n = 13; 25 ± 4 years) and older (n = 12; 58 ± 6 years) healthy adults. CBF and cerebrovascular control were measured using middle cerebral artery blood velocity (MCAv mean ) and its reactivity to hypercapnia (CVR HYPER ) and hypocapnia (CVR HYPO ), respectively. Cognitive function was assessed using a computerized battery including response time tasks. Baseline comparisons revealed that older adults had 14% lower MCAv mean and 15% lower cognitive performance (all P ≤ 0.048), but not lower CVR HYPER/HYPO (P ≥ 0.26). Linear and rank-based mixed models revealed that indomethacin decreased MCAv mean by 31% (95% confidence interval = -35 to -26), CVR HYPER by 68% [interquartile range (IQR) = -94 to -44] and CVR HYPO by 50% (IQR = -83 to -33) (treatment-effect; all P < 0.01), regardless of age. Baseline CVR HYPER/HYPO values were strongly associated with their indomethacin-induced reductions (r = 0.70 to 0.89, P < 0.01). Mental switching performance was impaired 7% (IQR = 0-19) after indomethacin (P = 0.04), but not significantly associated with reductions in MCAv mean (Young: rho = -0.31, P = 0.30; Older: rho = 0.06, P = 0.86). In conclusion, indomethacin reduced MCAv mean and impaired cognition slightly; however, no clear association was evident in younger or older adults. Older adults had poorer cognition and lower MCAv mean , but similar CVR HYPER/HYPO ., (© 2020 The Authors. The Journal of Physiology © 2020 The Physiological Society.)

The objective of this study was to compare acute effects of prolonged sitting, prolonged standing and sitting interrupted with regular activity breaks on vascular function and postprandial glucose metabolism. In a randomized cross-over trial, 18 adults completed: 1. Prolonged Sitting; 2. Prolonged Standing and 3. Sitting with 2-min walking (5 km/h, 10% incline) every 30 min (Regular Activity Breaks). Flow mediated dilation (FMD) was measured in the popliteal artery at baseline and 6 h. Popliteal artery hemodynamics, and postprandial plasma glucose and insulin were measured over 6 h. Neither raw nor allometrically-scaled FMD showed an intervention effect (p = 0.285 and 0.159 respectively). Compared to Prolonged Sitting, Regular Activity Breaks increased blood flow (overall effect of intervention p<0.001; difference = 80%; 95% CI 34 to 125%; p = 0.001) and net shear rate (overall effect of intervention p<0.001; difference = 72%; 95% CI 30 to 114%; p = 0.001) at 60 min. These differences were then maintained for the entire 6 h. Prolonged Standing increased blood flow at 60 min only (overall effect of intervention p<0.001; difference = 62%; 95% CI 28 to 97%; p = 0.001). Regular Activity Breaks decreased insulin incremental area under the curve (iAUC) when compared to both Prolonged Sitting (overall effect of intervention P = 0.001; difference = 28%; 95% CI 14 to 38%; p<0.01) and Prolonged Standing (difference = 19%; 95% CI 4 to 32%, p = 0.015). There was no intervention effect on glucose iAUC or total AUC (p = 0.254 and 0.450, respectively). In normal-weight participants, Regular Activity Breaks induce increases in blood flow, shear stress and improvements in postprandial metabolism that are associated with beneficial adaptations. Physical activity and sedentary behaviour messages should perhaps focus more on the importance of frequent movement rather than simply replacing sitting with standing., Competing Interests: The authors have declared that no competing interests exist.

Cardiopulmonary exercise testing is performed increasingly for cardiorespiratory fitness assessment and pre-operative risk stratification. Lower limb osteoarthritis is a common comorbidity in surgical patients, meaning traditional cycle ergometry-based cardiopulmonary exercise testing is difficult. The purpose of this study was to compare cardiopulmonary exercise testing variables and subjective responses in four different exercise modalities. In this crossover study, 15 patients with osteoarthritis scheduled for total hip or knee arthroplasty (mean (SD) age 68 (7) years; body mass index 31.4 (4.1) kg.m -2 ) completed cardiopulmonary exercise testing on a treadmill, elliptical cross-trainer, cycle and arm ergometer. Mean (SD) peak oxygen consumption was 20-30% greater on the lower limb modalities (treadmill 21.5 (4.6) (p < 0.001); elliptical cross-trainer (21.2 (4.1) (p < 0.001); and cycle ergometer (19.4 (4.2) ml.min -1 .kg -1 (p = 0.001), respectively) than on the arm ergometer (15.7 (3.7) ml.min -1 .kg -1 ). Anaerobic threshold was 25-50% greater on the lower limb modalities (treadmill 13.5 (3.1) (p < 0.001); elliptical cross-trainer 14.6 (3.0) (p < 0.001); and cycle ergometer 10.7 (2.9) (p = 0.003)) compared with the arm ergometer (8.4 (1.7) ml.min -1 .kg -1 ). The median (95%CI) difference between pre-exercise and peak-exercise pain scores was greater for tests on the treadmill (2.0 (0.0-5.0) (p = 0.001); elliptical cross-trainer (3.0 (2.0-4.0) (p = 0.001); and cycle ergometer (3.0 (1.0-5.0) (p = 0.001)), compared with the arm ergometer (0.0 (0.0-1.0) (p = 0.406)). Despite greater peak exercise pain, cardiopulmonary exercise testing modalities utilising the lower limbs affected by osteoarthritis elicited higher peak oxygen consumption and anaerobic threshold values compared with arm ergometry., (© 2020 Association of Anaesthetists.)

New Findings: What is the central question of this study? How does resistance exercise affect peripheral haemodynamics in the active and inactive limb? What is the main finding and its importance? Preliminary data indicate that resistance exercise increases flow and shear rate in the active limb transiently. The same exercise has minimal, short-lasting influence on peripheral haemodynamics in the inactive limb, but further research is required to elaborate on resistance exercise-mediated changes in vascular function in active and inactive limbs., Abstract: Current evidence indicates that to achieve maximum health benefits, regular resistance exercise should be a key component of structured physical activity. Several studies have revealed that regular resistance exercise may be associated with impaired vascular function, although this finding is inconsistent. Proposed explanations for impairment include substantial increases in blood pressure and increased retrograde blood flow in active limbs promoted by resistance exercise. However, few studies have examined the acute haemodynamics of resistance exercise in active - and even fewer in inactive - limbs. The purpose of this study was to characterise the haemodynamic responses in peripheral arteries in active and inactive limbs in response to resistance exercise using upper and lower limbs. Ten participants (five male, five female) familiar with resistance training performed three sets of 10 isotonic repetitions of right-sided bicep curls or knee extensions on separate days. Blood flow, shear rate and muscle oxygenation in the active and inactive limb, and blood pressure were measured before and for 3 min after each set. Blood flow increased in response to resistance exercise in the active limb (∼8-fold and ∼6-fold for the upper and lower limb respectively), with concurrent significant increases in mean and antegrade shear rate. In the inactive limb, blood flow more than doubled for both upper and lower limb exercise, transiently, with no significant change in retrograde shear rate. These acute blood flow profiles following resistance exercise are not indicative of long-term vessel impairment based on current understanding of blood flow and shear stress patterns., (© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.)

Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.

The increasing number of older adults has seen a corresponding growth in those affected by neurovascular diseases, including stroke and dementia. Since cures are currently unavailable, major efforts in improving brain health need to focus on prevention, with emphasis on modifiable risk factors such as promoting physical activity. Moderate-intensity continuous training (MICT) paradigms have been shown to confer vascular benefits translating into improved musculoskeletal, cardiopulmonary and cerebrovascular function. However, the time commitment associated with MICT is a potential barrier to participation, and high-intensity interval training (HIIT) has since emerged as a more time-efficient mode of exercise that can promote similar if not indeed superior improvements in cardiorespiratory fitness for a given training volume and further promote vascular adaptation. However, randomised controlled trials (RCTs) investigating the impact of HIIT on the brain are surprisingly limited. The present review outlines how the HIIT paradigm has evolved from a historical perspective and describes the established physiological changes including its mechanistic bases. Given the dearth of RCTs, the vascular benefits of MICT are discussed with a focus on the translational neuroprotective benefits including their mechanistic bases that could be further potentiated through HIIT. Safety implications are highlighted and components of an optimal HIIT intervention are discussed including practical recommendations. Finally, statistical effect sizes have been calculated to allow prospective research to be appropriately powered and optimise the potential for detecting treatment effects. Future RCTs that focus on the potential clinical benefits of HIIT are encouraged given the prevalence of cognitive decline in an ever-ageing population., (© 2020 The Authors. The Journal of Physiology © 2020 The Physiological Society.)

Purpose: Cognition, cerebral blood flow (CBF) and its major regulator (i.e., arterial CO 2 ), increase with submaximal exercise and decline with severe exercise. These responses may depend on fitness. We investigated whether exercise-related changes in cognition are mediated in part by concomitant changes in CBF and CO 2 , in ten active (26 ± 3 years) and ten inactive (24 ± 6 years) healthy adults., Methods: Participants completed two randomised sessions; exercise and a resting CO 2 -control-wherein end-tidal CO 2 (PETCO 2 ) was matched between sessions and clamped across conditions at exercise-associated increases (+ 3 mmHg) and hypercapnia (+ 10 mmHg). Exercise comprised inclined walking at submaximal and severe intensities. CBF was indexed using right middle cerebral artery blood velocity (MCAv). Cognition (visuomotor, switching and inhibitory response time) was measured before, during, and after exercise., Results: MCAv and its inverted-U response to exercise were comparable between groups, whereas visuomotor performance improved during submaximal exercise in the active group only (p = 0.046). Submaximal, but not severe (p = 0.33), exercise increased MCAv (p ≤ 0.03). Hypercapnia increased MCAv during the CO 2 -control (27 ± 12%) and during submaximal exercise (39 ± 17%; p < 0.01). Despite the acute increases in MCAv, cognition was impaired during both levels of increased PETCO 2 (3-6%; p ≤ 0.04), regardless of session. Overall, resting or exercise-related changes in PETCO 2 and MCAv did not associate with changes in cognition (r ≤ 0.29 ± 0.34). Fitness ([Formula: see text]O 2MAX ) was associated with baseline cognition (r ≥ 0.50)., Conclusion: Acute increases in PETCO 2 and MCAv were not associated with improved cognition. In fact, cognitive performance was impaired at both levels of increased PETCO 2 , regardless of session. Finally, fitter people were found to have better cognition.

Purpose: Recent studies have determined that ambient humidity plays a more important role in aerobic performance than dry-bulb temperature does in warm environments; however, no studies have kept humidity constant and independently manipulated temperature. Therefore, the purpose of this study was to determine the contribution of dry-bulb temperature, when vapor pressure was matched, on the thermoregulatory, perceptual and performance responses to a 30-min cycling work trial., Methods: Fourteen trained male cyclists (age: 32 ± 12 year; height: 178 ± 6 cm; mass: 76 ± 9 kg; [Formula: see text]: 59 ± 9 mL kg -1  min -1 ; body surface area: 1.93 ± 0.12 m 2 ; peak power output: 393 ± 53 W) volunteered, and underwent 1 exercise bout in moderate heat (MOD: 34.9 ± 0.2 °C, 50.1 ± 1.1% relative humidity) and 1 in mild heat (MILD: 29.2 ± 0.2 °C, 69.4 ± 0.9% relative humidity) matched for vapor pressure (2.8 ± 0.1 kPa), with trials counterbalanced., Results: Despite a higher weighted mean skin temperature during MOD (36.3 ± 0.5 vs. 34.5 ± 0.6 °C, p < 0.01), none of rectal temperature (38.0 ± 0.3 vs. 37.9 ± 0.4 °C, p = 0.30), local sweat rate (1.0 ± 0.3 vs. 0.9 ± 0.4 mg cm -2  min -1 , p = 0.28), cutaneous blood flow (283 ± 116 vs. 287 ± 105 PU, p = 0.90), mean power output (206 ± 37 vs. 205 ± 41 W, p = 0.87) or total work completed (371 ± 64 vs. 369 ± 70 kJ, p = 0.77) showed any difference between environments during the work trial. However, all perceptual measures (perceived exertion, thermal discomfort, thermal sensation, skin wettedness, pleasantness, all p < 0.05) were affected detrimentally during MOD compared to MILD., Conclusion: In a warm and compensable environment, dry-bulb temperature did not influence high-intensity cycling performance when vapor pressure was maintained, whilst the perceptual responses were affected.

Purpose: To examine the interactive effects of VM and isometric resistance exercise on cerebral haemodynamics., Methods: Eleven healthy participants (mean ± SD 28 ± 9 years; 2 females) completed 20-s bilateral isometric leg extension at 50% of maximal voluntary contraction with continued ventilation (RE), a 20-s VM at mouth pressure of 40 mmHg (VM), and a combination (RE + VM), in randomised order. Mean beat-to-beat blood velocity in the posterior (PCAv mean ) and middle cerebral arteries (MCAv mean ), vertebral artery blood flow, end-tidal partial pressure of CO 2 and mean arterial pressure (MAP) were measured. RE data were time aligned to RE + VM and analysed according to standard VM phases., Results: Interaction effects (VM phase × condition) were observed for MCAv mean , PCAv mean , vertebral artery blood flow and MAP (all ≤ 0.010). Phase I MCAv mean was greatest for RE [88 ± 19, vs. 71 ± 11 and 78 ± 12 cm s -1 for VM (P = 0.008) and RE + VM (P = 0.021), respectively]. Greater increases in MCAv mean than PCAv mean occurred in phase I of RE only (24 ± 15% vs. 16 ± 16%, post hoc P = 0.044). In phase IIb, MAP was lower in RE than RE + VM (115 ± 15 vs. 138 ± 21 mmHg, P = 0.004), but did not reduce MCAv mean (78 ± 8 vs. 79 ± 9 cm s -1 , P = 0.579) or PCAv mean (45 ± 11 vs .46 ± 11 cm s -1 , P = 0.617). Phase IIb MCAv mean and PCAv mean was lowest in VM (66 ± 6 and 39 ± 8 cm s -1 , respectively, all P < 0.001), whereas in Phase IV, MCAv mean , PCAv mean and MAP were greater in VM than in RE and RE + VM (all P < 0.020)., Conclusion: RE and RE + VM produce similar cerebrovascular responses despite different MAP profiles. However, the VM produced the greatest cerebrovascular challenge afterward.

Alternative routes of administration are one approach that could be used to bypass the blood-brain barrier (BBB) for effective drug delivery to the central nervous system (CNS). Here, we focused on intranasal delivery of polymer nanoparticles. We hypothesized that surface modification of poly(lactic- co -glycolic acid) (PLGA) nanoparticles with rabies virus glycoprotein (RVG29) would increase residence time and exposure of encapsulated payload to the CNS compared to non-targeted nanoparticles. Delivery kinetics and biodistribution were analyzed by administering nanoparticles loaded with the carbocyanine dye 1,1'-Dioctadecyl-3,3,3',3'-Tetramethylindotricarbocyanine Iodide (DiR) to healthy mice. Intranasal administration yielded minimal exposure of nanoparticle payload to most peripheral organs and rapid, effective delivery to whole brain. Regional analysis of payload delivery within the CNS revealed higher delivery to tissues closest to the trigeminal nerve, including the olfactory bulb, striatum, midbrain, brainstem, and cervical spinal cord. RVG29 surface modifications presented modest targeting benefits to the striatum, midbrain, and brainstem 2 h after administration, although targeting was not observed 30 min or 6 h after administration. Payload delivery to the trigeminal nerve was 3.5× higher for targeted nanoparticles compared to control nanoparticles 2 h after nanoparticle administration. These data support a nose-to-brain mechanism of drug delivery that closely implicates the trigeminal nerve for payload delivery from nanoparticles via transport of intact nanoparticles and eventual diffusion of payload. Olfactory and CSF routes are also observed to play a role. These data advance the utility of targeted nanoparticles for nose-to-brain drug delivery of lipophilic payloads and provide mechanistic insight to engineer effective delivery vectors to treat disease in the CNS., Competing Interests: The authors declare no conflict of interest.

Key Points: Thermal and hypoxic stress commonly coexist in environmental, occupational and clinical settings, yet how the brain tolerates these multi-stressor environments is unknown Core cooling by 1.0°C reduced cerebral blood flow (CBF) by 20-30% and cerebral oxygen delivery (CDO 2 ) by 12-19% at sea level and high altitude, whereas core heating by 1.5°C did not reliably reduce CBF or CDO 2 Oxygen content in arterial blood was fully restored with acclimatisation to 4330 m, but concurrent cold stress reduced CBF and CDO 2 Gross indices of cognition were not impaired by any combination of thermal and hypoxic stress despite large reductions in CDO 2 Chronic hypoxia renders the brain susceptible to large reductions in oxygen delivery with concurrent cold stress, which might make monitoring core temperature more important in this context ABSTRACT: Real-world settings are composed of multiple environmental stressors, yet the majority of research in environmental physiology investigates these stressors in isolation. The brain is central in both behavioural and physiological responses to threatening stimuli and, given its tight metabolic and haemodynamic requirements, is particularly susceptible to environmental stress. We measured cerebral blood flow (CBF, duplex ultrasound), cerebral oxygen delivery (CDO 2 ), oesophageal temperature, and arterial blood gases during exposure to three commonly experienced environmental stressors - heat, cold and hypoxia - in isolation, and in combination. Twelve healthy male subjects (27 ± 11 years) underwent core cooling by 1.0°C and core heating by 1.5°C in randomised order at sea level; acute hypoxia ( P ET , O 2  = 50 mm Hg) was imposed at baseline and at each thermal extreme. Core cooling and heating protocols were repeated after 16 ± 4 days residing at 4330 m to investigate any interactions with high altitude acclimatisation. Cold stress decreased CBF by 20-30% and CDO 2 by 12-19% (both P < 0.01) irrespective of altitude, whereas heating did not reliably change either CBF or CDO 2 (both P > 0.08). The increases in CBF with acute hypoxia during thermal stress were appropriate to maintain CDO 2 at normothermic, normoxic values. Reaction time was faster and slower by 6-9% with heating and cooling, respectively (both P < 0.01), but central (brain) processes were not impaired by any combination of environmental stressors. These findings highlight the powerful influence of core cooling in reducing CDO 2 . Despite these large reductions in CDO 2 with cold stress, gross indices of cognition remained stable., (© 2019 The Authors. The Journal of Physiology © 2019 The Physiological Society.)

Administration of substances directly into the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord is one approach that can circumvent the blood-brain barrier to enable drug delivery to the central nervous system (CNS). However, molecules that have been administered by intrathecal injection, which includes intraventricular, intracisternal, or lumbar locations, encounter new barriers within the subarachnoid space. These barriers include relatively high rates of turnover as CSF clears and potentially inadequate delivery to tissue or cellular targets. Nanomedicine could offer a solution. In contrast to the fate of freely administered drugs, nanomedicine systems can navigate the subarachnoid space to sustain delivery of therapeutic molecules, genes, and imaging agents within the CNS. Some evidence suggests that certain nanomedicine agents can reach the parenchyma following intrathecal administration. Here, we will address the preclinical and clinical use of intrathecal nanomedicine, including nanoparticles, microparticles, dendrimers, micelles, liposomes, polyplexes, and other colloidalal materials that function to alter the distribution of molecules in tissue. Our review forms a foundational understanding of drug delivery to the CSF that can be built upon to better engineer nanomedicine for intrathecal treatment of disease., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

New Findings: What is the central question of this study? Does habitual resistance and endurance exercise modify dynamic cerebral autoregulation? What is the main finding and its importance? To the authors' knowledge, this is the first study to directly assess dynamic cerebral autoregulation in resistance-trained individuals, and potential differences between exercise training modalities. Forced oscillations in blood pressure were induced by repeated squat-stands, from which dynamic cerebral autoregulation was assessed using transfer function analysis. These data indicate that dynamic cerebral autoregulatory function is largely unaffected by habitual exercise type, and further document the systemic circulatory effects of regular exercise., Abstract: Regular endurance and resistance exercise produce differential but desirable physiological adaptations in both healthy and clinical populations. The chronic effect of these different exercise modalities on cerebral vessels' ability to respond to rapid changes in blood pressure (BP) had not been examined. We examined dynamic cerebral autoregulation (dCA) in 12 resistance-trained (mean ± SD, 25 ± 6 years), 12 endurance-trained (28 ± 9 years) and 12 sedentary (26 ± 6 years) volunteers. The dCA was assessed using transfer function analysis of forced oscillations in BP vs. middle cerebral artery blood velocity (MCAv), induced via repeated squat-stands at 0.05 and 0.10 Hz. Resting BP and MCAv were similar between groups (interaction: both P ≥ 0.544). The partial pressure of end-tidal carbon dioxide ( P ETC O 2 ) was unchanged (P = 0.561) across squat-stand manoeuvres (grouped mean for absolute change +0.6 ± 2.3 mmHg). Gain and normalized gain were similar between groups across all frequencies (both P ≥ 0.261). Phase showed a frequency-specific effect between groups (P = 0.043), tending to be lower in resistance-trained (0.63 ± 0.21 radians) than in endurance-trained (0.90 ± 0.41, P = 0.052) and -untrained (0.85 ± 0.38, P = 0.081) groups at slower frequency (0.05 Hz) oscillations. Squat-stands induced mean arterial pressure perturbations differed between groups (interaction: P = 0.031), with greater changes in the resistance (P < 0.001) and endurance (P = 0.001) groups compared with the sedentary group at 0.05 Hz (56 ± 13 and 49 ± 11 vs. 35 ± 11 mmHg, respectively). The differences persisted at 0.1 Hz between resistance and sedentary groups (49 ± 12 vs. 33 ± 7 mmHg, P < 0.001). These results indicate that dCA remains largely unaltered by habitual endurance and resistance exercise with a trend for phase to be lower in the resistance exercise group at lower fequencies., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

New Findings: What is the central question of the study? What are the effects of acute mental stress on the mechanisms regulating cerebral blood flow? What is the main finding and its importance? The major new findings are as follows: (i) high mental stress and hypercapnia had an interactive effect on mean middle cerebral artery blood velocity; (ii) high mental stress altered the regulation of cerebral blood flow; (iii) the increased cerebrovascular hypercapnic reactivity was not driven by changes in mean arterial pressure alone; and (iv) this increased perfusion with mental stress appeared not to be justified functionally by an increase in oxygen demand (as determined by near-infrared spectroscopy-derived measures)., Abstract: In this study, we examined the effects of acute mental stress on cerebrovascular function. Sixteen participants (aged 23 ± 4 years; five female) were exposed to low and high mental stress using simple arithmetic (counting backwards from 1000) and more complex arithmetic (serial subtraction of 13 from a rapidly changing four-digit number), respectively. During consecutive conditions of baseline, low stress and high stress, end-tidal partial pressure of CO 2 ( P ET , C O 2 ) was recorded at normocapnia (37 ± 3 mmHg) and clamped at two elevated levels (P < 0.01): 41 ± 1 and 46 ± 1 mmHg. Mean right middle cerebral artery blood velocity (MCAv mean ; transcranial Doppler ultrasound), right prefrontal cortex haemodynamics (near-infrared spectroscopy) and mean arterial blood pressure (MAP; finger photoplethysmography) were measured continuously. Cerebrovascular hypercapnic reactivity (ΔMCAv mean /Δ P ET , C O 2 ), cerebrovascular conductance (CVC; MCAv mean /MAP), CVC CO 2 reactivity (ΔCVC/Δ P ET , C O 2 ) and total peripheral resistance (MAP/cardiac output) were calculated. Acute high mental stress increased MCAv mean by 7 ± 7%, and more so at higher P ET , C O 2 (32 ± 10%; interaction, P = 0.03), illustrating increased sensitivity to CO 2 (i.e. its major regulator). High mental stress also increased MAP (17 ± 9%; P ≤ 0.01), coinciding with increased near-infrared spectroscopy-derived prefrontal haemoglobin volume and saturation measures. High mental stress elevated both cerebrovascular hypercapnic and conductance reactivities (main effect of stress, P ≤ 0.04). These findings indicate that the cerebrovascular response to acute high mental stress results in a coordinated regulation between multiple processes., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

Both acute and regular exercise influence vascular and cognitive function. Upright aquatic exercise increases mean middle cerebral artery blood velocity (MCAv mean ) and has been suggested as favorable for cerebrovascular adaptations. However, MCAv mean has not been reported during swimming. Thus, we examined the cerebrovascular and cognitive effects of swimming. Ten land-based athletes (22 ± 5 years) and eight swimmers (19 ± 1 years) completed three cognitive tasks and four conditions that were used to independently and collectively delineate the swimming-related factors (i.e., posture, immersion, CO 2 retention [end-tidal CO 2 ; PETCO 2 ], and motor involvement). Measurements of MCAv mean and PETCO 2 were taken throughout each condition. Prone posture increased MCAv mean by 11% (P < 0.01 vs. upright land). Water immersion independently increased MCAv mean when upright (12%; P < 0.01) but not prone (P = 0.76). The consequent rise in PETCO 2 during head-out, breast-stroke swimming (50% heart rate range) independently increased MCAv mean by 14% (P < 0.01), while the motor involvement of swimming per se did not significantly change MCAv mean (P = 0.32). While accounting for sex, swimmers had ~17% lower MCAv mean during all rest conditions (P ≤ 0.05). However, in a subset of participants, both groups had similar internal carotid artery diameters (P = 0.99) and velocities (P = 0.97). Water immersion per se did not alter cognition (P ≥ 0.15), but 20 min of moderate-intensity swimming improved visuomotor performance by 4% (P = 0.03), regardless of athlete group (P = 0.12). In conclusion, breast-stroke swimming increased MCAv mean mostly due to postural and PETCO 2 effects, with minimal contributions from water immersion or motor activity. Lastly, swimming improved cognitive functioning acutely, regardless of athlete group. Future research should explore the chronic effects of swimming on cerebrovascular function and cognition, particularly in aging., (© 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

Tokyo 2020 will likely be the most heat stressful Olympics to date, so preparation to mitigate the effects of humid heat will be essential for performance in several of the 33 sports. One key consideration is heat acclimation (HA); the repeated exposure to heat to elicit physiological and psychophysical adaptations that improve tolerance and exercise performance in the heat. Heat can be imposed in various ways, including exercise in the heat, hot water immersion, or passive exposure to hot air ( e.g ., sauna). The physical requirements of each sport will determine the impact that the heat has on performance, and the adaptations required from HA to mitigate these effects. This review focuses on one key adaptation, plasma volume expansion (PVE), and how the mode of HA may affect the kinetics of adaptation. PVE constitutes a primary HA-mediated adaptation and contributes to functional adaptations (e.g., lower heart rate and increased heat loss capacity), which may be particularly important in athletes of "sub-elite" cardiorespiratory fitness ( e.g ., team sports), alongside athletes of prolonged endurance events. This review: i) highlights the ability of exercise in the heat, hot-water immersion, and passive hot air to expand PV, providing the first quantitative assessment of the efficacy of different heating modes; ii) discusses how this may apply to athletes at Tokyo 2020; and iii) provides recommendations regarding the protocol of HA and the prospect for achieving PVE (and the related outcomes)., Competing Interests: No potential conflict of interest was reported by the authors., (© 2019 Informa UK Limited, trading as Taylor & Francis Group.)

Peripheral arterial disease (PAD) is characterized by lower limb atherosclerosis impairing blood supply and causing walking-induced leg pain or claudication. Adherence to traditional exercise training programs is poor due to these symptoms despite exercise being a mainstay of conservative treatment. Heat therapy improves many cardiovascular health outcomes, so this study tested if this was a viable alternative cardiovascular therapy for PAD patients. Volunteers with PAD were randomized to 12 wk of heat ( n = 11; mean age 76 ± 8 yr, BMI 28.7 ± 3.5 kg/m 2 , 4 females) or exercise ( n = 11; 74 ± 10 yr, 28.5 ± 6.8 kg/m 2 , 3 females). Heat involved spa bathing at ∼39°C, 3-5 days/wk for ≤30 min, followed by ≤30 min of callisthenics. Exercise involved ≤90 min of supervised walking and gym-based exercise, 1-2 days/wk. Following the interventions, total walking distance during a 6-min walk test increased (from ∼350 m) by 41 m (95% CI: [13, 69], P = 0.006) regardless of group, and pain-free walking distance increased (from ∼170 m) by 43 m ([22, 63], P < 0.001). Systolic blood pressure was reduced more following heat (-7 mmHg, [-4, -10], P < 0.001) than following exercise (-3 mmHg, [0, -6], P = 0.078), and diastolic and mean arterial pressure decreased by 4 mmHg in both groups ( P = 0.002). There were no significant changes in blood volume, ankle-brachial index, or measures of vascular health. There were no differences in the improvement in functional or blood pressure outcomes between heat and exercise in individuals with PAD. NEW & NOTEWORTHY Heat therapy via hot-water immersion and supervised exercise both improved walking distance and resting blood pressure in peripheral arterial disease (PAD) patients over 12 wk. Adherence to heat therapy was excellent, and the heat intervention was well tolerated. The results of the current study indicate that heat therapy can improve functional ability and has potential as an effective cardiovascular conditioning tool for individuals with PAD.

Temperature of the skin (T Sk ) and core (T C ) play key roles in sleep-wake regulation. The diurnal combination of low T Sk and high T C facilitates alertness, whereas the transition to high T Sk and low T C correlates with sleepiness. Sleepiness and deteriorating vigilance are induced with peripheral warming, whereas peripheral cooling appears to transiently improve vigilance in narcolepsy. This study aimed to test the hypothesis that foot cooling would maintain vigilance during extended wakefulness in healthy adults. Nine healthy young adult participants with habitually normal sleep completed three constant-routine trials in randomized crossover order. Trials began at 22:30 hours, and involved continuous mild foot cooling (30°C), moderate foot cooling (25°C) or no foot cooling, while undertaking six × 10-min Psychomotor Vigilance Tasks and seven × 7-min Karolinska Drowsiness Tasks, interspersed with questionnaires of sleepiness and thermal perceptions. Foot temperatures in control, mild and moderate cooling averaged 34.5 ± 0.5°C, 30.8 ± 0.2°C and 26.4 ± 0.1°C (all p < .01), while upper-limb temperatures remained stable (34-35°C) and T C declined (approximately -0.12°C per hr) regardless of trial (p = .84). Foot cooling did not improve vigilance (repeated-measures-ANOVA interaction for response speed: p = .45), but transiently reduced subjective sleepiness (-0.8 ± 0.8; p = .004). Participants felt cooler throughout cooling trials, but thermal comfort was unaffected (p = .43), as were almost all Karolinska Drowsiness Tasks' encephalographic parameters. In conclusion, mild or moderate cooling of the feet did not attenuate declines in vigilance or core temperature of healthy young adults during the period of normal sleep onset and early sleep, and any effect on sleepiness was small and transient., (© 2018 European Sleep Research Society.)

Type 2 diabetes is associated with reduced left ventricular reserve. It is unclear whether exercise training improves left ventricular function in people with type 2 diabetes., Purpose: This study aimed to determine whether 3 months of high-intensity interval training (HIIT) improves left ventricular function during exercise in adults with type 2 diabetes., Methods: Participants performed a V˙O2peak test and received a DXA scan and total blood volume measurement at baseline. Left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), and left ventricular stroke volume (LVSV) were then measured at rest and during low- and moderate-intensity semirecumbent exercise in adults with type 2 diabetes before and after 3 months of HIIT (n = 11) or no training (control) (n = 5). The effects of HIIT were determined using repeated-measures ANOVA., Results: HIIT increased V˙O2peak by approximately 15% (P < 0.002) but did not change body composition or total blood volume. LVESV decreased and LVEDV and LVSV increased from rest to moderate-intensity exercise in both groups at baseline (all P < 0.01). Three months of HIIT increased LVEDV (P = 0.008) and LVSV (P = 0.02) at all conditions, but there was no difference in controls (all P > 0.05). HIIT augmented the reduction in LVESV from rest to moderate-intensity exercise (P < 0.04), but LVESV was unchanged in controls. Increased LVEDV explained 51% of the change in LVSV after HIIT intervention. Mitral inflow parameters and mitral annular velocities were unaffected by HIIT (all P > 0.05)., Conclusions: HIIT training increased the LVSV response to exercise in adults with type 2 diabetes. These data suggest that HIIT can improve LV filling and emptying during exercise and reverse early cardiac consequences of type 2 diabetes.

A growing body of evidence indicates regular physical activity benefits older adults' cognitive functioning, particularly when a high level of cognitive control is required. Recent research has pointed to improved cerebrovascular function as one mechanism through which such benefits might arise. This study built on previous research by investigating in 51 healthy older adults aged 60-72 years relationships between habitual physical activity, cerebrovascular function (indicated by resting cerebral blood flow velocity in the middle cerebral artery [n = 42], and its responsiveness to hypercapnia [n = 26] and hypocapnia [n = 25]), and cognitive control (inhibition and switching). Linear regression analyses showed moderate positive associations between physical activity and inhibitory control, but not cerebrovascular function. There were also no significant relationships between the cerebrovascular measures and cognitive control. These results indicate that regular engagement in physical activity is associated with superior inhibitory control in older adulthood, but cerebrovascular function was not found to explain those relationships. Taken together, the current findings reinforce reports of positive links between habitual physical activity and cognition in healthy older adults, but also signal that interrelationships with cerebrovascular function may be more complex than currently indicated by the literature, necessitating further research to elucidate the role cerebrovascular function might play in accounting for physical activity-cognition links in healthy older adults., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Key Points: One in two female athletes chronically take a combined, monophasic oral contraceptive pill (OCP). Previous thermoregulatory investigations proposed that an endogenous rhythm of the menstrual cycle still occurs with OCP usage. Forthcoming large international sporting events will expose female athletes to hot environments differing in their thermal profile, yet few data exist on how trained women will respond from both a thermoregulatory and performance stand-point. In the present study, we have demonstrated that a small endogenous rhythm of the menstrual cycle still affects T core and also that chronic OCP use attenuates the sweating response, whereas behavioural thermoregulation is maintained. Furthermore, humid heat affects both performance and thermoregulatory responses to a greater extent than OCP usage and the menstrual cycle does., Abstract: We studied thermoregulatory responses of ten well-trained ( V ̇ O 2 max , 57 ± 7 mL min -1  kg -1 ) women taking a combined, monophasic oral contraceptive pill (OCP) (≥12 months) during exercise in dry and humid heat, across their active OCP cycle. They completed four trials, each of resting and cycling at fixed intensities (125 and 150 W), aiming to assess autonomic regulation, and then a self-paced intensity (30-min work trial) to assess behavioural regulation. Trials were conducted in quasi-follicular (qF) and quasi-luteal (qL) phases in dry (DRY) and humid (HUM) heat matched for wet bulb globe temperature (WBGT) (27°C). During rest and exercise at 125 W, rectal temperature was 0.15°C higher in qL than qF (P = 0.05) independent of environment (P = 0.17). The onset threshold and thermosensitivity of local sweat rate and forearm blood flow relative to mean body temperature was unaffected by the OCP cycle (both P > 0.30). Exercise performance did not differ between quasi-phases (qF: 268 ± 31 kJ, qL: 263 ± 26 kJ, P = 0.31) but was 5 ± 7% higher during DRY than during HUM (273 ± 29 kJ, 258 ± 28 kJ; P = 0.03). Compared to matched eumenorrhoeic athletes, chronic OCP use impaired the sweating onset threshold and thermosensitivity (both P < 0.01). In well-trained, OCP-using women exercising in the heat: (i) a performance-thermoregulatory trade-off occurred that required behavioural adjustment; (ii) humidity impaired performance as a result of reduced evaporative power despite matched WBGT; and (iii) the sudomotor but not behavioural thermoregulatory responses were impaired compared to matched eumenorrhoeic athletes., (© 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.)

The application of molecular techniques to exercise biology has provided novel insight into the complexity and breadth of intracellular signaling networks involved in response to endurance-based exercise. Here we discuss several strategies that have high uptake by athletes and, on mechanistic grounds, have the potential to promote cellular adaptation to endurance training in skeletal muscle. Such approaches are based on the underlying premise that imposing a greater metabolic load and provoking extreme perturbations in cellular homeostasis will augment acute exercise responses that, when repeated over months and years, will amplify training adaptation., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (T c ; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5-2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAv mean ; transcranial Doppler), partial pressure of end-tidal carbon dioxide ([Formula: see text]), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, -15, -30, and -45 mmHg). Four subjects became intolerant before +2.0°C T c , unrelated to hydration status. Without LBNP, decreases in [Formula: see text] accounted fully for reductions in MCAv mean across all T c . With LBNP at heat tolerance (+1.5 or +2.0°C), [Formula: see text] accounted for 69 ± 25% of the change in MCAv mean . The HYPO condition did not affect MCAv mean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAv mean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in T c are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.

Background: Attenuated increases in ventricular stroke volume during exercise are common in type 2 diabetes and contribute to reduced aerobic capacity. The purpose of this study was to determine whether impaired ventricular filling or reduced systolic ejection were responsible for the attenuated stroke volume reserve in people with uncomplicated type 2 diabetes., Methods: Peak aerobic capacity and total blood volume were measured in 17 people with diabetes and 16 non-diabetic controls with no evidence of cardiovascular disease. Left ventricular volumes and other systolic and diastolic functional parameters were measured with echocardiography at rest and during semi-recumbent cycle ergometry at 40 and 60% of maximal aerobic power and compared between groups., Results: People with diabetes had reduced peak aerobic capacity and heart rate reserve, and worked at lower workloads than non-diabetic controls. Cardiac output, stroke volume and ejection fraction were not different at rest, but increased less in people with diabetes during exercise. Left ventricular end systolic volume was not different between groups in any condition but end diastolic volume, although not different at rest, was smaller in people with diabetes during exercise. Total blood volume was not different between the groups, and was only moderately associated with left ventricular volumes., Conclusions: People with type 2 diabetes exhibit an attenuated increase in stroke volume during exercise attributed to an inability to maintain/increase left ventricular filling volumes at higher heart rates. This study is the first to determine the role of filling in the blunted cardiac reserve in adults with type 2 diabetes.