ArticleLiterature Review

Reducing the risk of heat-related decrements to physical activity in young people

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Abstract

The purpose of this review is to highlight differences in thermoregulatory responses during activity of children and adolescents compared with adults. Some differences are due to movement inefficiency and physical size such as body surface area to body mass ratio, and body composition. Identified physiological differences in sweat rates appear to alter with maturation, at least in boys, but the research remains incomplete. A number of findings from hydration studies with young people exercising in the heat are also discussed. The research on clothing is adult-based, but key concepts from this research also apply to children. The final section addresses the limited research on acclimatization of children to hot conditions. Specific recommendations for children who are active in the heat conclude this review.

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... Children may experience more rapid heat exchanges in extreme environments [48,87,91,92]. In a hot environment, dry convective heat loss (C) is the mechanism that mainly drives heat loss from their body instead of evaporative heat loss (E) that is for adults [93]. ...
... Surface area-to-body mass ratio Higher Higher heat absorption [78,79] Metabolic rate Higher Higher heat production [48,79] Height Lower height. Body closer to the ground Thermal impacts of long-wave heat fluxes of high surface temperatures [6,33,95] Skin More sensitive [33] Physical activity Higher Higher metabolic heat production [96,97] Heat loss Dry convective compared to adults evaporative heat loss [93] Thermoregulation Inferior [83][84][85][86] Undeveloped sweat gland capacity [78,85,87,88] Lower sweat rate [83,84,94] Lower evaporation heat exchange [12,48,89,90] Adaptive behaviour Less adaptive Less knowledge for sun protection [33] Heat exchanges Rapid Establishment of heat stress condition in short time [6,48,87,91,92] Thermal perception Inferior [12,48,89,90] Vanos [6] discussed how the differences between children's and adult's physiology can potentially introduce inaccuracies in steady state models and thermal indices outcomes. Regarding body surface area (BSA), assuming an average BSA of 1.8 m 2 (PET) and 1.86 m 2 (UTCI) for an adult and a BSA of 0.72m 2 for a five-year old child, and the same heat production of 90W for both, the result would be an average metabolic rate of 125 W m 2 for the child and 50 W m 2 for the adult (resting). ...
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Urban outdoor thermal conditions, and its impacts on the health and well-being for the city inhabitants have reached increased attention among biometeorological studies during the last two decades. Children are considered more sensitive and vulnerable to hot ambient conditions compared to adults, and are a�ected strongly by their thermal environment. One of the urban outdoor environments that children spend almost one third of their school time is the schoolyard. The aims of the present manuscript were to review studies conducted worldwide, in order to present the biophysical characteristics of the typical design of the urban schoolyard. This was done to assess, in terms of bioclimatology, the interactions between the thermal environment and the children’s body, to discuss the adverse e�ects of thermal environment on children, especially the case of heat stress, and to propose measures that could be applied to improve the thermal environment of schoolyards, focusing on vegetation. Human thermal comfort monitoring tools are mainly developed for adults, thus, further research is needed to adapt them to children. The schemes that are usually followed to design urban schoolyards create conditions that favour the exposure of children to excessive heat, inducing high health risks to them. The literature survey showed that typical urban schoolyard design (i.e., dense surface materials, absence of trees) triggered high surface temperatures (that may exceed 58 �C) and increased absorption of radiative heat load (that may exceed 64 �C in terms of Mean Radiant Temperature) during a clear day with intense solar radiation. Furthermore, vegetation cover has a positive impact on schoolyard’s microclimate, by improving thermal comfort and reducing heat stress perception of children. Design options for urban schoolyards and strategies that can mitigate the adverse e�ects of heat stress are proposed with focus on vegetation cover that a�ect positively their thermal environment and improve their aesthetic and functionality.
... The surface area-to-mass ratio affects the heat acceptance of a person (Falk et al. 1992;Inbar et al. 2004;Naughton and Carlson 2008;Kenny et al. 2018). Children's surface area-tomass ratio is higher than adults'. ...
... It suggests that under extreme cold or hot conditions, the estimated energy budget value of children using the COMFA-kid model was lower or higher respectively to the conditions, than adults' value using the original COMFA model. These results are concurrent with the previous studies that the children are under the risk of more rapid heat exchanges in extreme environments (Haymes et al. 1974;Drinkwater et al. 1977;Inoue et al. 1996;Naughton and Carlson 2008). ...
Article
Many children growing up in cities are spending less time outdoors to escape the heat. This is contributing to childhood obesity and the prospect of a range of diseases in adulthood. When landscape architects and urban designers use a human thermal comfort model to test their designs for children’s comfort, they would have to use a model essentially designed to simulate healthy adults. Yet there are many differences between the body of a child and an adult. The aim of this paper was to modify the thermal comfort model COMFA into a children’s energy budget model through the consideration of the heat exchange of a child. The energy budget of a child can be up to 21 W/m2 higher than adults in hot summertime conditions, and 26 W/m2 lower in cold conditions. The model was validated through field studies of 65 children (32 boys and 33 girls) aged from 7-12 years old in 9 days from March to June in 2019, in 68 different microclimates ranging from cool to hot. A 5-point thermal comfort scale of energy budget for children was created using multinomial logistic regression, which revealed that children have a different range of thermal acceptability than adults. The frequency distribution of the actual thermal sensation and the predicted thermal comfort was improved using the new scale. The actual thermal sensation responses from children and the predicted thermal sensation using the model was determined to be positively significantly related. The accuracy of the model was 93.26%. This study has provided an effective children’s energy budget model to predict children’s thermal comfort. Its application can contribute to the design of thermally comfortable children’s outdoor play areas by landscape architects and urban designers.
... 164 Kod djece i mladih je temperaturni prag pri kojem nastupa znojenje viši. 186 Djeca imaju manju koncentraciju elektrolita u znoju, što doprinosi učinkovitijoj evaporaciji. 188 Broj žlijezda znojnica određen je već u dobi od 2 do 3 godine, pa se s rastom veličine i površine tijela gustoća žlijezda smanjuje. ...
... 188 Broj žlijezda znojnica određen je već u dobi od 2 do 3 godine, pa se s rastom veličine i površine tijela gustoća žlijezda smanjuje. 186 Metode ublažavanja utjecaja hladnoće. ...
... Based on these observations, prepubertal children have been traditionally considered "less effective thermoregulators than adults", at increased risk for exerciseinduced heat illness as well as diminished tolerance for exercise in hot climatic conditions (7,11). As a consequence of this concern, particular guidelines for fluid intake and sports activities in the heat have been formulated for child athletes (2,6,36). This view of physically active youth as an at-risk group for heat injury and exercise intolerance in the heat has been based on a group of early studies which often lacked direct child-adult comparisons, failed to match subjects by relative exercise intensity, or involved extremes of T a. ...
... A number of studies performed in adult subjects have supported this concept (16,30). Other authors have criticized this concept as being oversimplistic (22,36). ...
Article
Children possess certain physiological and anatomic characteristics that have traditionally been considered to impair thermoregulatory responses to exercise in the heat: low exercise economy, high ratio of body surface area to mass, diminished sweating capacity, and less cardiac output at the same work load compared with adults. Consequently, children have been regarded as an at-risk group for not only decrements of physical performance but also heat injury during physical activities performed in conditions of high ambient temperature. Recent investigations that have directly compared thermoregulatory responses to exercise in the heat in children and adults have challenged these traditional concepts. Such studies have failed to indicate group differences in heat dispersal when adult-child comparisons are appropriately considered in respect to relative exercise intensity. These findings imply that no maturational differences exist in thermal balance or endurance performance during exercise in the heat, nor that child athletes are more vulnerable to heat injury.
... It has been studied that the skin temperature of the different measurement points on the face varies greatly, among which the forehead skin temperature is the highest [30]. The external measured surface temperature is mainly a value reflected by the convection and radiant heat exchange between the human skin and the surrounding air [31]. The uncertainty of the skin reflectivity and some other factors will affect this process, which will lead to an inhomogeneous distribution of our measured surface temperature, such as the forehead region's inhomogeneous temperature distribution. ...
Article
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Unlabelled: When the ambient temperature, in which a person is situated, fluctuates, the body's surface temperature will alter proportionally. However, the body's core temperature will remain relatively steady. Consequently, using body surface temperature to characterize the core body temperature of the human body in varied situations is still highly inaccurate. This research aims to investigate and establish the link between human body surface temperature and core body temperature in a variety of ambient conditions, as well as the associated conversion curves. Methods: Plan an experiment to measure temperature over a thousand times in order to get the corresponding data for human forehead, axillary, and oral temperatures at varying ambient temperatures (14-32 °C). Utilize the axillary and oral temperatures as the core body temperature standards or the control group to investigate the new approach's accuracy, sensitivity, and specificity for detecting fever/non-fever conditions and the forehead temperature as the experimental group. Analyze the statistical connection, data correlation, and agreement between the forehead temperature and the core body temperature. Results: A total of 1080 tests measuring body temperature were conducted on healthy adults. The average axillary temperature was (36.7 ± 0.41) °C, the average oral temperature was (36.7 ± 0.33) °C, and the average forehead temperature was (36.2 ± 0.30) °C as a result of the shift in ambient temperature. The forehead temperature was 0.5 °C lower than the average of the axillary and oral temperatures. The Pearson correlation coefficient between axillary and oral temperatures was 0.41 (95% CI, 0.28-0.52), between axillary and forehead temperatures was 0.07 (95% CI, -0.07-0.22), and between oral and forehead temperatures was 0.26 (95% CI, 0.11-0.39). The mean differences between the axillary temperature and the oral temperature, the oral temperature and the forehead temperature, and the axillary temperature and the forehead temperature were -0.08 °C, 0.49 °C, and 0.42 °C, respectively, according to a Bland-Altman analysis. Finally, the regression analysis revealed that there was a linear association between the axillary temperature and the forehead temperature, as well as the oral temperature and the forehead temperature due to the change in ambient temperature. Conclusion: The changes in ambient temperature have a substantial impact on the temperature of the forehead. There are significant differences between the forehead and axillary temperatures, as well as the forehead and oral temperatures, when the ambient temperature is low. As the ambient temperature rises, the forehead temperature tends to progressively converge with the axillary and oral temperatures. In clinical or daily applications, it is not advised to utilize the forehead temperature derived from an uncorrected infrared thermometer as the foundation for a body temperature screening in public venues such as hospital outpatient clinics, shopping malls, airports, and train stations.
... The impact of heat on individual health can range from feeling unwell, to dehydration or even more severe life-threatening conditions such as heat stroke (Casa et al., 2015). Local, event-level risk factors associated with exercise-related heat illness are generally well understood by experts and appropriate countermeasures are relatively straightforward to implement, such as changing the start time of events, providing extra breaks and ensuring there is adequate shade and water available for participants and spectators (Bergeron et al., 2011;Lipman et al., 2019;Naughton & Carlson, 2008). Beyond these localised, and specific measures, there is little known about the broader, systemic risk factors and associated opportunities for mitigation in unstructured outdoor activity settings. ...
Article
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Active participation in the outdoors is beneficial for health and wellbeing. However, the impact of extreme weather, particularly heat, on safe participation is causing concern for organisations who lead these activities. Local mitigation strategies and acute management of heat- and sun-related illness (HSRI) are generally well understood by researchers and medical practitioners, however, cases continue to occur so further understanding of why this happens is required. This study aimed to identify the number, nature and contributory factors of HSRI in Australian led outdoor activities in order to seek opportunities for their prevention. This study presents a descriptive analysis of contributory factors to HSRI occurring during led outdoor activities. Cases were prospectively collected across 3 years (2014-2017) from a national Australian incident reporting system. Cases were included by identification of keywords linked with sun or heat exposure. From 2,015 incident cases, 48 cases were included: 25 termed heat stroke and 23 as “other adverse outcomes related to sun or heat.” One in three (35%) cases occurred during outdoor walking or running, and one in four occurred while camping. A total 146 contributory factors were identified. These factors were attributed to the activity participant (e.g. competence, decision making); equipment and resources (e.g. food/drink, dehydration); and environment (e.g. hot weather.). Mild to moderate HSRI was identifiable by signs/symptoms. Contributory factors were linked to the individual participant. Potentially, these factors could be mitigated through system focused approaches. Awareness of wider responsibility for preventing HSRI should be promoted across led outdoor activities.
... During exercise in cool, neutral, or even mild heat environments, ambient temperature (T a ) is lower than skin temperature (T sk ). In these conditions children have been shown to effectively thermoregulate mainly via dry heat loss mechanisms, where convective and radiant heat exchanges occur between the skin and the surrounding air (Bar-Or 1980;Naughton and Carlson 2008). Children's larger body surface area to mass ratio (BSA/M) compared to adults allows them to have effective dry heat losses (Davies 1981). ...
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Purpose To determine sweating responses of pre-pubertal children during intermittent exercise in a warm environment and create whole-body maps of regional sweat rate (RSRs) distribution across the body. Methods Thirteen pre-pubertal children; six girls and seven boys (8.1 ± 0.8 years) took part. Sweat was collected using the technical absorbent method in the last 5 min of a 30-min intermittent exercise protocol performed at 30 ℃, 40% relative humidity and 2 m·s⁻¹ frontal wind. Results Mean gross sweat loss (GSL) was 126 ± 47 g·m⁻²·h⁻¹ and metabolic heat production was 278 ± 50 W·m². The lower anterior torso area had the lowest RSR with a median (IQR) sweat rate (SR) of 40 (32) g·m⁻²·h⁻¹. The highest was the forehead with a median SR of 255 (163) g·m⁻²·h⁻¹. Normalised sweat maps (the ratio of each region’s SR to the mean SR for all measured pad regions) showed girls displayed lower ratio values at the anterior and posterior torso, and higher ratios at the hands, feet and forehead compared to boys. Absolute SRs were similar at hands and feet, but girls sweated less in most other areas, even after correction for metabolic rate. Conclusion Pre-pubertal children have different RSRs across the body, also showing sex differences in sweat distribution. Distributions differ from adults. Hands and feet RSR remain stable, but SR across other body areas increase with maturation. These data can increase specificity of models of human thermoregulation, improve the measurement accuracy of child-sized thermal manikins, and aid companies during product design and communication.
... Factors that predict a person will be at increased risk include being confined to bed, not leaving home daily, and being unable to care for oneself; 516 various general indicators of being socially isolated (such as living alone, the presence of or frequency of social contacts, or being isolated linguistically); 516,517,518,519 and persons who are socioeconomically disadvantaged. 516,517,518,519 Dehydration in general and dehydration associated with medications (neurological and non-neurological) that impair thermoregulation or thirst regulation were also associated with elevated risk of mortality during the 2003 heat wave in France. 520 The role of prescription medications in altering the risk for heat-associated illness or death is of growing interest and concern. ...
... A higher surface area to mass ratio of children is responsible for increased absorption of heat. 3 Additionally, children display a higher metabolic turnover rate, which is further enhanced by high temperatures, resulting in increased oxygen consumption with hyperpnea and tachycardia. 4 Within the European Union, 15.6 % of the population, accordingly 115 million people, are currently below the age of 14 years (Data source: Eurostat; accessed July 11, 2019), representing a substantial and potentially vulnerable population in case of catastrophic temperature-related events. ...
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This study investigates patterns of extreme temperature-related events in Europe and its significance for the public health, with a focus on the vulnerable pediatric population. A generalized additive model of average surface temperature development for the European countries is described and discussed with an in-depth analysis of the influence of temperature on evolutional and behavioral aspects. Methods: Extreme temperature related events are recorded in the publicly available epidemiological database of Emergency Events (EM-DAT). A comparative and descriptive statistical analysis of this data was conducted with a focus on (prospective) records from 1988 onwards. Average surface temperature data was provided by the World Bank's Climate Change Knowledge Portal. The criteria for strengthening the reporting of observational studies in epidemiology (STROBE) were respected. Results: Within EM-DAT, extreme temperature-related disasters in Europe were categorized as either heat waves, drought, forest or land fires, or cold waves and severe winter conditions, accordingly. The most frequent type of event recorded were cold waves (36.2%). However, cold waves and severe winter conditions only accounted for about 6,460 casualties (4.4%), while heat waves were responsible for a total of 137,533 casualties (95.1%). During the prospective observational period of the EM-DAT database, heat waves in 2003, 2006, 2010, and 2015, claimed a total of 119,760 casualties. These most severe heatwaves were geographically distributed over Russia (2010), as well as France, Italy, Spain, and Germany, each in 2003. Accordingly, analysis of temperature data revealed an increasing average surface temperature for all assessed European countries, correlating with in an increasing frequency of extreme temperature-related events. Conclusion: This study shows that according to EM-DAT data extreme temperatures are an increasingly important public health threat to the European population as the average European surface temperatures are rising. Although cold waves are more frequently reported in EM-DAT, heat waves are the major cause for temperature-related casualties. Therefore, we conclude that evolutional and cultural resilience against cold and drought is significantly higher than it is against heat. Our results project that the frequency, duration and intensity of heat waves will further increase due to current climatic changes and become a more prevalent problem for future generations. Hence, we propose an emergency plan to inform the public and authorities about measurements to be taken in such extreme heat conditions to overcome the prevailing lack of information available to the public.
... [2] . [17] . ...
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Resumo Objetivo: Avaliar a perda hídrica, a densidade e a coloração da urina em estudantes do ensino médio submetidos a jogos de futsal, durante a aula de Educação Física. Amostra: Foram avaliados 12 estudantes do ensino médio, com idade média de 16,58 ± 0,67 anos, durante duas aulas de Educação Física, de 50 minutos de duração, que simularam jogos de futsal. Métodos: O peso corporal (PC), a densidade (D u) e a coloração (U cor) da urina foram medidos antes e após os jogos. Os avaliados consumiram água ad libitum, sendo monitorada a quantidade de líquido. A taxa de sudorese (T suor), a perda hídrica relativa (PHR) e absoluta (PHA) foram calculadas ao final de cada jogo. Todos os procedimentos éticos para pesquisas com seres humanos foram observados. O tratamento dos dados constou da análise descritiva, e do teste de Wilcoxon, para comparação das variáveis antes e depois dos jogos, adotando-se p<0,05. Resultados: A T suor média foi de 16,44 ± 5,35 mL/min, não influenciando a PHA (0,82 ± 0,27 Kg) e PHR (1,28 ± 0,33%), de maneira a produzir diferença significante no PC. Não houve diferenças significantes, para a D u e U cor iniciais e finais. Conclusão: Nos 50 minutos de prática de futsal, os alunos não apresentaram risco de desidratação, decorrente da baixa PHA e PHR, apesar de uma T suor elevada. A D u e U cor , também indicaram bom nível de hidratação.
... Insufficient voluntary fluid intake is common among active young people [6] and if they fail to replace fluid loss during and after exercise, it could lead to more heat storage in the body [7,8]. Hypohydration affects prolonged aerobic exercise more than it affects short, high-intensity anaerobic ...
Article
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This study assessed the relationship between physical activity and beverage consumption among adolescents with a population based cross-sectional survey was carried out in the Balearic Islands, Spain (n = 1988; 12-17 years old). Body composition, educational and income level, physical activity (PA), and beverage consumption and energy intake were assessed. Sixty-two percent of adolescents engaged in >300 min/week of PA. Boys were more active than girls, younger adolescents were more active than older counterparts, low parental income was associated with physical inactivity, and time spent watching TV (including, TV, Internet or handheld cellular devices) was inversely associated with PA practice. The average beverage intake of the studied adolescents was 0.9 L/day, higher in boys than in girls. Beverage intake was positively associated with PA practice, and the highest amount of energy intake from beverages was observed in active boys and girls. Most of the studied adolescent population met the PA recommendations. Gender, age, parental income, and time spent watching TV were significant determinants of PA. Type and amount of beverages drunk varied according to gender and PA, and general daily total beverage intake was lower than recommended adequate fluid intake. PA behavior should be considered when analyzing beverage consumption in adolescents.
... Both individual and regional-level factors of heat vulnerability have been identified. On an individual level, age, physical fitness, and general health have been shown to affect thermoregulation of body temperature [27,[29][30][31], with the very young, very old, and overweight individuals at higher risk of adverse outcomes. Regionally, the Pacific Northwest is considered to be one of the more vulnerable areas of the U.S. [32] and a stronger association between temperature and mortality has been reported in northern U.S. cities than southern U.S. cities [3]. ...
Article
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Exposure to excessive heat kills more people than any other weather-related phenomenon, aggravates chronic diseases, and causes direct heat illness. Strong associations between extreme heat and health have been identified through increased mortality and hospitalizations and there is growing evidence demonstrating increased emergency department visits and demand for emergency medical services (EMS). The purpose of this study is to build on an existing regional assessment of mortality and hospitalizations by analyzing EMS demand associated with extreme heat, using calls as a health metric, in King County, Washington (WA), for a 6-year period. Relative-risk and time series analyses were used to characterize the association between heat and EMS calls for May 1 through September 30 of each year for 2007–2012. Two EMS categories, basic life support (BLS) and advanced life support (ALS), were analyzed for the effects of heat on health outcomes and transportation volume, stratified by age. Extreme heat was model-derived as the 95th (29.7 °C) and 99th (36.7 °C) percentile of average county-wide maximum daily humidex for BLS and ALS calls respectively. Relative-risk analyses revealed an 8 % (95 % CI: 6–9 %) increase in BLS calls, and a 14 % (95 % CI: 9–20 %) increase in ALS calls, on a heat day (29.7 and 36.7 °C humidex, respectively) versus a non-heat day for all ages, all causes. Time series analyses found a 6.6 % increase in BLS calls, and a 3.8 % increase in ALS calls, per unit-humidex increase above the optimum threshold, 40.7 and 39.7 °C humidex respectively. Increases in “no” and “any” transportation were found in both relative risk and time series analyses. Analysis by age category identified significant results for all age groups, with the 15–44 and 45–64 year old age groups showing some of the highest and most frequent increases across health conditions. Multiple specific health conditions were associated with increased risk of an EMS call including abdominal/genito-urinary, alcohol/drug, anaphylaxis/allergy, cardiovascular, metabolic/endocrine, diabetes, neurological, heat illness and dehydration, and psychological conditions. Extreme heat increases the risk of EMS calls in King County, WA, with effects demonstrated in relatively younger populations and more health conditions than those identified in previous analyses.
... 96,98 -101 Appropriate sport clothing, uniforms, or protective equipment should be used to minimize heat retention. 102 ...
Article
Global climate change is projected to increase the frequency and duration of periods of extremely high temperatures. Both the general populace and public health authorities often underestimate the impact of high temperatures on human health. To highlight the vulnerable populations and illustrate approaches to minimization of health impacts of extreme heat, the authors reviewed the studies of heat-related morbidity and mortality for high-risk populations in the U.S. and Europe from 1958 to 2012. Heat exposure not only can cause heat exhaustion and heat stroke but also can exacerbate a wide range of medical conditions. Vulnerable populations, such as older adults; children; outdoor laborers; some racial and ethnic subgroups (particularly those with low SES); people with chronic diseases; and those who are socially or geographically isolated, have increased morbidity and mortality during extreme heat. In addition to ambient temperature, heat-related health hazards are exacerbated by air pollution, high humidity, and lack of air-conditioning. Consequently, a comprehensive approach to minimize the health effects of extreme heat is required and must address educating the public of the risks and optimizing heatwave response plans, which include improving access to environmentally controlled public havens, adaptation of social services to address the challenges required during extreme heat, and consistent monitoring of morbidity and mortality during periods of extreme temperatures.
... Fluid intake for adults during exercise could also be applied to adolescents (≥ 50kg) ranging between 0.4 -0.8 L.h -1 , the lower recommendation is for lighter athletes competing in cooler environments and the higher rates for faster, heavier athletes competing in warm environments (Sawka et al., 2007). In a recent review Naughton and Carlson (2008) concluded that fluid recommendations for young athletes should be individualized according to estimated body weight losses surrounding events. Drinking tap water should be adequate during short term exercise. ...
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Chapter
Climate change and desertification is a global problem, and Turkey and the Middle East region are among the mostly affected areas of the world. By the end of this century, Turkey and the Middle East region are expected to have an increased mean temperature about 3–5 °C and a 20–40% decline in precipitation. The Intergovernmental Panel on Climate Change (IPPC) warns that desertification is likely to become irreversible, if the environment becomes drier and the soil becomes further degraded through erosion and compaction. According to United Nations Environment Program (UNEP), most of areas in Turkey are under desertification and/or high potential for desertification and only small parts of the areas in Turkey are non-risky places. Climate models predict a hotter, drier, and less predictable climate for the Middle East region, and degradation and desertification are expected to accelerate due to global warming. Climate change and desertification is acting as a risk for water loss, decline in agriculture, and loss of biodiversity. Climate change has a negative impact on human health by indirect effects including air, water, and food supplies and by direct effects especially on elderly, children, and chronically ill population. This chapter examines the potential impacts of climate change and desertification on the environmental parameters and human health in Turkey and the Middle East.
Chapter
Globally, heat waves account for dramatic increases in mortality and morbidity; however, there is increasing awareness that day-to-day increases in temperature contribute to a significant risk of heat-related morbidity and mortality (HRMM) that over one or more warm seasons may exceed the public health burden of heat waves. Climate change has already and will continue to increase both average ambient temperatures and the frequency and intensity of excursions above those averages (i.e., heat waves or extreme heat events) and will thereby lead directly and indirectly to amplification of the risk of HRMM. This chapter provides a brief synopsis of our current knowledge about thermoregulation, thermotolerance, and the pathophysiology of heat stroke, and the multiple determinants of health and illness that influence the risk of HRMM and that collectively define vulnerability. A particular focus is on two vulnerable populations, older adults and children. An Environmental Health Multiple-Determinants Model of Vulnerability is presented as a conceptual framework to integrate that knowledge, with the intent of providing a tool that can facilitate compilation and translation of the information to interventions and adaptation strategies relevant at the individual level and/or subpopulation and population levels and at one or more geopolitical scales in developing and/or developed nations. Three overarching strategies for HRMM risk reduction are discussed, including Extreme Heat Event and Warm Season Heat Preparedness and Response Action Plans, Promote Good Health and Access to Quality Healthcare (reduces risk and increases resiliency), and Reduce/Manage Potential Exposure(s) (individual, community) to Ambient Heat and Other Physical Environmental Stressors. A key focus of this chapter is on integration and translation of knowledge.
Chapter
Globally, heat waves account for dramatic increases in mortality and morbidity; however, there is increasing awareness that day-to-day increases in temperature contribute to a significant risk of heat-related morbidity and mortality (HRMM) that over one or more warm seasons may exceed the public health burden of heat waves. Climate change has already and will continue to increase both average ambient temperatures and the frequency and intensity of excursions above those averages (i.e., heat waves or extreme heat events) and will thereby lead directly and indirectly to amplification of the risk of HRMM. This chapter provides a brief synopsis of our current knowledge about thermoregulation, thermotolerance and the pathophysiology of heat stroke, and the multiple determinants of health and illness that influence the risk of HRMM and that collectively define vulnerability. A particular focus is on two vulnerable populations, older adults and children. An Environmental Health Multiple-Determinant Model of Vulnerability is presented as a conceptual framework to integrate that knowledge, with the intent of providing a tool that can facilitate compilation and translation of the information to interventions and adaptation strategies relevant at the individual level and/or subpopulation and population levels and at one or more geopolitical scales in developing and/or developed nations. Three overarching strategies for HRMM risk reduction are discussed, including Extreme Heat Event and Warm Season Heat Preparedness and Response Action Plans, Promote Good Health and Access to Quality Healthcare (reduces risk and increases resiliency), and Reduce/Manage Potential Exposure(s) (individual, community) to Ambient Heat and Other Physical Environmental Stressors. A key focus of this chapter is on integration and translation of knowledge.
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Abstract Introduction: Young soccer players are exposed day after day into the training and competitions routine in conditions of elevated temperatures in much of the times. Children and adolescents have different thermoregulatory and metabolic characteristics in comparison of the adults when they are submitted to the effort. Under extreme temperature conditions young soccer players has the performance deteriorated and are more vulnerable to the injuries provoked by the heat. Objective: The aim of this review is to assemble data about differences thermoregulatory and metabolic responses between children and adults and show the relevant discussion for the elaboration plans of hydration for the children soccer players. Conclusion: Children don’t restitute liquids adequately. The strategies of hydration for young soccer players must to be discussed and elaborated carefully considering them anatomical and physiological characteristics. The diary individual evaluation of hydration state has very importance for young players engaged in structured training. Young athletes must to be guided so that they develop good hydration habits. Key Words: children, soccer, hydration, heat.
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http://dx.doi.org/10.5007/1980-0037.2009v11n2p134 Soccer is a sport whose worldwide acceptance has been growing year after year, and is one of the most important events in the sports world. A growing number of children and teenagers are engaged in this activity, but studies regarding risk factors such as adiposity and negative impacts such as dehydration and hyperthermia are scarce. The aim of this study was to evaluate the anthropometric profile, sweat rate and risk of dehydration among young soccer players. For anthropometric assessment, weight, height, circumference measures and skinfold thickness were collected and used for the determination of body mass index and percent body fat of each player. For determination of the sweat rate, players were weighed before and after pre-competition training. Analysis of fat percentage (14.4 ± 3.6%) and the sum of skinfolds showed that the players presented an optimal percentage and activity pattern, probably related to their role in the game. Although low (8.8 ± 6.6 mL/min), the sweat rate varied widely among players, wit the observation of a significant reduction (p < 0.05) in final weight. The risk of dehydration was low, but the same cannot be stated for the risk of hyperthermia. Further studies involving this population are necessary to establish an adequate hydration strategy, with emphasis on the monitoring of signs of hyperthermia.
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Objective: To review possible peculiarities in biological mechanisms related to responses of thermoregulatory and specific sweat glands in exercise performed by children in hot environments. Data sources: Review of 47 articles published between 1960 and 2011 in the electronic databases MedLine and SciELO Brazil using the following key-words: 'children', 'heat', 'sweating', 'thermoregulation', 'sweat gland', and 'exercise', alone or in combination, in addition to a doctoral thesis about the subject. Data synthesis: Pre-pubertal sweat rate during exercise is lower than among adults. Children have different thermoregulatory characteristics, with a small sweat output rate due to small sweat glands. High ratio between surface and body mass increases the absorption of heat during exercise under thermal stress in children, raising the risk of hyperthermia symptoms. However, great blood flow to skin contributes to the better control of thermal homeostasis in children. Small size of the gland, low cholinergic sensibility, low levels of circulating catecholamines during stress, and lack of androgenic hormone explain the occurrence of low elimination of sweat in exercises performed by children. Conclusions: Children present immature sweat glands. Thus, physical activity combined with high temperatures is not well-tolerated by children and youngsters, with great vulnerability to thermal injury. In the heat, strict control of fluid intake and attentive monitoring of weather conditions should have especial attention for the safe practice of exercises.
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Children and adults employ different thermoregulatory strategies, particularly in dealing with heat stress. Children rely more on 'dry' heat exchange, while evaporative heat loss is adults' foremost heat-dissipation venue. Several anatomical, physiological, and psychological factors can affect differential risk of thermal injury in the child vs. the adult athlete, in some situations. Children have greater surface-area- to-mass ratio, lower sweating rate, higher peripheral blood flow in the heat, and a greater extent of vasoconstriction in the cold. They can acclimatise to a similar extent but do so at a lower rate than adults. Differences in perceived exertion and thermal strain, cumulative experience, cognitive development, and decision-making capacity may negatively affect the young athlete's behaviour under competitive and other situations, possibly subjecting him/her to sub-par performance or to greater risk of thermal injury. However, except for very limited environmental conditions, children in general, and young athletes in particular, are physiologically as capable as adults to handle environmental challenges.
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Heat illnesses contribute to significant morbidity and occasional mortality in athletic populations. Sunburn increases the risk of various skin carcinomas. This report provides an overview of the etiology, symptomatology, risk identification, prevention, and treatment for heat related illnesses and sunburn. Four cases are presented to illustrate the diagnosis and immediate treatment of exercise related heat illness and sunburn. Identification of signs and symptoms combined with prompt treatment, achieved resolution in three athletes presenting with exercise related heat illness and one athlete with sunburn. The best treatment approach is prevention. Chiropractors can be an important resource for information regarding prevention and treatment strategies. For mild to moderate heat illness, quick identification of signs and symptoms, followed by rapid cooling and re-hydration comprises treatment. For heat stroke, rapid and aggressive cooling is essential to reduce mortality. Best evidence treatment of sunburn is symptomatic relief with emollients and pain control via medications.
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Soccer is a sport whose worldwide acceptance has been growing year after year, and is one of the most important events in the sports world. A growing number of children and teenagers are engaged in this activity, but studies regarding risk factors such as adiposity and negative impacts such as dehydration and hyperthermia are scarce. The aim of this study was to evaluate the anthropometric profile, sweat rate and risk of dehydration among young soccer players. For anthropometric assessment, weight, height, circumference measures and skinfold thickness were collected and used for the determination of body mass index and percent body fat of each player. For determination of the sweat rate, players were weighed before and after pre-competition training. Analysis of fat percentage (14.4 ± 3.6%) and the sum of skinfolds showed that the players presented an optimal percentage and activity pattern, probably related to their role in the game. Although low (8.8 ± 6.6 mL/min), the sweat rate varied widely among players, wit the observation of a significant reduction (p<0.05) in final weight. The risk of dehydration was low, but the same cannot be stated for the risk of hyperthermia. Further studies involving this population are necessary to establish an adequate hydration strategy, with emphasis on the monitoring of signs of hyperthermia.
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The first edition of Exercise Physiology: Human Bioenergetics and Its Applications was a departure in terms of focus on human bioenergetics in describing muscle performance in terms of energy transduction at cellular levels. Our approach came out of the then (early 1970s) burgeoning field of exercise biochemistry and use of various techniques such as electron microscopy and mitochondrial respirometry. In the second and third editions we utilized findings of human metabolism based on use of isotope tracers to study metabolism. That technique resulted in articulation of the Crossover Concept and proving of the Lactate Shuttle hypothesis in human subjects. In the fourth edition of Exercise Physiology this theme has been retained, but the approach has become increasingly mechanistic due to many developments, including the use of molecular and cellular biology and isotope tracer technology in the field. Now, in the fifth edition we continue in traditions of the first four editions, but adjust and revise as the ever-increasing appreciation of exercise physiology increases, as reflected in the Exercise is Medicine, and publication of the 2018 Physical Activity guidelines and the application of exercise physiology to develop countermeasures for space travel.
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Seven lean and five obese boys, aged 9-12 yr, exercised in four environments: 21.1, 26.7, 29.4, and 32.2 degrees C Teff. Subjects walked on a treadmill at 4.8 km/h, 5% grade for three 20-min exercise bouts separated by 5-min rest periods. Rectal temperature (Tre), skin temperature (Tsk), heart rate (HR), sweat rate, and oxygen uptake (VO2) were measured periodically throughout the session. Lean boys had lower Tre and HR than obese boys in each of the environments. Increases in Tre were significantly greater for the obese at 26.7 and 29.4 degrees C Teff. No significant differences in Tsk and sweat rate (g-m-2-h-1) were observed between lean and obese boys. Obese boys had significantly lower oxygen consumptions per kg but worked at a significantly higher percentage of VO2max than lean boys when performing submaximal work. Responses of the obese boys to exercise in the heat were similar to those of heavy prepubertal girls studied previously, except that the boys were more tolerant of exercise at 32.2 degrees C Teff than the girls. Lean boys had lower HR than lean girls in each environment, but lower Tre only at 32.2 degrees C Teff.
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Two heat-acclimatization protocols were studied in 8- to 10-yr-old boys: exercise in dry heat (WH, n = 9) and exercise in neutral climate (W, n = 9). Five 90-min acclimatization sessions were conducted within a 12-day period. Base-line (BL) and criterion (CT) tests sessions were held at 43 degrees C db and 24 degrees C wb, with three 20-min exercise bouts at approximately 40 Ws. With acclimatization, the WH group showed a significant reduction in heart rate (HR) (11.4 beat x min-1), mean skin temperature (0.64 degrees C), and an increase in the population density of heat-activated sweat glands (HASG) (25.2 glands x cm-2). The W group showed a significant reduction in HR (13.4 beat x min-1) and rectal temperature (0.24 C). Total sweat rate per body surface area did not increase significantly in either group. However, the sweat rate relative to rise in core temperature increased in both groups. No significant differences were found between the two acclimatization procedures in any of the variables studies except for the HASG, which showed a greater increase in the WH group. It is suggested that in 8- to 10-yr-old boys physiological changes compatible with heat acclimatization could be achieved either by exercise in heat or by mere physical conditioning (approximately 65% of VO2max), in neutral climate. It is postulated that age-related factors associated with the thermoregulatory system prevent children from deriving full effectiveness of exercise-in-heat acclimatization protocol as used in this study.
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This study was performed to determine whether a) children voluntarily dehydrate while exercising in hot climate; b) such dehydration affects their well-being and thermoregulation. Eleven 10p to 12-yr old, partially acclimatized boys underwent two work-in-the-heat protocols (cycle rides, 45% aerobic capacity at 39 degrees C, 45% rh). During one session they drank only voluntarily when thirsty (VD). In the other, drinking was forced (FD) to replenish fluid losses. VD induced a progressively increasing fluid loss (0.3% of body wt.h-1) due to insufficient drinking (72% of intake in FD). URinary output was lower (55.7 vs. 81.6 ml.h-1) and its osmolality higher (880 vs. 523 meq.1-1) than during FD. Sweat rate, rectal (Tre) and mean skin (T-sk) temperatures, heart rate, rate of perceived exertion, sweat gland counts, blood hemoglobin, hematocrit (Hct), serum electrolytes, and total proteins did not differ between sessions. However, the rise of Tre, Hct, and proteins positively correlated with hypohydration level. It is concluded that exercising children progressively dehydrate when not forced to drink. At equal levels of % weight loss they have greater Tre rise than do lean adults.
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Exercise in the heat is usually associated with reduced performance; both dehydration and hyperthermia adversely affect mental and physical performance. For athletes from temperate climates, the negative effects of heat had humidity can be attenuated by a period of acclimatization. This requires up to 10-14 days. Endurance-trained individuals already show some of the adaptations that accompany acclimatization, but further adaptation occurs with training in the heat. Prior dehydration has a negative effect even on exercise of short duration where sweat losses are small. The athlete must begin exercise fully hydrated and regular ingestion of fluids is beneficial where the exercise duration exceeds 40 min. Dilute carbohydrate-electrolyte (sodium) drinks are best for fluid replacement and also supply some substrate for the exercising muscles. Post-exercise rehydration requires electrolyte as well as volume replacement. In extreme conditions, neither acclimatization nor fluid replacement will allow hard exercise to be performed without some risk of heat illness.
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It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise. 5) Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water. 6) During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g.h(-1) to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.
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This study examined the effects of beverage composition on the voluntary drinking pattern, body fluid balance, and thermoregulation of heat-acclimatized trained boys exercising intermittently in outdoor conditions (wet bulb globe temperature 30.4 +/- 1.0 degreesC). Twelve boys (age 13.4 +/- 0.4 yr) performed two 3-h sessions, each consisting of four 20-min cycling bouts at 60% maximal aerobic power alternating with 25-min rest. One of two beverages was assigned: unflavored water (W) or flavored water plus 6% carbohydrate and 18 mmol/l Na (CNa). Drinking was ad libitum. Total intake was higher (P < 0.05) during CNa (1,943 +/- 190 g) compared with W (1,470 +/- 143 g). Euhydration was maintained with CNa (+0.18% body wt), but a mild dehydration resulted with W (-0.94% body wt; P < 0.05). Sweat loss, much higher than previously published for children of similar age, was similar between conditions (CNa = 1,644.7 +/- 117.5; W = 1,750.2 +/- 152.7 g). The increase in rectal temperature (CNa = 0.86 +/- 0.3; W = 0.76 +/- 0.1 degreesC), heart rate, and all perceptual variables did not differ between conditions. In conclusion, a flavored carbohydrate-electrolyte drink prevents voluntary dehydration in trained heat-acclimatized boys exercising in a tropical climate despite their large sweat losses. Because hydration changes were minor, the thermoregulatory strain observed was similar between conditions.
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We measured substrate utilization during exercise performed with water (W), exogenous glucose (G), and exogenous fructose plus glucose (FG) ingestion in boys age 10-14 yr. Subjects (n = 12) cycled for 90 min at 55% maximal O(2) uptake while ingesting either W (25 ml/kg), 6% G (1.5 g/kg), or 3% F plus 3% G (1.5 g/kg). Fat oxidation increased during exercise in all trials but was higher in the W (0.28 +/- 0.023 g/min) than in the G (0.24 +/- 0.023 g/min) and FG (0.25 +/- 0.029 g/min) trials (P = 0.04). Conversely, total carbohydrate (CHO) oxidation decreased in all trials and was lower in the W (0.63 +/- 0.05 g/min) than in the G (0.78 +/- 0.051 g/min) and FG (0.74 +/- 0.056 g/min) trials (P = 0.009). Exogenous CHO oxidation, as determined by expired (13)CO(2), reached a maximum of 0.36 +/- 0.032 and 0.31 +/- 0.030 g/min at 90 min in G and FG, respectively (P = 0.04). Plasma insulin levels decrease during exercise in all trials but were twofold higher in G than in W and FG (P < 0.001). Plasma glucose levels decreased transiently after the onset of exercise in all trials and then returned to preexercise values in the W and FG (approximately 4.5 mmol/l) trials but were elevated by approximately 1.0 mmol/l in the G trial (P < 0.001). Plasma lactate concentrations decreased after the onset of exercise in all trials but were lower by approximately 0.5 mmol/l in W than in G and FG (P = 0.02). Thus, in boys exercising at a moderate intensity, the oxidation rate of G plus F is slightly less than G alone, but both spare endogenous CHO and fat to a similar extent. In addition, compared with flavored W, the ingestion of G alone and of G plus F delays exhaustion at 90% peak power by approximately 25 and 40%, respectively, after 90 min of moderate-intensity exercise.
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To determine whether the relative utilization of exogenous carbohydrate (CHO(exo)) differs between children and adults, substrate utilization during 60 min of cycling at 70% peak O(2) uptake was studied in 12 pre- and early pubertal boys (9.8 +/- 0.1 yr) and 10 men (22.1 +/- 0.5 yr) on two occasions. Subjects consumed either a placebo or a (13)C-enriched 6% CHO(exo) beverage (total volume per trial: 24 ml/kg). Substrate utilization was calculated for the final 30 min of exercise. During both trials, total fat oxidation was higher (5.4 +/- 0.5 vs. 3.0 +/- 0.4 mg x kg(-1) x min(-1), P < 0.001) and total CHO oxidation lower (27.4 +/- 1.5 vs. 34.8 +/- 1.2 mg x kg(-1) x min(-1), P < 0.001) in boys than in men, respectively. During the CHO(exo) trial, CHO(exo) oxidation was higher (P < 0.001) in boys (8.8 +/- 0.5 mg x kg(-1) x min(-1)) than in men (6.2 +/- 0.5 mg x kg(-1) x min(-1)) and provided a greater (P < 0.001) relative proportion of total energy in boys (21.8 +/- 1.4%) than in men (14.6 +/- 0.9%). These results suggest that, although endogenous CHO utilization during exercise is lower, the relative oxidation of ingested CHO is considerably higher in boys than in men. The greater reliance on CHO(exo) in boys may be important in preserving endogenous fuels and may be related to pubertal status.
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Temperature regulation during exercise in the cold was examined in 13 adolescent female individuals, aged 13-18 yr. Six girls with established menstrual cycles comprised the eumenorrheic menarcheal (EM) group, and seven nonmenstruating girls comprised the premenarcheal (PM) group. During the first visit, maximal oxygen consumption (Vo2 max), height, weight, and percent body fat were measured. The second visit included a determination of metabolic rate in thermoneutrality (21°C), consisting of a 10-min rest period and 20 min of cycling (30% of Vo2 max), and a cold test (5°C, 40% humidity, <0.3 m/s air velocity) involving a 20-min rest period and 40 min of cycling (30% of Vo2 max). Subjects in the EM group were tested twice in the chamber: once during the follicular and once during the luteal phase. Heat production per kilogram in thermoneutrality and in the cold was significantly (P < 0.05) higher in the PM compared with the EM girls. However, the PM girls had a significantly (P < 0.05) lower core temperature in the cold than the EM group. PM girls also had a significantly higher body surface area-to-mass ratio compared with the EM girls. Although percent body fat between groups was not significantly different, within the PM group percent body fat explained 79% (P < 0.01) of the variance in the decrease of core temperature. There were no menstrual phase-related differences in temperature regulation in either the thermoneutral or cold environment. In conclusion, menstrual phase does not influence temperature regulation in female individuals during adolescence. EM girls had lower metabolic heat production but maintained their core temperature more effectively in the cold than did the PM girls. This thermoregulatory difference between PM and EM girls is mainly a function of geometric differences with maturation-related peripheral vasoconstrictive differences maybe limiting the effectiveness of the mechanism of increased heat storage in younger female individuals.
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The purpose of this investigation was to compare the thermoregulatory responses during exercise in a hot climate among three age categories. Eight prepubertal (PP), eight young adult (Y) and eight elderly (O) male subjects cycled at an intensity of 50 +/- 1% of their maximum oxygen uptake (V(O2peak)) for 85 min (three 20 min bouts with three 7 min rest periods) in hot and dry conditions (41 +/- 0.67 degrees C, 21 +/- 1% relative humidity). During the exercise-in-heat protocol, rectal temperature (T(re)) skin temperatures (T(sk)), heart rate (HR), V(O2), V(CO2) V(E), RER, sweat rate, and the number of heat activated sweat glands (HASG) were determined. Despite highest and lowest end-exposure T(re) in the Y and O groups, respectively, the rise in rectal temperature (accounting for differences in baseline T(re)) was similar in all age groups. Changes in body heat storage (DeltaS), both absolute and relative to body mass, were highest in the Y and O groups and lowest in the PP group. While end-session as well as changes in mean skin temperature were similar in all three age groups, HR (absolute and percentage of maximum) was significantly lower for the O compared with the PP and Y groups. Total body as well as per body surface sweating rate was significantly lower for the PP group, while body mass-related net metabolic heat production ((M -- W) kg(-1)) and heat gained from the environment were highest in the PP and lowest in the O group. Since mass-related evaporative cooling (E(sk) kg(-1)) and sweating efficiency (E(sk)/M(sw) kg(-1)) were highest in the PP and lowest in the O group, the mass-dependent heat stored in the body (DeltaS kg(-1)) was lowest in the PP (1.87 +/- 0.03 W kg(-1)) and highest in Y and O groups (2.19 +/- 0.08 and 1.97 +/- 0.11 W kg(-1), respectively). Furthermore, it was calculated that while the O group required only 4.1 +/- 0.5 W of heat energy to raise their body core temperature by 1 degrees C, and the Y group needed 6.9 +/- 0.9 W (1 degrees C)(-1), the PP group required as much as 12.3 +/- 0.7 W to heat up their body core temperature by 1 degrees C. These results suggest that in conditions similar to those imposed during this study, age and age-related characteristics affect the overall rate of heat gain as well as the mechanisms through which this heat is being dissipated. While prepubertal boys seem to be the most efficient thermoregulators, the elderly subjects appear to be the least efficient thermoregulators.
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The purpose of this study was to quantify the variability and stability of 1st morning body mass (BM) fluctuations during daily exercise in the heat while following traditional fluid intake guidance. Data from 65 men were examined retrospectively. BM fluctuations were monitored over 4 to 15 consecutive days. Group daily variation in BM was 0.51+/-0.20 kg. Group coefficient of variation was 0.66+/-0.24%, normally distributed, and not related to either absolute BM (r = 0.04) or number of measurements (r = 0.34). Three days resulted in a similar variability estimate compared to 6 or 9 d, although precision was improved with 9 d. In conclusion, 3 consecutive BM measurements provide an accurate assessment of daily BM variability, which is less than 1% for active men when replacing 100% of sweat losses during exercise. The data also suggest that daily BM is a sufficiently stable physiological parameter for potential daily fluid balance monitoring.
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To study the age difference in sweating during muscular exercise, two series of experiments were conducted under constant climatic conditions (29 ± 1°C, DB, 60 ± 5% RH, 0.45 ± 0.05 m/sec air flow). In series A, 7 to 20 years old male subjects undertook 5-minute running or pedalling of a bicycle ergometer in various seasons. In this series of experiments, pectoral sweat volume, sweat chloride concentration, rectal and mean skin temperatures were in general determined every 5 minutes and, when necessary, the total body sweat volume was calculated from the body weight loss. In series B. the age difference in the sweating in relation to physical training was studied. Subjects, 3 to 20 years old received experimental physical training of 5-minute or 500m-running. Before and after the training, a work load or 3- or 5-minute outdoor running was assigned to them. Furthermore, before and after the training, 10 an 11 years old subjects were given a fixed mechanical work rate on a bicycle ergometer. In these experiments, most of the parameters described above were measured. In series A, age differences in sweating during exercise were noticed to be dependent on the intensity of work load between pre- and post-adolescents. When the work load was heavy enough to cause a rapid increase in rectal temperature, the sweat volume became significantly less, the mean skin temperature was far higher, and the sweat chloride concentration was remarkably smaller in the pre-adolescent subjects than in the post-adolescent ones. In series B, an age difference in the effect of physical training was also found on sweating during exercise. The effect of physical training on sweating in the pre-adolescent individuals was generally less significant than in adults and sometimes showed a different pattern from that of adults. From these results, it can be concluded that sweating in the pre-adolescents is less adaptive, particularly to continuous severe exercise and that physical training is less effective in them than in the post-adolescents.
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Children involved in sports should be encouraged to participate in a variety of different activities and develop a wide range of skills. Young athletes who specialize in just one sport may be denied the benefits of varied activity while facing additional physical, physiologic, and psychologic demands from intense training and competition. This statement reviews the potential risks of high-intensity training and sports specialization in young athletes. Pediatricians who recognize these risks can have a key role in monitoring the health of these young athletes and helping reduce risks associated with high-level sports participation.
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For morphologic and physiologic reasons, exercising children do not adapt as effectively as adults when exposed to a high climatic heat stress. This may affect their performance and well-being, as well as increase the risk for heat-related illness. This policy statement summarizes approaches for the prevention of the detrimental effects of children's activity in hot or humid climates, including the prevention of exercise-induced dehydration.
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We compared ad libitum fluid consumption in adolescent (n = 15) and adult athletes (n = 34) exercising in similar environmental conditions (26.5 °C, 27.3% relative humidity) and engaging in similar modes and intensities of exercise (80-85% of their age-predicted maximum heart rate). Throughout 1 hr of exercise, participants had access to sports bottles containing a sports drink (6% carbohydrate with electrolytes and identical flavoring). Sweat rate (SR) and percent dehydration were calculated from the change in body weight corrected for urine loss and fluid intake (FI). FI was significantly higher for the adults than for the adolescents. SR was also higher for the adults compared with that of the adolescents. Compared with adults, adolescents had significantly lower FI and SR, the combination of which allowed them to meet their fluid needs more closely during exercise. Minimal voluntary dehydration occurred in either group during exercise, possibly because of the nature of the exercise (non-competitive) or the beverage characteristics (presence of sodium and sweetness) or availability of the beverage.
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Although children and older adults appear more susceptible to heat stress, the mechanisms responsible for their lower tolerance are not fully understood. Many studies dealing with the effect of age on temperature regulation have concluded that an inadequate sweating response is primarily responsible for the low tolerance of children and the elderly to exercise in the heat. However, the dependence of core temperature on relative exercise intensity and sweat rate on absolute exercise intensity makes it difficult to avoid the confounding effects of exercise on thermoregulation when aerobic power (Vo2max) varies across age groups. When 38 non-acclimatized females, ages 12 to 68 years, exercised at 30-35% Vo2max in the heat, the degree of cardiovascular stability was the primary predictor of tolerance time. Age was not a significant predictor. However, it was evident that individuals at either end of the age continuum were more likely to be at risk. For children the risk was associated with the instability of an immature cardiovascular system; for older women, a marked decrement in aerobic power. Sweat rate added significantly to the prediction of tolerance time for all subjects regardless of age. Whether the decrease in responsiveness of sweating noted for some older individuals is an age related change or a reflection of their lower fitness levels is not known.
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Thermoregulatory studies often investigate thermal responses without considering the influences of clothing. These studies have expanded our understanding of basic human responses to various environmental conditions. However, human thermoregulation is variable and modified by heat transfer interactions between skin surface area, clothing and environment. Much of the original work on the influence of clothing on work performance was the result of ergonomic concerns. Currently, the importance of clothing and the influence of new clothing technology aimed at minimising thermal stress has spawned a new interest. For hot climates, new fabrics have been developed with improved wicking properties to keep the wearer cooler and drier, and to enhance heat transfer from the body while providing greater comfort. In contrast, the challenge of cold environments requires a different approach to clothing, which tries to minimise the free movement of air and water along the skin surface of the body. The materials used should also be able to absorb radiant heat from the environment and be nonconductive. In a cold climate, the wearer needs to balance the need for a clothing barrier for warmth with the potential for accumulating too much heat as the result of metabolic heat production from exercise. To counteract this potential problem, it is suggested that cold-weather clothing be worn in layers that can be removed during exercise and replaced during less active periods. Protective clothing for firefighters, hazardous waste workers and astronauts, and athletic protective gear, have specialised design requirements which may be influenced by considerations, for example, of environmental conditions, garment weight, the need for durability, impact forces.
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Exercise-heat tolerance (EHT) in children is influenced by many physiological factors, including sweat gland activity, cardiac output, exercise economy, ability to acclimate to heat, and maturation of organ systems. It is generally believed that children cannot tolerate hot environments as well as adults, although some children exhibit EHT that is superior to that of adults. There has been no research showing large exercise-induced differences between the core body temperatures of children versus adults, but differences in the time to onset of syncope and fatigue have been observed. This suggests that the greatest risk of heat illness for children is heat exhaustion (i.e., cardiovascular instability) and not heat stroke (i.e., hyperthermia). Therefore this review (a) examines the conclusions of previous studies to clarify misinterpretations of data, and (b) identifies research questions that require future study.
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The second edition of "Growth, Maturation, and Physical Activity" has been expanded with almost 300 new pages of material, making it the most comprehensive text on the biological growth, maturation, physical performance, and physical activity of children and adolescents. The new edition retains all the best features of the original text, including the helpful outlines at the beginning of each chapter that allow students to review major concepts. This edition features updates on basic content, expanded and modified chapters, and the latest research findings to meet the needs of upper undergraduate and graduate students as well as researchers and professionals working with children and young adults. The second edition also includes these new features: -10 lab activities that encourage students to investigate subject matter outside of class and save teachers time-A complete reference list at the end of each chapter -Chapter-ending summaries to make the review process easy for students-New chapters that contain updates on thermoregulation, methods for the assessment of physical activity, undernutrition, obesity, children with clinical conditions, and trends in growth and performance-Discussions that span current problems in public health, such as the quantification of physical activity and energy expenditure, persistent undernutrition in developing countries, and the obesity epidemic in developed countriesThe authors are three of the world's foremost authorities on children's growth and development. In 29 chapters, they address introductory concepts and prenatal growth, postnatal growth, functional development, biological maturation, influencing factors in growth, maturation and development, and specific applications to public health and sport. In addition, secular trends in growth, maturation, and performance over the past 150 years are considered. You'll be able to recognize risk factors that may affect young athletes; you'll also be able to make informed decisions about appropriate physical activities, program delivery, and performance expectations. "Growth, Maturation, and Physical Activity, Second Edition, " covers many additional topics, including new techniques for the assessment of body composition, the latest advances in the study of skeletal muscle, the human genome, the hormonal regulation of growth and maturation, clarification of dietary reference intakes, and the study of risk factors for several adult diseases. This is the only text to focus on the biological growth and maturation process of children and adolescents as it relates to physical activity and performance. With over 300 new pages of material, this text expertly builds on the successful first edition.
Article
The thermoregulatory response to exercise in the heat, especially sweating pattern, differs between children and adults. This study investigated the changes with physical maturation in the thermoregulatory response to exercise (50% V̇O2max) in the heat (42°C 20% RH) among circum-pubertal boys, using a mixed cross-sectional, longitudinal design. Subjects were initially divided into three groups, based on Tanner (pubic hair) criteria: 16 pre-pubertal (PP, stage I), 15 mid-pubertal (MP, stages II, III, IV), and 5 late-pubertal (LP, stage V). The thermoregulatory response was observed every 6 months for a period of 18 months (4 sessions). Thirty of the 36 boys completed the four sessions. During each session, the exercise task consisted of three 20-min bouts of cycling with 10-min rest periods. Measurements included rectal and skin temperatures and heart rate continuously, V̇O2 at the midpoint of the second bout, sweat collection during each bout, photography of sweat drops after bouts 1 and 2, and whole body sweating rate. During each session, body temperatures tended to be higher among LP relative to the other two groups; however, the rate of increase in body temperatures was similar among groups. Sweating rate per body surface area and per gland were consistently higher among LP compared to PP. This was accompanied by lower sweat lactate concentrations during the initial stages of exercise and lower activated sweat gland population density. Longitudinal observations tended to support cross-sectional findings. It is concluded that physical maturation is characterized by enhanced sweating rate per body surface area and per gland, and that this may be associated with increased sweat gland anaerobic metabolism. © 1992 Wiley-Liss, Inc.
Article
Thirty-two elite junior athletes in two age categories, older than or equal to 15 years old (O15) (8 females and 9 males) and less than 15 years old (U15) (8 females and 7 males), performed a laboratory-based duathlon (run-ride-run). At the completion of the event, significant body mass losses were recorded for all groups. Compared with the other three groups, the O15 males lost body mass at a greater absolute rate (1.26 +/- 0.06 kg.hr-1 vs. a mean of 0.62 +/- 0.11 kg.hr-1 for the other three groups) and a greater relative rate (1.95 +/- 0.10%BM.hr-1 vs. a mean of 1.23 +/- 0.19%BM.hr-1 for the other three groups) (p < .05). No differences were observed between groups for fluid consumption. Subjects consumed more fluid (p < .05) during the cycle phase and postevent than preevent or during the run phases. Results indicated that the athletes' fluid intake practices were insufficient to maintain adequate hydration during the simulated event.
Article
Five prepubertal females and five college women, matched for aerobic power, walked on a treadmill at approximately 30% VO2 max for two 50-min periods in three environments: 1) 28 degrees C, 45% rh, 2) 35 degrees C, 65% rh, and 3) 48 degrees C, 10% rh. In the mild heat (28 degrees C) both groups were able to work 100 min with no discomfort. At 35 and 48 degrees C tolerance time for the prepubertal subjects averaged 84.4 and 37.0 min, respectively; for adults, 100 and 75.0 min. At all temperatures the girls had higher heart rates and a lower stroke index, and finished the walks with a higher rectal temperature. There were no differences between groups in cardiac index, mean skin temperature, forearm blood flow, or percent loss in body weight. The proportion of the thermal load dissipated by the two groups was similar but the route for heat transfer was related to the BSA/wt ratio and environmental conditions. Marked circulatory instability was a primary factor in the lower tolerance of the prepubertal girls to work in the heat probably due to a shift in blood volume from the central to the peripheral circulation.
Article
Sweating rate (SR) of boys is lower than that of men. To assess the association between the response of individual sweat glands and physical growth and maturation, three groups of circumpubertal boys cycled at 50% VO2max in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 16 were classified as prepubertal (PP, Tanner 1), 15 as midpubertal (MP, Tanner 2-4), and five as late-pubertal (LP, Tanner 5). Population density (PD) of the heat-activated sweat glands, the mean area of sweat drops (DA), and the proportion of skin covered by sweat (%A) were measured by skin photography and computer-assisted imaging analysis. Other measurements included rectal and skin temperatures (Tre, Tsk, respectively), heart rate (HR), and total body SR. The rise in HR, Tre and Tsk did not differ among groups. Whole body SR was significantly higher in the LP group compared with PP (PP = 4.95 +/- 0.23, MP = 5.79 +/- 0.20, LP = 6.70 +/- 0.42 ml.min-1.m-2) (mean +/- SEM). PD was significantly higher in the PP group (PP = 128 +/- 8, MP = 97 +/- 9, LP = 74 +/- 9 glands.cm-2), while DA was higher in the LP group (PP = 5.47 +/- 0.59, MP = 6.92 +/- 0.47, LP = 12.83 +/- 1.41 microns2.10(4)). %A did not differ among groups. The calculated SR per gland was higher among the LP groups compared with the less mature ones (PP = 4.6 +/- 0.3, MP = 7.2 +/- 0.8, LP = 9.6 +/- 1.0 nl.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Eight minimally dressed pre- and early pubescent boys (age 11-12 yr) and 11 young adult men (age 19-34 yr) rested for 20 min and exercised on a cycle ergometer for 40 min at approximately 30% of their maximum oxygen consumption (VO2max) at 5 degrees C. To quantify the added increase in metabolic rate because of cold, a separate test was carried out at 21 degrees C at rest and at equal work rates as in the cold. Both groups were similar in subcutaneous fat thickness and VO2max per kilogram body weight. Rectal temperature increased slightly during the exposure to the cold, but no significant difference was observed between the boys and men. In the cold, the boys had lower skin temperatures than the adults in their extremities but not in the trunk. The boys increased their metabolic rates in the cold more than did the men. As a result, the boys maintained their core temperature as effectively as the adults. Similar age-related differences in thermoregulatory responses to cold were observed when two boys and two men with equal body sizes were compared. Our results suggest that there may be maturation-related differences in thermoregulation in the cold between children and adults.
Article
During exercise in a hot climate, children have been reported to have a less effective temperature regulation capability, compared with adults. It is likely that the transition from a child-like to an adult-like response occurs during puberty. To assess the association between the thermoregulatory response and physical maturation, three groups of circum-pubertal boys cycled at 50% VO2max (three 20-min bouts with 10-min rests), in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 10 were classified as prepubertal (PP), 13 as midpubertal (MP), and eight as late pubertal (LP). Measurements included rectal and skin temperatures (Tre, Tsk), heart rate (HR), sweating rate (SR), oxygen consumption (VO2), and forearm blood flow (FBF). Tre, Tsk, and HR increased with time, with no significant difference among groups. Relative VO2 (ml O2.kg-1) was similar among groups. FBF was consistently higher in PP compared with LP. In spite of the higher SR (PP = 4.9 +/- 0.2, MP = 5.7 +/- 0.3, LP = 6.6 +/- 0.4 ml.min-1.m-2) (mean +/- SEM) among LP compared with PP, the rate of heat storage (PP = 5.5 +/- 0.4, MP = 5.3 +/- 0.4, LP = 6.8 +/- 0.3, kJ.h-1.kg-1) was also significantly higher among those in the LP group. Three of eight LP did not complete the session due to high Tre, while two of the 10 PP were unable to complete the session even though the physiologic heat strain was not high. The results suggest that the transition from a child-like to an adult-like thermoregulatory effectiveness in a hot, dry climate may occur at a somewhat later stage, but not during puberty.
Article
Intense exercise (i.e.; above 60% VO2max) can be maintained for prolonged periods provided sufficient carbohydrate is available for energy and the heat generated from muscle metabolism does not cause excessive hyperthermia and/or dehydration due to sweating. It is clear that people should ingest carbohydrate during prolonged exercise (i.e.; longer than 1-2 h), which causes fatigue because of an inadequate supply of blood glucose and that fluids should also be ingested in an attempt to offset dehydration and reduce hyperthermia. Ingestion of approximately 30-60 g of carbohydrate (i.e.; glucose, sucrose, or starch) during each hour of exercise will generally be sufficient to maintain blood glucose oxidation late in exercise and delay fatigue. Since the average rates of gastric emptying and intestinal absorption can reach 1 l.h-1 for water and solutions containing up to 8% carbohydrate, exercising people can be supplemented with both carbohydrate and fluids at relatively high rates (over 60 g.h-1 of carbohydrate and 1 l.h-1 of fluid). Therefore, when sweat rate is not high (i.e.; less than 1 l.h-1), the addition of carbohydrate to fluids, and vice versa, does not prevent adequate supplementation of each, especially if large volumes are consumed to keep the stomach somewhat full and thus increase gastric emptying. Therefore, in most situations there are no trade-offs between fluid and carbohydrate.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
This study attempts to explain some of the individual variability in sweating pattern by comparing prepubescents and pubescents. Sweating rate and muscular anaerobic capacity are higher in adults than in children; thus we hypothesized that sweat gland anaerobic metabolism, as reflected by lactate excretion, might be higher with advanced physical maturity (PM). Lactate concentration in sweat ([LAC]sw) was measured at various stages of PM in boys who exercised in the heat. The subjects were divided into three groups on the basis of Tanner staging: prepubertal (PP, n = 16), midpubertal (MP, n = 15), and late pubertal (LP, n = 5). Subjects cycled at 50% of maximal O2 uptake for three 20-min bouts, with 10-min rest periods, in 42 degrees C and 18% relative humidity. Sweat samples were harvested, and population density of activated sweat glands was determined after each exercise bout. [LAC]sw during bout 1 was higher in PP than in LP [PP = 22.2 +/- 2.2, MP = 19.5 +/- 1.4, LP = 14.3 +/- 1.3 (SE) mmol/l]. In all groups, [LAC]sw decreased during subsequent bouts, and there were no intergroup differences in [LAC]sw during bout 3 (PP = 11.2 +/- 0.4, MP = 10.6 +/- 0.5, LP = 9.7 +/- 0.2 mmol/l). [LAC]sw was inversely related to sweating rate. Lactate excretion rate per gland was greater with the increase in PM (PP = 61.0 +/- 8.2, MP = 79.1 +/- 11.3, LP = 99.9 +/- 11.0 pmol/min; P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The primary mechanism for maintaining normal body temperature during physical exercise in the heat is the evaporation of sweat. With profuse sweating, water loss far exceeds electrolyte loss. Rigorous exercise in the heat places the athlete at risk for thermoregulatory dysfunction from dehydration. Because children are inherently less efficient thermoregulators than adults, they are at even greater risk for heat illness. The three primary syndromes of heat illness are heat cramps, heat exhaustion, and heat stroke. Treatment of heat illness is based on reduction of body temperature and rehydration. Heat stroke is a true medical emergency with a high mortality rate; immediate reduction of body temperature is critical to the survival of these patients. Prevention of heat illness is based on reducing known risk factors. Physical activity should be modified in the face of high ambient temperature and humidity. The athlete should begin exercise well hydrated; frequent consumption of cold water during exercise decreases likelihood of significant dehydration. After exercise, the athlete should continue drinking to replace fluid losses. Clothing should be lightweight; the more skin exposed, the greater the available evaporative surface. A preseason conditioning program, when combined with an 8- to 14-day period of acclimatization, further reduces the risk of heat injury. Although athletes engaged in endurance sports may benefit from drinking carbohydrate/electrolyte-containing solutions, for the majority of young athletes, cold water remains the preferred choice for fluid replacement during exercise. The relatively greater body surface area of young athletes also places them at risk for hypothermia. Special attention should be given when these athletes are competing under cold environmental conditions.
Thermal balance was studied in 11 boys, aged 10–12 years, with various values for maximal oxygen uptake (\(\dot V_{O_{2 max} } \)), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (T db) 45° C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual\(\dot V_{O_{2 max} } \) (T db 20° C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to\(\dot V_{O_{2 max} } \) in children, in contrast to adults.
Article
Twelve girls, ages 9 to 11 yr, were exposed to 4 different environments to determine their tolerance of exercise in dry heat. The subjects, who were divided into lean and heavy groups on the basis of body density, walked on a treadmill at 4.8 km per hr, 5% grade for 1 hr at 21.1, 26.7, 29.4, and 32.2°C T(eff). In the warmest environment, 32.2°C T(eff), lean subjects had higher rectal temperatures [T(re)] and greater changes in T(re) during the session [ΔT(re)] than heavy subjects. Only 2 girls completed 60 min of exercise at 32.2°C T(eff). Little difference between the 2 groups was observed in the other environments except that the lean girls had higher mean skin temperatures. Compared with adults the girls appeared to have more heat exchange through radiation and convection, more evaporative heat loss, and a higher heat production per unit mass. It was concluded that prepubertal girls, like prepubertal boys, have less tolerance for exercise in the heat at 32.2°C T(eff) than adults.
Article
In an attempt to examine the effect of physical training on thermoregulatory responses in prepubertal boys, three series of experiments were performed, in summer. To all the subjects with swimming pants a heat stress was given through a foot bath of 42 degrees C in a hot climate, and a cold stress through exposure to an atmosphere at 20 degrees C Ta and 60% RH. Physical training increased work performance, whereas no significant effects were observed on rectal and mean skin temperatures. Metabolic rate was measured of children exposed alternately to 30-min heat and 30-min cold for 2 hr, and exposed to 60-min heat and 60-min cold separately, respectively. The mean skin temperature increased and decreased more on exposure to heat and cold, respectively, but the metabolic rate increased less remarkably in the children than in the adults. It was postulated thermoregulation might respond less distinctly to physical training in the children than in the adults, and that the decreased effect of training on the children might originate from an undifferentiated thermoregulatory system.
Article
This study examined changes in children's thirst and drink preferences during exercise-induced hypohydration and their spontaneous rehydration during a 30-min recovery. Twenty-four 9- to 13-year-old children (14 females, 10 males) participated in four intermittent 90-min cycling sessions in the heat (35 degrees C, 20% relative humidity); the sessions differed in the drinks the children were sampling (apple, orange, water, and grape). Thirst and drink preferences were assessed (analog and category scales) while children dehydrated up to about 0.76% of their initial body weight. During 90 min dehydration, there was an increase in thirst intensity for all drinks. The grape was the preferable drink throughout the dehydration phase, but its desirability did not increase as much as the desirability of the orange, apple, and water drinks. During the 30-min recovery, most subjects rehydrated spontaneously, exceeding baseline levels by 0.76 +/- 0.15% (M +/- SEM) for grape, 0.40 +/- 0.15 for apple, 0.71 +/- 0.18 for orange, and 0.48 +/- 0.16 for water. Although full rehydration was achieved with all drinks, the magnitude of rehydration was statistically greater with grape and orange than water and apple (p < .05). It was concluded that mild hypohydration during exercise increased children's thirst and drink desirability. In general, spontaneous overshoot of fluid consumption occurred during recovery.
Article
This article reviews studies, mostly from the authors' laboratory, on children's sweating rates and composition, voluntary drinking patterns during prolonged exercise in the heat, taste perception of beverages, and the importance of fluid flavor and composition in preventing voluntary dehydration. Subjects were children, exposed for 90 to 180 min to intermittent bouts of cycling (45-50% maximal O2 uptake) in a climatic chamber (mostly at 35 degrees C, 40-50% relative humidity). There were five main findings: When given unflavored water ad libitum, children dehydrated progressively and their core temperature increased faster than in adults. When offered drinks with various flavors, children preferred grape to other flavors. When given grape-flavored water during intermittent exercise in the heat, children voluntarily drank 44.5% more than with unflavored water. When given grape-flavored carbohydrate-electrolyte solution, they voluntarily drank 91% more than with unflavored water. Finally, such consumption of carbohydrate-electrolyte solution was sufficient to prevent voluntary dehydration during 180-min intermittent exercise in the heat.
To examine thermoregulatory responses of prepubertal children to cold stress, 11 boys (aged 8 years) and 11 young men (aged 19–23 years), wearing only trunks, participated in this study. They sat in air at 28°C for 30 min (equilibrium period) and then in conditions where air temperature (T a) was decreased linearly from 28 to 15°C (at a constant rate of 0.22°C · min−1) for 60 min, at a fixed relative humidity of 65%. In the equilibrium period there was no significant difference between the groups for rectal temperature [T re, mean 37.30 (SEM 0.10) and mean 37.43 (SEM 0.14)°C in the boys and the men, respectively] or for the respective skin temperatures (except for the forehead), but metabolic heat production (\(\dot M\)) was significantly greater for the boys [mean 57.1 (SEM 1.2) and mean 52.0 (SEM 0.9)W. m−2,P <0.005]. With decliningT a, the skin temperatures decreased in both groups (P <0.001), but the decrease was significantly greater for the boys (P < 0.05), especially on the limbs as represented by the thigh and forearm. No significant correlations were observed between the limb skin temperatures compared to surface area-to-mass ratio or limb skinfold thicknesses in either group. The rate of increase in\(\dot M\) asT a decreased was significantly lower for the boys (P < 0.01) largely because of a higher\(\dot M\) before the cold exposure. Thus, the mean\(\dot M\) during the cold exposure did not differ between the groups [mean 63.6 (SEM 1.1) and mean 61.6 (SEM 1.1) W · m−2 in boys and men, respectively]. When theT a was lowered,T re in the boys started falling (P < 0.001), whereas theT re in the young men did not change for 60 min. TheT re during the 60-min exposure was significantly lower (P < 0.001) for the boys [mean 37.01 (SEM 0.13) and mean 37.48 (SEM 0.18)°C at the end of the exposure]. It was concluded that whenT a was lowered, the prepubertal boys appeared to vasoconstrict more in their limbs and to be somewhat more hypothermic, compared to the young men.
Article
This study was intended to assess the influence of drink flavor and composition on voluntary drinking and hydration status in children exercising intermittently at 35 +/- 1 degrees C and 45-50% relative humidity. Twelve boys (9-12 yr) performed three 3-h identical sessions (four 20-min cycling bouts at 50% maximal O2 uptake followed by 25-min rest). One of three beverages (chilled to 8-10 degrees C) was assigned to each session in a Latin-square sequence: unflavored water (W), grape-flavored water (FW), and grape-flavored water plus 6% carbohydrate and 18 mmol/l NaCl (CNa). Drinking was ad libitum. Body weight, heart rate, rectal and skin temperatures, and thirst and stomach fullness perceptions were monitored periodically. Total intake was 610, 882, and 1,157 g in W, FW, and CNa, respectively (CNa-W and CNa-FW; P < 0.05). Hypohydration was observed with W (-0.65% body wt) and FW (-0.32% body wt), but drinking CNa resulted in slight overhydration (+0.47% body wt, CNa-W, CNa-FW; P < 0.05). Other physiological and all perceptual variables were insignificantly different among trails. In conclusion, while flavoring of water reduces children's voluntary dehydration, further addition of 6% carbohydrates and 18 mmol/l NaCl prevents it altogether.
Article
Thermoregulatory studies often investigate thermal responses without considering the influences of clothing. These studies have expanded our understanding of basic human responses to various environmental conditions. However, human thermoregulation is variable and modified by heat transfer interactions between skin surface area, clothing and environment. Much of the original work on the influence of clothing on work performance was the result of ergonomic concerns. Currently, the importance of clothing and the influence of new clothing technology aimed at minimising thermal stress has spawned a new interest. For hot climates, new fabrics have been developed with improved wicking properties to keep the wearer cooler and drier, and to enhance heat transfer from the body while providing greater comfort. In contrast, the challenge of cold environments requires a different approach to clothing, which tries to minimise the free movement of air and water along the skin surface of the body. The materials used should also be able to absorb radiant heat from the environment and be nonconductive. In a cold climate, the wearer needs to balance the need for a clothing barrier for warmth with the potential for accumulating too much heat as the result of metabolic heat production from exercise. To counteract this potential problem, it is suggested that cold-weather clothing be worn in layers that can be removed during exercise and replaced during less active periods. Protective clothing for firefighters, hazardous waste workers and astronauts, and athletic protective gear, have specialised design requirements which may be influenced by considerations, for example, of environmental conditions, garment weight, the need for durability, impact forces.
Article
Thermoregulation during exposure to hot or cold environments differs between children and adults. Many physical and physiological changes occur during growth and maturation that can affect thermoregulation during rest as well as during exercise. Thus, physical as well as physiological differences between children and adults may explain the different response to thermal stress. The main physical difference between children and adults affecting thermoregulation is the much higher surface—area-to-mass ratio of children. In a warm environment this allows them to rely more on dry heat loss and less on evaporative cooling. However, in extreme conditions, hot or cold, the greater surface—areato- mass ratio results in a higher rate of heat absorption or heat loss, respectively. The lower body fat in girls compared with women provides lower insulation and presents a disadvantage in a cold environment. The smaller blood volume in children compared with adults, even relative to body size, may limit the potential for heat transfer during heat exposure and may compromise exercise performance in the heat. The main physiological difference between children and adults is in the sweating mechanism, affecting their thermoregulation in the heat, but not in the cold. The lower sweating rate characteristic of children is due to a lower sweating rate per gland and not to a lower number of sweat glands. In fact, children are characterised by a higher density of heat-activated sweat glands. The lower sweating rate per gland may be explained by the smaller sweat gland size, a lower sensitivity of the sweating mechanism to thermal stimuli and, possibly, a lower sweat gland metabolic capacity. Other physiological differences between children and adults that may affect thermoregulation include metabolic, circulatory and hormonal disparities. The higher metabolic cost of locomotion in children provides an added strain on the thermoregulatory system during exercise in the heat. On the other hand, during acute exposure to cold it may prove advantageous by increasing heat production. Circulatory differences, such as a lower cardiac output at any given exercise intensity and the lower haemoglobin concentration in boys compared with men, are likely to increase the cardiovascular strain during exercise in the heat, although their effects in a cold environment are unknown. Finally, testosterone and prolactin are 2 hormones that differ in baseline levels between children and adults and may affect sweat gland function and sweat composition. These possible effects need to be further investigated. The effectiveness of thermoregulation is reflected by the stability of core temperature. In a thermoneutral environment, children are characterised by a similar rectal temperature and a higher skin temperature when compared with adults. The latter may reflect the higher reliance on dry heat loss compared with evaporative cooling in children. In a hot environment, children’s body temperatures are higher compared with adults while walking and running but not necessarily while cycling. This may be related to the higher metabolic cost, and therefore higher heat production, in children while walking or running but not while cycling. In a cold environment, children are characterised by lower skin temperatures, reflecting greater vasoconstriction. Their metabolic heat is increased in the cold to a greater extent than that of adults, although this appears to be sufficient to maintain their body temperature during exercise but not during prolonged rest. Neither children nor adults sufficiently replace fluid loss during exercise in the heat. Nevertheless, recent studies suggest that in children, when the available beverage is flavoured and enriched with NaCl and carbohydrates, dehydration can be prevented. The hypohydration, which frequently accompanies exercise in the heat, and the resultant added cardiovascular strain, may be more detrimental in children than in adults, because children rely more on dry heat loss, and therefore on elevated skin blood flow, to dissipate body heat. Based on a few studies, it appears that acclimation to heat is similar in children and adults. The main difference is the slower rate of heat acclimation in children. No studies are available on cold acclimatisation or acclimation in children or adolescents. Physical training results in enhanced thermoregulation during heat stress in children as in adults. Limited data suggest that training may improve thermoregulation during cold exposure in children. However, the effects of training on the thermoregulatory response to cold stress in children and adolescents need to be studied further.
Article
Most research on human thermoregulation has focused on young adult males. Much less information is available regarding females, children and the elderly. The following is a brief review of factors that have impeded research in this field, as well as of the main age- and gender-related differences in sweating responses to the combined stresses of exercise and ambient heat. For more comprehensive reviews, see Drinkwater and Horvath (1975), Kenney (1985; 1995) and Bar-Or (1989; 1996).
Article
Participation in organized sports provides an opportunity for young people to increase their physical activity and develop physical and social skills. However, when the demands and expectations of organized sports exceed the maturation and readiness of the participant, the positive aspects of participation can be negated. The nature of parental or adult involvement can also influence the degree to which participation in organized sports is a positive experience for preadolescents. This updates a previous policy statement on athletics for preadolescents and incorporates guidelines for sports participation for preschool children. Recommendations are offered on how pediatricians can help determine a child's readiness to participate, how risks can be minimized, and how child-oriented goals can be maximized.
Article
We investigated whether temperature regulation is improved during exercise in moderate heat by the use of clothing constructed from fabric that was purported to promote sweat evaporation compared with traditional fabrics. Eight well-trained, euhydrated males performed three exercise bouts wearing garments made from an evaporative polyester fabric (SYN), wearing garments made from traditional cotton fabric (COT), or dressed seminude (S-N) in random order. Bouts consisted of 15 min seated rest, 30 min running at 70% .VO(2max), 15 min walking at 40% .VO(2max), and 15 min seated rest, all at 30 +/- 1 degrees C and 35 +/- 5% relative humidity. COT and SYN clothing ensembles consisted of crew neck, short sleeve T-shirts, cycling shorts, and anklet socks made from their respective materials, and running shoes. The S-N condition consisted of a Lycra swim suit, polyester socks, and running shoes. Mean skin temperature was lower for S-N during preexercise rest when compared with SYN and COT. No differences in mean body temperature, rectal temperature, or mean skin temperature were observed during or after exercise. No differences in VO2 or heart rate were observed. No differences in comfort sensations were observed. In summary, before, during, or after exercise in a moderately warm environmental condition, neither the addition of a modest amount of clothing nor the fabric characteristics of this clothing alters physiological, thermoregulatory, or comfort sensation responses.
Article
During endurance exercise, about 75% of the energy produced from metabolism is in the form of heat, which cannot accumulate. The remaining 25% of energy available can be used for movement. As running pace increases, the rate of heat production increases. Also, the larger one's body mass, the greater the heat production at a particular pace. Sweat evaporation provides the primary cooling mechanism for the body, and for this reason athletes are encouraged to drink fluids to ensure continued fluid availability for evaporation and circulatory flow to the tissues. Elite level runners could be in danger of heat illness if they race too quickly in hot/humid conditions and may collapse at the end of their event. Most marathon races are scheduled at cooler times of the year or day, however, so that heat loss to the environment is adequate. Typically, this postrace collapse is due simply to postural hypotension from decreased skeletal muscle massage of the venous return circulation to the heart on stopping. Elite athletes manage adequate hydration by ingesting about 200-800 mL/hour, and such collapse is rare. Athletes "back in the pack" are moving at a much slower pace, however, with heat accumulation unlikely and drinking much easier to manage. They are often urged to drink "as much as tolerable," ostensibly to prevent dehydration from their hours out on the race course. Excessive drinking among these participants can lead to hyponatremia severe enough to cause fatalities. A more reasonable approach is to urge these participants not to drink as much as possible but to drink ad libitum (according to the dictates of thirst) no more than 400-800 mL/hour.
Article
Exercise increases heat production. During exercise in both warm and cold conditions, the major dilemma is the dissipation of the heat produced from muscular activity. The use of clothing generally represents a layer of insulation and as such imposes a barrier to heat transfer and evaporation from the skin surface. In warm environments, additional clothing increases thermal insulation causing more rapid increases in temperature during exercise and imposes a barrier to sweat evaporation. However, clothing can serve a protective function by reducing radiant heat gain and thermal stress. Recent research suggests that neither the inclusion of modest amounts of clothing nor the clothing fabric alter thermoregulation or thermal comfort during exercise in warm conditions. In the cold, most reports do not support an effect of clothing fabric on thermoregulation; however, there are reports demonstrating an effect. Clothing construction does alter thermoregulation during and following exercise in the cold, where fishnet construction offers greater heat dissipation. Future research should include conditions that more closely mimic outdoor conditions, where high work rates, large airflow and high relative humidity can significantly impact thermoregulation.
Article
This paper addresses the ways in which heat loss effector functions change with maturation and aging, using data obtained in our laboratory. Prepubertal children have an underdeveloped sweat function compared with young adults; this is compensated by a greater surface area-to-mass ratio and relatively greater heat loss from cutaneous vasodilation on the head and trunk when the air temperature is lower than the skin temperature. As the heat dissipation depends greatly on the evaporation of sweat, the core temperature of prepubertal children is greater than that of young adults owing to the underdevelopment of sweating. In the elderly the heat loss effector function decreases with aging. The decrease may first involve cutaneous vasodilation, then sweat output per gland, and finally active sweat gland density; and it may proceed from the lower limbs to the back of the upper body, the front of the upper body, then the upper limbs and finally to the head.