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1.
J Manipulative Physiol Ther ; 44(5): 420-431, 2021 06.
Article in English | MEDLINE | ID: mdl-34376321

ABSTRACT

OBJECTIVE: The purpose of the present study was to determine the neuroendocrine response after a thoracic spinal manipulation in people with Achilles tendinopathy. METHODS: This was a randomized 2-sequence, 2-period crossover trial. A total of 24 participants, mean (standard deviation) age of 48 (7) years, with a diagnosis of Achilles tendinopathy (>3 mo) were randomly assigned into sequence 1 (sham intervention and then thoracic spinal manipulation) or sequence 2 (thoracic spinal manipulation and then sham intervention). The trial was conducted at a university laboratory with a washout period of 1 week. The primary outcome measure was the testosterone/cortisol (T/C) ratio (salivary samples). The secondary outcome measures included heart rate variability (measured with electrocardiography) and total oxygenation index (nmol/L) of calf muscle and Achilles tendon (measured with near-infrared spectroscopy). A 2-way mixed-model analysis of variance was performed. The statistic of interest was the condition by time interaction. RESULTS: A statistically significant condition by time interaction was found for the T/C ratio (mean difference: -0.16; confidence interval: -0.33 to 0.006; interaction: P < .05) and the total oxygenation index (mean difference: 1.35; confidence interval: -1.3 to 4.1; interaction: P < .05) of calf muscle but not for Achilles tendon (P = .6); however, no difference was found for heart rate variability (P = .5). CONCLUSION: In people with Achilles tendinopathy, thoracic spinal manipulation resulted in immediate increase in the total oxygenation index in the calf muscle followed by an increase in the T/C ratio 6 hours post-intervention.


Subject(s)
Achilles Tendon , Manipulation, Spinal , Tendinopathy , Cross-Over Studies , Humans , Middle Aged , Muscle, Skeletal , Tendinopathy/therapy
2.
Int J Sport Nutr Exerc Metab ; 31(3): 244-249, 2021 Jan 28.
Article in English | MEDLINE | ID: mdl-33508779

ABSTRACT

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.


Subject(s)
Body Composition , Dehydration/diagnostic imaging , Organism Hydration Status , Subcutaneous Fat/diagnostic imaging , Ultrasonography , Adiposity , Adult , Body Mass Index , Cross-Over Studies , Dehydration/etiology , Drinking , Drinking Water/administration & dosage , Female , Humans , Male , Middle Aged
3.
Eur J Appl Physiol ; 121(4): 1061-1071, 2021 Apr.
Article in English | MEDLINE | ID: mdl-33426575

ABSTRACT

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 (ΔO2Hb-deO2Hb: 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.

4.
PLoS One ; 16(1): e0244841, 2021.
Article in English | MEDLINE | ID: mdl-33395691

ABSTRACT

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.


Subject(s)
Arterial Pressure/physiology , Exercise/physiology , Hyperglycemia/metabolism , Adult , Area Under Curve , Blood Glucose/metabolism , Cross-Over Studies , Female , Glucose/metabolism , Hemodynamics/physiology , Humans , Insulin/metabolism , Insulin, Regular, Human/metabolism , Male , Postprandial Period , Sedentary Behavior , Sitting Position , Standing Position , Triglycerides/blood , Walking/physiology
5.
Mil Med Res ; 7(1): 58, 2020 11 29.
Article in English | MEDLINE | ID: mdl-33248459

ABSTRACT

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.


Subject(s)
Acclimatization/physiology , Military Personnel/statistics & numerical data , Heart Rate/physiology , Hot Temperature/adverse effects , Humans , Oxygen Consumption/physiology , United States , Warfare/statistics & numerical data , Warfare/trends
6.
Exp Physiol ; 105(12): 2099-2109, 2020 12.
Article in English | MEDLINE | ID: mdl-33058304

ABSTRACT

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.

7.
Eur J Appl Physiol ; 120(7): 1637-1649, 2020 Jul.
Article in English | MEDLINE | ID: mdl-32476054

ABSTRACT

PURPOSE: Cognition, cerebral blood flow (CBF) and its major regulator (i.e., arterial CO2), 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 CO2, in ten active (26 ± 3 years) and ten inactive (24 ± 6 years) healthy adults. METHODS: Participants completed two randomised sessions; exercise and a resting CO2-control-wherein end-tidal CO2 (PETCO2) 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 CO2-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 PETCO2 (3-6%; p ≤ 0.04), regardless of session. Overall, resting or exercise-related changes in PETCO2 and MCAv did not associate with changes in cognition (r ≤ 0.29 ± 0.34). Fitness ([Formula: see text]O2MAX) was associated with baseline cognition (r ≥ 0.50). CONCLUSION: Acute increases in PETCO2 and MCAv were not associated with improved cognition. In fact, cognitive performance was impaired at both levels of increased PETCO2, regardless of session. Finally, fitter people were found to have better cognition.


Subject(s)
Carbon Dioxide/metabolism , Cerebrovascular Circulation/physiology , Exercise/physiology , Oxygen Consumption/physiology , Adult , Blood Flow Velocity/physiology , Blood Pressure/physiology , Cognition/physiology , Female , Humans , Male , Middle Cerebral Artery/physiology
8.
J Physiol ; 598(13): 2513-2530, 2020 07.
Article in English | MEDLINE | ID: mdl-32347544

ABSTRACT

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.


Subject(s)
Cardiorespiratory Fitness , High-Intensity Interval Training , Brain , Exercise
9.
Eur J Appl Physiol ; 120(4): 841-852, 2020 Apr.
Article in English | MEDLINE | ID: mdl-32072226

ABSTRACT

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 m2; 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.


Subject(s)
Body Temperature Regulation , Exercise/physiology , Heat-Shock Response/physiology , Hot Temperature , Humidity , Adult , Bicycling/physiology , Humans , Male , Young Adult
10.
Eur J Appl Physiol ; 120(2): 467-479, 2020 Feb.
Article in English | MEDLINE | ID: mdl-31912226

ABSTRACT

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 (PCAvmean) and middle cerebral arteries (MCAvmean), vertebral artery blood flow, end-tidal partial pressure of CO2 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 MCAvmean, PCAvmean, vertebral artery blood flow and MAP (all ≤ 0.010). Phase I MCAvmean 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 MCAvmean than PCAvmean 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 MCAvmean (78 ± 8 vs. 79 ± 9 cm s-1, P = 0.579) or PCAvmean (45 ± 11 vs .46 ± 11 cm s-1, P = 0.617). Phase IIb MCAvmean and PCAvmean was lowest in VM (66 ± 6 and 39 ± 8 cm s-1, respectively, all P < 0.001), whereas in Phase IV, MCAvmean, PCAvmean 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.


Subject(s)
Blood Flow Velocity/physiology , Isometric Contraction/physiology , Middle Cerebral Artery/physiology , Resistance Training/methods , Valsalva Maneuver , Adult , Female , Humans , Male , Young Adult
11.
Physiol Rep ; 7(20): e14247, 2019 10.
Article in English | MEDLINE | ID: mdl-31637867

ABSTRACT

Both acute and regular exercise influence vascular and cognitive function. Upright aquatic exercise increases mean middle cerebral artery blood velocity (MCAvmean ) and has been suggested as favorable for cerebrovascular adaptations. However, MCAvmean 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, CO2 retention [end-tidal CO2 ; PETCO2 ], and motor involvement). Measurements of MCAvmean and PETCO2 were taken throughout each condition. Prone posture increased MCAvmean by 11% (P < 0.01 vs. upright land). Water immersion independently increased MCAvmean when upright (12%; P < 0.01) but not prone (P = 0.76). The consequent rise in PETCO2 during head-out, breast-stroke swimming (50% heart rate range) independently increased MCAvmean by 14% (P < 0.01), while the motor involvement of swimming per se did not significantly change MCAvmean (P = 0.32). While accounting for sex, swimmers had ~17% lower MCAvmean 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 MCAvmean mostly due to postural and PETCO2 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.


Subject(s)
Blood Flow Velocity/physiology , Cerebrovascular Circulation/physiology , Cognition/physiology , Heart Rate/physiology , Swimming/physiology , Adolescent , Adult , Female , Humans , Inhibition, Psychological , Male , Middle Cerebral Artery/physiology , Neuropsychological Tests , Reaction Time/physiology , Swimming/psychology , Young Adult
12.
Exp Physiol ; 104(12): 1780-1789, 2019 12.
Article in English | MEDLINE | ID: mdl-31549452

ABSTRACT

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.


Subject(s)
Brain/physiology , Cerebrovascular Circulation/physiology , Habits , Homeostasis/physiology , Physical Endurance/physiology , Resistance Training/methods , Adult , Brain/blood supply , Brain/diagnostic imaging , Cohort Studies , Female , Humans , Male , Resistance Training/trends , Ultrasonography, Doppler/methods , Ultrasonography, Doppler/trends
13.
Exp Physiol ; 104(11): 1678-1687, 2019 11.
Article in English | MEDLINE | ID: mdl-31465595

ABSTRACT

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 CO2 ( 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 (MCAvmean ; transcranial Doppler ultrasound), right prefrontal cortex haemodynamics (near-infrared spectroscopy) and mean arterial blood pressure (MAP; finger photoplethysmography) were measured continuously. Cerebrovascular hypercapnic reactivity (ΔMCAvmean /Δ P ET , C O 2 ), cerebrovascular conductance (CVC; MCAvmean /MAP), CVC CO2 reactivity (ΔCVC/Δ P ET , C O 2 ) and total peripheral resistance (MAP/cardiac output) were calculated. Acute high mental stress increased MCAvmean by 7 ± 7%, and more so at higher P ET , C O 2 (32 ± 10%; interaction, P = 0.03), illustrating increased sensitivity to CO2 (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.


Subject(s)
Blood Pressure/physiology , Cerebrovascular Circulation/physiology , Hypercapnia/physiopathology , Middle Cerebral Artery/physiology , Stress, Physiological/physiology , Adult , Blood Flow Velocity/physiology , Carbon Dioxide/metabolism , Cardiac Output/physiology , Female , Hemodynamics/physiology , Humans , Hypercapnia/metabolism , Male , Middle Cerebral Artery/metabolism , Partial Pressure , Young Adult
15.
Am J Physiol Heart Circ Physiol ; 316(6): H1495-H1506, 2019 06 01.
Article in English | MEDLINE | ID: mdl-31002283

ABSTRACT

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/m2, 4 females) or exercise (n = 11; 74 ± 10 yr, 28.5 ± 6.8 kg/m2, 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.


Subject(s)
Exercise Therapy , Hot Temperature , Hydrotherapy , Peripheral Arterial Disease/therapy , Aged , Aged, 80 and over , Blood Pressure , Exercise Tolerance , Female , Humans , Male , Middle Aged , New Zealand , Peripheral Arterial Disease/diagnosis , Peripheral Arterial Disease/physiopathology , Quality of Life , Recovery of Function , Time Factors , Treatment Outcome , Walking
16.
Neuropsychologia ; 125: 62-69, 2019 03 04.
Article in English | MEDLINE | ID: mdl-30682349

ABSTRACT

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.


Subject(s)
Brain/blood supply , Brain/physiology , Cognition/physiology , Executive Function/physiology , Exercise , Habits , Aged , Female , Humans , Hypercapnia/psychology , Hypocapnia/psychology , Inhibition, Psychological , Male , Middle Aged , Middle Cerebral Artery/physiology
17.
Temperature (Austin) ; 7(2): 129-148, 2019 Sep 03.
Article in English | MEDLINE | ID: mdl-33015241

ABSTRACT

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).

18.
J Physiol ; 597(1): 71-88, 2019 01.
Article in English | MEDLINE | ID: mdl-30320879

ABSTRACT

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 Tcore 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.


Subject(s)
Bicycling/physiology , Body Temperature Regulation , Contraceptives, Oral/pharmacology , Estradiol/blood , Exercise/physiology , Progesterone/blood , Adult , Female , Hot Temperature , Humans , Humidity , Ovary/physiology , Young Adult
19.
J Sleep Res ; 28(3): e12701, 2019 06.
Article in English | MEDLINE | ID: mdl-29749043

ABSTRACT

Temperature of the skin (TSk ) and core (TC ) play key roles in sleep-wake regulation. The diurnal combination of low TSk and high TC facilitates alertness, whereas the transition to high TSk and low TC 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 TC 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.


Subject(s)
Cold Temperature , Foot/blood supply , Psychomotor Performance/physiology , Sleep/physiology , Sleepiness , Adult , Female , Healthy Volunteers , Humans , Male , Young Adult
20.
J Appl Gerontol ; 38(6): 755-774, 2019 06.
Article in English | MEDLINE | ID: mdl-28799443

ABSTRACT

This study examined the impact of personalized versus generalized education about environmental fall prevention recommendations on older adults' adherence with recommendations. Secondary aims focused on the impact of recent falls and perceived susceptibility of future falls on adherence with recommendations. Twenty-four community-dwelling older adults aged 65 to 89 years were randomized into two groups to receive either personalized or generalized education intervention on environmental fall prevention recommendations. A significant difference was found in the mean total percentage of adherence with recommendations of those receiving personalized education (69%) compared with those receiving generalized education (37%). No statistically significant relationship was found between sustaining recent falls, nor perceived susceptibility to future falls, and their extent of adherence with environmental fall prevention recommendations. Providing personalized education for environmental fall prevention recommendations may improve older adults' adherence with the recommendations given.


Subject(s)
Accident Prevention , Accidental Falls/prevention & control , Exercise Therapy , Patient Compliance/statistics & numerical data , Patient Education as Topic , Aged , Aged, 80 and over , Female , Health Behavior , Humans , Male , Risk Assessment , Risk Factors
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