Assuntos
Aclimatação , Mudança Climática , Humanos , Aclimatação/fisiologia , Temperatura Alta , AnimaisRESUMO
NEW FINDINGS: What is the central question of this study? Hyperoxia enhances endurance performance by increasing O2 availability to locomotor muscles. We investigated whether hyperoxia can also improve prolonged self-paced exercise in conditions of elevated thermal and cardiovascular strain. What is the main finding and its importance? Hyperoxia improved self-paced exercise performance in hot and cool conditions. However, the extent of the improvement (increased work rate relative to normoxia) was greater in cool conditions. This suggests that the development of thermal and cardiovascular strain during prolonged self-paced exercise under heat stress might attenuate the hyperoxia-mediated increase in O2 delivery to locomotor muscles. ABSTRACT: The aim of this study was to determine whether breathing hyperoxic gas when self-paced exercise performance is impaired under heat stress enhances power output. Nine well-trained male cyclists performed four 40 min cycling time trials: two at 18°C (COOL) and two at 35°C (HOT). For the first 30 min, participants breathed ambient air, and for the remaining 10 min normoxic (fraction of inspired O2 0.21; NOR) or hyperoxic (fraction of inspired O2 0.45; HYPER) air. During the first 30 min of the time trials, power output was lower in the HOT (â¼250 W) compared with COOL (â¼273 W) conditions (P < 0.05). In the final 10 min, power output was higher in HOT-HYPER (264 ± 25 W) than in HOT-NOR (244 ± 31 W; P = 0.008) and in COOL-HYPER (315 ± 28 W) than in COOL-NOR (284 ± 25 W; P < 0.001). The increase in absolute power output in COOL-HYPER was greater than in HOT-HYPER (â¼12 W; P = 0.057), as was normalized power output (â¼30%; P < 0.001). The peripheral capillary percentage oxygen saturation increased in HOT-HYPER and COOL-HYPER (P < 0.05), with COOL-HYPER being higher than HOT-HYPER (P < 0.01). Heart rate was higher during the HOT compared with COOL trials (P < 0.01), as were mean skin temperature (P < 0.001) and peak rectal temperature (HOT, â¼39.5°C and COOL, â¼38.9°C; P < 0.01). Thermal discomfort was also higher in the HOT compared with COOL (P < 0.01), whereas ratings of perceived exertion were similar (P > 0.05). Hyperoxia enhanced performance during the final 25% of a 40 min time trial in both HOT and COOL conditions compared with normoxia. However, the attenuated increase in absolute and normalized power output noted in the HOT condition suggests that heat stress might mitigate the influence of hyperoxia.
Assuntos
Regulação da Temperatura Corporal/fisiologia , Exercício Físico/fisiologia , Hiperóxia/fisiopatologia , Adulto , Ciclismo/fisiologia , Temperatura Corporal/fisiologia , Temperatura Baixa , Frequência Cardíaca/fisiologia , Transtornos de Estresse por Calor/fisiopatologia , Resposta ao Choque Térmico/fisiologia , Temperatura Alta , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Esforço Físico/fisiologia , Troca Gasosa Pulmonar/fisiologiaRESUMO
AIM: 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 FiO2 : 0.145) conditions. METHODS: 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 ß-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. RESULTS: Both α- and ß-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 ß-activity remained similar. ß-activity was higher in HYP than in HOT (P < 0.05). sLORETA revealed that α- and ß-activity increased at the onset of exercise in the primary somatosensory and motor cortices in CON and HYP, while only ß-activity increased in HOT. A decrease in α- and ß-activity occurred thereafter in all conditions, with α-activity being lower in the somatosensory and somatosensory association cortices in HOT relative to CON. CONCLUSION: 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.
Assuntos
Encéfalo/fisiopatologia , Exercício Físico/fisiologia , Transtornos de Estresse por Calor/fisiopatologia , Temperatura Alta/efeitos adversos , Hipóxia/fisiopatologia , Adulto , Atletas , Ciclismo , Feminino , Resposta ao Choque Térmico/fisiologia , Humanos , MasculinoRESUMO
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 amplitude 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.
Assuntos
Regulação da Temperatura Corporal/fisiologia , Resposta ao Choque Térmico/fisiologia , Contração Isométrica/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Termotolerância/fisiologia , Adulto , Temperatura Alta , Humanos , MasculinoRESUMO
This study examined the relationship between exhaustive exercise in the heat at moderate and high intensities on the intracellular heat shock protein 72 (iHsp72) response. Twelve male subjects cycled to exhaustion at 60 and 75% of maximal oxygen uptake in hot conditions (40 °C, 50% RH). iHsp72 concentration was measured in monocytes before, at exhaustion and 24 h after exercise. Rectal temperature, heart rate and oxygen uptake were recorded during exercise. Volitional exhaustion occurred at 58.9 ± 12.1 and 27.3 ± 9.5 min (P < 0.001) and a rectal temperature of 39.8 ± 0.4 and 39.2 ± 0.6 °C (P = 0.002), respectively, for 60 and 75 %. The area under the curve above a rectal temperature of 38.5 °C was greater at 60 % (17.5 ± 6.6 °C min) than 75 % (3.4 ± 4.8 °C min; P < 0.001), whereas the rate of increase in rectal temperature was greater at 75 % (5.1 ± 1.7 vs. 2.2 ± 1.4 °C h(-1); P < 0.001). iHsp72 concentration increased similarly at exhaustion relative to pre-exercise (P = 0.044) and then increased further at 24 h (P < 0.001). Multiple regression analysis revealed no predictor variables associated with iHsp72 expression; however, a correlation was observed between exercise intensities for the increase in iHsp expression at exhaustion and 24 h (P < 0.05). These results suggest that iHsp72 expression increased in relation to the level of hyperthermia attained and sustained at 60 % and the higher metabolic rate and greater rate of increase in core temperature at 75 %, with the further increase in iHsp72 concentration 24 h after exercise reinforcing its role as a chaperone and cytoprotective agent.
Assuntos
Exercício Físico/fisiologia , Proteínas de Choque Térmico HSP72/metabolismo , Temperatura Alta/efeitos adversos , Monócitos/metabolismo , Adulto , Temperatura Corporal/fisiologia , Frequência Cardíaca/fisiologia , Humanos , Masculino , Músculo Esquelético/metabolismo , Adulto JovemRESUMO
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 optimise performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimise performance is to heat acclimatise. Heat acclimatisation should comprise repeated exercise-heat exposures over 1-2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimise dehydration during exercise. Following the development of commercial cooling systems (eg, 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 organisers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimising the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples 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.
Assuntos
Exercício Físico/fisiologia , Temperatura Alta , Esportes/fisiologia , Aclimatação/fisiologia , Desempenho Atlético/fisiologia , Bebidas , Regulação da Temperatura Corporal/fisiologia , Vestuário , Temperatura Baixa , Exercícios de Desaquecimento/fisiologia , Desidratação/prevenção & controle , Hidratação/métodos , Transtornos de Estresse por Calor/fisiopatologia , Transtornos de Estresse por Calor/prevenção & controle , Humanos , Medicina Esportiva/métodosRESUMO
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 examples 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.
Assuntos
Aclimatação/fisiologia , Comportamento de Ingestão de Líquido/fisiologia , Exercício Físico/fisiologia , Transtornos de Estresse por Calor/prevenção & controle , Temperatura Alta/efeitos adversos , Esportes/fisiologia , Desempenho Atlético/fisiologia , Regulação da Temperatura Corporal/fisiologia , Desidratação/complicações , Desidratação/prevenção & controle , Desidratação/terapia , Hidratação , Transtornos de Estresse por Calor/etiologia , Transtornos de Estresse por Calor/terapia , HumanosRESUMO
Exercise heat acclimation induces physiological adaptations that improve thermoregulation, attenuate physiological strain, reduce the risk of serious heat illness, and improve aerobic performance in warm-hot environments and potentially in temperate environments. The adaptations include improved sweating, improved skin blood flow, lowered body temperatures, reduced cardiovascular strain, improved fluid balance, altered metabolism, and enhanced cellular protection. The magnitudes of adaptations are determined by the intensity, duration, frequency, and number of heat exposures, as well as the environmental conditions (i.e., dry or humid heat). Evidence is emerging that controlled hyperthermia regimens where a target core temperature is maintained, enable more rapid and complete adaptations relative to the traditional constant work rate exercise heat acclimation regimens. Furthermore, inducing heat acclimation outdoors in a natural field setting may provide more specific adaptations based on direct exposure to the exact environmental and exercise conditions to be encountered during competition. This review initially examines the physiological adaptations associated with heat acclimation induction regimens, and subsequently emphasizes their application to competitive athletes and sports.
Assuntos
Aclimatação/fisiologia , Exercício Físico/fisiologia , Transtornos de Estresse por Calor/prevenção & controle , Temperatura Alta/efeitos adversos , Esportes/fisiologia , Desempenho Atlético/fisiologia , Regulação da Temperatura Corporal/fisiologia , Metabolismo Energético/fisiologia , Transtornos de Estresse por Calor/etiologia , Transtornos de Estresse por Calor/fisiopatologia , Humanos , Sudorese/fisiologia , Equilíbrio Hidroeletrolítico/fisiologiaRESUMO
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.
Assuntos
Ciclismo/fisiologia , Exercício Físico/fisiologia , Transtornos de Estresse por Calor/fisiopatologia , Temperatura Alta/efeitos adversos , Artéria Cerebral Média/fisiopatologia , Resistência Física/fisiologia , Adulto , Velocidade do Fluxo Sanguíneo , Feminino , Transtornos de Estresse por Calor/etiologia , Humanos , MasculinoRESUMO
OBJECTIVES: The purpose of this study was to determine the impact of changes in oxidative stress and antioxidant status in response to playing tennis in HOT (â¼36°C and 35% relative humidity (RH)) and COOL (â¼22°C and 70% RH) conditions. METHODS: 10 male tennis players undertook two matches for an effective playing time (ie, ball in play) of 20 min, corresponding to â¼122 and â¼107 min of total play in HOT and COOL conditions, respectively. Core body temperature, body mass and indirect markers of oxidative stress (diacrons reactive oxygen metabolic test) and antioxidant status (biological antioxidant potential test) were assessed immediately prematch, midmatch and postmatch, and 24 and 48 h into recovery. RESULTS: Regardless of the condition, oxidative stress remained similar throughout play and into recovery. Likewise, match-play tennis in the COOL had no impact on antioxidant status. However, antioxidants status increased significantly in the HOT compared with COOL environment (p<0.05). Body mass losses (â¼0.5 kg) were similar between conditions. Rectal temperature increased during both matches (p<0.05), but with a greater magnitude in the HOT (39.3±0.5°C) versus COOL (38.7±0.2°C) environment (p<0.05). CONCLUSIONS: Match-play tennis in the heat does not exacerbate the development of oxidative stress, but significantly increases antioxidant status. These data suggest that the heat stress observed in the HOT environment may provide a necessary signal for the upregulation of antioxidant defence, dampening cellular damage.
Assuntos
Antioxidantes/metabolismo , Temperatura Alta , Estresse Oxidativo/fisiologia , Tênis/fisiologia , Biomarcadores/metabolismo , Temperatura Corporal/fisiologia , Temperatura Baixa , Humanos , Masculino , Sudorese/fisiologia , Equilíbrio Hidroeletrolítico/fisiologia , Adulto JovemRESUMO
OBJECTIVES: To examine with a parallel group study design the performance and physiological responses to a 14-day off-season 'live high-train low in the heat' training camp in elite football players. METHODS: Seventeen professional Australian Rules Football players participated in outdoor football-specific skills (32 ± 1°C, 11.5 h) and indoor strength (23 ± 1°C, 9.3 h) sessions and slept (12 nights) and cycled indoors (4.3 h) in either normal air (NORM, n=8) or normobaric hypoxia (14 ± 1 h/day, FiO2 15.2-14.3%, corresponding to a simulated altitude of 2500-3000 m, hypoxic (HYP), n=9). They completed the Yo-Yo Intermittent Recovery level 2 (Yo-YoIR2) in temperate conditions (23 ± 1°C, normal air) precamp (Pre) and postcamp (Post). Plasma volume (PV) and haemoglobin mass (Hb(mass)) were measured at similar times and 4 weeks postcamp (4WPost). Sweat sodium concentration ((Na(+))(sweat)) was measured Pre and Post during a heat-response test (44°C). RESULTS: Both groups showed very large improvements in Yo-YoIR2 at Post (+44%; 90% CL 38, 50), with no between-group differences in the changes (-1%; -9, 9). Postcamp, large changes in PV (+5.6%; -1.8, 5.6) and (Na(+))sweat (-29%; -37, -19) were observed in both groups, while Hb(mass) only moderately increased in HYP (+2.6%; 0.5, 4.5). At 4WPost, there was a likely slightly greater increase in Hb(mass) (+4.6%; 0.0, 9.3) and PV (+6%; -5, 18, unclear) in HYP than in NORM. CONCLUSIONS: The combination of heat and hypoxic exposure during sleep/training might offer a promising 'conditioning cocktail' in team sports.
Assuntos
Altitude , Futebol Americano/fisiologia , Aclimatação/fisiologia , Desempenho Atlético/fisiologia , Pressão Atmosférica , Austrália , Volume Sanguíneo/fisiologia , Exercício Físico/fisiologia , Hemoglobinas/metabolismo , Temperatura Alta , Humanos , Hipóxia/fisiopatologia , Corrida/fisiologia , Sono/fisiologiaRESUMO
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.
Assuntos
Desidratação/fisiopatologia , Exercício Físico/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiopatologia , Resistência Física/fisiologia , Adulto , Eletromiografia , Fadiga/fisiopatologia , Humanos , Contração Isométrica , MasculinoRESUMO
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). However, total daily energy expenditure was similar during all testing periods (506±156, 542±219 and 545±207 Kcal.day - 1, respectively), partly explaining the lack of influence of Ramadan on body mass (70.9±11, 70.0±9 and 70.8±9 Kg, respectively) and composition (all 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.