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American College of Sports Medicine position stand. Exercise and Fluid Replacement
Abstract
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.
... Inappropriate responses to dehydration may result in the decline of physical function and performance [7] and also increases the risk of exertional heat stroke [8]. The adequacy of fluid intake during training can be determined from the change in body mass measured before and after the training and it has been suggested that more than 2% of weight loss can impair the aerobic performance of athletes [9,10]. ...
... Furthermore, the large exposure of body extremities is also considered important [16]. To date, national and international organizations such as the American College of Sports Medicine (ACSM), the National Athletic Trainers' Association (NATA), and the International Olympic Committee (IOC) have proposed position stands that specifically focus on hydration [9,17,18]. In Japan, the Japan Sports Association (JSPO) published a guidebook for the prevention of heat stroke during sports activities [16]. ...
... While this technique is popular, it is important to acknowledge that comparing body mass measurements before and after training sessions alone cannot detect the presence of dehydration prior to training. A number of studies reported the dehydrated status of athletes even before training [7][8][9]. Considering the possibility that Kendo players may also be dehydrated before their training [45], it may be recommended to examine the pre-training hydration status of Kendo players in future research. ...
Background/Objectives: Global warming and the rise in the average temperature in recent years have increased the risk of heat stroke and also deteriorated performance among athletes. Kendo, a traditional Japanese martial art and also a competitive sport, is reported to have high incidents of heat stroke and related mortality. However, there is no heat management guideline for this specific sport to date and research on its heat management practices and risk factors for heat stroke are limited. The present study conducted a scoping review on studies focused on heat stress and the heat management practices of Kendo players. Methods: A literature search was conducted using five databases (PubMed, SCOPUS, Ichu-shi Web, CiNii, and Google Scholar) and also manually from the references of searched articles. Results: Overall, the studies that have investigated the heat stress of Kendo players are scarce and outdated. Of the 15 references that met screening criteria, 11 studies were conducted in a field setting. The vast majority were conducted on male university students and there was a lack of research on females and on different age groups. Common measures of heat management practices used in previous studies were weight changes before and after training (n = 14), body temperature (n = 9), and heart rate (n = 8). Only a few studies used multiple measures to determine heat stress. Conclusions: Considering the continuation of global warming and the increasing risk of heat stroke, further investigation on heat stress, its association with health and performance, and current heat management practices in Kendo players are warranted.
... When performing in warm and humid conditions, players' heat production from intense physical activity often exceeds their ability to dissipate excessive heat, which may increase the risk of exertional heat illness 9,10 . In response to prolonged exercise in a hot environment, intense sweating is triggered, which may result in dehydration of the body 11,12 . It is estimated that dehydration above 2% of the body weight adversely affects cognitive functions, physical and intellectual capabilities, and also inhibits the body's thermoregulatory mechanisms 13 , while dehydration of 3-4% of body weight significantly compromises soccer players' performance 14 . ...
... Ov index was calculated according to 67 using Eqs. (11)(12)(13) derived from the Clapeyron equation: ...
This study investigates the risk of severe heat stress and associated potential water losses in professional soccer players, considering as well the oxygen content of the inhaled air in the context of the 2026 FIFA World Cup. For the 16 stadiums, hourly values of biometeorological indices (adjusted Universal Thermal Climate Index – UTCI, Water loss – SW and Oxygen volume - Ov) were calculated. UTCI adjustments included modifications to activity levels, movement speeds and clothing configurations to better reflect the level of thermal stress on soccer player during a match. Ten out of the sixteen sites of the 2026 FIFA World Cup are at very high risk of experiencing extreme heat stress conditions. The highest risk of uncompensable thermal stress due to very high average hourly UTCI values above 49.5 °C and excessive water loss (> 1.5 kg/h) occur in the afternoon in stadiums located in Arlington, Houston (USA) and in Monterrey (Mexico). The results of this study will enable optimization of match schedules at individual venues, taking into account the health risks associated with extreme heat stress, but also the physiological reactions to heat potentially affecting the performance of players on the pitch.
... Sodium in particular, is purported to be key for maintaining plasma osmolality and regulating fluid movement between the intra-and extra-cellular compartments (Baker and Wolfe 2020). The concentration of sweat sodium ([Na + ]) has been documented to vary significantly between individuals, ranging from as low as 10 mmoL·L −1 to exceeding 100 mmoL·L −1 (Baker et al. 2022;Sawka et al. 2007). The variability in sweat composition is associated with several factors such as exercise intensity (Baker et al. 2022), acclimation status (Kirby and Convertino 1986), sex (Lobeck and Huebner 1962) and dietary sodium intake (Allsopp et al. 1998). ...
... Consequently, it is recommended that athletes adopt personalised hydration strategies, often incorporating sodium replenishment, so as Communicated by George Havenith. to reduce the risk of exercise-induced hypohydration, heat cramps, and decrements in exercise performance (Sawka et al. 2007). ...
... Özellikle dayanıklılık ve kuvvet antrenmanlarının sürdürülebilirliği açısından, protein sentezini destekleyecek ve kas dokusunun yenilenmesini sağlayacak beslenme stratejilerinin uygulanması gerekmektedir. Ayrıca, hidrasyon durumu da adaptasyonların sürdürülebilirliği için önemlidir, çünkü dehidrasyon, antrenman performansını ve kasların toparlanma sürecini olumsuz etkileyebilir (Sawka et al., 2007). ...
... Dehidrasyon, kas dokusunun kan akışını ve oksijen taşıma kapasitesini azaltarak kas onarımını ve protein sentezini olumsuz etkileyebilir (Maughan & Shirreffs, 2010). Ayrıca, dehidrasyon durumunda, kaslarda meydana gelen mikrotravmaların iyileşme süresi uzayabilir ve kasların adaptasyon kapasitesi düşebilir (Sawka et al., 2007). Sporcuların antrenman öncesi, sırası ve sonrasında yeterli miktarda su tüketmeleri, kasların optimal bir şekilde çalışmasını ve antrenman sonrası adaptasyonların sürdürülebilir olmasını sağlar (Casa et al., 2000). ...
Antrenman bilimi, sporcuların performansını artırmak ve uzun vadeli başarı sağlamak için sürekli gelişen bir alan olmuştur. Ancak günümüzün dinamik spor dünyasında, sadece kısa vadeli performans artışı değil, uzun süreli sürdürülebilir bir gelişim de giderek daha fazla önem kazanmaktadır. Sürdürülebilirlik kavramı, antrenman bilimi içinde, hem sporcuların fiziksel ve zihinsel sağlığını korumayı hem de spor kaynaklarını ve çevresel etkiyi optimize etmeyi içerir. Bu bağlamda, sürdürülebilir bir antrenman yönetimi, sporcuların uzun yıllar boyunca en üst düzeyde performans gösterebilmesi ve sporun gelecek nesiller için aynı etkiyi devam ettirebilmesi açısından kritik bir rol oynamaktadır. Antrenman bilimi alanında sürdürülebilirlik, üç temel bileşen etrafında şekillenir: fizyolojik, psikolojik ve çevresel. Fizyolojik sürdürülebilirlik, sporcuların aşırı antrenman, sakatlık ve yorgunluk gibi sorunlarla karşılaşmadan gelişimlerini sürdürebilmelerini sağlamayı hedefler. Psikolojik sürdürülebilirlik ise sporcuların zihinsel dayanıklılığını artırarak, motivasyonlarının uzun süre devam etmesine katkı sağlar. Çevresel sürdürülebilirlik ise antrenman süreçlerinde kullanılan malzeme, ekipman ve tesislerin çevre dostu olmasını ve antrenmanların doğaya minimum zarar vermesini içerir. Bu noktada, nitel araştırmalar, sürdürülebilir antrenman uygulamalarının anlaşılması ve geliştirilmesi açısından önemli bir yöntemdir. Niteliksel araştırma yöntemleri, sporcuların bireysel deneyimlerini, antrenörlerin stratejilerini ve uzun vadeli başarı planlarını daha derinlemesine anlamamıza olanak tanır. Mülakatlar, vaka incelemeleri ve katılımcı gözlem gibi nitel yöntemler, sürdürülebilir antrenman programlarının nasıl yapılandırılması gerektiği konusunda değerli bilgiler sunar. Örneğin, nitel araştırmalar yoluyla sporcuların antrenman süreçlerinde karşılaştıkları zorluklar, motivasyon kayıpları ya da sürdürülebilir bir başarı için hangi stratejilerin daha etkili olduğu gibi sorulara yanıt bulmak mümkündür. Aynı şekilde, antrenörlerin sürdürülebilirlik konusundaki bakış açıları, bu alandaki politikaların ve uygulamaların iyileştirilmesine yardımcı olabilir. Bu kitap, antrenman bilimi alanında sürdürülebilirlik konusunu derinlemesine ele almakta ve bu süreçte nitel araştırmaların nasıl bir katkı sağladığını irdelemektedir. Kitap boyunca, antrenmanların sürdürülebilirliğini artırmak için kullanılabilecek stratejilere ve bu stratejilerin uygulanabilirliğini destekleyen nitel araştırma bulgularına yer verilecektir. Sporcu sağlığı ve performansının sürdürülebilirliği üzerine odaklanan bu çalışma hem akademisyenler hem de pratikte çalışan antrenörler için değerli bir kaynak olmayı hedeflemektedir. Ayrıca bu kitap Sürdürülebilir Spor ve Niteliksel Araştırmalar Serimizin üçüncü kitabını oluşturmaktadır. Alan yazına bilimsel olarak büyük anlamlar katacak bir araştırma kitabı olması temennisiyle.
... Notably, sweat rate values during physical activity have been reported to be in the range of 0.5-2.0 L/h (kg/h) [10], values obtained by means of the whole-body method. Also, it has been demonstrated that individualized hydration routines (linked to each person's physiology) are more successful in preserving peak performance and averting consequences associated with dehydration [11,12]. ...
Sweat rate magnitude is a desired outcome for any wearable sensing patch dedicated to sweat analysis. Indeed, sweat rate values can be used two-fold: self-diagnosis of dehydration and correction/normalization of other physiological metrics, such as Borg scale, VO2, and different chemical species concentrations. Herein, a reliable sweat rate belt device for sweat rate monitoring was developed. The device measures sweat rates in the range from 1.0 to 5.0 µL min−1 (2 to 10 µL min−1 cm−2), which covers typical values for humans. The working mechanism is based on a new direct current (DC) step protocol activating a series of differential resistance measurements (spatially separated by 800 µm) that is gradually initiated by the action of sweat, which flows along a customized microfluidic track (~600 µm in width, 10 mm in length, and 235 µm in thickness). The device has a volumetric capacity of ~16 µL and an acquisition frequency between 0.010 and 0.043 Hz within the measured sweat rate range. Importantly, instead of using a typical and rather complex AC signal interrogation and acquisition, we put forward the DC approach, offering several benefits, such as simplified circuit design for easier fabrication and lower costs, as well as reduced power consumption and suitability for wearable applications. For the validation, either the commercial sweat collector (colorimetric) or the developed device was performed. In five on-body tests, an acceptable variation of ca. 10% was obtained. Overall, this study demonstrates the potential of the DC-based device for the monitoring of sweat rate and also its potential for implementation in any wearable sweat platform.
... Exertional-heat stress presents numerous challenges for health and performance. In relation to hydration status, exercise in the heat elevates metabolic heat production, whereby increases in sweat rate maintain thermal homeostasis via evaporative fluid losses from the skin [26]. If fluid losses are not sufficiently replaced, reductions in total body water and plasma volume (P V ) adversely alter cutaneous blood flow, elevate T c , and exacerbate cardiovascular responses during exercise [27,28]. ...
Global warming is attributed to an increased frequency of high ambient temperatures and humidity, elevating the prevalence of high-temperature-related illness and death. Evidence over recent decades highlights that tailored nutritional strategies are essential to improve performance and optimise health during acute and chronic exertional-heat exposure. Therefore, the purpose of this review is to discuss the efficacy of various nutritional strategies and ergogenic aids on responses during and following acute and chronic exertional-heat exposure. An outline is provided surrounding the application of various nutritional practices (e.g., carbohydrate loading, fluid replacement strategies) and ergogenic aids (e.g., caffeine, creatine, nitrate, tyrosine) to improve physiological, cognitive, and recovery responses to acute exertional-heat exposure. Additionally, this review will evaluate if the magnitude and time course of chronic heat adaptations can be modified with tailored supplementation practices. This review highlights that there is robust evidence for the use of certain ergogenic aids and nutritional strategies to improve performance and health outcomes during exertional-heat exposure. However, equivocal findings across studies appear dependent on factors such as exercise testing modality, duration, and intensity; outcome measures in relation to the ergogenic aid’s proposed mechanism of action; and sex-specific responses. Collectively, this review provides evidence-based recommendations and highlights areas for future research that have the potential to assist with prescribing specific nutritional strategies and ergogenic aids in populations frequently exercising in the heat. Future research is required to establish dose-, sex-, and exercise-modality-specific responses to various nutritional practices and ergogenic aid use for acute and chronic exertional-heat exposure.
... Contrary to our fndings, Silva and Mündel [32] found that the mean hydration status, measured by urine specifc gravity, indicated that youth players were dehydrated pretraining on MD-2 and MD-1 in youth Brazilian football players, although this may be attributable to the diferences in ambient temperature between the two studies. Below < 700 mOsmol/kg for urine osmolality is indicative of dehydration [33]. As can be seen from the average data, in the current study, most players were dehydrated on the morning of testing, indicating familiarity with proper hydration strategies, at least before exercise. ...
Introduction: The aim of this study was to assess match time courses on hydration, wellness, and sleep as well as the interrelationship between these variables in youth national soccer players.
Materials and Methods: Under-17 and under-19 youth national soccer players (age range: 16.96 ± 1.17 years) completed a perceptual wellness questionnaire, self-reported their sleep, and carried out hydration assessments each morning during a period of competitive match play.
Results: Players reported having significantly more sleep leading into the day of a match (MD) compared to both the evening after a match (MD-2; p<0.001; CI = 7.972 and 8.212) and the evening before a match (MD-1; p<0.001; CI = 7.996 and 8.174). Furthermore, players reported better health and wellbeing scores on MD compared to both MD-1 (p<0.001; CI = 19.231 and 19.692) and MD-2 (p<0.001; CI = 18.911 and 19.489). When self-reported sleep was correlated with the individual components of health and wellbeing, it was highlighted that there were significant effects for fatigue (r = 0.304, p<0.001; CI = 0.250 and 0.383), mood (r = 0.170, p<0.001; CI = 0.112 and 0.243), general muscle soreness (r = 0.225, p<0.001; CI = 0.162 and 0.306), and stress (r = 0.203, p<0.001; CI = 0.147 and 0.274).
Conclusion: It is important to consider sleep strategies to mitigate the potential impact of lack of sleep following match play. Self-reported sleep seems to be appropriate for estimating individual components of health and wellbeing, and therefore may be a suitable replacement for perceptual wellness questionnaires.
Objectives: This study was planned to determine the hydration status and tissue oxygen saturation of underwater hockey players during exercise. Materials and Methods: Hydration status (fluid intake/loss amounts, repeatedly weight measurements) and tissue oxygen saturation measurements of 14 underwater hockey players were performed before and after the land/water training, separately. Hydration status was assessed by monitoring weight and urine specific gravity (USG) measurements, whereas tissue oxygen saturation was measured by using finger-type pulse oximeter. Results: The study was completed with14 elite players (age=19.4±6.2 years, female=4(29%), and male=10(71%)). The body fat percentage was calculated to be male:14.2±9.4%; female: 18.8±4.0%. The mean USG of athletes was determined to be 1020.1±5.6 g/cm3. During the water training, only 5 athletes consumed water (680±383.4 mL). All the athletes (except for 1 athlete [7.1%]) completed the training with loss of body fluid. Mean loss of water was 310±213.2 mL after land training and 723.1±501.9 mL after water training. Dehydration ratio was measured 0.97±0.64% after trainings. The first oxygen saturation was measured 96.1±1.6, that was decreased after water training (94.6±2.2; p=0.044, p=0.049). Pulse increased after water training in reverse proportion to oxygen saturation (p=0.004), but there was no difference between before and after land training (p=0.132). Conclusion: It was found that several Underwater hockey players began training dehydrated and loss of water continued since they didn’t consume enough water during training. Oxygen saturation significantly decreased after water training. Fluid consumption of underwater hockey players, especially during water training, should be monitored and adequate fluid consumption should be ensured.
Forest trail difficulty levels must be investigated to promote their safe usage. However, exercise-based physiological changes are difficult to estimate in a forest environment. Hence, studies comparing indoor and outdoor environmental activities are required. We aimed to investigate the physiological traits associated with different usage grades of national forest trails in the Republic of Korea. We conducted both field and indoor experiments to measure different variables of 20 healthy participants aged 40–50 years to evaluate the exercise intensity and physiological effects of hiking on these trails. Significant variations in physiological responses were observed based on trail difficulty, with the highest heart rate and energy expenditure recorded during the most challenging uphill segments. Specifically, the heart rate increased from 115.4 ± 13.7 bpm in easy segments to 140.3 ± 15.6 bpm in difficult segments, whereas energy expenditure ranged from 404.1 ± 112.2 kcal/h to 518.1 ± 131.0 kcal/h. This study highlights the importance of considering both objective trail difficulty and users’ physiological reactions, including perceived exertion, to enhance user safety and optimize the health benefits of national forest trails. These findings provide essential data for developing comprehensive exercise programs and improving the national forest trail usage grade system.
Background: Dehydration, a common condition where the amount water lost from the body exceeds intake, disrupts metabolic processes and negatively impacts health and performance. Rehydration, the process of restoring body fluids and electrolytes to normal levels, is crucial for maintaining physiological health. In vivo dehydration models are experimental systems used to study the effects of dehydration on living organisms. However, a comprehensive summary of in vivo models and the application of human rehydration strategies is lacking. Methods: This review provides a comprehensive overview of various in vivo models and rehydration strategies. Results: In vivo models, stimulated by fluid restriction, exercise, thermal exposure, and chemicals, have been used to study dehydration. Importantly, the principles, characteristics, and limitations of the in vivo models are also discussed, along with rehydration administration methods, including oral, intestinal, intravenous, subcutaneous, and intraperitoneal routes. Additionally, rehydration strategies and the application for managing different dehydration conditions both in daily life and clinical settings have been summarized. Conclusions: Overall, this review aims to enhance the understanding of the conditions in which in vivo dehydration models and rehydration strategies are applicable, thereby advancing research into the physiological and pathological mechanisms of dehydration and supporting the development of effective rehydration therapies.
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-h 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° and 22°C (59° and 72°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 an oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.
Objective: To record weight changes, fluid intake and changes in serum sodium concentration in ultradistance triathletes.
Design: Descriptive research.
Setting: Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). Air temperature at 1200 h was 21°C, (relative humidity 91%). Water temperature was 20.7°C.
Participants: 18 triathletes.
Interventions: None.
Main Outcome Measures: Subjects were weighed and had blood drawn for serum sodium concentration [Na], hemoglobin, and hematocrit, pre-race, post-race, and at 0800 h on the morning following the race (recovery); subjects were also weighed at transitions. Fluid intake during the race was estimated by athlete recall.
Results: Median weight change during the race = -2.5 kg (p < 0.0006). Subjects lost weight during recovery (median = -1.0 kg) (p < 0.03). Median hourly fluid intake = 716 ml/h (range 421-970). Fluid intakes were higher on the bike than on the run (median 889 versus 632 ml/h, p = 0.03). Median calculated fluid losses cycling were 808 ml/h and running were 1,021 ml/h. No significant difference existed between pre-race and post-race [Na] (median 140 versus 138 mmol/L) or between post-race and recovery [Na] (median 138 versus 137 mmol/L). Plasma volume increased during the race, median + 10.8% (p = 0.0005). There was an inverse relationship between change in [Na] pre-race to post-race and relative weight change (r = -0.68, p = 0.0029). Five subjects developed hyponatremia ([Na] 128-133 mmol/L).
Conclusions: Athletes lose 2.5 kg of weight during an ultra-distance triathlon, most likely from sources other than fluid loss. Fluid intakes during this event are more modest than that recommended for shorter duration exercise. Plasma volume increases during the ultradistance triathlon. Subjects who developed hyponatremia had evidence of fluid overload despite modest fluid intakes.
While exercise heat stress and hydration status are known to independently influence heart rate variability (HRV), the combined effect of these physiological stressors is unknown. Thus, heat-acclimated subjects (n=5) performed exercise heat trials (40 °C, 20% relative humidity) in the euhydrated and hypohydrated state (3.9±0.7% body weight loss). During each trial, cardiac cycle R–R interval data were collected for 45 min at rest (pre-) and after (post-) completing 90 min of cycle ergometer exercise. Pre- and post-exercise RRI data were analyzed by Fast Fourier Power Spectral analysis to determine the high-frequency (HF), low-frequency (LF), very low-frequency (VLF), and total power (TP) components of HRV. Overall HRV was decreased by both hypohydration and exercise heat stress. Hypohydration reduced TP, LF, VLF, and LF:HF ratio (P<0.05) while HF was significantly higher. The change in both LF and HF power (pre- vs. post-exercise) were blunted during hypohydration compared to euhydration. These data suggest that dehydration alone positively influences the parasympathetic (HF) control of HRV, but the reduction in overall HRV and the blunted oscillations in LF and HF power following exercise heat stress support an overall deleterious effect of dehydration on autonomic cardiac stability.
Dehydration by means of exercise, heat, diuretics, semistarvation, or a combination of these is common practice among competitors in weight class sports. Many studies have demonstrated a reduced aerobic work capacity following each of these forms of dehydration. The effects of these practices on performance that requires energy derived primarily from anaerobic sources is not well documented. The purpose of this study was to examine the effects of progressive, acute, thermal dehydration on performance of an anaerobic criterion task. Eleven collegiate wrestlers performed the Wingate Anaerobic Test (WAnT) prior to and after each of the following mean weight losses: 2%, 4%, and 5%. Weight loss was induced by passive thermal dehydration (56°C, 15% RH). Approximately 2 h were required in the environmental chamber to lose the required weight at each stage. There was no significant change (P > 0.05) in the ability to perform the WAnT or its various indices at any stage of dehydration, nor were blood lactate concentrations post WAnT significantly different from predehydration levels. This suggests that anaerobic performance may not be impaired to the extent that aerobic performance is by passive, thermal dehydration to a 5% body weight loss. However, deleterious physiologic effects may result from dehydration practices even though performance levels are maintained.
To determine the differences in sweat composition between sweat induced by thermal stress alone and that induced by physical exercise, seven young healthy men first sat in a hot room and then performed running exercise. A 20-minute stay in a climate chamber at 40°C resulted in a 5% reduction in body weight. The same body weight loss was induced by running exercise. Both sodium and chloride concentrations were much lower in the sweat induced by thermal exposure than that induced by the running exercise (p<0.01), while urea nitrogen and creatinine concentrations were significantly higher after thermal exposure than after the running exercise (p<0.01). Potassium concentrations did not differ significantly with either procedure. These findings suggest that sweat composition varies with the kind of induction and that more salt seems to be lost through exercise-induced sweating than by just sitting in a hot environment.
The aim of this study was to examine if the pattern of fluid intake with a carbohydrate-electrolyte solution during 4 h recovery from prolonged, submaximal running would influence the subsequent endurance capacity. Seven well-trained athletes aged 19.8 +/- 0.3 years (mean +/- s(mean)) took part in the study, which had university ethical committee approval. They ran at 70% VO2 max on a level treadmill for 90 min (T1), or until volitional fatigue, whichever came first, on two occasions, at least 7-10 days apart. Four hours later, the subjects ran at the same speed for as long as possible (T2), as a measure of their endurance capacity. During the 4 h rehydration recovery period, the runners were allowed to drink a carbohydrate-electrolyte solution (6.9% Lucozade-Sport; sodium, 24 mmol l(-1); potassium, 2.6 mmol l(-1); calcium, 1.2 mmol l(-1); osmolality, 300 mOsm kg(-1)) ad libitum on one occasion. On the other occasion, the volume of the same fluid was prescribed from calculations of the body mass loss during T1 (2.6% of pre-exercise body mass). All subjects completed the 90 min run during T1 on both trials. However, during T2, in the prescribed intake trial, the exercise time to exhaustion was 16% longer (P< 0.05) than during T2 in the ad libitum trial (69.9 +/- 9.1 vs 60.2 +/- 10.2 min). Although there was no difference between conditions in the total volume ingested (1499 +/- 155 vs 1405 +/- 215 ml), the volume of carbohydrate-electrolyte solution ingested in the fourth hour of the rehydration recovery period was greater in the prescribed intake trial than in the ad libitum trial (258 +/- 52 vs 78 +/- 34 ml; P< 0.05). The amount of glucose ingested in this period during the prescribed intake trial was also greater than during the ad libitum trial (17.8 +/- 3.6 vs 5.4 +/- 2.4 g; P< 0.05). There was a higher blood lactate concentration at the start of T2 in the prescribed intake trial than in the ad libitum trial (1.12 +/- 0.20 vs 0.94 +/- 0.09 mmol l(-1); P< 0.05), but there were no differences in blood glucose, plasma insulin, free fatty acid concentrations or urine volume between trials. The results of this study suggest that drinking a prescribed volume of a carbohydrate-electrolyte solution after prolonged exercise, calculated to replace the body fluid losses, restores endurance capacity to a greater extent than ad libitum rehydration during 4 h of recovery, even though the total volumes ingested were the same between trials.
To examine the effects of rapid dehydration on isometric muscular strength and endurance, seven men were tested at baseline (control) and after a dehydration (dHST) and a euhydration (eHST) heat stress trial. The dHST consisted of intermittent sauna exposure until 4% of body mass was lost, whereas the eHST consisted of intermittent sauna exposure (same duration as dHST) with water replacement. Peak torque was determined for the knee extensors and elbow flexors during three isometric maximal voluntary contractions. Time to fatigue was determined by holding a maximal voluntary contraction until torque dropped below 50% peak torque for 5 s. Strength and endurance were assessed 3.5 h after the HSTs (no food or water intake). Body mass was decreased 3.8+/-0.4% post dHST and 0.4+/-0.3% post eHST. Plasma volume was decreased 7.5+/-4.6% and 5.7+/-4.4%, 60 and 120 min post dHST, respectively. A small (1.6 mEq x L[-1]) but significant increase was found for serum Na+ concentration 60 min post dHST but had returned to predehydration level 120 min post dHST. Serum K+ and myoglobin concentrations were not affected by HSTs. Peak torque was not different (P > 0.05) among control, dHST, and eHST for the knee extensors (Mean (Nm)+/-SD, 285+/-79, 311+/-113, and 297+/-79) and elbow flexors (79+/-12, 83+/-15, and 80+/-12). Time to fatigue was not different (P > 0.05) among control, dHST and eHST for the knee extensors (Mean (s)+/-SD. 42.4+/-11.5, 45.3+/-7.6, and 41.8+/-6.0) and elbow flexors (48.2+/-8.9, 44.0+/-9.4, and 46.0+/-6.4). These results provide evidence that isometric strength and endurance are unaffected 3.5 h after dehydration of approximately 4% body mass.
Exertional rhabdomyolysis is an uncommon diagnosis, but because its complications can be severe, clinicians need a thorough understanding of this syndrome. When skeletal muscle cell membranes are damaged, their intracellular contents enter the bloodstream and can cause potentially serious sequelae, even death. Intense exercise, some viral infections, and certain genetic disorders increase the risk. Serum creatine kinase levels are the diagnostic gold standard. The treatment of rhabdomyolysis consists of early detection, therapy for the underlying cause, measures to prevent renal failure, and correction of metabolic complications.
Evaporative water loss was measured in 8 Sudanese soccer players during 3 olympic qualifying matches in 3 different environmental conditions. Losses of up to 3% of body weight were found. Fluid replacement during half time interval were found to be inadequate and the results are discussed.