ORCID Profile
0000-0002-6266-4246
Current Organisation
The University of Canberra
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Functional Materials | Environmental Nanotechnology | Materials Engineering
Management of Greenhouse Gas Emissions from Manufacturing Activities | Management of Greenhouse Gas Emissions from Electricity Generation |
Publisher: Human Kinetics
Date: 2020
Abstract: It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete’s nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.
Publisher: BMJ
Date: 28-01-2020
DOI: 10.1136/BJSPORTS-2019-100781
Abstract: Assess the health status and heat preparation strategies of athletes competing in a World Cycling Ch ionships held in hot ambient conditions (37°C, 25% relative humidity, wet-bulb-globe-temperature 27°C) and monitor the medical events arising during competition. 69 cyclists (~9% of the world ch ionships participants) completed a pre-competition questionnaire. Illnesses and injuries encountered by the Athlete Medical Centre (AMC) were extracted from the race reports. 22% of respondents reported illness symptoms in the 10 days preceding the Ch ionships. 57% of respondents had previously experienced heat-related symptoms (cr ing most commonly) while 17% had previously been diagnosed with exertional heat illness. 61% of the respondents had undergone some form of heat exposure prior to the Ch ionships, with 38% acclimating for 5 to 30 days. In addition, several respondents declared to live in warm countries and all arrived in Qatar ~5 days prior to their event. 96% of the respondents used a pre-cooling strategy for the time trials and 74% did so before the road race (p .001), with ice vests being the most common. The AMC assessed 46 injuries and 26 illnesses in total, with three cyclists diagnosed with heat exhaustion. The prevalence of previous heat illness in elite cyclists calls for team and event organisation doctors to be trained on heat illness management, including early diagnosis and rapid on-site cooling. Some cyclists had been exposed to the heat prior to the Ch ionships, but few had a dedicated plan, calling for additional education on the importance of heat acclimation. Pre-cooling was widely adopted.
Publisher: Human Kinetics
Date: 03-2019
Abstract: High-level athletes are always looking at ways to maximize training adaptations for competition performance, and using altered environmental conditions to achieve this outcome has become increasingly popular by elite athletes. Furthermore, a series of potential nutrition and hydration interventions may also optimize the adaptation to altered environments. Altitude training was first used to prepare for competition at altitude, and it still is today however, more often now, elite athletes embark on a series of altitude training c s to try to improve sea-level performance. Similarly, the use of heat acclimation/acclimatization to optimize performance in hot/humid environmental conditions is a common practice by high-level athletes and is well supported in the scientific literature. More recently, the use of heat training to improve exercise capacity in temperate environments has been investigated and appears to have positive outcomes. This consensus statement will detail the use of both heat and altitude training interventions to optimize performance capacities in elite athletes in both normal environmental conditions and extreme conditions (hot and/or high), with a focus on the importance of nutritional strategies required in these extreme environmental conditions to maximize adaptations conducive to competitive performance enhancement.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 27-03-2023
Publisher: Human Kinetics
Date: 09-2023
Abstract: Purpose : To investigate the effects of a training c with heat and/or hypoxia sessions on hematological and thermoregulatory adaptations. Methods : Fifty-six elite male rugby players completed a 2-week training c with 5 endurance and 5 repeated-sprint sessions, rugby practice, and resistance training. Players were separated into 4 groups: CAMP trained in temperate conditions at sea level, HEAT performed the endurance sessions in the heat, ALTI slept and performed the repeated sprints at altitude, and H + A was a combination of the heat and altitude groups. Results : Blood volume across all groups increased by 140 mL (95%CI, 42–237 P = .006) and plasma volume by 97 mL (95%CI 28–167 P = .007) following the training c . Plasma volume was 6.3% (0.3% to 12.4%) higher in HEAT than ALTI ( P = .034) and slightly higher in HEAT than H + A (5.6% [−0.3% to 11.7%] P = .076). Changes in hemoglobin mass were not significant ( P = .176), despite a ∼1.2% increase in ALTI and H + A and a ∼0.7% decrease in CAMP and HEAT. Peak rectal temperature was lower during a postc heat-response test in HEAT (0.3 °C [0.1–0.5] P = .010) and H + A (0.3 °C [0.1–0.6] P = .005). Oxygen saturation upon waking was lower in ALTI (3% [2% to 5%] P .001) and H + A (4% [3% to 6%] P .001) than CAMP and HEAT. Conclusion : Although blood and plasma volume increased following the c , sleeping at altitude impeded the increase when training in the heat and only marginally increased hemoglobin mass. Heat training induced adaptations commensurate with partial heat acclimation however, combining heat training and altitude training and confinement during a training c did not confer concomitant hematological adaptations.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2018
Publisher: BMJ
Date: 10-04-2020
Publisher: Elsevier BV
Date: 04-2020
DOI: 10.1016/J.JSAMS.2019.10.024
Abstract: To investigate whether self-reported health complaints and choice of heat stress prevention strategies during the taper predicted peaking at an athletics ch ionship in hot conditions. Cohort study. Data on health and heat stress prevention were collected before the 2015 World Athletics Ch ionship in Beijing, China. Peaking was defined using the athlete's pre-competition ranking and final competition rank. Baseline and endpoint data were fitted into multiple logic regression models. Two hundred forty-five (29%) of 841 eligible athletes participated. Both sprint ower (Odds ratio (OR) 0.33 (95% Confidence interval (CI) 0.11 to 0.94), P=0.038) and endurance/combined events (OR 0.38 (95% CI 0.14 to 1.00), P=0.049) athletes having sustained concern-causing health complaints during the taper were less likely to peak. Endurance/combined events athletes who chose pre-cooling to mitigate heat stress were less likely to peak (OR 0.35 (95% CI 0.15 to 0.80), P=0.013), while sprint ower athletes reporting a sudden-onset injury complaint during the taper displayed increased peaking (OR 4.47 (95% CI 1.28 to 15.59), P=0.019). Health complaints that caused the athlete concern during the taper were predictive of failure to peak at a major athletics competition. Sprint ower athletes who experienced an acute injury symptom during the taper appeared to benefit from rest. Pre-cooling strategies seem to require further validation during real-world endurance/combined events. It appears that athletics athletes' self-reported health should be monitored during the taper, concerns addressed, and heat stress prevention strategies in idually tested before ch ionships in hot conditions.
Publisher: Elsevier BV
Date: 2020
DOI: 10.1016/J.JSAMS.2019.08.292
Abstract: To examine iron stores, hemoglobin mass, and performance before, during and after intermittent altitude exposure in a professional male rugby player experiencing iron overload following blood transfusions for treatment for acute myeloid leukemia. Longitudinal, repeated measures, single case-study. The player was followed prior to (control), and during (study), an in-season block of altitude training. During the control period two venesections were performed for a total of 750mL of blood removal. Internal and external training load, match statistics, blood volume, plasma volume, haemoglobin mass, serum ferritin and reticulocyte count were monitored throughout. During the control period serum ferritin declined following the two venesections (∼51%) as did haemoglobin mass (∼2%), reticulocyte count remained stable. During the study period serum ferritin further declined (∼30%), however haemoglobin mass and reticulocyte count increased (∼4% and ∼14% respectively). Internal training load for the control and study period was similar, however external training load was lower in the study period. Match statistics were not favourable for the player during the control period, however they improved during the study period. This case supports the theory that in iduals with elevated iron availability are well placed to achieve increases in haemoglobin mass. Furthermore, although therapeutic venesections may still be required to manage iron overload, the addition of altitude exposure may be a method to assist in reducing total body iron by means of mobilising available (excessive) iron to incorporate into haemoglobin. Altitude exposure did not hinder the players' performance. Further research is encouraged.
Publisher: Springer Science and Business Media LLC
Date: 05-2013
Publisher: Georg Thieme Verlag KG
Date: 12-04-2012
Abstract: This study investigated the effects of moderate dehydration (~2.5% body weight) on muscle strength and endurance using percutaneous electrical stimulation to quantify central and peripheral fatigue, and isolate the combined effects of exercise-heat stress and dehydration, vs. the effect of dehydration alone. Force production and voluntary activation were calculated in 10 males during 1 brief and 15 repeated maximal voluntary isometric contractions performed prior to (control) walking in the heat (35°C), immediately following exercise, and the next morning (dehydration). The protocol was also performed in a euhydrated state. During the brief contractions, force production and voluntary activation were maintained in all trials. In contrast, force production decreased throughout the repeated contractions, regardless of hydration status (P<0.001). The decline in force was greater immediately following exercise-heat stress dehydration compared with control and euhydration (P<0.001). When dehydration was isolated from acute post-exercise dehydration, force production was maintained similarly to control and euhydration. Despite the progressive decline in force production and the increased fatigability observed during the repeated contractions, voluntary activation remained elevated throughout each muscle function test. Therefore, moderate dehydration, isolated from acute exercise-heat stress, does not appear to influence strength during a single contraction or enhance fatigability.
Publisher: Human Kinetics
Date: 07-2020
Abstract: Purpose : The core temperature responses during exercise and effects of different cooling strategies on endurance performance under heat stress have been investigated in recreational athletes. This investigation aimed to determine peak rectal temperatures during elite racewalking competitions and to detail any cooling strategies used. Methods : Rectal temperature was measured in 14 heat-adapted elite reelite race walkers (9 females) via a telemetric capsule across 4 outdoor events, including the 2018 Commonwealth Games (race 1: 20 km, 25°C, 74% relative humidity [RH], n = 2) and 3 International Association of Athletics Federations–sanctioned 10-km events (race 2: 19°C, 34% RH, n = 2 race 3: 29°C, 47% RH, n = 14 and race 4: 23°C, 72% RH, n = 11). All athletes completed race 3, and a subs le completed the other events. Their use of cooling strategies and symptoms of heat illness were determined. Results : Peak rectal temperatures °C were observed in all events. The highest rectal temperature observed during an event was 41.2°C. These high rectal temperatures were observed without concomitant heat illness, with the exception of cr ing in one athlete during race 1. The rectal temperatures tended to reach a steady state in the second half of the 20-km event, but no steady state was observed in the 10-km events. The athletes used cooling strategies in race 1 only, implementing different combinations of cold-water immersion, ice-slurry ingestion, ice-towel application, ice-vest application, and facial water spraying. Conclusions : Elite reelite race walkers experience rectal temperatures °C during competition despite only moderate-warm conditions, and even when precooling and midcooling strategies are applied.
Publisher: Elsevier BV
Date: 04-2016
DOI: 10.1016/J.AUTNEU.2016.02.002
Abstract: This review examines the cardiovascular adaptations along with total body water and plasma volume adjustments that occur in parallel with improved heat loss responses during exercise-heat acclimation. The cardiovascular system is well recognized as an important contributor to exercise-heat acclimation that acts to minimize physiological strain, reduce the risk of serious heat illness and better sustain exercise capacity. The upright posture adopted by humans during most physical activities and the large skin surface area contribute to the circulatory and blood pressure regulation challenge of simultaneously supporting skeletal muscle blood flow and dissipating heat via increased skin blood flow and sweat secretion during exercise-heat stress. Although it was traditionally held that cardiac output increased during exercise-heat stress to primarily support elevated skin blood flow requirements, recent evidence suggests that temperature-sensitive mechanisms may also mediate an elevation in skeletal muscle blood flow. The cardiovascular adaptations supporting this challenge include an increase in total body water, plasma volume expansion, better sustainment and/or elevation of stroke volume, reduction in heart rate, improvement in ventricular filling and myocardial efficiency, and enhanced skin blood flow and sweating responses. The magnitude of these adaptations is variable and dependent on several factors such as exercise intensity, duration of exposure, frequency and total number of exposures, as well as the environmental conditions (i.e. dry or humid heat) in which acclimation occurs.
Publisher: Springer Science and Business Media LLC
Date: 25-07-2023
DOI: 10.1007/S40279-023-01885-2
Abstract: Fluid loss during prolonged exercise in hot conditions poses thermoregulatory and cardiovascular challenges for athletes that can lead to impaired performance. Pre-exercise hyperhydration using nutritional aids is a strategy that may prevent or delay the adverse effects of dehydration and attenuate the impact of heat stress on exercise performance. The aim of this systematic review was to examine the current literature to determine the effect of pre-exercise hyperhydration on performance, key physiological responses and gastrointestinal symptoms. English language, full-text articles that compared the intervention with a baseline or placebo condition were included. An electronic search of Medline Complete, SPORTDiscus and Embase were used to identify articles with the final search conducted on 11 October 2022. Studies were assessed using the American Dietetic Association Quality Criteria Checklist. Thirty-eight studies involving 403 participants ( n = 361 males) were included in this review ( n = 22 assessed exercise performance or capacity). Two studies reported an improvement in time-trial performance (range 5.7–11.4%), three studies reported an improvement in total work completed (kJ) (range 4–5%) and five studies reported an increase in exercise capacity (range 14.3–26.2%). During constant work rate exercise, nine studies observed a reduced mean heart rate (range 3–11 beats min −1 ), and eight studies reported a reduced mean core temperature (range 0.1–0.8 °C). Ten studies reported an increase in plasma volume (range 3.5–12.6%) compared with a control. Gastrointestinal symptoms were reported in 26 studies, with differences in severity potentially associated with factors within the ingestion protocol of each study (e.g. treatment, dose, ingestion rate). Pre-exercise hyperhydration may improve exercise capacity during constant work rate exercise due to a reduced heart rate and core temperature, stemming from an acute increase in plasma volume. The combination of different osmotic aids (e.g. glycerol and sodium) may enhance fluid retention and this area should continue to be explored. Future research should utilise valid and reliable methods of assessing gastrointestinal symptoms. Furthermore, studies should investigate the effect of hyperhydration on different exercise modalities whilst implementing a strong level of blinding. Finally, females are vastly underrepresented, and this remains a key area of interest in this area.
Publisher: Human Kinetics
Date: 02-2023
Publisher: Springer Science and Business Media LLC
Date: 12-08-2015
Publisher: American Physiological Society
Date: 09-2021
DOI: 10.1152/JAPPLPHYSIOL.01059.2020
Abstract: This is the first study to investigate the effects of dry-bulb temperature (13, 20, 28, and 36°C) on self-paced exercise performance by minimizing differences in the skin-to-air vapor pressure gradient (i.e., evaporative potential) between conditions. Performance was similar in 13°C and 20°C with a matched evaporative potential, whereas it was reduced at 28°C and further impaired at 36°C in association with a large decrease in dry heat loss and moderate reduction in evaporative potential.
Publisher: BMJ
Date: 26-11-2013
Publisher: Wiley
Date: 25-07-2017
DOI: 10.1111/APHA.12916
Abstract: Heat stress and hypoxia independently influence cerebrocortical activity and impair prolonged exercise performance. This study examined the relationship between electroencephalography (EEG) activity and self-paced exercise performance in control (CON, 18 °C, 40% RH), hot (HOT, 35 °C, 60% RH) and hypoxic (HYP, 18 °C, 40% RH FiO Eleven well-trained cyclists completed a 750 kJ cycling time trial in each condition on separate days in a counterbalanced order. EEG activity was recorded with α- and β-activity evaluated in the frontal (F3 and F4) and central (C3 and C4) areas. Standardized low-resolution brain electromagnetic tomography (sLORETA) was also utilized to localize changes in cerebrocortical activity. Both α- and β-activity decreased in the frontal and central areas during exercise in HOT relative to CON (P < 0.05). α-activity was also lower in HYP compared with CON (P < 0.05), whereas β-activity remained similar. β-activity was higher in HYP than in HOT (P < 0.05). sLORETA revealed that α- and β-activity increased at the onset of exercise in the primary somatosensory and motor cortices in CON and HYP, while only β-activity increased in HOT. A decrease in α- and β-activity occurred thereafter in all conditions, with α-activity being lower in the somatosensory and somatosensory association cortices in HOT relative to CON. High-intensity prolonged self-paced exercise induces cerebrocortical activity alterations in areas of the brain associated with the ability to inhibit conflicting attentional processing under hot and hypoxic conditions, along with the capacity to sustain mental readiness and arousal under heat stress.
Publisher: BMJ
Date: 25-03-2014
Publisher: Informa UK Limited
Date: 30-06-2017
DOI: 10.1080/02640414.2017.1346275
Abstract: The primary aim of this study was to determine whether facial feature tracking reliably measures changes in facial movement across varying exercise intensities. Fifteen cyclists completed three, incremental intensity, cycling trials to exhaustion while their faces were recorded with video cameras. Facial feature tracking was found to be a moderately reliable measure of facial movement during incremental intensity cycling (intra-class correlation coefficient = 0.65-0.68). Facial movement (whole face (WF), upper face (UF), lower face (LF) and head movement (HM)) increased with exercise intensity, from lactate threshold one (LT1) until attainment of maximal aerobic power (MAP) (WF 3464 ± 3364mm, P < 0.005 UF 1961 ± 1779mm, P = 0.002 LF 1608 ± 1404mm, P = 0.002 HM 849 ± 642mm, P < 0.001). UF movement was greater than LF movement at all exercise intensities (UF minus LF at: LT1, 1048 ± 383mm LT2, 1208 ± 611mm MAP, 1401 ± 712mm P < 0.001). Significant medium to large non-linear relationships were found between facial movement and power output (r
Publisher: Frontiers Media SA
Date: 28-05-2021
Publisher: American Physiological Society
Date: 2017
DOI: 10.1152/AJPREGU.00431.2016
Abstract: The aim of this study was to investigate the effect of repeated passive heat exposure (i.e., acclimation) on muscle contractility in humans. Fourteen nonheat-acclimated males completed two trials including electrically evoked twitches and voluntary contractions in thermoneutral conditions [Cool: 24°C, 40% relative humidity (RH)] and hot ambient conditions in the hyperthermic state (Hot: 44–50°C, 50% RH) on consecutive days in a counterbalanced order. Rectal temperature was ~36.5°C in Cool and was maintained at ~39°C throughout Hot. Both trials were repeated after 11 days of passive heat acclimation (1 h per day, 48–50°C, 50% RH). Heat acclimation decreased core temperature in Cool (−0.2°C, P 0.05), increased the time required to reach 39°C in Hot (+9 min, P 0.05) and increased sweat rate in Hot (+0.7 liter/h, P 0.05). Moreover, passive heat acclimation improved skeletal muscle contractility as evidenced by an increase in evoked peak twitch litude both in Cool (20.5 ± 3.6 vs. 22.0 ± 4.0 N·m) and Hot (20.5 ± 4.7 vs. 22.0 ± 4.0 N·m) (+9%, P 0.05). Maximal voluntary torque production was also increased both in Cool (145 ± 42 vs. 161 ± 36 N·m) and Hot (125 ± 36 vs. 145 ± 30 N·m) (+17%, P 0.05), despite voluntary activation remaining unchanged. Furthermore, the slope of the relative torque/electromyographic linear relationship was improved postacclimation ( P 0.05). These adjustments demonstrate that passive heat acclimation improves skeletal muscle contractile function during electrically evoked and voluntary muscle contractions of different intensities both in Cool and Hot. These results suggest that repeated heat exposure may have important implications to passively maintain or even improve muscle function in a variety of performance and clinical settings.
Publisher: Wiley
Date: 06-05-2015
DOI: 10.1111/SMS.12467
Abstract: Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise-heat exposures over 1-2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vest), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent ex les of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat.
Publisher: Informa UK Limited
Date: 17-11-2022
Publisher: Wiley
Date: 15-10-2023
DOI: 10.1111/SMS.14520
Publisher: BMJ
Date: 25-03-2014
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2016
Publisher: American Physiological Society
Date: 08-2022
DOI: 10.1152/AJPREGU.00328.2021
Abstract: Both adult females and children have been reported to have a lower sweating capacity and thus reduced evaporative heat loss potential that may increase their susceptibility to exertional hyperthermia in the heat. Compared with males, females have a lower maximal sweat rate and thus a theoretically lower maximum skin wettedness due to a lower sweat output per gland. Similarly, children have been suggested to be disadvantaged in high ambient temperatures due to a lower sweat production and therefore reduced evaporative capacity, despite modifications of heat transfer due to physical attributes and possible evaporative efficiency. The reported reductions in the sudomotor activity of females and children suggest a lower sweating capacity in girls. However, because of the complexities of isolating sex and maturation from the confounding effects of morphological differences (e.g., body surface area-to-mass ratio) and metabolic heat production, limited evidence exists supporting whether children, and, more specifically, girls are at a thermoregulatory disadvantage. Furthermore, a limited number of child-adult comparison studies involve females and very few studies have directly compared regional and whole body sudomotor activity between boys and girls. This minireview highlights the exercise-induced sudomotor response of females and children, summarizes previous research investigating the sudomotor response to exercise in girls, and suggests important areas for further research.
Publisher: Frontiers Media SA
Date: 25-11-2015
Publisher: Wiley
Date: 12-05-2017
Publisher: Frontiers Media SA
Date: 23-03-2017
Publisher: BMJ
Date: 12-2018
DOI: 10.1136/BJSPORTS-2018-099881
Abstract: To characterise the core temperature response and power output profile of elite male and female cyclists during the 2016 UCI Road World Ch ionships. This may contribute to formulating environmental heat stress policies. Core temperature was recorded via an ingestible capsule in 10, 15 and 15 cyclists during the team time trial (TTT), in idual time trial (ITT) and road race (RR), respectively. Power output and heart rate were extracted from in idual cycling computers. Ambient conditions in direct sunlight were hot (37°C±3°C) but dry (25%±16% relative humidity), corresponding to a wet-bulb globe temperature of 27°C±2°C. Core temperature increased during all races (p .001), reaching higher peak values in TTT (39.8°C±0.9°C) and ITT (39.8°C±0.4°C), relative to RR (39.2°C±0.4°C, p .001). The highest temperature recorded was 41.5°C (TTT). Power output was significantly higher during TTT (4.7±0.3 W/kg) and ITT (4.9±0.5 W/kg) than RR (2.7±0.4 W/kg, p .001). Heart rate increased during the TTs (p .001) while power output decreased (p .001). 85% of the cyclists participating in the study (ie, 34 of 40) reached a core temperature of at least 39°C with 25% (ie, 10 of 40) exceeding 40°C. Higher core temperatures were reached during the time trials than the RR.
Publisher: Human Kinetics
Date: 05-2021
Abstract: Purpose : The risk of exercise-induced endotoxemia is increased in the heat and is primarily attributable to changes in gut permeability resulting in the translocation of lipopolysaccharides (LPS) into the circulation. The purpose of this study was to quantify the acute changes in gut permeability and LPS translocation during submaximal continuous and high-intensity interval exercise under heat stress. Methods : A total of 12 well-trained male runners (age 37 [7] y, maximal oxygen uptake [VO 2 max] 61.0 [6.8] mL·min −1 ·kg −1 ) undertook 2 treadmill runs of 2 × 15-minutes at 60% and 75% VO 2 max and up to 8 × 1-minutes at 95% VO 2 max in HOT (34°C, 68% relative humidity) and COOL (18°C, 57% relative humidity) conditions. Venous blood s les were collected at the baseline, following each running intensity, and 1 hour postexercise. Blood s les were analyzed for markers of intestinal permeability (LPS, LPS binding protein, and intestinal fatty acid–binding protein). Results : The increase in LPS binding protein following each exercise intensity in the HOT condition was 4% (5.3 μg·mL −1 , 2.4–8.4 mean, 95% confidence interval, P .001), 32% (4.6 μg·mL −1 , 1.8–7.4 P = .002), and 30% (3.0 μg·mL −1 , 0.03–5.9 P = .047) greater than in the COOL condition. LPS was 69% higher than baseline following running at 75% VO 2 max in the HOT condition (0.2 endotoxin units·mL −1 , 0.1–0.4 P = .011). Intestinal fatty acid–binding protein increased 43% (2.1 ng·mL −1 , 0.1–4.2 P = .04) 1 hour postexercise in HOT compared with the COOL condition. Conclusions : Small increases in LPS concentration during exercise in the heat and subsequent increases in intestinal fatty acid–binding protein and LPS binding protein indicate a capacity to tolerate acute, transient intestinal disturbance in well-trained endurance runners.
Publisher: Springer Science and Business Media LLC
Date: 30-01-2021
Publisher: BMJ
Date: 04-11-2016
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 16-08-2022
DOI: 10.1249/MSS.0000000000003028
Abstract: This study aimed to characterize the thermal and cardiovascular strain of professional cyclists during the 2019 Tour Down Under and determine the associations between thermal indices and power output, and physiological strain. Gastrointestinal temperature ( T gi ), heart rate (HR), and power output were recorded during the six stages (129–151.5 km) of the Tour Down Under in ≤22 male participants. Thermal indices included dry-bulb, black-globe, wet-bulb, and wet-bulb-globe (WBGT) temperature relative humidity (RH), Heat Index Humidex and universal thermal climate index. The heat stress index (HSI), which reflects human heat strain, was also calculated. Dry-bulb temperature was 23°C–37°C, and RH was 18%–72% (WBGT: 21°C–29°C). Mean T gi was 38.2°C–38.5°C, and mean peak T gi was 38.9°C–39.4°C, both highest values recorded during stage 3 (WBGT: 27°C). Peak in idual T gi was ≥40.0°C in three stages and ≥39.5°C in 14%–33% of cyclists in five stages. Mean HR was 131–147 bpm (68%–77% of peak), with the highest mean recorded in stage 3 ( P ≤ 0.005). Mean power output was 180–249 W, with the highest mean recorded during stage 4 ( P 0.001 21°C WBGT). The thermal indices most strongly correlated with power output were black-globe temperature ( r = −0.778), RH ( r = 0.768), universal thermal climate index ( r = −0.762), and WBGT ( r = −0.745 all P 0.001). Mean T gi was correlated with wet-bulb temperature ( r = 0.495), HSI ( r = 0.464), and Humidex ( r = 0.314 all P 0.05), whereas mean HR was most strongly correlated with HSI ( r = 0.720), along with T gi ( r = 0.599) and power output ( r = 0.539 all P 0.05). Peak T gi reached 40.0°C in some cyclists, although most remained .5°C with an HR of ~73% of peak. Power output was correlated with several thermal indices, primarily influenced by temperature, whereas T gi and HR were associated with the HSI, which has potential for sport-specific heat policy development.
Publisher: Wiley
Date: 06-05-2015
DOI: 10.1111/SMS.12448
Publisher: Springer Science and Business Media LLC
Date: 17-03-2014
DOI: 10.1007/S00726-014-1721-3
Abstract: We investigated the effect of exercise in the heat on both intracellular and extracellular Hsp72 in athletes with a prior history of exertional heat illness (EHI). Two groups of runners, one consisting of athletes who had a previous history of EHI, and a control group (CON) of similar age (29.7 ± 1.2 and 29.1 ± 2 years CON vs. EHI) and fitness [maximal oxygen consumption [Formula: see text] 65.7 ± 2 and 64.5 ± 3 ml kg(-1) min(-1) CON vs. EHI] were recruited. Seven subjects in each group ran on a treadmill for 1 h at 72 % [Formula: see text] in warm conditions (30 °C, 40 % RH) reaching rectal temperatures of ~39.3 (CON) and ~39.2 °C (EHI). Blood was collected every 10 min during exercise and plasma was analysed for extracellular Hsp72. Intracellular Hsp72 levels were measured in both monocytes and lymphocytes before and immediately after the 60-min run, and then after 1 h recovery at an ambient temperature of 24 °C. Plasma Hsp72 increased from 1.18 ± 0.14 and 0.86 ± 0.08 ng/ml (CON vs. EHI) at rest to 4.56 ± 0.63 and 4.04 ± 0.45 ng/ml (CON vs. EHI, respectively) at the end of exercise (p < 0.001), with no difference between groups. Lymphocyte Hsp72 was lower in the EHI group at 60 min of exercise (p < 0.05), while monocyte Hsp72 was not different between groups. The results of the present study suggest that the plasma Hsp72 response to exercise in athletes with a prior history of EHI remained similar to that of the CON group, while the lymphocyte Hsp72 response was reduced.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2015
Publisher: Frontiers Media SA
Date: 12-11-2021
DOI: 10.3389/FPHYS.2021.740121
Abstract: Permissive dehydration during exercise heat acclimation (HA) may enhance hematological and cardiovascular adaptations and thus acute responses to prolonged exercise. However, the independent role of permissive dehydration on vascular and cardiac volumes, ventricular-arterial (VA) coupling and systemic hemodynamics has not been systematically investigated. Seven males completed two 10-day exercise HA interventions with controlled heart rate (HR) where euhydration was maintained or permissive dehydration (-2.9 ± 0.5% body mass) occurred. Two experimental trials were conducted before and after each HA intervention where euhydration was maintained (-0.5 ± 0.4%) or dehydration was induced (-3.6 ± 0.6%) via prescribed fluid intakes. Rectal (T re ) and skin temperatures, HR, blood (BV) and left ventricular (LV) volumes, and systemic hemodynamics were measured at rest and during bouts of semi-recumbent cycling (55% V̇O 2 peak ) in 33°C at 20, 100, and 180 min. Throughout HA sweat rate (12 ± 9%) and power output (18 ± 7 W) increased ( P & 0.05), whereas T re was 38.4 ± 0.2°C during the 75 min of HR controlled exercise ( P = 1.00). Neither HA intervention altered resting and euhydrated exercising T re , BV, LV diastolic and systolic volumes, systemic hemodynamics, and VA coupling ( P & 0.05). Furthermore, the thermal and cardiovascular strain during exercise with acute dehydration post-HA was not influenced by HA hydration strategy. Instead, elevations in T re and HR and reductions in BV and cardiac output matched pre-HA levels ( P & 0.05). These findings indicate that permissive dehydration during exercise HA with controlled HR and maintained thermal stimulus does not affect hematological or cardiovascular responses during acute endurance exercise under moderate heat stress with maintained euhydration or moderate dehydration.
Publisher: Frontiers Media SA
Date: 11-12-2019
Publisher: Springer International Publishing
Date: 07-11-2019
Publisher: Springer International Publishing
Date: 2019
Publisher: BMJ
Date: 08-11-2016
DOI: 10.1136/BJSPORTS-2016-096580
Abstract: To determine preparticipation predictors of injury and illness at a major Athletics ch ionship. A cohort study design was used. Before the 2015 International Association of Athletics Federations World Ch ionships in Athletics, all 207 registered national teams were approached about partaking in a study of preparticipation health 50 teams accepted. The athletes (n=957) in the participating teams were invited to complete a preparticipation health questionnaire (PHQ). New injuries and illnesses that occurred at the ch ionships were prospectively recorded. Logistic regression analyses were performed with simple and multiple models using any in-ch ionship injury and in-ch ionship illness as outcomes. The PHQ was completed by 307 (32.1%) of the invited athletes 116 athletes (38.3%) reported an injury symptom during the month before the ch ionships, while 40 athletes (13%) reported an illness symptom. 20 (6.5%) of the participating athletes sustained a health problem during the ch ionships. Endurance athletes were almost 10-fold more likely to sustain an in-ch ionship illness than speed ower athletes (OR, 9.88 95% CI 1.20 to 81.31 p=0.033). Participants reporting a preparticipation gradual-onset injury symptom were three times more likely (OR, 3.09 95% CI 1.08 to 8.79 p=0.035) and those reporting an illness symptom causing anxiety were fivefold more likely (OR, 5.56 95% CI 1.34 to 23.15 p=0.018) to sustain an in-ch ionship injury. Analyses of preparticipation predictors of injury and illness at a major Athletics ch ionship suggest that endurance athletes require particular clinical attention. Preparticipation symptoms causing anxiety are interesting predictors for in-ch ionship health problems.
Publisher: American Physiological Society
Date: 11-2020
DOI: 10.1152/AJPHEART.00466.2020
Abstract: This study demonstrates that 10 days of exercise heat acclimation has minimal effects on left ventricular volumes, intrinsic cardiac function, and systemic hemodynamics during prolonged, repeated semirecumbent exercise in moderate heat, where heart rate and blood volume are similar to preacclimation levels. However, progressive dehydration is consistently associated with similar degrees of hyperthermia and tachycardia and reductions in blood volume, diastolic filling of the left ventricle, stroke volume, and cardiac output, regardless of acclimation state.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 26-02-2020
DOI: 10.1249/MSS.0000000000002320
Abstract: This study aimed to characterize the adaptive responses to heat acclimation (HA) with controlled heart rate (HR) and determine whether hydration strategy alters adaptations. The influence of HA on maximal oxygen uptake (V˙O 2max ) in cool conditions and self-paced exercise in the heat was also determined. Eight men (V˙O 2max , 55 ± 7 mL·kg −1 ·min −1 ) completed two 10-d interventions in a counterbalanced crossover design. Fluid intakes differed between interventions to either maintain euhydration (HA-EUH) or elicit similar daily body mass deficits (2.85% ± 0.26% HA-DEH). HA consisted of 90 min of cycling in 40°C and 40% relative humidity. Initial workload (172 ± 22 W) was adjusted over the last 75 min to maintain exercising HR equivalent to 65% V˙O 2max . A V˙O 2max test in cool conditions and 30-min time trial in hot-humid conditions were completed before and after HA. HR at the end of the initial 15 min workload was 10 ± 5 bpm lower on day 10 in both interventions ( P 0.001). The workload necessary to maintain exercising HR (145 ± 7 bpm) increased throughout HA-EUH (25 ± 10 W, P = 0.001) and HA-DEH (16 ± 18 W, P = 0.02). There was a main effect of HA on sweat rate ( P = 0.014), which tended to increase with HA-EUH (0.19 ± 0.18 L·h −1 , P = 0.06), but not HA-DEH ( P = 0.12). Skin temperature decreased during HA-EUH (0.6°C ± 0.5°C, P = 0.03), but not HA-DEH ( P = 0.30). There was a main effect of HA on V˙O 2max (~3 mL·kg −1 ·min −1 , P = 0.02) however, neither intervention independently increased V˙O 2max (both, P = 0.08). Time-trial performance increased after HA-EUH (19 ± 16 W, P = 0.02), but not HA-DEH ( P = 0.21). Controlled HR exercise in the heat induces several HA adaptations, which may be optimized by maintaining euhydration. HA-EUH also improves self-paced exercise performance in the heat. However, HA does not seem to significantly increase V˙O 2max in cool conditions.
Publisher: BMJ
Date: 14-07-2015
Publisher: Springer Science and Business Media LLC
Date: 31-05-2012
DOI: 10.1007/S00421-012-2427-4
Abstract: This study examined whether a rise in thermal and cardiovascular strain during exercise to exhaustion in the heat at different intensities is associated with compromised muscle and cerebral oxygenation. Using near-infrared spectroscopy, oxygenation changes in the vastus lateralis and prefrontal cortex of ten subjects cycling to exhaustion in 40 °C conditions at 60 % (H60%) and 75 % (H75%) maximal oxygen uptake (VO₂(max)) and for 60 min in 18 °C conditions at 60 % VO₂(max) (C60%) were examined. Thermoregulatory and cardiovascular responses were also monitored. Rectal temperature reached 38.1 °C in the C60% trial, 39.7 °C (~60 min) and 39.0 °C (~27 min) in the H60% and H75% trials, respectively (P 97 % of maximum heart rate and accompanied by significant declines in stroke volume, cardiac output and mean arterial pressure (P < 0.01). Vastus lateralis oxygen saturation (SmO(2)) declined at the onset of exercise in all conditions, remaining similarly depressed at exhaustion in the heat. Prefrontal cortex oxygen saturation (ScO(2)) was ~10 % lower at exhaustion in the H60% and H75% trials compared with C60% (P < 0.01), which remained above baseline from 15 min onward. These findings indicate that changes in SmO(2) and ScO(2) are associated with the development of thermal and cardiovascular strain during exercise to exhaustion in the heat, which is accelerated by exercise intensity. In locomotor muscles, a potential reduction in oxygen delivery may develop, whereas in the brain, the progressive reduction in ScO(2) may induce mental fatigue.
Publisher: BMJ
Date: 19-08-2020
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2011
Publisher: American Physiological Society
Date: 09-2003
DOI: 10.1152/JAPPLPHYSIOL.00361.2003
Abstract: The hypothesis that exercise causes an increase in the postexercise esophageal temperature threshold for onset of cutaneous vasodilation through an alteration of active vasodilator activity was tested in nine subjects. Increases in forearm skin blood flow and arterial blood pressure were measured and used to calculate cutaneous vascular conductance at two superficial forearm sites: one with intact α-adrenergic vasoconstrictor activity (untreated) and one infused with bretylium tosylate (bretylium treated). Subjects remained seated resting for 15 min (no-exercise) or performed 15 min of treadmill running at either 55, 70, or 85% of peak oxygen consumption followed by 20 min of seated recovery. A liquid-conditioned suit was used to increase mean skin temperature (∼4.0°C/h), while local forearm temperature was cl ed at 34°C, until cutaneous vasodilation. No differences in the postexercise threshold for cutaneous vasodilation between untreated and bretylium-treated sites were observed for either the no-exercise or exercise trials. Exercise resulted in an increase in the postexercise threshold for cutaneous vasodilation of 0.19 ± 0.01, 0.39 ± 0.02, and 0.53 ± 0.02°C above those of the no-exercise resting values for the untreated site ( P 0.05). Similarly, there was an increase of 0.20 ± 0.01, 0.37 ± 0.02, and 0.53 ± 0.02°C for the treated site for the 55, 70, and 85% exercise trials, respectively ( P 0.05). It is concluded that reflex activity associated with the postexercise increase in the onset threshold for cutaneous vasodilation is more likely mediated through an alteration of active vasodilator activity rather than through adrenergic vasoconstrictor activity.
Publisher: Springer International Publishing
Date: 2019
Publisher: Frontiers Media SA
Date: 29-07-2020
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2019
DOI: 10.1249/MSS.0000000000001745
Abstract: We sought to determine the effect of low and moderate normobaric hypoxia on oxygen consumption and anaerobic contribution during interval running at different exercise intensities. Eight runners (age, 25 ± 7 yr, V˙O 2max : 72.1 ± 5.6 mL·kg −1 ·min −1 ) completed three separate interval sessions at threshold (4 × 5 min, 2-min recovery), V˙O 2max (8 × 90 s, 90-s recovery), and race pace (10 × 45 s, 1 min 45 s recovery) in each of normoxia (elevation: 580 m, FiO 2 : 0.21), low (1400 m, 0.195) or moderate (2100 m, 0.18) normobaric hypoxia. The absolute running speed for each intensity was kept the same at each altitude to evaluate the effect of FiO 2 on physiological responses. Expired gas was collected throughout each session, with total V˙O 2 and accumulated oxygen deficit calculated. Data were compared using repeated-measures ANOVA. There were significant differences between training sessions for peak and total V˙O 2 , and anaerobic contribution ( P 0.001, P = 0.01 respectively), with race pace sessions eliciting the lowest and highest responses respectively. Compared to 580 m, total V˙O 2 at 2100 m was significantly lower ( P 0.05), and anaerobic contribution significantly higher ( P 0.05) during both threshold and V˙O 2max sessions. No significant differences were observed between altitudes for race pace sessions. To maintain oxygen flux, completing acute exercise at threshold and V˙O 2max intensity at 1400 m simulated altitude appears more beneficial compared with 2100 m. However, remaining at moderate altitude is a suitable when increasing the anaerobic contribution to exercise is a targeted response to training.
Publisher: American Physiological Society
Date: 10-2017
DOI: 10.1152/JAPPLPHYSIOL.00430.2017
Abstract: This study aimed to clarify the pathway mediating hyperthermia-induced alterations in neural drive transmission and determine if heat acclimation protects voluntary muscle activation and cognitive function in hyperthermic humans. Electrically evoked potentials (H reflex and M wave), executive function (special planning and working memory), and maximal voluntary isometric contractions (120 s) were assessed in 14 participants in control conditions [CON, 24°C, 40% relative humidity (RH)] and in a hyperthermic state (HYP, 44–50°C, 50% RH) on consecutive days in a counterbalanced order. Thereafter, participants were passively heat acclimated for 11 days (1 h per day, 48–50°C, 50% RH) before repeating the initial assessments. Heat acclimation decreased rectal temperature in CON (−0.2°C, P 0.05), but participants were maintained at ~39°C in HYP. Heat acclimation increased the time required to reach 39°C (+9 min), along with sweat rate (+0.7 l/h), and serum extracellular expression of heat shock protein 72 (eHSP72 +20%) in HYP ( P 0.05). M-wave and H-reflex litudes were lower in HYP than CON ( P 0.05) and were not protected by heat acclimation. Nerve conduction velocity was faster in HYP than CON ( P 0.05) without being influenced by heat acclimation. These results suggest that peripheral neural drive transmission in the hyperthermic state is primarily affected by axonal conduction velocity rather than synaptic failure. Executive function, voluntary activation, and the ability to sustain torque were impaired in HYP ( P 0.05). However, despite no perceptual changes ( P 0.05), heat acclimation restored executive function, while protecting the ability to sustain voluntary activation and torque production during a prolonged contraction in hyperthermia ( P 0.05). Ultimately, heat acclimation induces beneficial central but not peripheral neural adaptations. NEW & NOTEWORTHY Heat acclimation restores planning accuracy and working memory in hyperthermic humans, together with the supraspinal capacity to sustain motor drive during a sustained maximal voluntary contraction. Electrically evoked potential data (M wave, H reflex) indicate that heat acclimation does not protect against hyperthermia-induced impairments in peripheral neural drive transmission. Heat acclimation induces beneficial central but not peripheral neural adaptations.
Publisher: Springer Science and Business Media LLC
Date: 11-11-2017
Publisher: Wiley
Date: 13-10-2010
DOI: 10.1113/EXPPHYSIOL.2010.054213
Abstract: It has been proposed that self-paced exercise in the heat is regulated by an anticipatory reduction in work rate based on the rate of heat storage. However, performance may be impaired by the development of hyperthermia and concomitant rise in cardiovascular strain increasing relative exercise intensity. This study evaluated the influence of thermal strain on cardiovascular function and power output during self-paced exercise in the heat. Eight endurance-trained cyclists performed a 40 km simulated time trial in hot (35°C) and thermoneutral conditions (20°C), while power output, mean arterial pressure, heart rate, oxygen uptake and cardiac output were measured. Time trial duration was 64.3 ± 2.8 min (242.1 W) in the hot condition and 59.8 ± 2.6 min (279.4 W) in the thermoneutral condition (P < 0.01). Power output in the heat was depressed from 20 min onwards compared with exercise in the thermoneutral condition (P < 0.05). Rectal temperature reached 39.8 ± 0.3 (hot) and 38.9 ± 0.2°C (thermoneutral P < 0.01). From 10 min onwards, mean skin temperature was ~7.5°C higher in the heat, and skin blood flow was significantly elevated (P < 0.01). Heart rate was ~8 beats min(-1) higher throughout hot exercise, while stroke volume, cardiac output and mean arterial pressure were significantly depressed compared with the thermoneutral condition (P < 0.05). Peak oxygen uptake measured during the final kilometre of exercise at maximal effort reached 77 (hot) and 95% (thermoneutral) of pre-experimental control values (P < 0.01). We conclude that a thermoregulatory-mediated rise in cardiovascular strain is associated with reductions in sustainable power output, peak oxygen uptake and maximal power output during prolonged, intense self-paced exercise in the heat.
Publisher: Elsevier BV
Date: 10-2023
Publisher: American Physiological Society
Date: 05-2022
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2017
Publisher: American Physiological Society
Date: 12-2003
DOI: 10.1152/JAPPLPHYSIOL.00651.2003
Abstract: The hypothesis that the magnitude of the postexercise onset threshold for sweating is increased by the intensity of exercise was tested in eight subjects. Esophageal temperature was monitored as an index of core temperature while sweat rate was measured by using a ventilated capsule placed on the upper back. Subjects remained seated resting for 15 min (no exercise) or performed 15 min of treadmill running at either 55, 70, or 85% of peak oxygen consumption (V̇o 2 peak ) followed by a 20-min seated recovery. Subjects then donned a liquid-conditioned suit used to regulate mean skin temperature. The suit was first perfused with 20°C water to control and stabilize skin and core temperature before whole body heating. Subsequently, the skin was heated (∼4.0°C/h) until sweating occurred. Exercise resulted in an increase in the onset threshold for sweating of 0.11 ± 0.02, 0.23 ± 0.01, and 0.33 ± 0.02°C above that measured for the no-exercise resting values ( P 0.05) for the 55, 70, and 85% of V̇o 2 peak exercise conditions, respectively. We did note that there was a greater postexercise hypotension as a function of exercise intensity as measured at the end of the 20-min exercise recovery. Thus it is plausible that the increase in postexercise threshold may be related to postexercise hypotension. It is concluded that the sweating response during upright recovery is significantly modified by exercise intensity and may likely be influenced by the nonthermal baroreceptor reflex adjustments postexercise.
Publisher: Journal of Athletic Training/NATA
Date: 04-2021
Abstract: To provide best-practice recommendations for developing and implementing heat-acclimatization strategies in secondary school athletics. An extensive literature review on topics related to heat acclimatization and heat acclimation was conducted by a group of content experts. Using the Delphi method, action-oriented recommendations were developed. A period of heat acclimatization consisting of ≥14 consecutive days should be implemented at the start of fall preseason training or practices for all secondary school athletes to mitigate the risk of exertional heat illness. The heat-acclimatization guidelines should outline specific actions for secondary school athletics personnel to use, including the duration of training, the number of training sessions permitted per day, and adequate rest periods in a cool environment. Further, these guidelines should include sport-specific and athlete-specific recommendations, such as phasing in protective equipment and reintroducing heat acclimatization after periods of inactivity. Heat-acclimatization guidelines should be clearly detailed in the secondary school's policy and procedures manual and disseminated to all stakeholders. Heat-acclimatization guidelines, when used in conjunction with current best practices surrounding the prevention, management, and care of secondary school student-athletes with exertional heat stroke, will optimize their health and safety.
Publisher: Springer International Publishing
Date: 2017
Publisher: Oxford University Press (OUP)
Date: 11-03-2019
Publisher: Informa UK Limited
Date: 02-04-2016
Publisher: Frontiers Media SA
Date: 11-01-2018
Publisher: SAGE Publications
Date: 19-04-2019
Abstract: In this review, we detail the impact of environmental stress on cognitive and military task performance and highlight any in idual characteristics or interventions which may mitigate any negative effect. Military personnel are often deployed in regions markedly different from their own, experiencing hot days, cold nights, and trips both above and below sea level. In spite of these stressors, high-level cognitive and operational performance must be maintained. A systematic review of the electronic databases Medline (PubMed), EMBASE (Scopus), PsycINFO, and Web of Science was conducted from inception up to September 2018. Eligibility criteria included a healthy human cohort, an outcome of cognition or military task performance and assessment of an environmental condition. The search returned 113,850 records, of which 124 were included in the systematic review. Thirty-one studies examined the impact of heat stress on cognition 20 of cold stress 59 of altitude exposure and 18 of being below sea level. The severity and duration of exposure to the environmental stressor affects the degree to which cognitive performance can be impaired, as does the complexity of the cognitive task and the skill or familiarity of the in idual performing the task. Strategies to improve cognitive performance in extreme environmental conditions should focus on reducing the magnitude of the physiological and perceptual disturbance caused by the stressor. Strategies may include acclimatization and habituation, being well skilled on the task, and reducing sensations of thermal stress with approaches such as head and neck cooling.
Publisher: Springer Science and Business Media LLC
Date: 06-01-2012
Publisher: American Physiological Society
Date: 15-05-2015
DOI: 10.1152/JAPPLPHYSIOL.00084.2015
Abstract: This study examined the time course and extent of decrease in peak oxygen uptake (V̇o 2peak ) during self-paced exercise in HOT (35°C and 60% relative humidity) and COOL (18°C and 40% relative humidity) laboratory conditions. Ten well-trained cyclists completed four consecutive 16.5-min time trials (15-min self-paced effort with 1.5-min maximal end-spurt to determine V̇o 2peak ) interspersed by 5 min of recovery on a cycle ergometer in each condition. Rectal temperature increased significantly more in HOT (39.4 ± 0.7°C) than COOL (38.6 ± 0.3°C P 0.001). Power output was lower throughout HOT compared with COOL ( P 0.001). The decrease in power output from trial 1 to 4 was ∼16% greater in HOT ( P 0.001). Oxygen uptake (V̇o 2 ) was lower throughout HOT than COOL ( P 0.05), except at 5 min and during the end-spurt in trial 1. In HOT, V̇o 2peak reached 97, 89, 85, and 85% of predetermined maximal V̇o 2 , whereas in COOL 97, 94, 93, and 92% were attained. Relative exercise intensity (%V̇o 2peak ) during trials 1 and 2 was lower in HOT (∼84%) than COOL (∼86% P 0.05), decreasing slightly during trials 3 and 4 (∼80 and ∼85%, respectively P 0.05). However, heart rate was higher throughout HOT ( P = 0.002), and ratings of perceived exertion greater during trials 3 and 4 in HOT ( P 0.05). Consequently, the regulation of self-paced exercise appears to occur in conjunction with the maintenance of %V̇o 2peak within a narrow range (80-85% V̇o 2peak ). This range widens under heat stress, however, when exercise becomes protracted and a disassociation develops between relative exercise intensity, heart rate, and ratings of perceived exertion.
Publisher: Springer Science and Business Media LLC
Date: 23-04-2022
DOI: 10.1007/S40279-022-01677-0
Abstract: Physiological heat adaptations can be induced following various protocols that use either artificially controlled (i.e. acclimation) or naturally occurring (i.e. acclimatisation) environments. During the summer months in seasonal climates, adequate exposure to outdoor environmental heat stress should lead to transient seasonal heat acclimatisation. The aim of the systematic review was to assess the available literature and characterise seasonal heat acclimatisation during the summer months and identify key factors that influence the magnitude of adaptation. English language, full-text articles that assessed seasonal heat acclimatisation on the same s le of healthy adults a minimum of 3 months apart were included. Studies were identified using first- and second-order search terms in the databases MEDLINE, SPORTDiscus, CINAHL Plus with Full Text, Scopus and Cochrane, with the last search taking place on 15 July 2021. Studies were independently assessed by two authors for the risk of bias using a modified version of the McMaster critical review form. Data for the following outcome variables were extracted: participant age, sex, body mass, height, body fat percentage, maximal oxygen uptake, time spent exercising outdoors (i.e. intensity, duration, environmental conditions), heat response test (i.e. protocol, time between tests), core temperature, skin temperature, heart rate, whole-body sweat loss, whole-body and local sweat rate, sweat sodium concentration, skin blood flow and plasma volume changes. Twenty-nine studies were included in this systematic review, including 561 participants across eight countries with a mean summer daytime wet-bulb globe temperature (WBGT) of 24.9 °C (range: 19.5–29.8 °C). Two studies reported a reduction in resting core temperature (0.16 °C p 0.05), 11 reported an increased sweat rate (range: 0.03–0.53 L·h −1 p 0.05), two observed a reduced heart rate during a heat response test (range: 3–8 beats·min −1 p 0.05), and six noted a reduced sweat sodium concentration (range: − 22 to − 59% p 0.05) following summer. The adaptations were associated with a mean summer WBGT of 25.2 °C (range: 19.6–28.7 °C). The available studies primarily focussed on healthy male adults and demonstrated large differences in the reporting of factors that influence the development of seasonal heat acclimatisation, namely, exposure time and duration, exercise task and environmental conditions. Seasonal heat acclimatisation is induced across various climates in healthy adults. The magnitude of adaptation is dependent on a combination of environmental and physical activity characteristics. Providing environmental conditions are conducive to adaptation, the duration and intensity of outdoor physical activity, along with the timing of exposures, can influence seasonal heat acclimatisation. Future research should ensure the documentation of these factors to allow for a better characterisation of seasonal heat acclimatisation. CRD42020201883.
Publisher: American Physiological Society
Date: 10-2021
DOI: 10.1152/PHYSREV.00038.2020
Abstract: A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.
Publisher: BMJ
Date: 03-09-2021
Publisher: Human Kinetics
Date: 04-2021
Abstract: Purpose : Hot-water immersion (HWI) after training in temperate conditions has been shown to induce thermophysiological adaptations and improve endurance performance in the heat however, the potential additive effects of HWI and training in hot outdoor conditions remain unknown. Therefore, this study aimed to determine the effect of repeated postexercise HWI in athletes training in a hot environment. Methods : A total of 13 (9 female) elite reelite racewalkers completed a 15-day training program in outdoor heat (mean afternoon high temperature = 34.6°C). Athletes were ided into 2 matched groups that completed either HWI (40°C for 30–40 min) or seated rest in 21°C (CON), following 8 training sessions. Pre–post testing included a 30-minute fixed-intensity walk in heat, laboratory incremental walk to exhaustion, and 10,000-m outdoor time trial. Results : Training frequency and volume were similar between groups ( P = .54). Core temperature was significantly higher during immersion in HWI (38.5 [0.3]) than CON (37.8°C [0.2°C] P .001). There were no differences between groups in resting or exercise rectal temperature or heart rate, skin temperature, sweat rate, or the speed at lactate threshold 2, maximal O 2 uptake, or 10,000-m performance ( P .05). There were significant ( P .05) pre–post differences for both groups in submaximal exercising heart rate (∼11 beats·min −1 ), sweat rate (0.34–0.55 L·h −1 ) and thermal comfort (1.2–1.5 arbitrary units), and 10,000-m racewalking performance time (∼3 min). Conclusions : Both groups demonstrated significant improvement in markers of heat adaptation and performance however, the addition of HWI did not provide further enhancements. Improvements in adaptation appeared to be maximized by the training program in hot conditions.
Publisher: Human Kinetics
Date: 10-2021
Abstract: Purpose: To investigate whether including heat and altitude exposures during an elite team-sport training c induces similar or greater performance benefits. Methods: The study assessed 56 elite male rugby players for maximal oxygen uptake, repeated-sprint cycling, and Yo-Yo intermittent recovery level 2 (Yo-Yo) before and after a 2-week training c , which included 5 endurance and 5 repeated-sprint cycling sessions in addition to daily rugby training. Players were separated into 4 groups: (1) control (all sessions in temperate conditions at sea level), (2) heat training (endurance sessions in the heat), (3) altitude (repeated-sprint sessions and sleeping in hypoxia), and (4) combined heat and altitude (endurance in the heat, repeated sprints, and sleeping in hypoxia). Results: Training increased maximal oxygen uptake (4% [10%], P = .017), maximal aerobic power (9% [8%], P .001), and repeated-sprint peak (5% [10%], P = .004) and average power (12% [14%], P .001) independent of training conditions. Yo-Yo distance increased (16% [17%], P .001) but not in the altitude group ( P = .562). Training in heat lowered core temperature and increased sweat rate during a heat-response test ( P .05). Conclusion: A 2-week intensified training c improved maximal oxygen uptake, repeated-sprint ability, and aerobic performance in elite rugby players. Adding heat and/or altitude did not further enhance physical performance, and altitude appears to have been detrimental to improving Yo-Yo.
Publisher: Springer Science and Business Media LLC
Date: 06-10-2023
Publisher: Human Kinetics
Date: 11-2023
Abstract: Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM −1 ·day −1 ) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet ( n = 10) low-CHO, high-fat diet (LCHF: n = 8 g/day CHO, energy availability = 40 kcal·kg FFM −1 ·day −1 ) and low energy availability ( n = 10 65% CHO, energy availability = 15 kcal·kg FFM −1 ·day −1 ) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group ( p = .001). Similar findings were observed for soluble CD14 ( p .001) and lipopolysaccharide-binding protein ( p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed ( p .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.
Publisher: Wiley
Date: 14-09-2022
DOI: 10.1113/EP090686
Abstract: What is the topic of this review? Exertional heat stroke epidemiology in sport and military settings, along with common risk factors and strategies and policies designed to mitigate its occurrence. What advances does it highlight? In idual susceptibility to exertional heat stroke risk is dependent on the interaction of intrinsic and extrinsic factors. Heat policies in sport should assess environmental conditions, as well as the characteristics of the athlete, clothing/equipment worn and activity level of the sport. Exertional heat stroke risk reduction in the military should account for factors specific to training and personnel. Exertional heat illness occurs along a continuum, developing from the relatively mild condition of muscle cr s, to heat exhaustion, and in some cases to the life‐threatening condition of heat stroke. The development of exertional heat stroke (EHS) is associated with an increase in core temperature stemming from inadequate heat dissipation to offset the rate of metabolically generated heat. Susceptibility to EHS is linked to the interaction of several factors including environmental conditions, in idual characteristics, health conditions, medication and drug use, behavioural responses, and sport/organisational requirements. Two settings in which EHS is commonly observed are competitive sport and the military. In sport, the exact prevalence of EHS is unclear due to inconsistent exertional heat illness terminology, diagnostic criteria and data reporting. In contrast, exertional heat illness surveillance in the military is facilitated by standardised case definitions, a requirement to report all heat illness cases and a centralised medical record repository. To mitigate EHS risk, several strategies can be implemented by athletes and military personnel, including heat acclimation, ensuring adequate hydration, cold‐water immersion and mandated work‐to‐rest ratios. Organisations may also consider developing sport or military task‐specific heat stress policies that account for the evaporative heat loss requirement of participants, relative to the evaporative capacity of the environment. This review examines the epidemiology of EHS along with the strategies and policies designed to reduce its occurrence in sport and military settings. We highlight the nuances of identifying in iduals at risk of EHS and summarise the benefits and shortcomings of various mitigation strategies.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2015
Publisher: Springer Science and Business Media LLC
Date: 23-09-2011
DOI: 10.1007/S00421-011-2165-Z
Abstract: The aim of this study was to examine the influence of aerobic fitness and exercise intensity on the development of thermal and cardiovascular strain in uncompensable heat stress conditions. In three separate trials, eight aerobically trained and eight untrained subjects cycled to exhaustion at 60% (H60%) and 75% (H75%) of maximal oxygen uptake [Formula: see text] in 40°C conditions, and for 60 min at 60% [Formula: see text] in 18°C conditions (CON). Training status had no influence on time to exhaustion between trained (61 ± 10 and 31 ± 9 min) and untrained (58 ± 12 and 26 ± 10 min) subjects (H60% and H75%, respectively). Rectal temperature at exhaustion was also not significantly different between trained (39.8 ± 0.3, 39.3 ± 0.6 and 38.2 ± 0.3°C) and untrained (39.4 ± 0.5, 38.8 ± 0.5 and 38.2 ± 0.4°C) subjects, but was different between trials (H60%, H75% and CON, respectively P 96% of maximum heart rate in both cohorts and was accompanied by significant declines in stroke volume (15-26%), cardiac output (5-10%) and mean arterial pressure (9-13%) (P < 0.05). The increase in cardiovascular strain appears to represent the foremost factor precipitating fatigue during moderate and high intensity aerobic exercise in the heat in both trained and untrained subjects.
Publisher: BMJ
Date: 25-03-2014
Publisher: BMJ
Date: 25-03-2014
Publisher: BMJ
Date: 25-03-2014
Publisher: Elsevier BV
Date: 03-2018
DOI: 10.1016/J.JSAMS.2017.05.017
Abstract: We compared the utility of four cooling interventions for reducing heat strain during simulated tennis match-play in an environment representative of the peak conditions possible at the Australian Open (45°C, <10% RH, 475W/m Nine trained males undertook four trials in a climate chamber, each time completing 4 sets of simulated match-play. During ITF-mandated breaks (90-s between odd-numbered games 120-s between sets), either iced towels (ICE), an electric fan (FAN After set 3, T Fan use must be used with skin wetting to be effective in hot/dry conditions. This strategy and the currently recommended ICE intervention both reduced T
Publisher: Springer Science and Business Media LLC
Date: 21-10-2015
Publisher: Wiley
Date: 26-07-2019
DOI: 10.1113/EP087864
Publisher: Informa UK Limited
Date: 03-07-2017
Publisher: SAGE Publications
Date: 22-04-2020
Abstract: To identify and detail physiological factors that influence cognition in military personnel. Maintenance of cognitive and task performance is important under several scenarios, none more so than in a military context. Personnel are prepared for and trained to tolerate many of the stressors they encounter however, consideration of stressors typically extends only as far as the physical, psychological, and environmental requirements of a given task. While considering these factors certainly characterizes the broader picture, several physiological states and traits can influence cognition and thus, should also be considered. A systematic review of the electronic databases Medline (PubMed), EMBASE (Scopus), PsycINFO, and Web of Science was conducted from inception up to January 2019. Eligibility criteria included current military personnel, an outcome of cognition, and the assessment of a physiological factor. The search returned 60,564 records, of which 60 were included in the review. Eleven studies examined the impact of demographic factors on cognition, 16 examined fatigue, 10 investigated nutrition, and 24 the impact of biological factors on cognitive performance. Factors identified as having a positive impact on cognition include aerobic fitness, nutritional supplementation, and visual acuity. In contrast, factors identified as having a negative impact include fatigue arising from sustained operations, dehydration, undernutrition, and an exaggerated physiological stress response to a cognitive task or a stressor. A further subset of these factors was considered modifiable. The modifiable factors identified provide avenues for training and preparation to enhance cognition in ways previously unconsidered.
Publisher: Springer Science and Business Media LLC
Date: 13-06-2020
Publisher: Elsevier BV
Date: 11-2018
Publisher: Wiley
Date: 18-10-2016
Publisher: Informa UK Limited
Date: 22-09-2011
DOI: 10.3109/17549507.2011.582520
Abstract: Speech-language pathologists manage communication and swallowing disorders, both of which can occur in patients after tracheostomy insertion. An audit on the incidence and timing of speech-language pathology intervention for adults with tracheostomies has not previously been published. Data were retrospectively extracted from the medical records of all patients who were tracheostomized at Royal Prince Alfred Hospital, NSW, Australia, from October 2007 for 1 year. Extracted data included diagnosis, date and type of tracheostomy, time to speech-language pathologist involvement, time to phonation, and time to oral intake. Among the 140 patients (mean age 58 years, range 16-85), diagnoses were neurological (32%), head and neck (25%), cardiothoracic (24%), respiratory (6%), and other (13%). Speech-language pathology was involved with 78% of patients, with initial assessment on average 14 days after tracheostomy insertion (14 days to 166 days). Median time from tracheostomy insertion to phonation was 12 days (range 1-103). Median time from tracheostomy insertion to oral intake was 15 days (range 1-142). Only 20% of patients returned to verbal communication within 1 week after tracheostomy insertion. Further research into access to and timing of speech-language pathology intervention in the critical care setting is warranted.
Publisher: Public Library of Science (PLoS)
Date: 02-2017
Publisher: Springer International Publishing
Date: 21-11-2019
Publisher: Wiley
Date: 06-05-2015
DOI: 10.1111/SMS.12379
Abstract: This study examined the influence of hyperthermia on middle cerebral artery mean blood velocity (MCA Vmean). Eleven cyclists undertook a 750 kJ self-paced time trial in HOT (35 °C) and COOL (20 °C) conditions. Exercise time was longer in HOT (56 min) compared with COOL (49 min P < 0.001). Power output in HOT was significantly lower from 40% of work completed onward (P < 0.01). Rectal temperature increased to 39.6 ± 0.6 °C (HOT) and 38.8 ± 0.5 °C (COOL P < 0.01). Skin temperature, skin blood flow, and heart rate were higher throughout HOT compared with COOL (P < 0.05). A similar increase in ventilation (P < 0.05) and decrease in end-tidal partial pressure of CO2 (PETCO2 P < 0.05) occurred in both conditions. Arterial blood pressure and oxygen uptake were lower from 50% of work completed onward in HOT compared with COOL (P < 0.01). MCA Vmean increased at 10% in both conditions (P < 0.01), decreasing thereafter (P < 0.01) and to a greater extent in HOT from 40% of work completed onward (P < 0.05). Therefore, despite a comparable ventilatory response and PETCO2 in the HOT and COOL conditions, the greater level of thermal strain developing in the heat appears to have exacerbated the reduction in MCA Vmean, in part via increases in peripheral blood flow and a decrease in arterial blood pressure.
Publisher: SAGE Publications
Date: 30-12-2021
DOI: 10.1177/00187208211065548
Abstract: To quantify the impact of performing challenging cognitive, physical and psychological tasks on subsequent cognitive performance, and whether differences in performance are predicted by psychological variables. Successful performance in many occupations depends on resilient cognition: the degree to which cognitive functions can withstand, or are resilient to, the effects of stress. Several studies have examined the effect of in idual stressors on cognition however, the capacity to compare different types of stress across studies is limited. Fifty-eight participants completed cognitive, physical, psychological and control interventions, immediately preceded, and followed, by a battery of cognitive tasks. Self-efficacy and cognitive appraisal were reported at baseline. Perceived stress was recorded post-intervention. Subjective workload was recorded for each cognitive battery and intervention. Cognitive performance was impaired by the cognitive, physical and psychological interventions, with the greatest effect following the cognitive intervention. The subjective workload reported for the post-intervention cognitive battery was higher following the cognitive and physical interventions. Neither self-efficacy, cognitive appraisal, perceived stress nor subjective workload of the intervention strongly predicted post-intervention performance. Given the differences among interventions and cognitive domains, it appears that challenges to resilient cognition are broad and varied, and the mechanism(s) by which impairment occurs is complex. Considering the increase in subjective workload for the post-intervention cognitive battery, a combination of subjective and objective measures of cognitive performance monitoring should be considered.
Publisher: BMJ
Date: 25-03-2014
Publisher: BMJ
Date: 11-06-2015
Publisher: Human Kinetics
Date: 05-2022
Abstract: Introduction : Athletes engaged in repeated-sprint training in the heat can be at an increased risk of gastrointestinal ischemia and damage in response to a redistribution of blood to working skeletal muscles and the skin. This study investigated the effects of repeated sprinting in hot and cool conditions on markers of gastrointestinal damage. Methods : Twenty-five, well-trained, nonheat acclimated male team-sport athletes completed a five-session, repeated-sprint training regimen over 7 days in either HOT (40 °C and 40% relative humidity [RH]) or COOL (20 °C and 40% RH) conditions. Participants underwent a 20-min warm-up and four sets of 5 × 6-s maximal cycling sprints, with 24-s rest and 5-min recovery between sets. Venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for intestinal fatty acid binding protein, lipopolysaccharide binding protein, soluble CD14, and heat-shock protein. Results : Intestinal fatty acid binding protein concentrations were significantly increased ( p .004) postexercise (593 and 454 pg/ml) and 1 hr postexercise (466 and 410 pg/ml) on both Days 1 and 5 in HOT. Soluble CD14 increased by 398 and 308 ng/ml postexercise ( p = .041), and lipopolysaccharide binding protein increased by 1,694 ng/ml postexercise on Day 1 in HOT ( p .05) and by 1,520 ng/ml on Day 5 in COOL ( p = .026). Core and skin temperature, rating of perceived exertion, and thermal sensation were higher ( p .05) in HOT on Days 1 and 5 during sprinting. Conclusions : Repeated sprinting in the heat induced greater thermal strain and mild changes in gastrointestinal damage, likely attributable to the combination of environmental conditions and maximal-intensity exercise.
Publisher: Springer Science and Business Media LLC
Date: 28-12-2010
DOI: 10.1007/S00421-010-1781-3
Abstract: Muscle weakness following constant load exercise under heat stress has been associated with hyperthermia-induced central fatigue. However, evidence of central fatigue influencing intense self-paced exercise in the heat is lacking. The purpose of this investigation was to evaluate force production capacity and central nervous system drive in skeletal muscle pre- and post-cycle ergometer exercise in hot and cool conditions. Nine trained male cyclists performed a 20-s maximal voluntary isometric contraction (MVC) prior to (control) and following a 40-km time trial in hot (35°C) and cool (20°C) conditions. MVC force production and voluntary activation of the knee extensors was evaluated via percutaneous tetanic stimulation. In the cool condition, rectal temperature increased to 39.0°C and reached 39.8°C in the heat (P < 0.01). Following exercise in the hot and cool conditions, peak force declined by ~90 and ~99 N, respectively, compared with control (P < 0.01). Mean force decreased by 15% (hot) and 14% (cool) (P < 0.01 vs. control). Voluntary activation during the post-exercise MVC declined to 93.7% (hot) and 93.9% (cool) (P < 0.05 vs. control). The post-exercise decline in voluntary activation represented ~20% of the decrease in mean force production in both conditions. Therefore, the additional increase in rectal temperature did not exacerbate the loss of force production following self-paced exercise in the heat. The impairment in force production indicates that the fatigue exhibited by the quadriceps is mainly of peripheral origin and a consequence of the prolonged contractile activity associated with exercise.
Publisher: Georg Thieme Verlag KG
Date: 17-04-2012
Abstract: This study investigated the effects of Ramadan on activity patterns, body composition and muscle function. 11 moderately active Muslim males were screened 1 month and 1 week before, in the last week of, and 1 month after Ramadan. Activity patterns were assessed during 72 h using a tri-axial accelerometer, body composition was evaluated via bio-electrical impedance and muscle function during maximal isometric contractions with EMG recordings. Data showed a modification of the activity pattern during Ramadan with a higher level of activity from 02:00 to 05:00 h (29±26, 364±323 and 27±22 steps.h - 1 before, during and after Ramadan, respectively, P 0.05). Maximal force, associated electrical activity and neuromuscular efficiency (torque/EMG ratio) were maintained during Ramadan (torque: 254.6±30 N.m - 1, Neuromuscular efficiency: 1.0±0.4 a.u.) to levels observed before (244.3±26 N.m, 1.1±0.5 a.u.) and after the holy month (252.5±31 N.m, 1.1±0.5 a.u.). In summary, our data suggest that the influence of Ramadan should be considered as a modification in the distribution of activity times during the day.
Publisher: Springer Science and Business Media LLC
Date: 21-09-2015
Publisher: Springer International Publishing
Date: 2018
Publisher: Wiley
Date: 24-09-2014
DOI: 10.1002/MUS.24228
Abstract: We examined the extent to which fatiguing cycling exercise in the heat influences contractile function in modulating the force-frequency relationship. Before (∽37.0 °C) and after (∽38.5 °C) exercise (ExH) and passive (PaH) hyperthermia, an 8-s train of stimulation at 10, 20, 50, and 100 Hz (2 s per frequency) and a potentiated twitch were evoked on the relaxed knee extensors using percutaneous stimulation. ExH and PaH produced a decrease in the 20:50 Hz force ratio, indicative of low-frequency fatigue (P < 0.01). This adjustment was more pronounced after ExH than PaH (P < 0.01). A rightward displacement in the force-frequency relationship occurred after ExH and PaH (P < 0.05) and was exacerbated by ExH (P < 0.05). Peak twitch force also decreased after ExH (P < 0.05). ExH reduces force summation due to development of skeletal muscle fatigue, exacerbating the shift in force-frequency to the right relative to PaH.
Publisher: Frontiers Media SA
Date: 14-12-2021
DOI: 10.3389/FPHYS.2021.803430
Abstract: Purpose: The effects of two different high-intensity training methods on 2,000 m rowing ergometer performance were examined in a feasibility study of 24 national-level rowers aged 18–27 years (17 males, 2,000 m ergometer time trial 6:21.7 ± 0:14.6 (min:s) and seven females, 2,000 m ergometer 7:20.3 ± 0:12.1. Habitual training for all participants was ~12–16 h per week). Methods : 16 high-intensity ergometer sessions were completed across two 3-week periods. Participants were allocated into two groups according to baseline 2,000 m time. High-intensity interval session-sprint-interval session (HIIT-SIT) completed eight HIIT (8 × 2.5 min intervals 95% of 2,000 m wattage) followed by eight SIT (three sets of 7 × 30 s intervals maximum effort). SIT-HIIT completed eight SIT sessions followed by eight HIIT sessions. Both a 2,000-m time trial and a progressive incremental test finishing with 4 min “all-out” performance were completed before and after each 3-week phase. Results: Both groups showed similar improvements in 2,000 m time and 4 min “all-out” distance after the first 3 weeks (2,000 m time: HIIT-SIT: −2.0 ± 0.6%, mean ± 90% CL, p = 0.01 SIT-HIIT: −1.5 ± 0.3%, p = 0.01) with no significant difference between groups. HIIT-SIT demonstrated the greatest improvements in submaximal heart rate (HR) during the progressive incremental test with eight sessions of HIIT showing a greater reduction in submaximal HR than eight sessions of SIT. The net improvement of 16 high-intensity sessions on 2,000 m time was −2.5% for HIIT-SIT (−10.6 ± 3.9 s, p = 0.01) and − 2.2% for SIT-HIIT (−9.0 ± 5.7 s, p = 0.01) and for 4 min “all-out” performance was 3.1% for HIIT-SIT (36 ± 25 m, p = 0.01) and 2.8% for SIT-HIIT (33 ± 27 m, p = 0.01). Conclusion: Eight sessions of high-intensity training can improve 2,000 m ergometer rowing performance in national-level rowers, with a further eight sessions producing minimal additional improvement. The method of high-intensity training appears less important than the dose.
Publisher: Frontiers Media SA
Date: 27-08-2020
Publisher: Wiley
Date: 10-10-2013
DOI: 10.1113/EXPPHYSIOL.2013.074583
Abstract: This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise-induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38°C conditions and the PaH by sitting in a 48°C climate chamber. Ten men performed brief (≈ 5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1°C) and during moderate (MOD, ≈ 38.5°C) and severe (SEV, ∼39.5°C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV-ExH (-8%) and SEV-PaH (-6% P < 0.05 versus CON). Sustained MVC force also decreased during MOD-ExH (-10%), SEV-ExH (-13%) and SEV-PaH (-7% P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (≈ 3%) and SEV (≈ 5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV-ExH and SEV-PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV-PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV-PaH.
Publisher: Springer International Publishing
Date: 2019
Publisher: Human Kinetics
Date: 07-2021
Abstract: Along with digestion and absorption of nutrients, the gastrointestinal epithelium acts as a primary intestinal defense layer, preventing luminal pathogens from entering the circulation. During exercise in the heat, epithelial integrity can become compromised, allowing bacteria and bacterial endotoxins to translocate into circulation, triggering a systemic inflammatory response and exacerbating gastrointestinal damage. While this relationship seems clear in the general population in endurance/ultraendurance exercise, the aim of this systematic review was to evaluate the effect of exercise in the heat on blood markers of gastrointestinal epithelial disturbance in well-trained in iduals. Following the 2009 Preferred Reporting Items for Systematic Reviewed and Meta-Analyses guidelines, five electronic databases were searched for appropriate research, and 1,885 studies were identified. Five studies met the inclusion criteria and were subject to full methodological appraisal by two reviewers. Critical appraisal of the studies was conducted using the McMasters Critical Review Form. The studies investigated changes in markers of gastrointestinal damage (intestinal fatty acid–binding protein, endotoxin, and/or lipopolysaccharide-binding protein) following acute exercise in warm to hot conditions (≥ 30 °C) and included trained or well-trained participants with direct comparisons to a control temperate condition (≤ 22 °C). The studies found that prolonged submaximal and strenuous exercise in hot environmental conditions can acutely increase epithelial disturbance compared with exercise in cooler conditions, with disturbances not being clinically relevant. However, trained and well-trained populations appear to tolerate exercise-induced gastrointestinal disturbance in the heat. Whether this is an acquired tolerance related to regular training remains to be investigated.
Publisher: BMJ
Date: 25-03-2014
Location: Qatar
Start Date: 06-2022
End Date: 06-2025
Amount: $698,441.00
Funder: Australian Research Council
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