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Abstract

To describe the drinking behaviors of elite male marathon runners during major city marathons. Retrospective analysis of drinking behaviors. Institutional. Ten (9 winners and 1 second position) male marathon runners during 13 major city marathons. Total drinking durations and fluid intake rates during major city marathons. The ambient conditions during the 13 studied marathon races were 15.3°C ± 8.6°C and 59% ± 17% relative humidity; average marathon competition time was 02:06:31 ± 00:01:08 (hours:minutes:seconds). Total drinking duration during these races was 25.5 ± 15.0 seconds (range, 1.6-50.7 seconds) equating to an extrapolated fluid intake rate of 0.55 ± 0.34 L/h (range, 0.03-1.09 L/h). No significant correlations were found between total drink duration, fluid intake (rate and total), running speed, and ambient temperature. Estimated body mass (BM) loss based on calculated sweat rates and rates of fluid ingestion was 8.8% ± 2.1% (range, 6.6%-11.7%). Measurements of the winner in the 2009 Dubai marathon revealed a BM loss of 9.8%. The most successful runners, during major city marathons, drink fluids ad libitum for less than approximately 60 seconds at an extrapolated fluid ingestion rate of 0.55 ± 0.34 L/h and comparable to the current American College of Sports Medicine's recommendations of 0.4-0.8 L/h. Nevertheless, these elite runners do not seem to maintain their BM within current recommended ranges of 2%-3%.

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... The very same mechanisms which effectively dissipate heat under the equatorial midday sun have made our taxon prone to dehydration. In hot environments, humans sweat at rates between 1.0 and 1.7 kg h À1 during walking (Adolph and Dill, 1938) and up to 3.2 kg h À1 during running (Beis et al., 2012) which is exceptionally high in comparison to our poor ability to preload with water and our low dehydration tolerance. Humans can ingest about one liter of water before reaching the limits of stomach capacity. ...
... Consequently, humans in deserts regularly lose water equivalent to 3e5% of body mass between meals (Schmidt-Nielsen, 1964). Water losses of up to 10% body mass were reported for 2-h runs at aerobic velocities even under moderate climate in marathon winners (Beis et al., 2012). The 10% body mass loss seems to be at the upper limit of dehydration a highly motivated hunter would willingly undergo, since at only 12% body mass loss humans lose the ability to swallow and rehydration is then possible only with assistance (Schmidt-Nielsen, 1964). ...
... The longest reported successful persistence kudu hunt by modern hunters took 5 h (Liebenberg, 2006) at which time H. erectus would lose about 9.0% of body mass. Such a degree of dehydration is not life-threatening for humans and other primates (Adolph, 1947;Schmidt-Nielsen, 1964;Zurovsky et al., 1984;Beis et al., 2012). Thus, the persistence hunting of prey of similar or lower endurance to modern-day kudu by H. erectus in Kalahari-like savanna conditions would not be limited by a lack of water containers. ...
Article
Persistence hunting has been suggested to be a key strategy for meat acquisition in Homo erectus. However, prolonged locomotion in hot conditions is associated with considerable water losses due to sweating. Consequently, dehydration has been proposed to be a critical limiting factor, effectively curtailing the usefulness of persistence hunting prior to the invention of water containers. In this study, we aimed to determine the extent to which dehydration limited persistence hunting in H. erectus. We simulated ambient conditions and spatiotemporal characteristics of nine previously reported persistence hunts in the Kalahari. We used a newly developed and validated heat exchange model to estimate the water loss in H. erectus and a recent Kalahari hunter. Water loss equivalent to 10% of the hunter's body mass was considered the physiological limit of a hunt with no drinking. Our criterion for ruling dehydration out of being a limit for persistence hunting was the ability to hunt without drinking for at least 5 h, as this was the longest duration reported for a successful persistence hunt of large prey. Our results showed that H. erectus would reach the dehydration limit in 5.5–5.7 h of persistence hunting at the reported Kalahari conditions, which we argue represent a conservative model also for Early Pleistocene East Africa. Maximum hunt duration without drinking was negatively related to the relative body surface area of the hunter. Moreover, H. erectus would be able to persistence hunt over 5 h without drinking despite possible deviations from modern-like heat dissipation capacity, aerobic capacity, and locomotor economy. We conclude that H. erectus could persistence hunt large prey without the need to carry water.
... Despite previous work demonstrating negative physical effects of even modest dehydration, some work has reported high levels of body water loss among elite athletes during competition (Beis, Wright-Whyte, Fudge, Noakes, & Pitsiladis, 2012;Goulet, 2012). Beis et al. (2012) found an average body mass loss of 8.8% ± 2.1%, ranging between 6.6% and 11.7%, among 10 marathon runners across 13 marathons. ...
... Despite previous work demonstrating negative physical effects of even modest dehydration, some work has reported high levels of body water loss among elite athletes during competition (Beis, Wright-Whyte, Fudge, Noakes, & Pitsiladis, 2012;Goulet, 2012). Beis et al. (2012) found an average body mass loss of 8.8% ± 2.1%, ranging between 6.6% and 11.7%, among 10 marathon runners across 13 marathons. Faster runners often had more severe dehydration; the winner of the 2009 Dubai marathon lost 9.8% of his body mass (Beis et al., 2012). ...
... Beis et al. (2012) found an average body mass loss of 8.8% ± 2.1%, ranging between 6.6% and 11.7%, among 10 marathon runners across 13 marathons. Faster runners often had more severe dehydration; the winner of the 2009 Dubai marathon lost 9.8% of his body mass (Beis et al., 2012). These findings run counter to those of Cheuvront and others (eg, Cheuvront & Montain, 2017;Cheuvront, Montain, & Sawka, 2007;King, Cooke, Carroll, & O'Hara, 2008;Maughan, Shirreffs, & Leiper, 2007), who have pointed out that changes in body mass during competition reflect fuel oxidation as well as water loss. ...
Article
Objectives: To discuss the environmental and lifestyle determinants of water balance in humans and identify the gaps in current research regarding water use across populations. Methods: We investigated intraspecific variation in water turnover by comparing data derived from a large number of human populations measured using either dietary survey or isotope tracking. We also used published data from a broad sample of mammalian species to identify the interspecific relationship between body mass and water turnover. Results: Water facilitates nearly all physiological tasks and water turnover is strongly related to body size among mammals (r2=0.90). Within humans, however, the effect of body size is small. Instead, water intake and turnover vary with lifestyle and environmental conditions. Notably, despite living physically active lives in conditions that should increase water demands, the available measures of water intake and turnover among small-scale farming and pastoralist communities are broadly similar to those in less active, industrialized populations. Conclusions: More work is required to better understand the environmental, behavioral, and cultural determinants of water turnover in humans living across a variety of ecosystems and lifestyles. The results of such work are made more vital by the climate crisis, which threatens the water security of millions around the globe.
... As such, drinking to the dictates of thirst is considered the optimal fluid ingestion strategy (Noakes, 2010), and therefore, efforts by researchers to control weight loss (dehydration) may exacerbate performance in the laboratory, and perhaps artificially enhance interventions which affect thirst. Unlike cyclists however, elite runners do not carry fluid during races and aid stations are commonly 5 km apart in elite marathon races (Beis, Wright-Whyte, Fudge, Noakes, & Pitsiladis, 2012). Poor access to fluid combined with the high intensity demands of marathon running may limit fluid ingestion duration to an average of only 25 sec across an entire marathon (Beis et al., 2012). ...
... Unlike cyclists however, elite runners do not carry fluid during races and aid stations are commonly 5 km apart in elite marathon races (Beis, Wright-Whyte, Fudge, Noakes, & Pitsiladis, 2012). Poor access to fluid combined with the high intensity demands of marathon running may limit fluid ingestion duration to an average of only 25 sec across an entire marathon (Beis et al., 2012). Therefore, running performance inherently contains a component of fluid restriction, which should be simulated in the laboratory for best ecological validity. ...
Article
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Sports performance testing is one of the most common and important measures used in sport science. Performance testing protocols must have high reliability to ensure any changes are not due to measurement error or inter-individual differences. High validity is also important to ensure test performance reflects true performance. Time-trial protocols commonly have a coefficient of variation (CV) of <5%, however, familiarization, well-trained subjects and/or conducting the trial outdoors in the athlete’s most familiar environment can lead to CVs of < 1%. Long duration time-trials or the inclusion of sprints within a time-trial appears to not negatively influence reliability. Few studies have assessed the validity of endurance performance tests, and as such more research should evaluate different ways of simulating outdoor performances in the laboratory. The use of warm-up, simulation of convection load, and implementation of race specific hydration practices are important considerations for researchers regarding test validity.
... Racing in the winter and/or at night when ambient temperatures are cooler is likely optimal for body temperature regulation. Based on video recordings of hydration behavior during several major city marathons, Beis et al. [56] estimated that elite marathon runners lose *8.8% body weight due to dehydration. In addition, actual weight measurements showed that former world record-holder Haile Gebrselassie lost 9.8% body weight during the 2009 Dubai marathon, when he ran 2:05:29 [56]. ...
... Based on video recordings of hydration behavior during several major city marathons, Beis et al. [56] estimated that elite marathon runners lose *8.8% body weight due to dehydration. In addition, actual weight measurements showed that former world record-holder Haile Gebrselassie lost 9.8% body weight during the 2009 Dubai marathon, when he ran 2:05:29 [56]. Together, these observations indicate that it might be better to limit dehydration during the race rather than further reducing body weight through intentional dehydration. ...
Article
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A sub-2-hour marathon requires an average velocity (5.86 m/s) that is 2.5% faster than the current world record of 02:02:57 (5.72 m/s) and could be accomplished with a 2.7% reduction in the metabolic cost of running. Although supporting body weight comprises the majority of the metabolic cost of running, targeting the costs of forward propulsion and leg swing are the most promising strategies for reducing the metabolic cost of running and thus improving marathon running performance. Here, we calculate how much time could be saved by taking advantage of unconventional drafting strategies, a consistent tailwind, a downhill course, and specific running shoe design features while staying within the current International Association of Athletic Federations regulations for record purposes. Specifically, running in shoes that are 100 g lighter along with second-half scenarios of four runners alternately leading and drafting, or a tailwind of 6.0 m/s, combined with a 42-m elevation drop could result in a time well below the 2-hour marathon barrier.
... Ad libitum or drink to thirst studies involving endurance running [50] and half marathon [24] and marathon [51] events have reported greater cardiovascular and thermoregulatory strain [24] but no differences in plasma volume or osmolality [49], and no differences in running performance [24,50,51]. Ad libitum cycling studies have reported that cardiovascular responses [52], thermoregulation [52,53], and performance [52,53] are not different from programmed drinking. ...
... Ad libitum or drink to thirst studies involving endurance running [50] and half marathon [24] and marathon [51] events have reported greater cardiovascular and thermoregulatory strain [24] but no differences in plasma volume or osmolality [49], and no differences in running performance [24,50,51]. Ad libitum cycling studies have reported that cardiovascular responses [52], thermoregulation [52,53], and performance [52,53] are not different from programmed drinking. ...
Article
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In humans, thirst tends to be alleviated before complete rehydration is achieved. When sweating rates are high and ad libitum fluid consumption is not sufficient to replace sweat losses, a cumulative loss in body water results. Body mass losses of 2% or greater take time to accumulate. Dehydration of ≥ 2% body mass is associated with impaired thermoregulatory function, elevated cardiovascular strain and, in many conditions (e.g., warmer, longer, more intense), impaired aerobic exercise performance. Circumstances where planned drinking is optimal include longer duration activities of > 90 min, particularly in the heat; higher-intensity exercise with high sweat rates; exercise where performance is a concern; and when carbohydrate intake of 1 g/min is desired. Individuals with high sweat rates and/or those concerned with exercise performance should determine sweat rates under conditions (exercise intensity, pace) and environments similar to that anticipated when competing and tailor drinking to prevent body mass losses > 2%. Circumstances where drinking to thirst may be sufficient include short duration exercise of < 1 h to 90 min; exercise in cooler conditions; and lower-intensity exercise. It is recommended to never drink so much that weight is gained.
... Blinded studies that bypassed conscious awareness of hydration status or thirst sensation during exercise demonstrated that dehydration [ 2% BW does not affect exercise performance [9,10]. In fact, a positive relationship has been observed between relative BW loss and performance in endurance events such as marathons and ultra-marathons [11][12][13], with elite marathoners frequently experiencing BW losses [ 8% [14]. Furthermore, it is even possible that some degree of BW loss (in the absence of thirst) may actually represent a biomechanical advantage during running, and thus an advantage in terms of running economy [14]. ...
... In fact, a positive relationship has been observed between relative BW loss and performance in endurance events such as marathons and ultra-marathons [11][12][13], with elite marathoners frequently experiencing BW losses [ 8% [14]. Furthermore, it is even possible that some degree of BW loss (in the absence of thirst) may actually represent a biomechanical advantage during running, and thus an advantage in terms of running economy [14]. Indeed, decreases in BW elicit almost proportional decreases in the metabolic cost of running [15], which suggests that those who finish the race with a lower BW could have benefited from an improving exercise economy as the race proceeded. ...
... 11,12 For instance, the 2009 Dubai marathon winner experienced a body mass loss of 9.8%. 13 Apart from this runner, the body mass loss of elite marathoners in that study was determined retrospectively from the estimated sweat rates under simulated running conditions and estimated fluid intake from video footages, which may not accurately reflect the actual dehydration level. Some studies 14,15,16 have quantified dehydration from pre-to post-marathon body mass change but most data were collected from sub-elite or recreational runners. ...
... The high % body mass loss corroborates those previously recorded in elite marathoners (∼5−8%) from other studies 11,12,21 but this is noticeably higher than those elite runners competing in cool conditions (∼3%; 13.7-16 • C). 18 It has also been shown that despite the elite runners ingesting fluids at a rate comparable to or above recommended levels, it was not sufficient to avoid significant body mass loss. 11,13 Possible factors that discourage elite runners to rehydrate regularly during a marathon are gastrointestinal discomfort, 22 a heavier body load due to hydration, or a disruption to running pace. Furthermore, it has been shown that the ingestion of fluids at a rate beyond that of ad libitum intake did not improve 2 h running performance in a 25 • C environment. ...
Conference Paper
INTRODUCTION: Prolonged exercise under a hot and humid environment leads to rapid body fluid loss due to profuse sweating. This is especially important to marathon races conducted in the tropics where the rate of sweat loss will be the fastest. The amount of dehydration accrued in elite marathon runners has yet to be directly measured in the real-world setting. Hence, we recorded the body mass changes in local runners and international elite runners after a marathon organized in a tropical country (Standard Chartered Singapore Marathon; SCSM). METHODS: A total of 32 runners’ body mass data was collected in SCSM 2017. Immediately before and after the marathon, the participants weighed themselves in their race attire. Body mass was measured to the nearest 0.01kg with an electronic balance scale (Mettler-Toledo GmBH, Giessen, Germany) placed on a flat surface. To account for the sweat retained in the clothing after the run, a set of running attire was soaked in water and weighed. The measured mass was subtracted from the post-run body mass. Any water intake by the runners after the end of marathon was estimated as accurate as possible and was included in the calculation for body mass changes. The ambient temperature and humidity were measured by a heat stress monitor before and after the marathon. RESULTS: Valid race and body mass data was obtained from 20 runners - eight local runners (Singaporeans; SG) and 12 international elite runners (11 Kenyans and 1 Kazakhstan; INT). The runners were mixed gender (SG: 3 males, 5 females, INT: 6 males, 6 females) and their age ranged from 24 - 41 yrs old. Mean dry bulb temperature and humidity were 27.9°C and 78%. Median race timings for all runners was 160.7 mins. INT runners performed better than SG runners (155.9 mins vs 197.8 mins). Mean body mass loss and % mass loss for all runners were 2.6 kg and 4.8%. The mean body mass loss and % mass loss in SG runners were lower than the INT runners (2.0 kg vs 2.9 kg; 3.8% vs 5.5%). CONCLUSION: While it is uncertain if the INT runners could have performed better if they opted for a more aggressive hydration plan, our data nonetheless showed that elite INT runners opted to hydrate less during a self-paced marathon as compared to SG runners.
... The reason for the increase in oxygen uptake and reduction in running economy is unknown. A number of mechanisms have been postulated in the literature but most of them are speculative [12,[18][19][20], including an increase in oxygen uptake due to neuromuscular fatigue [21]. Without discussing here the various attempts that have been made for explaining this observation, we just conclude that every activated physiological system increases its own particular energy consumption with the duration of exercise. ...
... Characteristic paces are often defined by the pace that a runner can race (at current training status) for a prescribed duration or distance. When the physiological model parameters of a runner are known from sufficiently many recent race performances, the running velocities for a prescribed intensity and duration, or intensity and distance can be computed from Eqs (17) and (18), respectively. In the following we consider race paces for a given duration or distance, corresponding top ¼ 1 in these equations. ...
Article
Full-text available
Models for human running performances of various complexities and underlying principles have been proposed, often combining data from world record performances and bio-energetic facts of human physiology. The purpose of this work is to develop a novel, minimal and universal model for human running performance that employs a relative metabolic power scale. The main component is a self-consistency relation for the time dependent maximal power output. The analytic approach presented here is the first to derive the observed logarithmic scaling between world (and other) record running speeds and times from basic principles of metabolic power supply. Our hypothesis is that various female and male record performances (world, national) and also personal best performances of individual runners for distances from 800m to the marathon are excellently described by this model. Indeed, we confirm this hypothesis with mean errors of (often much) less than 1%. The model defines endurance in a way that demonstrates symmetry between long and short racing events that are separated by a characteristic time scale comparable to the time over which a runner can sustain maximal oxygen uptake. As an application of our model, we derive personalized characteristic race speeds for different durations and distances.
... High-performance runners are less able to consume fluid/CHO during the race than racewalkers because of the higher speed of movement and the lower number/increased time between drink stations; for example, ∼15-18 min for marathon runners with stations every 5 km versus 8-10 min for racewalkers with stations every 2 km. Furthermore, the impracticality of drinking large volumes despite high sweat rates explains BM losses of up to 10% in race winners in hot-weather marathons (e.g., Beis et al., 2012). We recommend that athletes develop a personalized and practiced race plan that optimizes fluid and CHO status within the prevailing conditions and opportunities of each event. ...
... Indeed, many concepts of periodizing CHO availability according to the needs of the session (Burke et al., 2018c) appear within these traditional practices. Although supplements are rarely used, data from observational studies (Beis et al., 2012) and accounts of recent attempts on world marathon records by male runners (Caesar, 2017;Hutchinson, 2013) note personalized race nutrition plans including proactive intakes of fluid and CHO, often with the involvement of Western sports scientists. ...
Article
Distance events in Athletics include cross country, 10,000-m track race, half-marathon and marathon road races, and 20- and 50-km race walking events over different terrain and environmental conditions. Race times for elite performers span ∼26 min to >4 hr, with key factors for success being a high aerobic power, the ability to exercise at a large fraction of this power, and high running/walking economy. Nutrition-related contributors include body mass and anthropometry, capacity to use fuels, particularly carbohydrate (CHO) to produce adenosine triphosphate economically over the duration of the event, and maintenance of reasonable hydration status in the face of sweat losses induced by exercise intensity and the environment. Race nutrition strategies include CHO-rich eating in the hours per days prior to the event to store glycogen in amounts sufficient for event fuel needs, and in some cases, in-race consumption of CHO and fluid to offset event losses. Beneficial CHO intakes range from small amounts, including mouth rinsing, in the case of shorter events to high rates of intake (75-90 g/hr) in the longest races. A personalized and practiced race nutrition plan should balance the benefits of fluid and CHO consumed within practical opportunities, against the time, cost, and risk of gut discomfort. In hot environments, prerace hyperhydration or cooling strategies may provide a small but useful offset to the accrued thermal challenge and fluid deficit. Sports foods (drinks, gels, etc.) may assist in meeting training/race nutrition plans, with caffeine, and, perhaps nitrate being used as evidence-based performance supplements.
... Numerous studies have reported a similar observation of gastrointestinal discomfort among runners during prolonged distance races (Peters et al. 2000;Sharwood et al. 2004;Dion et al. 2013). Indeed, survey data showed that 30-50% of endurance athletes experienced some level of gastrointestinal issues during prolonged exercise (Beis et al. 2012). ...
... However, our data revealed that CHO mouth rinsing was an effective ergogenic aid whilst subjects began exercise dehydrated (2% of body mass loss) and continued exercising to exhaustion in endurance-trained athletes. It should be taken into consideration that the exercise improvement in this study was significant up to dehydration of ~ 4.5% body mass loss and among well-trained runners that have a high tolerance to dehydration (Beis et al. 2012). The enhanced exercise performance with CHO mouth rinsing may be associated with the increased perceived arousal level without any variation in metabolic and cardiovascular processes. ...
Article
Full-text available
Purpose To examine the effect of carbohydrate (CHO) mouth rinsing on endurance running responses and performance in dehydrated individuals. Methods In a double blind, randomised crossover design, 12 well-trained male runners completed 4 running time to exhaustion (TTE) trials at a speed equivalent to 70% of VO2peak in a thermoneutral condition. Throughout each run, participants mouth rinsed and expectorated every 15 min either 25 mL of 6% CHO or a placebo (PLA) solution for 10 s. The four TTEs consisted of two trials in the euhydrated (EU-CHO and EU-PLA) and two trials in the dehydrated (DY-CHO and DY-PLA) state. Prior to each TTE run, participants were dehydrated via exercise and allowed a passive rest period during which they were fed and either rehydrated equivalent to their body mass deficit (i.e., EU trials) or ingested only 50 mL of water (DY trials). Results CHO mouth rinsing significantly improved TTE performance in the DY compared to the EU trials (78.2 ± 4.3 vs. 76.9 ± 3.8 min, P = 0.02). The arousal level of the runners was significantly higher in the DY compared to the EU trials (P = 0.02). There was no significant difference among trials in heart rate, plasma glucose and lactate, and psychological measures. Conclusions CHO mouth rinsing enhanced running performance significantly more when participants were dehydrated vs. euhydrated due to the greater sensitivity of oral receptors related to thirst and central mediated activation. These results show that level of dehydration alters the effect of brain perception with presence of CHO.
... This was nicely demonstrated by Dion et al. [91], who reported, in a controlled laboratory experiment with ad libitum drinking, that faster racing lead to a greater sweat rate and hypohydration at the end of a half marathon, but did not alter drink ingestion. However, the finding that endurance athletes can finish [80][81][82][83][84] and even win races in world-class times [92] with as much as 10% body mass loss is intriguing. Because of issues related to fluid availability (e.g. ...
... Therefore, this study suggests that repeated familiarisation (on five occasions) with a hypohydration stimulus can attenuate, but not abolish, the negative performance effects of hypohydration, at least for running. This might go some way to explaining why well-trained endurance athletes (who will likely have years of exposure to hypohydration) might be able to finish and seemingly perform well in competitive events, despite sometimes substantial hypohydration at the end of the race [84][85][86][87][88]92]. Clearly, further research is needed, but where maintenance of euhydration is not possible and athlete health and safety permits, perhaps strategic familiarisation with the anticipated hypohydration (method and magnitude) might be a prudent ergogenic strategy [95]. ...
Article
Full-text available
The impact of alterations in hydration status on human physiology and performance responses during exercise is one of the oldest research topics in sport and exercise nutrition. This body of work has mainly focussed on the impact of reduced body water stores (i.e. hypohydration) on these outcomes, on the whole demonstrating that hypohydration impairs endurance performance, likely via detrimental effects on a number of physiological functions. However, an important consideration, that has received little attention, is the methods that have traditionally been used to investigate how hypohydration affects exercise outcomes, as those used may confound the results of many studies. There are two main methodological limitations in much of the published literature that perhaps make the results of studies investigating performance outcomes difficult to interpret. First, subjects involved in studies are generally not blinded to the intervention taking place (i.e. they know what their hydration status is), which may introduce expectancy effects. Second, most of the methods used to induce hypohydration are both uncomfortable and unfamiliar to the subjects, meaning that alterations in performance may be caused by this discomfort, rather than hypohydration per se. This review discusses these methodological considerations and provides an overview of the small body of recent work that has attempted to correct some of these methodological issues. On balance, these recent blinded hydration studies suggest hypohydration equivalent to 2-3% body mass decreases endurance cycling performance in the heat, at least when no/little fluid is ingested.
... Research has not found a definite connection between higher humidity and consistently greater fluid intakes during exercise [33], but student-athletes in the current study consumed significantly more fluid during exercise indoors. The triathletes were experiencing the highest humidity due to the fact that their indoor training was completed in a small, poorly-ventilated room whereas the others exercised in a large pressurized inflatable dome. ...
... Earlier studies of fluid intakes for marathon runners in varying levels of ambient temperature and humidity in different areas of the world showed mixed results. While some runners had increased fluid intakes with higher levels of relative humidity, others had decreased fluid intakes in similar temperatures and humidity [33]. Fluid intake has also been linked to the length and amount of formal opportunities to drink for team sports [32]. ...
Article
Full-text available
The purpose was to determine differences in acute and chronic hydration status in female student-athletes (n = 40) practicing in moderate, dry conditions (17–25 °C, 30–57% humidity) indoors and outdoors. Body weight and urine samples were recorded before and after exercise as well as fluid intake. Sweat rates expressed as median and interquartile range did not differ, but fluid intake was significantly higher during indoor (0.64 [0.50, 0.83] L/h) vs. outdoor conditions (0.51 [0.43, 0.63] L/h), p = 0.001. Fluid intake compensated for indoor sweat rate but not outdoors. When exercising indoors, 49% of the student-athletes reported urine specific gravity (USG) values >1.020, and 24% of the day after morning samples were scored ≥4 on the color chart rating. The percentages increased to 58% and 31%, respectively, when exercising outdoors (p > 0.05). Thus, fluid intake was higher indoors vs. outdoors but sweat rate did not differ among athletes. Yet, chronic hydration status was impaired in more than 50% of the student-athletes with a discrepancy between USG scores and urine color scores identifying underhydration. This suggest that 24-h fluid intake should be taken into account and that hydration protocols may need to be tailored individually based on urine USG values. Practice location (indoors vs. outdoors) may further complicate hydration protocols.
... Subjects from an initial group of 64 participants, we selected 22 healthy and experienced amateur male runners (11 marathoners and 11 half-marathoners) based on their similarities in age and body characteristics. Their main morphological characteristics and training status While there is widespread scientific information about the physiological challenges imposed on elite endurance runners during endurance running competitions, [4][5][6][7] the physiological stress imposed by endurance running races is not completely understood in the amateur population. ...
... 14 endurance runners are particularly vulnerable to dehydration because of the difficulty of drinking whilst running and the likelihood of adverse environmental conditions present during outdoor events. although the deleterious effects of a body mass deficit >2% on endurance performance have been well established in laboratory studies, 15 athletes voluntarily dehydrate during running 6,9,16 likely due to the less evident effect of body water deficit in real endurance competitions. 17 one might assume that dehydration arises along running distance in endurance competitions and thus, body mass deficit >2% would be more frequent in marathoners than half-marathoners. ...
Article
Background: While there is widespread scientific information about the physiological challenges imposed on elite endurance runners during competitions, the information regarding the amateur population is scarce. The aim of this study was to compare the physical and physiological load imposed by competing in a real half-marathon vs a marathon race. Methods: From a larger group of participants, we selected 22 experienced runners who were matched in pairs (11 marathoners and 11 half-marathoners) for age and anthropometric data. Participants completed their respective distances on the same day and circuit while race time was measured by means of chip timing. Sweat samples were obtained during the race using sweat patches. Before and after the race, a sample of venous blood was obtained and jump height was measured during a countermovement jump. Participants also rated their perception of leg muscle pain at the end of the race. Results: Running pace was similar for half-marathoners vs marathoners (3.3±0.4 vs 3.1±0.4 m·s-1; P=0.36). At the end of the race, jump height reduction (-11±12% vs - 25±19%; P=0.03), serum myoglobin concentration (186.1±93.6 vs 564.1±370.7 μg·mL- 1; P<0.01) and self-reported muscle pain (3.0 ±2.3 vs 5.5 ±1.0 A.U.; P<0.01) were lower in half-marathoners vs marathoners. Sweat rate (~1.0±0.3 L·h-1; P=0.79) and sweat sodium concentration (47.8±29.4 and 39.3±24.1 mmol·L-1; P=0.47) were similar for both groups but body mass reduction (-1.9±0.8% vs -3.3±0.8%; P<0.01) and electrolyte imbalance were higher in marathoners. Conclusions: Completing a marathon induces higher muscle fatigue, greater muscle fiber damage and perceived muscle pain levels and higher body water and electrolyte deficits than finishing a half-marathon with a similar running speed. This information could be valuable to improve physical training for endurance running disciplines.
... 11,12 For instance, the 2009 Dubai marathon winner experienced a body mass loss of 9.8%. 13 Apart from this runner, the body mass loss of elite marathoners in that study was determined retrospectively from the estimated sweat rates under simulated running conditions and estimated fluid intake from video footages, which may not accurately reflect the actual dehydration level. Some studies 14,15,16 have quantified dehydration from pre-to post-marathon body mass change but most data were collected from sub-elite or recreational runners. ...
... The high % body mass loss corroborates those previously recorded in elite marathoners (∼5−8%) from other studies 11,12,21 but this is noticeably higher than those elite runners competing in cool conditions (∼3%; 13.7-16 • C). 18 It has also been shown that despite the elite runners ingesting fluids at a rate comparable to or above recommended levels, it was not sufficient to avoid significant body mass loss. 11,13 Possible factors that discourage elite runners to rehydrate regularly during a marathon are gastrointestinal discomfort, 22 a heavier body load due to hydration, or a disruption to running pace. Furthermore, it has been shown that the ingestion of fluids at a rate beyond that of ad libitum intake did not improve 2 h running performance in a 25 • C environment. ...
Article
Objectives The ACSM recommends drinking to avoid loss of body mass >2% during exercise to avert compromised performance. Our study aimed to assess the level of dehydration in elite runners following a city marathon in a tropical environment. Design Prospective cohort design. Methods Twelve elite runners (6 males, 6 females; age 24–41 y) had body mass measured to the nearest 0.01 kg in their race attire immediately before and after the 2017 Standard Chartered Singapore Marathon 2017. Body mass change was corrected for respiratory water loss, gas exchange, and sweat retained in clothing, and expressed as % of pre-race mass (i.e. % dehydration). Results Data are expressed as means ± SD (range). Dry bulb temperature and humidity were 27.9 ± 0.1 °C (27.4–28.3 °C) and 79 ± 2% (73–82%). Finish time was 155 ± 10 min (143−172 min). Male runners finishing positions ranged from 2–12 out of 7627 finishers, whilst female runners placed 1–8 out of 1754 finishers. Body mass change (loss) and % dehydration for all runners were 2.5 ± 0.5 kg (1.8–3.5 kg) and 4.6 ± 0.9% (3.6–6.8%). Male runners experienced body mass loss of 2.8 ± 0.5 kg and 4.9 ± 1.2% while females experienced body mass loss of 2.1 ± 0.2 kg and 4.3 ± 0.6%. Conclusions Despite experiencing dehydration (4.6% body mass loss) two-fold higher than current fluid replacement guidelines recommend (≤2%), elite male and female runners performed successfully and without medical complication in a hot weather marathon.
... L.h −1 in a range of environmental temperatures between 0°C and 30°C. 9 Hydration and nutrition recommendations prescribe sodium and carbohydrate ingestion, alongside/with appropriate fluid intake during prolonged endurance exercise in the heat. 2 18 19 The present data suggest these recommendations are well translated ...
... body mass loss previously estimated for elite marathoners. 9 Some surprising individual data were seen in the 20KRW where an athlete gained +2.5% of her body mass during the race due to excessive fluid intake, a strategy not conducive to performance gains and not recommended due to the risks for hyponatraemia. 2 The body mass loss may however have been underestimated due to sweat (or water dousing) being trapped in clothing, despite athletes towel drying and wearing minimal clothing (online supplemental appendix 1). Body mass loss has been previously shown to be inversely related to performance during mass participation marathons, with the best runners losing more weight than the slower runners. ...
Article
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Purpose To characterise hydration, cooling, body mass loss, and core (T core ) and skin (T sk ) temperatures during World Athletics Championships in hot-humid conditions. Methods Marathon and race-walk (20 km and 50 km) athletes (n=83, 36 women) completed a pre-race questionnaire. Pre-race and post-race body weight (n=74), T core (n=56) and T sk (n=49; thermography) were measured. Results Most athletes (93%) had a pre-planned drinking strategy (electrolytes (83%), carbohydrates (81%)) while ice slurry was less common (11%; p<0.001). More men than women relied on electrolytes and carbohydrates (91%–93% vs 67%–72%, p≤0.029). Drinking strategies were based on personal experience (91%) rather than external sources (p<0.001). Most athletes (80%) planned pre-cooling (ice vests (53%), cold towels (45%), neck collars (21%) and ice slurry (21%)) and/or mid-cooling (93%; head/face dousing (65%) and cold water ingestion (52%)). Menthol usage was negligible (1%–2%). Pre-race T core was lower in athletes using ice vests (37.5°C±0.4°C vs 37.8°C±0.3°C, p=0.024). T core (pre-race 37.7°C±0.3°C, post-race 39.6°C±0.6°C) was independent of event, ranking or performance (p≥0.225). Pre-race T sk was correlated with faster race completion (r=0.32, p=0.046) and was higher in non-finishers (did not finish (DNF); 33.8°C±0.9°C vs 32.6°C±1.4°C, p=0.017). Body mass loss was higher in men than women (−2.8±1.5% vs −1.3±1.6%, p<0.001), although not associated with performance. Conclusion Most athletes’ hydration strategies were pre-planned based on personal experience. Ice vests were the most adopted pre-cooling strategy and the only one minimising T core , suggesting that event organisers should be cognisant of logistics (ie, freezers). Dehydration was moderate and unrelated to performance. Pre-race T sk was related to performance and DNF, suggesting that T sk modulation should be incorporated into pre-race strategies.
... Large inter-individual differences also exist among elite runners. Fluid intake rates were determined for 10 men who placed 1st or 2nd (range of finish times, 2:03:59 to 2:10:55) during prestigious city marathons [98]. Each runner's drinking behavior was recorded on videotape and fluid intake was estimated by multiplying drinking time by 45.2 mL/s (i.e., a value determined by laboratory drinking simulations). ...
... The distinction between option 1 (using perceived thirst as the only signal to drink) and option 2 (consuming fluid whenever and in whatever volume desired) is subtle [101]. In fact, some professional organizations and experts have not recognized these as distinct behaviors and some authors use these terms synonymously [6,26,84,98,99,101]. However, a 2014 field study determined that cyclists could identify whether they typically used option 1 or 2 and self-selected into one of two study groups (n = 12 in each). ...
Article
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During endurance exercise, two problems arise from disturbed fluid–electrolyte balance: dehydration and overhydration. The former involves water and sodium losses in sweat and urine that are incompletely replaced, whereas the latter involves excessive consumption and retention of dilute fluids. When experienced at low levels, both dehydration and overhydration have minor or no performance effects and symptoms of illness, but when experienced at moderate-to-severe levels they degrade exercise performance and/or may lead to hydration-related illnesses including hyponatremia (low serum sodium concentration). Therefore, the present review article presents (a) relevant research observations and consensus statements of professional organizations, (b) 5 rehydration methods in which pre-race planning ranges from no advanced action to determination of sweat rate during a field simulation, and (c) 9 rehydration recommendations that are relevant to endurance activities. With this information, each athlete can select the rehydration method that best allows her/him to achieve a hydration middle ground between dehydration and overhydration, to optimize physical performance, and reduce the risk of illness.
... In the present laboratory study, the rate of BML was significantly higher in HUMID than in NEUTRAL). Yet, current studies completed in ecological conditions have suggested that BML is not directly linked to a decreased in aerobic performance [26]. Similar BMLs in hot/humid environment have been described for a 27-km trail running race, i.e., a decrease of 3.9 ± 1.1% [10]. ...
Article
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To determine the relationships between limiting factors and neuromuscular activity during a self-paced 20-km cycling time trial and evaluate the effect of environmental conditions on fatigue indices. Methods: Ten endurance-trained and heat-acclimated athletes performed in three conditions (ambient temperature, relative humidity): HUMID (30 °C, 90%), DRY (35 °C, 46%) and NEUTRAL (22 °C, 55%). Voluntary muscular contractions and electromagnetic stimulations were recorded before and after the time trials to assess fatigue. The data on performance, temperature, heat storage, electromyogram, heart rate and rating of perceived exertion data were analyzed. Results: Performance was impaired in DRY and HUMID compared with NEUTRAL environment (p < 0.05). The force developed by the vastus lateral muscle during stimulation of the femoral nerve remained unchanged across conditions. The percentage of integrated electromyogram activity, normalized by the value attained during the pre-trial maximal voluntary contraction, decreased significantly throughout the trial only in HUMID condition (p < 0.01). Neuromuscular activity in peripheral skeletal muscle started to fall from the 11th km in HUMID and the 15th km in DRY condition, although core temperature did not reach critical values. Conclusions: These alterations suggest that afferences from core/skin temperature regulate the central neural motor drive, reducing the active muscle recruited during prolonged exercise in the heat in order to prevent the system from hyperthermia.
... However, the required fluid intake to achieve this (1.6 L·h −1 or a total of 2.3 L) would be difficult to achieve in most cases, due to a combination of lack of opportunities to drink throughout a match, and likely poor gastrointestinal tolerance if it was attempted. Likewise in the elite marathon scenario, the required fluid intake to elicit a need for sodium replacement was ≥0.9 L·h −1 , a quantity unlikely to be achieved in elite male runners completing the race in 2 h 6 min (Beis, Wright-Whyte, Fudge, Noakes, & Pitsiladis, 2012;van Rooyen, Hew-Butler, & Noakes, 2010). ...
Article
Evidence suggests the focus for sodium replacement during exercise should be maintenance of plasma sodium concentration ([Na+]plasma) for any given total body water (TBW) volume. The sodium intake to achieve stable [Na+]plasma given known fluid and electrolyte intakes and losses can be mathematically estimated. Therefore the aim of this investigation was to model sodium requirements of athletes during exercise, observing the influence of sweat rate, exercise duration, body mass, baseline [Na+]plasma and sweat potassium [K+]sweat, and relevance to competition (soccer, elite marathon, and 160 km ultramarathon running). Models were constructed across a range of sweat sodium concentrations ([Na+]sweat) (20-80 mmol·L-1), sweat rates (0.5-2.5 L·h-1) and fluid replacement (10-90% of losses). In the competition-specific scenarios, fluid replacement was calculated to achieve 2% TBW losses. Sodium requirements were driven by fluid replacement (% of losses) and [Na+]sweat, with minimal or no influence of other variables. Replacing sodium was unnecessary in all realistic scenarios modelled for a soccer match and elite marathon. In contrast, the 160 km ultramarathon required ≥47% sodium replacement when [Na+]sweat was ≥40 mmol·L-1 and >80% of fluid losses were replaced. In conclusion, sodium requirements to maintain stable [Na+]plasma during exercise depend on both the proportion of fluid losses replaced, and [Na+]sweat. Only when prolonged exercise is coupled with aggressive fluid replacement (>80%) and whole body [Na+]sweat ≥40 mmol·L-1 does sweat composition testing and significant, targeted sodium replacement appear necessary.
... More recent studies have only added support for the ad libitum fluid plan. Beis et al. (5) used retrospective video analysis of 10 elite marathoners in 13 city marathons evaluating footage from the cameraman on a motorcycle following the lead pack and showed that while a variation of fluid intake occurred, most stayed within the 400 to 800 mLIh j1 recommendation, and one of the winners had almost 10% dehydration. Wall et al. (51) had 10 well-trained cyclists perform a 2-h laboratory submaximum training session of biking and walking to produce 3% dehydration. ...
Article
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Triathletes need to effectively fuel during training and racing to maximize their potential for success. While most research on fueling has focused on elite male triathletes, triathlon participation encompasses a broader demographic of racers ranging from those with aspirations of winning to those whose goals are completion. Carbohydrate is the primary macronutrient for fueling endurance activities. Athletes can usually tolerate 60 to 90 mg·h -1 in the form of multiple different carbohydrate sources. Athletes should drink as thirst dictates and consider sodium replacement of sweat loss especially in individuals with a history of exercise-associated muscle cramps. Caffeine is a known ergogenic aid that could be dosed at 3 mg·kg -1 to maximize benefits of mental alertness while limiting potential side effects. Athletes need to balance fueling with development of exercise-induced gastrointestinal syndrome. As demographics of race participants change, understanding the special fueling needs of obese triathletes can encourage participation while minimizing bad outcomes.
... The current scientifically based recommendation regarding fluid intake is 0.400 to 0.800 L/hr, depending on individual differences and ambient influences (Sawka et al., 2007). Still for completeness, it should be added that a recent field study has shown that winners of city marathons seem to lose more than 2 to 3% of their body mass, which suggests that elite runners may be able to perform excellently with body mass loses greater that 2% (Beis et al., 2012). ...
... Observational field data of elite endurance athletes winning international marathons have reported dehydration levels of 6.6% to 11.7% body mass [98]. Although these observations do not allow for a causative conclusion that dehydration does not influence performance, it is nevertheless a striking contrast to the classical viewpoint, which suggests that endurance performance would be impaired if dehydration exceeds 1-2% body mass loss [1]. ...
... This is~50% more than reported for ad libitum water consumption during a 100 km race [47], suggesting SG drank to a plan, as opposed to drinking to thirst. Elite runners have been shown to ingest 550 ± 340 mL/h (range 30-1090 mL/h), which is above SG's consumption, despite a higher running pace throughout [48]. Lower fluid intakes may also be advantageous to avoid hyponatraemia e.g., Kipps et al. [49] reported fluid intakes ranging from 3683 mL/843 mL/h for hyponatraemic runners and 1924 mL/451 mL/h for those without hyponatraemia during the London marathon. ...
Article
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Background: We describe the requirements and physiological changes when running 10 consecutive marathons in 10 days at the same consistent pace by a female ultra-endurance athlete. Methods: Sharon Gayter (SG) 54 yrs, 162.5 cm, 49.3 kg maximal oxygen uptake (VO2 max) 53 mL/kg-1/min-1. SG completed 42.195 km on a treadmill every day for 10 days. We measured heart rate (HR), Rating of Perceived Exertion (RPE), oxygen uptake (VO2), weight, body composition, blood parameters, nutrition, and hydration. Results: SG broke the previous record by ~2.5 h, with a cumulative completion time of 43 h 51 min 39 s. Over the 10 days, weight decreased from 51 kg to 48.4 kg, bodyfat mass from 9.1 kg to 7.2 kg (17.9% to 14.8%), and muscle mass from 23.2 kg to 22.8 kg. For all marathons combined, exercise intensity was ~60% VO2 max; VO2 1.6 ± 0.1 L.min-1/32.3 ± 1.1 mL.kg-1.min-1, RER 0.8 ± 0, HR 143 ± 4 b.min-1. Energy expenditure (EE) was 2030 ± 82 kcal/marathon, total EE for 10 days (including BMR) was 33,056 kcal, daily energy intake (EI) 2036 ± 418 kcal (20,356 kcal total), resulting an energy deficit (ED) of 12,700 kcal. Discussion: Performance and pacing were highly consistent across all 10 marathons without any substantial physiological decrements. Although overall EI did not match EE, leading to a significant ED, resulting in a 2.6 kg weight loss and decreases in bodyfat and skeletal muscle mass, this did not affect performance.
... Using the midway point of this range (15.75 mmol/L) as an example, this data can be combined with sweat rate data obtained during endurance events to explore the potential implications of dietary sodium intake on sweat sodium losses during these events. Using this approach, one might anticipate a difference in total sweat sodium losses of 1360mg during a marathon raced by amateurs in 3:45:53 in thermoneutral conditions [41], or 1736mg during a marathon raced by world class runners finishing in a time of 2:06:31 in a hot and humid environment [53]. This represents a difference of 2-3% of total body sodium stores lost, given that total body sodium is approximately 1g/kg body mass [54]. ...
Article
The collection, processing, and analysis of sweat samples to determine sodium losses during endurance exercise is common amongst sports and exercise nutrition practitioners, and necessary for researchers investigating sodium losses and replacement strategies. Several factors influence sweat sodium concentration ([Na+]) that need to be controlled or considered when interpreting results. Dietary sodium intake in the days preceding exercise is one factor that may influence sweat [Na+]. A systematic review was undertaking using six databases (CINAHL, Embase, Medline Ovid, Scopus, SPORTDiscus, and Web of Science) to determine the impact of dietary sodium intake on sweat [Na+] in response to endurance exercise. Six papers met the inclusion criteria. They varied in the level of sodium intake (<196 to 9177 mg/d), intervention timeframe (3 to 42 days), exercise modality (cycling ergometry, treadmill walking and running), and sweat collection method (whole body washdown and regional patch techniques). Two studies showed significant differences in sweat [Na+] due to diet, two showed no significant difference, and two were not analysed statistically. No relationship was found across studies comparing the difference in sodium intake between interventions and sweat [Na+]. Several limitations were identified, including lack of validation of the intervention, collecting regional sweat samples from limited sites or averaging results across sites or collection days, and lack of statistical analysis. It is concluded that the impact of dietary sodium intake on sweat [Na+] in response to endurance exercise remains uncertain, however the review provides useful insights into the optimal study design for future research in this area.
... While some sports offer opportunities for regular access to foods and fluids during competition, conditions in other events prevent optimal practice. Therefore, the real world includes scenarios in which successful athletes achieve substantial nutritional support (e.g., the road cyclist, aided by feed-zones and the ferrying of nutritional supplies by domestique teammates, who consumed 500 g CHO during a 5-h cycling stage towards a daily CHO intake of 18 g kg −1 body mass (BM); Fordyce, 2018) while other events present a mismatch between requirements and opportunities for intake (e.g., the winner of a hot weather marathon incurring fluid losses equivalent to 10% BM due to the practical challenge of drinking while running at ∼21 km h −1 from aid stations placed at every 5 km; Beis et al., 2012). Notwithstanding the athletes' villages and their sophisticated catering arrangements at many premier events (Pelly & Parker Simmons, 2019), the global nature of elite sport challenges athletes to achieve their competition practices in foreign environments, sometimes against a backdrop of reduced food availability, atypical food choices and customs, and sub-optimal food hygiene . ...
Article
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New findings: What is the topic of this review? The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them. What advances does it highlight? A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event-specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real-life sport for optimal implementation. Abstract: High-performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low-carbohydrate high-fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst-driven drinking) to fluid intake.
... Elite athletes sustain high rates of energy transformation (and hence heat production) for prolonged periods; running at $20-21 km/hr requires a metabolic rate of >20 W/kg body mass (BM) via oxidative metabolism, and myocytes must tolerate >50 W of thermal energy per kg of active muscle. Dissipating such a heat load relies disproportionately on evaporation; hence, top marathon runners may lose up to 8% BM in a race, predominantly via sweat losses (Beis et al., 2012). Cell metabolism is thus impacted by intra-muscular and systemic metabolic, thermal (and presumably volumetric) strain. ...
Article
The application of molecular techniques to exercise biology has provided novel insight into the complexity and breadth of intracellular signaling networks involved in response to endurance-based exercise. Here we discuss several strategies that have high uptake by athletes and, on mechanistic grounds, have the potential to promote cellular adaptation to endurance training in skeletal muscle. Such approaches are based on the underlying premise that imposing a greater metabolic load and provoking extreme perturbations in cellular homeostasis will augment acute exercise responses that, when repeated over months and years, will amplify training adaptation.
... Elite (Beis et al., 2011;Beis et al., 2012) and recreationally competitive runners (Byrne et al., 2006;Lee et al., 2010;O'Neal et al., 2012;Passe et al., 2007) consume no or minimal fluids while running even in hot environmental conditions. Recognition of this behavioral pattern emphasizes the importance of fluid consumption during recovery. ...
Article
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The legitimacy of urine specific gravity (USG) as a standalone measure to detect hydration status has recently been challenged. As an alternative to hydration status, the purpose of this study was to determine the diagnostic capability of using the traditional USG marker of >1.020 to detect insufficient recovery fluid consumption with consideration for moderate versus high sweat losses (2.00-2.99 or > 3% body mass respectively). Adequate recovery fluid intake (ARFI) was operationally defined as ≥100% beverage fluid intake plus food water from 1 or 2 meals and a snack. Runners (n = 59) provided 132 samples from 5 previous investigations in which USG was assessed 10-14 h after 60-90 minute runs in temperate-to-hot environments. Samples were collected after a meal (n = 54) and after waking (n = 68). When sweat losses exceeded 3% body mass (n = 60) the relationship between fluid replacement percentage and USG increased from r = -0.55 to r = -0.70. Correct diagnostic decision improved from 66.6% to 83.3%, and receiver operating characteristic AUC increased the diagnostic accuracy score from 0.76 to approaching excellent (0.86). Artifacts of significant pre-run hyperhydration (8 of 15 samples has USG <1.005) may explain false positive diagnoses, while almost all (84%) cases of false positives were found when sweat losses were <3.0% of body mass. Evidence from this study suggests that euhydrated runners' experiencing significant sweat losses that fail to reach ARFI levels can be identified by USG irrespective of acute meal and fluid intake ~12-h post-run.
... The reason for the increase in oxygen uptake and reduction in running economy is unknown. A number of mechanisms have been postulated in the literature but most of them are speculative [11,[17][18][19]. Without discussing here the various attempts that have been made for explaining this observation, we just conclude that every activated physiological system increases its own particular energy consumption with the duration of exercise. ...
Preprint
Models for human running performances of various complexities and underlying principles have been proposed, often combining data from world record performances and bio-energetic facts of human physiology. Here we present a novel, minimal and universal model for human running performance that employs a relative metabolic power scale. The main component is a self-consistency relation for the time dependent maximal power output. The analytic approach presented here is the first to derive the observed logarithmic scaling between world (and other) record running speeds and times from basic principles of metabolic power supply. Various female and male record performances (world, national) and also personal best performances of individual runners for distances from 800m to the marathon are excellently described by this model, with mean errors of (often much) less than 1%. The model defines endurance in a way that demonstrates symmetry between long and short racing events that are separated by a characteristic time scale comparable to the time over which a runner can sustain maximal oxygen uptake. As an application of our model, we derive personalized characteristic race speeds for different durations and distances.
... Collectively, ad libitum fluid consumption does not appear to degrade performance of endurance athletes training or competing for durations of 60-120 min bouts [34]. However, there are likely many individual endurance athletes that could potentially benefit from adjusting fluid intake strategies based on knowledge of expected sweat losses, particularly those of longer durations [35,36]. Although only anecdotal, following the O'Neal et al. [10] study investigators received unsolicited notifications from multiple participants expressing personal best events in long distance running or triathlon events after altering fluid intake patterns based on recognition of their actual sweat rates. ...
Article
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The main purposes of this review were to provide a qualitative description of nine investigations in which sweat losses were estimated by participants following exercise and to perform a quantitative analysis of the collective data. Unique estimations (n = 297) were made by 127 men and 116 women after a variety of exercise modalities in moderate to hot environmental conditions. Actual sweat loss exceeded estimated sweat loss (p < 0.001) for women (1.072 ± 0.473 vs. 0.481 ± 0.372 L), men (1.778 ± 0.907 vs. 0.908 ± 0.666 L) and when all data were combined (1.428 ± 0.806 vs. 0.697 ± 0.581 L), respectively. However, estimation accuracy did not differ between women (55.2 ± 51.5%) and men (62.4 ± 54.5%). Underestimation of 50% or more of sweat losses were exhibited in 168 (54%) of estimation scenarios with heavier sweaters displaying a higher prevalence and trend of greater underestimations in general. Most modern guidelines for fluid intake during and between training bouts are based on approximate sweat loss estimation knowledge. These guidelines will likely have minimal efficacy if greater awareness of how to determine sweat losses and accurate recognition of sweat losses is not increased by coaches and athletes.
... This data supports two separate investigations in which non-elite runners consumed similar volumes of water during 1-hour outdoor runs with similar drinking opportunities in temperate (18) or hot (19) environments and matches fluid intake rate in relation to body mass losses for male half-marathon runners competing in hot and humid race conditions (14). Elite African runners are unlikely to drink at all during training (1,9,22), and elite male marathoners are estimated to lose as much as 10% body mass during competition (2). Cumulatively, these findings help reinforce our position that between running bouts fluid consumption, not fluid consumption during running, is the most critical time phase for optimizing hydration status of runners. ...
... Numerous studies reported similar findings of gastrointestinal discomfort when consuming fluid, particularly, among runners, during exercise (Dion et al., 2013;Peters et al., 2000;Sharwood et al., 2004). Indeed ~50% of endurance runners of endurance athletes experience some level of gastrointestinal issues during exercise (Beis et al., 2012). Moreover, Martins and Waldschutz (2012) suggested that athletes should drink an adequate amount of fluids necessary to maintain the optimal hydration while exercising regularly to prevent the sensation of epigastric fullness during exercise. ...
... The dehydration threshold was defined here as water loss equivalent to 10% body mass for the hunter (Hora et al., 2020) and 30% body mass for the prey (Schmidt-Nielsen, 1964). Water loss equivalent to 10% of body mass was reported for marathon winners (Beis et al., 2012) and even 25% of body mass loss was anecdotally reported in the literature (Noakes, 2012). Nevertheless, to determine the sensitivity of our results to setting of the dehydration threshold, we modeled the dehydration threshold of the hunter also as water loss equivalent to 7.5% and 5.0% of body mass. ...
Article
"FREE LINK HERE: https://authors.elsevier.com/a/1fo1JAlZXQDcp" It has been proposed that humans' exceptional locomotor endurance evolved partly with foraging in hot open habitats and subsequently about 2 million years ago with persistence hunting, for which endurance running was instrumental. However, persistence hunting by walking, if successful, could select for locomotor endurance even before the emergence of any running-related traits in human evolution. Using a heat exchange model validated here in 73 humans and 55 ungulates, we simulated persistence hunts for prey of three sizes (100, 250, and 400 kg) and three sweating capacities (nonsweating, low, high) at 6237 combinations of hunter's velocity (1–5 m s⁻¹, intermittent), air temperature (25–45 °C), relative humidity (30–90%), and start time (8:00–16:00). Our simulations predicted that walking would be successful in persistence hunting of low- and nonsweating prey, especially under hot and humid conditions. However, simulated persistence hunts by walking yielded a 30–74% lower success rate than hunts by running or intermittent running. In addition, despite requiring 10–30% less energy, successful simulated persistence hunts by walking were twice as long and resulted in greater exhaustion of the hunter than hunts by running and intermittent running. These shortcomings of pursuit by walking compared to running identified in our simulations could explain why there is only a single direct description of persistence hunting by walking among modern hunter-gatherers. Nevertheless, walking down prey could be a viable option for hominins who did not possess the endurance-running phenotype of the proposed first persistence hunter, Homo erectus. Our simulation results suggest that persistence hunting could select for both long-distance walking and endurance running and contribute to the evolution of locomotor endurance seen in modern humans.
... This protocol required the subjects to walk on a treadmill for 10 min at 1.3 m/s and 7% grade while wearing a pack that weighed approximately 22.7 kg. The speed, grade, and load of this protocol was identical to a study previously performed in our laboratory (Deming et al., 2020) and was chosen to simulate occupations were load carriage (60% VO 2max ) over several kilometers is required, such as many military populations (aircrew, special operators, security forces, orienteering teams, and trainees), emergency personnel, and athletes (Sol et al., 2018;Nolte et al., 2019;Beis et al., 2012). ...
Article
Introduction To determine if electrolyte or carbohydrate supplementation vs. water would limit the magnitude of dehydration and decline in cognitive function in humans following long-duration hyperthermic-exercise. Methods 24 subjects performed 3 visits of 2hrs walking (3mph/7% grade) in an environmental chamber (33 °C/10% relative humidity). In random order, subjects consumed water (W), electrolytes (Gatorade Zero; E), or electrolytes+carbohydrates (Gatorade; E+C). Throughout exercise (EX), subjects carried a 23kg pack and drank ad-libitum. Pre-and post-EX, body mass (BM) and plasma osmolality (pOsm) were measured. Physiological Strain Index (PSI) and core temperature (TC) were recorded every 15mins. Plasma glucose (GLU) was measured every 30mins. Cognitive processing (SCWT) was measured post-EX and compared to baseline (BL). A subset of 8 subjects performed a normothermic (N) protocol (21 °C/ambient humidity) to ascertain how the exercise stimulus influenced hydration status and cognition without heat. Results There were no significant differences between fluid conditions (W, E, E+C) for BM loss (Δ2.5 ± 0.2, 2.5 ± 0.2, 2.3 ± 0.2kg), fluid consumption (1.9 ± 0.2, 1.9 ± 0.2, 1.8 ± 0.2L), pOsm (Δ1.5 ± 2.7, 2.2 ± 2.4, 2.0 ± 1.5mmol/L), peak-PSI (7.5 ± 0.4, 7.0 ± 0.6, 7.9 ± 0.5), and peak-TC (38.7 ± 0.1, 38.6 ± 0.2, 38.8 ± 0.2 °C). GLU decreased significantly in W and E, whereas it increased above BL in E+C at 60, 90, and 120mins (P < 0.05). Compared to BL values (43.6 ± 26ms), SCWT performance significantly decreased in all conditions (463 ± 93, 422 ± 83, 140 ± 52ms, P < 0.05). Importantly, compared to W and E, the impairment in SCWT was significantly attenuated in E+C (P < 0.05). As expected, when compared to the heat-stress protocol (W, E, E+C), N resulted in lower BM loss, fluid consumption, and peak-PSI (1.1 ± 0.1kg, 1.2 ± 0.7L, 4.8, respectively), and improved SCWT performance. Conclusions These data are the first to suggest that, independent of supplementation variety, cognitive processing significantly decreases immediately following long-duration exercise in the heat in healthy humans. Compared to water and fluids supplemented with only electrolytes, fluids supplemented with carbohydrates significantly blunts this decrease in cognitive function.
... Recent research has indicated that in trained individuals, mild to moderate hypohydration (>3% body mass loss) has minimal to no effect on exercise performance, furthermore cardiovascular and thermal strain are not significantly affected. Moreover, trained athletes have consistently been found to tolerate hypohydration of >6% during competitive exercise without succumbing to heat illness or other ill effect (Beis et al. 2012 ...
Research
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Chapter in Cheung et al (editors) for Cycling Science.
... This allows humans to work longer in the heat without severe consequences and rehydrate later. For example, humans have flexibility in body water loss as documented in extreme cases like endurance hunts (Noakes, 2010) as well as elite endurance competitions, where marathon runners have been shown to lose up to 11.7% of body weight (Beis et al., 2012). However, the average gut size (~500 mL) and the gastric emptying rate of humans means that humans can only consume~half a liter of water every 15 to 20 minutes and have to wait for this to empty before consuming more (Noakes, 2010). ...
Article
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Body water homeostasis is critical for optimal physiological and cognitive function for humans. The majority of research has illustrated the negative biological consequences of failing to meet water needs. The human body has several mechanisms for detecting, regulating, and correcting body water deficits and excesses. However, variation exists in total water intake and how people meet those water needs as well as thirst thresholds and how well people tolerate water restriction. An evolutionary and developmental framework provides an underexplored perspective into human water needs by examining how adaptations, early life experiences and environments, as well as life course changes in health states and behaviors may shape these critical factors in body water homeostasis. This article first reviews biological and behavioral adaptations to water scarcity among animals and humans. It then examines human variation in water intake in a mostly water secure environment through the analysis of National Health and Nutrition Examination Survey dietary data and the link between water intake patterns and hydration biomarkers. Next, it reviews existing evidence of how maternal water restriction in utero and during lactation shape vasopressin release, thirst thresholds, drinking patterns, and body water homeostasis for the infant. Early life water restriction appears to have implications for hydration status, body size, and cardiovascular health. Finally, it examines how life course changes in health states and behaviors, including obesity, sleep, and parasitic infection, affect body water homeostasis. This article poses new questions about the plasticity and shaping of human water needs, thirst, and hydration behaviors.
... The ability for endurance athletes to ingest food and fluids is frequently limited by gastrointestinal tolerance, as well as opportunities for consumption. For example, elite male marathon runners may allow less than 60 s to consume nutrition during competition (Beis et al., 2012), and anecdotal reports suggest great difficulty consuming and tolerating ideal fluid intake due to exercise intensity and the required ventilation. ...
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It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete’s nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.
... After a rest period, the subjects performed a "study day familiarization protocol" where they walked on a treadmill for 10 min at 1.3 m/s and 7% grade wearing a pack that weighed approximately 22.7 kg. The speed, grade, and load of this familiarization protocol was chosen to closely mimic occupations were load carriage over several miles is required, such as military populations (special operators, security forces, orienteering teams, and trainees), wildland firefighters, and athletes (Sol et al., 2018;Nolte et al., 2019;Beis et al., 2012). ...
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Introduction The purpose of this study was to determine the effects of ad libitum flavor and fluid intake on changes in body mass (BM) and physiological strain during moderate intensity exercise in the heat. Methods Ten subjects (24±3yrs, 7M/3F) performed 60 min of treadmill walking at 1.3 m/s and 7% grade in an environmental chamber set to 33 °C and 10% relative humidity while carrying a 22.7 kg pack on two different occasions. Subjects consumed either plain water or water plus flavored (Infuze), ad libitum, at each visit. Pre and post exercise, fluid consumption (change in fluid reservoir weight) and BM (nude) were measured. During exercise, heart rate (HR), systolic blood pressure (SBP), rate of perceived exertion (RPE), oxygen consumption (VO2), respiratory exchange ratio (RER), core temperature (TC), and physiological strain index (PSI) were recorded every 15 min during exercise. Results No significant differences were observed for fluid consumption between fluid conditions (512 ± 97.2 mL water vs. 414.3 ± 62.5 mL Infuze). Despite a significant decrease from baseline, there were no significant differences in overall change of BM (Δ −1.18 vs. −0.64 Kg) or percent body weight loss for water and Infuze conditions, respectively (1.58 ± 0.6 and 0.79 ± 0.2%). Furthermore, there were no significant differences in HR (144 ± 6 vs. 143 ± 8 bpm), SBP (157 ± 5 vs. 155 ± 5 mmHg), RPE, VO2 (27.4 ± 0.9 vs. 28.1 ± 1.2 ml/Kg/min), RER, TC (38.1 ± 0.1 vs. 37.0 ± 0.1 °C), and peak PSI (5.4 ± 0.4 vs. 5.7 ± 0.8) between conditions. Conclusions Offering individuals the choice to actively manipulate flavor strength did not significantly influence ad libitum fluid consumption, fluid loss, or physiological strain during 60 min of moderate intensity exercise in the heat.
... It may enhance adaptation to endurance effort and thus improve sports results. According to Beis et al. [16], the improvement in physical capacity and endurance is also related to higher oxidation of simple carbohydrates (aqueous solution of glucose + fructose 60g/h) that leads to better effects than doses of 30g/h or 15g/h. Big portions of simple sugars (> 90g/h) may cause higher production of energy, up to 20-50%. ...
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This document presents the recommendations developed by the IOC Medical and Scientific Commission and several international federations (IF) on the protection of athletes competing in the heat. It is based on a working group, meetings, field experience and a Delphi process. The first section presents recommendations for event organisers to monitor environmental conditions before and during an event; to provide sufficient ice, shading and cooling; and to work with the IF to remove regulatory and logistical limitations. The second section summarises recommendations that are directly associated with athletes’ behaviours, which include the role and methods for heat acclimation; the management of hydration; and adaptation to the warm-up and clothing. The third section explains the specific medical management of exertional heat stroke (EHS) from the field of play triage to the prehospital management in a dedicated heat deck, complementing the usual medical services. The fourth section provides an example for developing an environmental heat risk analysis for sport competitions across all IFs. In summary, while EHS is one of the leading life-threatening conditions for athletes, it is preventable and treatable with the proper risk mitigation and medical response. The protection of athletes competing in the heat involves the close cooperation of the local organising committee, the national and international federations, the athletes and their entourages and the medical team.
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The exploits of elite athletes delight, frustrate, and confound us as they strive to reach their physiological, psychological, and biomechanical limits. We dissect nutritional approaches to optimal performance, showcasing the contribution of modern sports science to gold medals and world titles. Despite an enduring belief in a single, superior “athletic diet,” diversity in sports nutrition practices among successful athletes arises from the specificity of the metabolic demands of different sports and the periodization of training and competition goals. Pragmatic implementation of nutrition strategies in real-world scenarios and the prioritization of important strategies when nutrition themes are in conflict add to this variation. Lastly, differences in athlete practices both promote and reflect areas of controversy and disagreement among sports nutrition experts.
Chapter
Hypohydration, defined as a deficit in total body water that exceeds normal daily fluid fluctuations, is typically set as a fluid loss equivalent to >2% of body mass. The evaporation of sweat provides the principle means of heat dissipation during exercise in the heat; typical sweat rates of 300–2000 mL/h during sporting activities are generally not matched by fluid intake, leading to hypohydration. Although there are shortcomings in the literature related to hypohydration and sports performance, it is likely that some scenarios (hot conditions, larger fluid losses and prolonged aerobic exercise) are more at risk of incurring impaired performance. Guidelines for fluid intake during exercise and sporting activity are contentious since they need to span situations in which it is easy to overdrink compared with sweat losses and others in which significant levels of hypohydration occur. Nevertheless, athletes can be guided to develop fluid intake plans that are suited to their specific needs.
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Endurance exercise performance has been shown to improved with carbohydrate (CHO) mouth rinsing. While multiple studies to elucidate the effectiveness of CHO mouth rinsing continue, most of the studies have utilized 6.4% CHO solutions. The impact of higher CHO concentration on exercise performance remains inconclusive. The aim of this study was to determine the effectiveness of various concentrations of CHO mouth rinse solutions on intermittent running performance. In a double-blind, placebo (PLA) controlled crossover design, 8 recreational endurance runners [age (mean ± SD): 22 ± 1 years; body mass: 62.9 ± 5.9 kg] completed 3 experimental trials. Each trial consisted of standardized breakfast (2 h prior) followed by Yo-Yo Intermittent Recovery Test-Level 1 (Yo-Yo IRT-1) run to exhaustion. Prior the start of the exercise, subjects mouth rinsed with 25 mL of either 6%, 21% CHO and a taste-matched PLA solution for 10 s. Distance covered, level of exhaustion, heart rate (HR), blood glucose, perceived exertion (RPE), perceived arousal scale (FAS) and gastrointestinal scale (GI) were recorded during each trial. There were no significant differences in distance covered (p = 0.07) or level of exhaustion (p = 0.17) between 6%, 21% and PLA trials. There was a significant effect of time on HR (p < 0.001); nevertheless, no significant difference between trials (p = 0.24). There was no difference on blood glucose (p = 0.69) or any of the psychological markers (RPE, p = 0.10; FAS, p = 0.85; GI, p = 0.37). In conclusion, CHO mouth rising with higher solutions concentration of 6% or 21% provide no ergogenic advantage over a PLA solution, and that there was no does-response relationship between solution concentration and Yo-Yo IRT-1 running performance. Further research is warranted to examine the possibility of any dose-response effect of CHO mouth rinse during exercise for more than 30 min.
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A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat, by examining the benefits of heat acclimation, cooling strategies and hyperhydration. Finally, contemporary controversies are summarized and future research directions provided.
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The purpose of this study was to determine the relationship between athletic performance and the change in body weight (BW) during a 42 km marathon in a large cohort of runners. The study took place during the 2009 Mont Saint-Michel Marathon (France). 643 marathon finishers (560 males and 83 females) were studied. The change in BW during the race was calculated from measurements of each runner's BW immediately before and after the race. BW loss was 2.3 ± 2.2% (mean±SEM) (p<0.01). BW loss was -3.1 ± 1.9% for runners finishing the marathon in less than 3 h; -2.5 ± 2.1% for runners finishing between 3 and 4 h; and -1.8 ± 2.4% for runners who required more than 4 h to complete the marathon. The degree of BW loss was linearly related to 42 km race finishing time (p<0.0000001). Neither age nor gender influenced BW loss during the race. BW loss during the marathon was inversely related to race finishing time in 643 marathon runners and was >3% in runners completing the race in less than 3 h. These data are not compatible with laboratory-derived data suggesting that BW loss greater than 2% during exercise impairs athletic performance. They match an extensive body of evidence showing that the most successful athletes in marathon and ultra-marathon running and triathlon events are frequently those who lose substantially more than 3-4% BW during competition.
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The Institute of Medicine expressed a need for improved sweating rate (msw) prediction models that calculate hourly and daily water needs based on metabolic rate, clothing, and environment. More than 25 years ago, the original Shapiro prediction equation (OSE) was formulated as msw (g.m(-2).h(-1))=27.9.Ereq.(Emax)(-0.455), where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment; OSE was developed for a limited set of environments, exposures times, and clothing systems. Recent evidence shows that OSE often overpredicts fluid needs. Our study developed a corrected OSE and a new msw prediction equation by using independent data sets from a wide range of environmental conditions, metabolic rates (rest to <or=450 W/m2), and variable exercise durations. Whole body sweat losses were carefully measured in 101 volunteers (80 males and 21 females; >500 observations) by using a variety of metabolic rates over a range of environmental conditions (ambient temperature, 15-46 degrees C; water vapor pressure, 0.27-4.45 kPa; wind speed, 0.4-2.5 m/s), clothing, and equipment combinations and durations (2-8 h). Data are expressed as grams per square meter per hour and were analyzed using fuzzy piecewise regression. OSE overpredicted sweating rates (P<0.003) compared with observed msw. Both the correction equation (OSEC), msw=147.exp (0.0012.OSE), and a new piecewise (PW) equation, msw=147+1.527.Ereq-0.87.Emax were derived, compared with OSE, and then cross-validated against independent data (21 males and 9 females; >200 observations). OSEC and PW were more accurate predictors of sweating rate (58 and 65% more accurate, P<0.01) and produced minimal error (standard error estimate<100 g.m(-2).h(-1)) for conditions both within and outside the original OSE domain of validity. The new equations provide for more accurate sweat predictions over a broader range of conditions with applications to public health, military, occupational, and sports medicine settings.
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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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The U.S. Army's fluid replacement guidelines emphasize fluid replacement during hot weather training to prevent degradation of performance and minimize the risk of heat injury. Little consideration has been given, however, to possible overhydration and development of water intoxication. Sufficient epidemiological evidence is available to demonstrate an increasing incidence of water intoxication during military training. This article summarizes the development and validation of revised fluid replacement guidelines for hot weather training. The end product is an easy-to-read table that provides the user with the appropriate hourly work time and fluid intake to support work during hot weather training. The guidelines include the range of hot weather conditions likely to be encountered during military training and cover a broad range of military activities. It is expected that the revised guidelines will sustain hydration and minimize the number of heat injuries during military training while protecting the soldier from becoming sick from overdrinking.
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During exercise in the heat, sweat output often exceeds water intake, resulting in a body water deficit (hypohydration) and electrolyte losses. Because daily water losses can be substantial, persons need to emphasize drinking during exercise as well as at meals. For persons consuming a normal diet, electrolyte supplementation is not warranted except perhaps during the first few days of heat exposure. Aerobic exercise is likely to be adversely affected by heat stress and hypohydration; the warmer the climate the greater the potential for performance decrements. Hypohydration increases heat storage and reduces a person's ability to tolerate heat strain. The increased heat storage is mediated by a lower sweating rate (evaporative heat loss) and reduced skin blood flow (dry heat loss) for a given core temperature. Heat-acclimated persons need to pay particular attention to fluid replacement because heat acclimation increases sweat losses, and hypohydration negates the thermoregulatory advantages conferred by acclimation. It has been suggested that hyperhydration (increased total body water) may reduce physiologic strain during exercise heat stress, but data supporting that notion are not robust. Research is recommended for 3 populations with fluid and electrolyte balance problems: older adults, cystic fibrosis patients, and persons with spinal cord injuries.
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The extreme physical endurance demands and varied environmental settings of marathon footraces have provided a unique opportunity to study the limits of human thermoregulation for more than a century. High post-race rectal temperatures (Tre) are commonly and consistently documented in marathon runners, yet a clear divergence of thought surrounds the cause for this observation. A close examination of the literature reveals that this phenomenon is commonly attributed to either biological (dehydration, metabolic rate, gender) or environmental factors. Marathon climatic conditions vary as much as their course topography and can change considerably from year to year and even from start to finish in the same race. The fact that climate can significantly limit temperature regulation and performance is evident from the direct relationship between heat casualties and Wet Bulb Globe Temperature (WBGT), as well as the inverse relationship between record setting race performances and ambient temperatures. However, the usual range of compensable racing environments actually appears to play more of an indirect role in predicting Tre by acting to modulate heat loss and fluid balance. The importance of fluid balance in thermoregulation is well established. Dehydration-mediated perturbations in blood volume and blood flow can compromise exercise heat loss and increase thermal strain. Although progressive dehydration reduces heat dissipation and increases Tre during exercise, the loss of plasma volume contributing to this effect is not always observed for prolonged running and may therefore complicate the predictive influence of dehydration on Tre for marathon running. Metabolic heat production consequent to muscle contraction creates an internal heat load proportional to exercise intensity. The correlation between running speed and Tre, especially over the final stages of a marathon event, is often significant but fails to reliably explain more than a fraction of the variability in post-marathon Tre. Additionally, the submaximal exercise intensities observed throughout 42 km races suggest the need for other synergistic factors or circumstances in explaining this occurrence. There is a paucity of research on women marathon runners. Some biological determinants of exercise thermoregulation, including body mass, surface area-to-mass ratio, sweat rate, and menstrual cycle phase are gender-discrete variables with the potential to alter the exercise-thermoregulatory response to different environments, fluid intake, and exercise metabolism. However, these gender differences appear to be more quantitative than qualitative for most marathon road racing environments.
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OBJECTIVE: To present recommendations for the prevention, recognition, and treatment of exertional heat illnesses and to describe the relevant physiology of thermoregulation. BACKGROUND: Certified athletic trainers evaluate and treat heat-related injuries during athletic activity in "safe" and high-risk environments. While the recognition of heat illness has improved, the subtle signs and symptoms associated with heat illness are often overlooked, resulting in more serious problems for affected athletes. The recommendations presented here provide athletic trainers and allied health providers with an integrated scientific and practical approach to the prevention, recognition, and treatment of heat illnesses. These recommendations can be modified based on the environmental conditions of the site, the specific sport, and individual considerations to maximize safety and performance. RECOMMENDATIONS: Certified athletic trainers and other allied health providers should use these recommendations to establish on-site emergency plans for their venues and athletes. The primary goal of athlete safety is addressed through the prevention and recognition of heat-related illnesses and a well-developed plan to evaluate and treat affected athletes. Even with a heat-illness prevention plan that includes medical screening, acclimatization, conditioning, environmental monitoring, and suitable practice adjustments, heat illness can and does occur. Athletic trainers and other allied health providers must be prepared to respond in an expedient manner to alleviate symptoms and minimize morbidity and mortality.
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Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss. To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses. Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race. Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups. Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.
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Hyponatremia has emerged as an important cause of race-related death and life-threatening illness among marathon runners. We studied a cohort of marathon runners to estimate the incidence of hyponatremia and to identify the principal risk factors. Participants in the 2002 Boston Marathon were recruited one or two days before the race. Subjects completed a survey describing demographic information and training history. After the race, runners provided a blood sample and completed a questionnaire detailing their fluid consumption and urine output during the race. Prerace and postrace weights were recorded. Multivariate regression analyses were performed to identify risk factors associated with hyponatremia. Of 766 runners enrolled, 488 runners (64 percent) provided a usable blood sample at the finish line. Thirteen percent had hyponatremia (a serum sodium concentration of 135 mmol per liter or less); 0.6 percent had critical hyponatremia (120 mmol per liter or less). On univariate analyses, hyponatremia was associated with substantial weight gain, consumption of more than 3 liters of fluids during the race, consumption of fluids every mile, a racing time of >4:00 hours, female sex, and low body-mass index. On multivariate analysis, hyponatremia was associated with weight gain (odds ratio, 4.2; 95 percent confidence interval, 2.2 to 8.2), a racing time of >4:00 hours (odds ratio for the comparison with a time of <3:30 hours, 7.4; 95 percent confidence interval, 2.9 to 23.1), and body-mass-index extremes. Hyponatremia occurs in a substantial fraction of nonelite marathon runners and can be severe. Considerable weight gain while running, a long racing time, and body-mass-index extremes were associated with hyponatremia, whereas female sex, composition of fluids ingested, and use of nonsteroidal antiinflammatory drugs were not.
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The development of symptomatic hyponatraemia consequent on participation in marathon and ultraendurance races has led to questions about its aetiology and prevention. To evaluate: (a) the assertion that sweat sodium losses cannot contribute to the development of hyponatraemia during endurance exercise; (b) the adequacy of fluid replacement recommendations issued by the International Marathon Medical Directors Association (IMMDA) for races of 42 km or longer; (c) the effectiveness of commercial sports drinks, compared with water, for attenuating plasma sodium reductions. A mathematical model was used to predict the effects of different drinking behaviours on hydration status and plasma sodium concentration when body mass, body composition, running speed, weather conditions, and sweat sodium concentration were systematically varied. Fluid intake at rates that exceed sweating rate is predicted to be the primary cause of hyponatraemia. However, the model predicts that runners secreting relatively salty sweat can finish ultraendurance exercise both dehydrated and hyponatraemic. Electrolyte-containing beverages are predicted to delay the development of hyponatraemia. The predictions suggest that the IMMDA fluid intake recommendations adequately sustain hydration over the 42 km distance if qualifiers-for example, running pace, body size-are followed. Actions to prevent hyponatraemia should focus on minimising overdrinking relative to sweating rate and attenuating salt depletion in those who excrete salty sweat. This simulation demonstrates the complexity of defining fluid and electrolyte consumption rates during athletic competition.
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This Position Stand provides guidance on fluid replacement to sustain appropriate hydration of individuals performing physical activity. The goal of prehydrating is to start the activity euhydrated and with normal plasma electrolyte levels. Prehydrating with beverages, in addition to normal meals and fluid intake, should be initiated when needed at least several hours before the activity to enable fluid absorption and allow urine output to return to normal levels. The goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance. Because there is considerable variability in sweating rates and sweat electrolyte content between individuals, customized fluid replacement programs are recommended. Individual sweat rates can be estimated by measuring body weight before and after exercise. During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water alone under certain circumstances. After exercise, the goal is to replace any fluid electrolyte deficit. The speed with which rehydration is needed and the magnitude of fluid electrolyte deficits will determine if an aggressive replacement program is merited.
Article
The extreme physical endurance demands and varied environmental settings of marathon footraces have provided a unique opportunity to study the limits of human thermoregulation for more than a century. High post-race rectal temperatures (Tre) are commonly and consistently documented in marathon runners, yet a clear divergence of thought surrounds the cause for this observation. A close examination of the literature reveals that this phenomenon is commonly attributed to either biological (dehydration, metabolic rate, gender) or environmental factors. Marathon climatic conditions vary as much as their course topography and can change considerably from year to year and even from start to finish in the same race. The fact that climate can significantly limit temperature regulation and performance is evident from the direct relationship between heat casualties and Wet Bulb Globe Temperature (WBGT), as well as the inverse relationship between record setting race performances and ambient temperatures. However, the usual range of compensable racing environments actually appears to play more of an indirect role in predicting Tre by acting to modulate heat loss and fluid balance. The importance of fluid balance in thermoregulation is well established. Dehydration-mediated perturbations in blood volume and blood flow can compromise exercise heat loss and increase thermal strain. Although progressive dehydration reduces heat dissipation and increases Tre during exercise, the loss of plasma volume contributing to this effect is not always observed for prolonged running and may therefore complicate the predictive influence of dehydration on Tre for marathon running. Metabolic heat production consequent to muscle contraction creates an internal heat load proportional to exercise intensity. The correlation between running speed and Tre, especially over the final stages of a marathon event, is often significant but fails to reliably explain more than a fraction of the variability in post-marathon Tre. Additionally, the submaximal exercise intensities observed throughout 42km races suggest the need for other synergistic factors or circumstances in explaining this occurrence There is a paucity of research on women marathon runners. Some biological determinants of exercise thermoregulation, including body mass, surface area-to mass ratio, sweat rate, and menstrual cycle phase are gender-discrete variables with the potential to alter the exercise-thermoregulatory response to different environments, fluid intake, and exercise metabolism. However, these gender differences appear to be more quantitative than qualitative for most marathon road racing environments.
Article
Purpose: In this study, we examined the effects of greater than ad libitum rates of fluid intake on 2-h running performances. Methods: Eight male distance runners performed three runs on a treadmill at 65% of peak oxygen uptake ((V) over dot O-2 peak) for 90 min and then ran "as far as possible" in 30 min in an air temperature of 25 degrees C, a relative humidity of 55% and a wind speed of 13-15 km.h(-1). During the runs, the subjects drank a 6.9% carbohydrate (CHO)-electrolyre solution either ad libitum or in set volumes of 150 or 350 mL.70 kg(-1) body mass (similar to 130 or 300 mL) every 15-20 min. Results: Higher (similar to 0.9 vs 0.4 L.h(-1)) rates of fluid intake in the 350 mL.70 kg(-1) trial than in the other trials had minimal effects on the subjects' urine production (similar to 0.1 L.h(-1)), sweat rates (similar to 1.2 L.h(-1)), declines in plasma volume (similar to 8%), and rises in serum osmolality (similar to 5 mosmol.L-1) and Na+ concentrations (similar to 7 mEq.L-1). A greater (similar to 1.0 vs 0.5 g.min(-1)) rate of CHO ingestion in the 350 mL.70 kg(-1) trial than in the other trials also did not affect plasma concentrations of glucose (similar to 5 mmol.L-1) and lactate (similar to 3 mmol.L-1) during the performance runs. In all three performance runs, increases in running speeds from similar to 14 to 15-16 km.h(-1) and rises in exercise intensities from similar to 65% to 75% of (V) over dot O-2 (peak) elevated plasma lactate concentrations from similar to 1.5 to 3 mmol.L-1 and accelerated CHO oxidation from similar to 13 to 15 mmol.min(-1). The only effect of the additional intake of similar to 1.0 L of fluid in the 350 mL.70 kg(-1) trial was to produce such severe gastrointestinal discomfort that two of the eight subjects failed to complete their performance runs. Conclusion: Greater rates of fluid ingestion had no measurable effects on plasma volume and osmolality and did not improve 2-h running performances in a 25 degrees C environment.
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It has been previously proposed that fluid ingestion might enhance performance and thermoregulation through the heat storage capacity of the ingested fluid. While accurate under certain conditions, in some situations this cannot account for differences in thermoregulatory and performance responses. To test this hypothesis seven subjects performed a 60 min self-paced cycling time trial on four occasions, differentiated by ambient temperature (moderate 19.8±0.6°C, warm 33.2±0.2°C; 63.3±0.6% relative humidity) and fluid ingestion regime (no fluid, NF; or sufficient fluid, F, to prevent any change in body mass). No differences were observed for total distance cycled or final core temperature during exercise where for the moderate-NF, moderate-F, warm-NF and warm-F conditions were 32.6±6.4, 30.8±5.7, 30.5±4.8, 30.1±5.0 km and 38.9±0.3°C, 38.6±0.4°C, 38.9±0.5°C, 38.7±0.4°C, respectively. Furthermore, pacing strategy, as indicated by distance covered during maximal sprint and submaximal sections of the trial were similar among conditions. Although this result is not dissimilar to previous findings, the data show that complete fluid replacement during exercise of 1 h does not provide the proposed heat sink sufficient to attenuate thermoregulatory strain and improve performance over no fluid replacement. The findings indicate that the ingestion of fluids replacing 100% of sweat losses has no effect on 1 h of self-paced cycling performance or thermoregulation in moderate and warm conditions.
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The aim of the study was to examine the effects of fluid replacement on thermoregulation and cycling performance in hot, humid conditions. Six male cyclists (PPO = 426 +/- 39 W) performed six 80 km time trials. Subjects replaced 0% (0); 33% (33); 66% (66); or 100% (100) of the weight lost during an "ad libitum" trial (Ad Lib). In another condition (WET), subjects rinsed their mouths at 10 km intervals. There was no trial effect on any thermoregulatory variables or on performance. When WET, 0, 33 ("LO") were compared to Ad Lib; 66, 100 ("HI"), power output was higher in HI (209 +/- 22 vs. 193 +/- 22 W, p < 0.05). Restricting fluid below ad libitum rates impaired performance (LO group). Rates greater than ad libitum did not result in further improvements. Ad libitum fluid ingestion is optimal as it prevents athletes from ingesting too little or too much fluid.
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A diuretic drug (40 mg of furosemide) was utilized to study the effects of dehydration (D) on competitive running performance, without prior thermal or exercise stress. Eight men competed in randomized races of 1,500, 5,000, and 10,000 m, while normally hydrated (H) and with mean plasma volume reductions of 9.9, 12.3, and 9.9%, respectively. As a result of the reduced body water (change in body weight = -1.9, -1.6, and -2.1%), mean outdoor performance times on a running track increased 0.16 min, 1.31 min (P less than 0.05), and 2.62 min (P less than 0.05) in the 1,500-m, 5,000-m, and 10,000-m trials. Running performance decrements due to dehydration were more strongly correlated with changes in body weight (r = -0.79, -0.65, and -0.40) than with urine volume or plasma volume differences. In addition, subjects were studied during submaximal and maximal treadmill exercise while H and D (mean change in plasma volume = -7.1%). Neither submaximal nor maximal oxygen uptake was significantly altered (P greater than 0.05) as a consequence of D. Mean treadmill run time to volitional exhaustion was reduced by 41.4 s (P less than 0.05) during the D treadmill trial. Therefore, it appears that competitive performance in trials of long duration (5,000 and 10,000 m) was affected to a greater extent by D than the shorter 1,500-m event, even though submaximal and maximal oxygen uptake was not altered.
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The mean weight loss of runners who completed the marathon course at the 1970 Commonwealth Games was 3·13 kg. (S.D. ± 0·88 kg.). Osmolalities of samples of urine collected after the race varied from 430 to 1340 mosmole per litre. These findings are discussed in relation to fluid balance and renal function. Two examples of transient neuromuscular abnormalities in racing cyclists are described.
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The mechanical power output and work done in running were measured for eight athletic runners by means of a strain gauge platform and 16mm cine camera. The angle between the line connecting the centre of gravity of the body with the foot on the ground and the horizontal line was about 110 degrees at the moment of foot contact with the ground, independent of running velocity. The external work by velocity change (Wf) increased curvilinearly with the running velocity up to about 630 Joule kg at maximum velocity. The mechanical power output per body weight in forward direction (Pf) increased as the 2nd power of the running velocity and the following equation was obtainedPf=0·436V fwhere Pf was expressed in Wkg and Vf in ms. At the velocity higher than 6ms, the mechanical power by forward velocity changes (Pf) increased gradually greater than that against gravity (Pv) but at the lower velocity than 5ms Pf was always less than Pv.