Hydration status in college football players during consecutive days of twice-a-day preseason practices

Customizing individual heat mitigation strategies to optimize performance in elite athletes

The aim of this review is twofold: 1) provide a brief discussion surrounding the interindividual variability that has been observed within the context of heat acclimation/acclimatization, body cooling, and hydration strategies, and 2) provide the reader with a practitioner-focused approach for creating individualized heat mitigation strategies. Considering individual variability for heat acclimation and heat acclimatization, various body cooling strategies, and hydration assessment/fluid replacement is important to maximize effects of these strategies, which lead to better performance and health outcomes. There are many factors to consider, and comprehensive approaches are required. The evidenced-informed decision is critical when making an individual approach, and data will help to make decisions effectively. It is important to keep adjusting the approach based on observed data as data is useful information to check if the approach is effective. Specific considerations to individualize the plan are discussed in this review.

Football Practices in Hot Environments Impact Subsequent Days' Hydration

ABSTRACT

Ashley, CD, Lopez, RM, and Tritsch, AJ. Football practices in hot environments impact subsequent days' hydration. J Strength Cond Res 38(1): 90-96, 2024-The impact of proper hydration to prevent exertional heat illness in American football has not been evaluated during high school preseason football practices in a hot environment (wet-bulb globe temperature = 31.3 ± 1.8° C). The purposes of this study were to examine the accuracy of urinary hydration measures to assess body mass (BM) changes and to examine carryover effects of consecutive practices by comparing postpractice with the next prepractice values. Before and after each of 7 outdoor practices, 31 male high school football players (age = 16 ± 1 years, height = 181.2 ± 12.0 cm, BM = 85.7 ± 19.1 kg, body mass index = 20.8 ± 1.8) provided a urine sample and were weighed to assess hydration. Sensitivity and specificity of urine color (Ucol) and urine-specific gravity (USG) to determine BM changes were determined using receiver operating characteristic (ROC) analysis. Paired samples t -tests assessed carryover effects between practices. Repeated-measures analysis of variance assessed carryover effects across practices. Significance was set at p < 0.05. Sensitivity and specificity for using Ucol or USG to determine BM changes was not significant. For Ucol, there was a carryover effect from practice numbers 2 to 3, 6 to 7 am , 7 am to 7 pm ( p < 0.001 for all), and 10 to 11 ( p = 0.004); most with less than 24 hours between practices. The %BM loss (%BML) was significantly greater ( p = 0.001 to 0.024) after 2-a-day practices. Effects of previous days' exercise in the heat, as evidenced by higher Ucol and %BL, are greater after 2-a-day practices, which occurred on later practice days. Athletes must replenish fluids during and between practices to remain euhydrated.

Accuracy of a smart bottle in measuring fluid intake by American football players during pre-season training

Rehydration is important for athlete performance and recovery. However, it can be challenging to follow appropriate fluid replacement practices due in part to difficulties in tracking fluid intake in real time. The purpose of this study was to determine the accuracy of a smart bottle in measuring fluid intake during exercise. Thirty male American football athletes drank from bottles equipped with a smart cap during outdoor pre-season practices (110 ± 30 min; 29.3 ± 3.0 °C; 75 ± 11% rh). The cap technology included optical sensors, microprocessors, batteries, and wireless connectivity that transmitted fluid volume data to a smartphone application in real-time. Reference measurements of fluid intake from the smart bottle were determined by gravimetry followed by conversion to volume using the density of the fluid consumed. There was no significant mean difference in fluid intake between the smart bottle and reference method (1220 ± 371 ml vs. 1236 ± 389 ml, p = 0.39 paired t test). Bland-Altman 95% limits of agreement between methods was - 212 to 180 ml. The smart bottle provided accurate measurements of fluid intake during exercise in real-world field conditions on a group level and within limits of agreement of - 212 to 180 ml (or approximately ± 15% of overall fluid intake) on an individual level.

Fluid Balance, Sodium Losses and Hydration Practices of Elite Squash Players during Training

Elite squash players are reported to train indoors at high volumes and intensities throughout a microcycle. This may increase hydration demands, with hypohydration potentially impairing many key performance indicators which characterise elite squash performance. Consequently, the main aim of this study was to quantify the sweat rates and sweat [Na+] of elite squash players throughout a training session, alongside their hydration practices. Fourteen (males = seven; females = seven) elite or world class squash player’s fluid balance, sweat [Na+] and hydration practices were calculated throughout a training session in moderate environmental conditions (20 ± 0.4 °C; 40.6 ± 1% RH). Rehydration practices were also quantified post-session until the players’ next training session, with some training the same day and some training the following day. Players had a mean fluid balance of −1.22 ± 1.22% throughout the session. Players had a mean sweat rate of 1.11 ± 0.56 L·h−1, with there being a significant difference between male and female players (p < 0.05), and a mean sweat (Na+) of 46 ± 12 mmol·L−1. Players training the following day were able to replace fluid and sodium losses, whereas players training again on the same day were not. These data suggest the variability in players hydration demands and highlight the need to individualise hydration strategies, as well as training prescription, to ensure players with high hydration demands have ample time to optimally rehydrate.

The Impact of Environmental Conditions on Player Loads During Preseason Training Sessions in Women's Soccer Athletes

ABSTRACT

Austin, AB, Collins, SM, Huggins, RA, Smith, BA, and Bowman, TG. The impact of environmental conditions on player loads during preseason training sessions in women's soccer athletes. J Strength Cond Res 35(10): 2775-2782, 2021-Our objective was to determine the impact of environmental conditions on player loads during preseason training sessions in women's soccer athletes. Eleven women's NCAA Division III soccer players (age = 20 ± 1 year, height = 167.28 ± 8.65 cm, body mass = 60.18 ± 5.42 kg, V̇o2max = 43.70 ± 3.95 ml·kg-1·min-1) volunteered to wear Global Positioning System (GPS) devices (Sports Performance Tracking, Melbourne, Australia) that provided measures of training session external intensity throughout all preseason practices (n = 15). We recorded wet-bulb globe temperature (WBGT), session Rating of Perceived Exertion-Training Load (sRPE-TL), and ΔBM during each preseason training session and set α ≤ 0.05. The combination of WBGT, sRPE-TL, and ΔBM explained 34% of the variance in GPS-based intensity score (proprietary measure) (F3,153 = 26.25, p < 0.001). Wet-bulb globe temperature (t156 = -2.58, p = 0.01), sRPE (t156 = 8.24, p < 0.001), and ΔBM (t156 = 2.39, p = 0.02) were significantly associated with intensity. The ΔBM from prepractice (60.00 ± 5.21 kg) to postpractice (59.61 ± 5.10 kg) was statistically significant (p < 0.001); however, ΔBM from the beginning of preseason (59.87 ± 5.31 kg) to the end of preseason (59.91 ± 5.58 kg) was not significant (p = 0.89). Despite relatively low to moderate environmental conditions, increases in WBGT were associated with reductions in GPS intensity and elevated internal load via sRPE-TL. Our findings support the association between exercise intensity and WBGT, internal load, and hydration status; thus, coaches and exercise scientists should take these factors into account when monitoring or interpreting intensity metrics. Furthermore, these findings support the continued use of environmental monitoring and hydration best-practice policies to limit exercise intensity in the heat so as to mitigate excessive heat stress.

Thermoregulation and Hydration in Female American Football Players During Practices

ABSTRACT

Lopez, RM, Ashley, CD, Zinder, SM, and Tritsch, AJ. Thermoregulation and hydration in female American football players during practices. J Strength Cond Res 35(9): 2552-2557, 2021-Little is known about hydration practices and thermoregulation in female tackle football players. The purpose of the study was to examine the thermoregulatory and hydration responses of female professional American football players. Fifteen females from the same tackle football team volunteered for this observational field study. Each subject was observed for 4 practices for the following measures: gastrointestinal temperature (TGI), maximum TGI, heart rate (HR), maximum HR (HRmax), fluid consumption, sweat rate, percent body mass loss (%BML), urine specific gravity (USG), urine color (Ucol), perceptual measures of thirst, thermal sensations, and rating of perceived exertion (RPE). Descriptive data (mean ± SD) were calculated for all measures. Main measures were analyzed using a repeated-measures analysis of variance. Trials took place during evening practices. Average TGI during practices was 38.0 ± 0.3° C while maximum TGI was 38.4 ± 0.3° C (n = 14). Average practice HR was 118 ± 11 b·min-1, while HRmax was 148 ± 13 b·min-1. Subjects arrived at practices with Ucol of 3 ± 1 and USG of 1.018 ± 0.007. Postpractice USG (1.022 ± 0.007) was significantly higher than prepractice across all days (p < 0.001). The average sweat rate across 4 practices was 0.6 ml·h-1. Average %BML was 0.3 ± 0.4%. Thirst and thermal sensations were moderate (4 ± 1 and 5 ± 1, respectively), while RPE was 11 ± 1. Female football players tended to have similar physiological responses to males. Although subjects seemed to adequately match their sweat losses with fluid consumed during practice, there was considerable variability in hydration indices and hydration habits, with some subjects experiencing hypohydration and others overestimating their fluid needs. Those working with this population should emphasize the need for hydration education and establish individualized hydration regimens.

Heart Rate Variability in College Football Players throughout Preseason Camp in the Heat

We aimed to characterize cardiac-autonomic responses to a 13-day preseason camp in the heat among an American college football team. Players were categorized as linemen (n=10) and non-linemen (n=18). RHR, natural logarithm of the root-mean square of successive differences multiplied by twenty (LnRMSSD), and subjective wellbeing (LnWellness) were acquired daily. Effect sizes±90% confidence interval showed that for linemen, LnRMSSD decreased (moderate) on day 2 (71.2±10.4) and increased (moderate) on day 12 (87.1±11.2) relative to day 1 (77.9±11.2) while RHR decreased (small-moderate) on days 6, 7, and 12 (67.7±9.3-70.4±5.5 b∙min-1) relative to day 1 (77.1±10.1 b∙min-1). For non-linemen, LnRMSSD increased (small-large) on days 3-5, 7, 12, and 13 (83.4±6.8-87.6±8.5) relative to day 1 (80.0±6.5) while RHR decreased (small-large) on days 3-9, 12, and 13 (62.1±5.2-67.9±8.1 b∙min-1) relative to day 1 (70.8±6.2 b∙min-1). Decrements in LnWellness were observed on days 4-10 and 13 for linemen (moderate) and on days 6-9, 12, and 13 for non-linemen (small-moderate). Despite reductions in LnWellness, cardiac-autonomic parameters demonstrated responses consistent with heat-acclimation, which possibly attenuated fatigue-related decrements.

Progressive Dehydration in Junior Laser Class Sailors During World Championship

The purpose of this article is to assess the hydration status of elite young sailing athletes during World Championship competition. Twelve young, elite, male, Laser Class sailors (age: 15.8 ± 1.1 y, height: 1.74 ± 0.1 m, weight: 65.1 ± 1.5 kg, body fat: 12.5 ± 3.1%, training experience: 7.0 ± 1.2 y) participated in this descriptive study. After three-day baseline bodyweight measurements, hydration status was assessed via pre- and post-race body weights, urine-specific gravity, and thirst ratings via a visual analog scale during four consecutive days of racing. Measurements and data collection took place at the same time each racing day, with mean environmental temperature, humidity, and wind speed at 23.0 ± 0.8°C, 64-70%, and 9 ± 1 knots, respectively. Average racing time was 130 ± 9 min. Body weight was significantly decreased following each race-day as compared to prerace values (Day 1: -1.1 ± 0.2, Day 2: -2.5 ± 0.1, Day 3: -2.8 ± 0.1, and Day 4: -3.0 ± 0.1% of body weight; p < 0.05). The participants exhibited dehydration of -2.9 ± 0.2 and -5.8 ± 0.2% of body weight before and after the fourth racing day as compared to the three-day baseline body weight. Urine-specific gravity (pre-post → Day 1: 1.014-1.017; Day 2: 1.019-1.024; Day 3: 1.021-1.026; Day 4: 1.022-1.027) and thirst (pre-post → Day 1: 2.0-5.2; Day 2: 3.2-5.5; Day 3: 3.7-5.7; Day 4: 3.8-6.8) were also progressively and significantly elevated throughout the four days of competition. The data revealed progressive dehydration throughout four consecutive days of racing as indicated by decreased body weight, elevated urine concentration, and high thirst.

Fluid Balance in Team Sport Athletes and the Effect of Hypohydration on Cognitive, Technical, and Physical Performance

Sweat losses in team sports can be significant due to repeated bursts of high-intensity activity, as well as the large body size of athletes, equipment and uniform requirements, and environmental heat stress often present during training and competition. In this paper we aimed to: (1) describe sweat losses and fluid balance changes reported in team sport athletes, (2) review the literature assessing the impact of hypohydration on cognitive, technical, and physical performance in sports-specific studies, (3) briefly review the potential mechanisms by which hypohydration may impact team sport performance, and (4) discuss considerations for future directions. Significant hypohydration (mean body mass loss (BML) >2%) has been reported most consistently in soccer. Although American Football, rugby, basketball, tennis, and ice hockey have reported high sweating rates, fluid balance disturbances have generally been mild (mean BML <2%), suggesting that drinking opportunities were sufficient for most athletes to offset significant fluid losses. The effect of hydration status on team sport performance has been studied mostly in soccer, basketball, cricket, and baseball, with mixed results. Hypohydration typically impaired performance at higher levels of BML (3-4%) and when the method of dehydration involved heat stress. Increased subjective ratings of fatigue and perceived exertion consistently accompanied hypohydration and could explain, in part, the performance impairments reported in some studies. More research is needed to develop valid, reliable, and sensitive sport-specific protocols and should be used in future studies to determine the effects of hypohydration and modifying factors (e.g., age, sex, athlete caliber) on team sport performance.

Individual fluid plans versus ad libitum on hydration status in minor professional ice hockey players

Background

Despite exercising in cool environments, ice hockey players exhibit several dehydration risk factors. Individualized fluid plans (IFPs) are designed to mitigate dehydration by matching an individual’s sweat loss in order to optimize physiological systems and performance.

Methods

A randomized control trial was used to examine IFP versus ad libitum fluid ingestion on hydration in 11 male minor professional ice hockey players (mean age = 24.4 ± 2.6 years, height = 183.0 ± 4.6 cm, weight = 92.9 ± 7.8 kg). Following baseline measures over 2 practices, participants were randomly assigned to either control (CON) or intervention (INT) for 10 additional practices. CON participants were provided water and/or carbohydrate electrolyte beverage to drink ad libitum. INT participants were instructed to consume water and an electrolyte-enhanced carbohydrate electrolyte beverage to match sweat and sodium losses. Urine specific gravity, urine color, and percent body mass change characterized hydration status. Total fluid consumed during practice was assessed.

Results

INT consumed significantly more fluid than CON (1180.8 ± 579.0 ml vs. 788.6 ± 399.7 ml, p = 0.002). However, CON participants replaced only 25.4 ± 12.9% of their fluid needs and INT 35.8 ± 17.5%. Mean percent body mass loss was not significantly different between groups and overall indicated minimal dehydration (<1.2% loss). Pre-practice urine specific gravity indicated CON and INT began hypohydrated (mean = 1.024 ± 0.007 and 1.024 ± 0.006, respectively) and experienced dehydration during practice (post = 1.026 ± 0.006 and 1.027 ± 0.005, respectively, p < 0.001). Urine color increased pre- to post-practice for CON (5 ± 2 to 6 ± 1, p < 0.001) and INT (5 ± 1 to 6 ± 1, p < 0.001).

Conclusions

Participants consistently reported to practice hypohydrated. Ad libitum fluid intake was not significantly different than IFP on hydration status. Based on urine measures, both methods were unsuccessful in preventing dehydration during practice, suggesting practice-only hydration is inadequate to maintain euhydration in this population when beginning hypohydrated.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Heat Illness in Football: Current Concepts

Despite growing health and safety concerns, American football remains a vastly popular sport in the United States. Unfortunately, even with increased efforts in promoting education and hydration, the incidence of death from exertional heat stroke continues to rise. General risk factors such as hydration status, obesity, fitness level, and football-specific risk factors such as timing of training camp and equipment all contribute to the development of heat illness. At the professional level, changes have been made to effectively reduce mortality from heat stroke with no deaths since August 2001. However, there have been at least 33 total deaths at the high school and collegiate levels since this time. More efforts need to be focused at these levels to mandate exertional heat illness prevention guidelines in order to reverse this trend of mortality in our younger athletes.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

The effect of selective head-neck cooling on physiological and cognitive functions in healthy volunteers

In general, brain temperatures are elevated during physical sporting activities; therefore, reducing brain temperature shortly after a sports-related concussion (SRC) could be a promising intervention technique. The main objective of this study was to examine the effects of head and neck cooling on physiological and cognitive function in normal healthy volunteers. Twelve healthy volunteers underwent two different sessions of combined head and neck cooling, one session with a cold pack and one session with a room temperature pack. Physiological measurements included: systolic/diastolic blood pressure, pulse oximetry, heart rate, and sublingual and tympanic temperature. Cognitive assessment included: processing speed, executive function, and working memory tasks. Physiological measurements were taken pre-, mid- and post-cooling, while cognitive assessments were done before and after cooling. The order of the sessions was randomized. There was a significant decrease in tympanic temperature across both sessions; however more cooling occurred when the cold pack was in the device. There was no significant decrease in sublingual temperature across either session. The observed heart rates, pulse oximetry, systolic and diastolic blood pressure during the sessions were all within range of a normal healthy adult. Cognitive assessment remained stable across each session for both pre- and post-cooling. We propose that optimizing brain temperature management after brain injury using head and neck cooling technology may represent a sensible, practical, and effective strategy to potentially enhance recovery and perhaps minimize the subsequent short and long term consequences from SRC.

Estado de hidratação de atletas em corrida de rua de 15 km sob elevado estresse térmico

INTRODUÇÃO: Um adequado estado de hidratação é de suma importância para os participantes de corridas de rua, tanto para um melhor desempenho esportivo, quanto na prevenção dos distúrbios causados pelo calor. OBJETIVO: O estudo visa avaliar o estado de hidratação de indivíduos do sexo masculino em corrida de rua de 15 km. MÉTODOS: A amostra foi composta por 15 indivíduos do sexo masculino (37,67±7,22 anos) praticantes habituais de corrida de rua. O estado de hidratação foi avaliado antes e após a corrida através dos seguintes parâmetros: peso corporal, coloração e gravidade específica da urina (GEU), análise da impedância bioelétrica (BIA), níveis de hemoglobina (Hb) e hematócrito (Ht). Na análise dos dados, foi utilizado o teste t de Student pareado ou o teste de Wilcoxon, aceitando-se como estatisticamente significante p < 0,01. RESULTADOS: Houve diminuição do peso corporal dos indivíduos após a corrida (p<0,0001), assim como elevação dos níveis de Hb e Ht. Apesar da diminuição observada na GEU após o exercício, não houve melhora significativa do padrão de coloração da urina ou diferença entre o conteúdo inicial e final de água corporal total. A temperatura ambiente (TA) e umidade relativa do ar (URA) foram de 38,75±1,79°C e 37,37±4,66%, respectivamente. CONCLUSÃO: O exercício no ambiente em questão conduziu os indivíduos a um estado de desidratação, apenas detectado pela análise da variação do peso corporal e de parâmetros sanguíneos através dos níveis de Hb e Ht. Parâmetros urinários como a coloração da urina e GEU, assim como aqueles obtidos através da BIA, provavelmente foram confundidos por variáveis não controladas pelo presente estudo.

Sonographic inferior vena cava measurements to assess hydration status in college football players during preseason camp

OBJECTIVES

The purpose of this study was to determine whether sonographic measurement of the inferior vena cava (IVC) in college football players during preseason camp is a reliable way to detect and monitor dehydration. Our primary hypothesis was that IVC diameter measurements, the postpractice caval index, and expiratory diameter were significantly related to percent weight loss after a preseason football practice.

METHODS

A prospective cohort sample of Division I intercollegiate football players in preseason training camp was recruited before practice. All football players on the active roster who were at least 18 years of age were eligible to participate in the study. Sonographic IVC measurements were obtained in the long axis using either the subcostal or subxiphoid approach during inspiration and expiration both before and after an approximately 3-hour practice with moderate to high levels of exertion at high ambient temperatures. Player weights were recorded in the locker room before and after practice.

RESULTS

A total of 27 prepractice and postpractice sonographic measurements were obtained. The postpractice expiratory IVC diameter was significantly related to percent weight loss after practice (R(2) = 0.153; P = .042), with the IVC diameter being significantly inversely correlated with percent weight loss; the regression coefficient was -1.07 (95% confidence interval, -2.09 to -0.04). There was no statistically significant relationship between percent weight loss and the postpractice caval index; the regression coefficient was 0.245 (95% confidence interval, -0.10 to 0.59; R(2) = 0.078; P = .16).

CONCLUSIONS

The postpractice expiratory IVC diameter was significantly related to percent weight loss after practice, whereas the caval index was not found to correlate with weight loss.

A novel head-neck cooling device for concussion injury in contact sports

Emerging research on the long-term impact of concussions on athletes has allowed public recognition of the potentially devastating effects of these and other mild head injuries. Mild traumatic brain injury (mTBI) is a multifaceted disease for which management remains a clinical challenge. Recent pre-clinical and clinical data strongly suggest a destructive synergism between brain temperature elevation and mTBI; conversely, brain hypothermia, with its broader, pleiotropic effects, represents the most potent neuro-protectant in laboratory studies to date. Although well-established in selected clinical conditions, a systemic approach to accomplish regional hypothermia has failed to yield an effective treatment strategy in traumatic brain injury (TBI). Furthermore, although systemic hypothermia remains a potentially valid treatment strategy for moderate to severe TBIs, it is neither practical nor safe for mTBIs. Therefore, selective head-neck cooling may represent an ideal strategy to provide therapeutic benefits to the brain. Optimizing brain temperature management using a National Aeronautics and Space Administration (NASA) spacesuit spinoff head-neck cooling technology before and/or after mTBI in contact sports may represent a sensible, practical, and effective method to potentially enhance recover and minimize post-injury deficits. In this paper, we discuss and summarize the anatomical, physiological, preclinical, and clinical data concerning NASA spinoff head-neck cooling technology as a potential treatment for mTBIs, particularly in the context of contact sports.

Ad libitum fluid consumption via self- or external administration

CONTEXT

During team athletic events, athletic trainers commonly provide fluids with water bottles. When a limited number of water bottles exist, various techniques are used to deliver fluids.

OBJECTIVE

To determine whether fluid delivered via water-bottle administration influenced fluid consumption and hydration status.

DESIGN

Crossover study.

SETTING

Outdoor field (22.2°C ± 3.5°C).

PATIENTS OR OTHER PARTICIPANTS

Nineteen participants (14 men, 5 women, age = 30 ± 10 years, height = 176 ± 8 cm, mass = 72.5 ± 10 kg) were recruited from the university and local running clubs.

INTERVENTION(S)

The independent variable was fluid delivery with 3 levels: self-administration with mouth-to-bottle direct contact (SA-DC), self-administration with no contact between mouth and bottle (SA-NC), and external administration with no contact between the mouth and the bottle (EA-NC). Participants warmed up for 10 minutes before completing 5 exercise stations, after which an ad libitum fluid break was given, for a total of 6 breaks.

MAIN OUTCOME MEASURE(S)

We measured the fluid variables of total volume consumed, total number of squirts, and average volume per squirt. Hydration status via urine osmolality and body-mass loss, and perceptual variables for thirst and fullness were recorded. We calculated repeated-measures analyses of variance to assess hydration status, fluid variables, and perceptual measures to analyze conditions across time.

RESULTS

The total volume consumed for EA-NC was lower than for SA-DC (P = .001) and SA-NC (P = .001). The total number of squirts for SA-DC was lower than for SA-NC (P = .009). The average volume per squirt for EA-NC was lower than for SA-DC (P = .020) and SA-NC (P = .009). Participants arrived (601.0 ± 21.3 mOsm/L) and remained (622.3 ± 38.3 mOsm/L) hydrated, with no difference between conditions (P = .544); however, the EA-NC condition lost more body mass than did the SA-DC condition (P = .001). There was no main effect for condition on thirst (P = .147) or fullness (P = .475).

CONCLUSIONS

External administration of fluid decreased total volume consumed via a decreased average volume per squirt. The SA-DC method requires fewer squirts within a specific time frame. Fluid breaks every 15 minutes resulted in maintenance of euhydration; however, loss of body mass was influenced by fluid administration. Athletic trainers should avoid external administration to promote positive hydration behaviors. When fluid is self-administered, individual bottles may be the best clinical practice because more volume can be consumed per squirt.

The acute effects of fluid intake on urine specific gravity and fluid retention in a mildly dehydrated state

Many athletes arrive at training sessions and competitions in a mildly hypohydrated (HYPO) state and are instructed to drink fluids before exercise to reach a euhydrated (HYD) state. Ten recreational athletes (6 women, 4 men; 71.9 ± 4.6 kg, 25.2 ± 0.9 years) participated in the studies to examine (a) the day-to-day variability of morning urine specific gravity (USG), (b) the effects of consuming 600 ml of water on the hydration status of HYD and HYPO (USG > 1.020) subjects, and (c) the effects of consuming water (W), salt-water (SW, 40 mM Na), a carbohydrate-electrolyte solution with 3% or light carbohydrate (CES-L, 20 mM Na) or a CES with 6% carbohydrate (CES, 20 mM Na) on the hydration status of HYPO subjects. The hydration status was assessed with USG and body mass measures and urine volume collections. The day-to-day variability in morning USG (coefficient of variation = 0.2 ± 0.1%) was low and the responses to 600 ml of W ingestion were repeatable. Pretrial USG was 1.022 ± 0.001 in the HYPO trial and decreased <1.020 by 45 minutes (1.013 ± 0.003). In the CES study, HYPO subjects reached HYD status at 45 minutes in all conditions (W 1.013 ± 0.003, SW 1.013 ± 0.003, CES-L 1.011 ± 0.003, CES 1.017 ± 0.004) because salt or CES ingestion did not affect fluid retention (W 68%, SW 72%, CES-L 68%, CES 76%). This study demonstrated that mildly HYPO subjects could reach euhydration within 45 minutes of the ingestion of 600 ml of W or a combination of salt and CES solutions. Following this practice will minimize the incidence of starting a practice or competition hypohydrated.

Personal food systems of male collegiate football players: a grounded theory investigation

CONTEXT

Factors that affect food choices include the physical and social environments, quality, quantity, perceived healthfulness, and convenience. The personal food choice process was defined as the procedures used by athletes for making food choices, including the weighing and balancing of activities of daily life, physical well-being, convenience, monetary resources, and social relationships.

OBJECTIVE

To develop a theoretical model explaining the personal food choice processes of collegiate football players.

DESIGN

Qualitative study.

SETTING

National Collegiate Athletic Association Division II football program.

PATIENTS OR OTHER PARTICIPANTS

Fifteen football players were purposefully sampled to represent various positions, years of athletic eligibility, and ethnic backgrounds.

DATA COLLECTION AND ANALYSIS

For text data collection, we used predetermined, open-ended questions. Data were analyzed using the constant comparison method. The athletes' words were used to label and describe their interactions and experiences with the food choice process. Member checks and an external audit were conducted by a qualitative methodologist and a nutrition specialist, and the findings were triangulated with the current literature to ensure trustworthiness of the text data.

RESULTS

Time was the core category and yielded a cyclic graphic of a theoretical model for the food choice system. Planning hydration, macronutrient strategies, snacks, and healthful food choices emerged as themes.

CONCLUSIONS

The athletes planned meals and snacks around their academic and athletic schedules while attempting to consume foods identified as healthful. Healthful foods were generally lower in fat but high in preferred macronutrients. High-protein foods were the players' primary goal; carbohydrate consumption was secondary. The athletes had established plans to maintain hydration. Professionals may use these findings to implement educational programs on food choices for football players.

Dehydration decreases saliva antimicrobial proteins important for mucosal immunity

The aim of the study was to investigate the effect of exercise-induced dehydration and subsequent overnight fluid restriction on saliva antimicrobial proteins important for host defence (secretory IgA (SIgA), α-amylase, and lysozyme). On two randomized occasions, 13 participants exercised in the heat, either without fluid intake to evoke progressive body mass losses (BML) of 1%, 2%, and 3% with subsequent overnight fluid restriction until 0800 h in the following morning (DEH) or with fluids to offset losses (CON). Participants in the DEH trial rehydrated from 0800 h until 1100 h on day 2. BML, plasma osmolality (Posm), and urine specific gravity (USG) were assessed as hydration indices. Unstimulated saliva samples were assessed for flow rate (SFR), SIgA, α-amylase, and lysozyme concentrations. Posm and USG increased during dehydration and remained elevated after overnight fluid restriction (BML = 3.5% ± 0.3%, Posm = 297 ± 6 mosmol·kg–1, and USG = 1.026 ± 0.002; P < 0.001). Dehydration decreased SFR (67% at 3% BML, 70% at 0800 h; P < 0.01) and increased SIgA concentration, with no effect on SIgA secretion rate. SFR and SIgA responses remained unchanged in the CON trial. Dehydration did not affect α-amylase or lysozyme concentration but decreased secretion rates of α-amylase (44% at 3% BML, 78% at 0800 h; P < 0.01) and lysozyme (46% at 3% BML, 61% at 0800 h; P < 0.01), which were lower than in CON at these time points (P < 0.05). Rehydration returned all saliva variables to baseline. In conclusion, modest dehydration (~3% BML) decreased SFR, α-amylase, and lysozyme secretion rates. Whether the observed magnitude of decrease in saliva AMPs during dehydration compromises host defence remains to be shown.

Fluid Balance and Dehydration in the Young Athlete

Many young athletes train and compete under conditions that put their body fluid balance at risk, and hypohydration is usually the major concern. Another less frequent condition is hyperhydration that—if accompanied by other risk factors—may cause hyponatremia. Water and electrolyte losses during physical activities occur primarily from sweat. Such losses have been identified mostly in active (but nonathletic) young populations under laboratory settings. Studies have been trying to estimate fluid losses in the athletic population under field conditions, taking into account the sport modality and environmental conditions. Besides these external conditions, young athletes adopt different drinking attitudes, which may depend on knowledge, education, and the opportunities to drink during the break periods as well as fluid availability. Focusing on the young athlete, this review will discuss water and sodium losses from sweat, the effects of hypohydration on performance, and fluid intake attitudes within and during practices and competitions. Some considerations related to the methods of identifying hydration status and guidelines are also given, with the understanding that they should be individually adapted for the athlete and activity. The young athlete, parents, coaches, and athletic/health professionals should be aware of such information to prevent fluid imbalances and the consequent hazardous effects on performance and health.

Heat acclimation decreased oxidative DNA damage resulting from exposure to high heat in an occupational setting

Heat acclimation is a physiologically and biochemically adapted process when species transition from one environmental temperature to one of the increased temperature. There is very limited epidemiological evidence on the heat-related impacts during exposure to extremely high heat in an occupational environment. This study sought to identify a potential biomarker of heat acclimation and the burden of heat on the body. The aim of this study was to elucidate oxidative DNA damage and heat acclimation through a self-comparison study design in navy boiler tenders, subjects exposed to extremely high heat in an occupational setting. Fifty-eight male soldiers who work in a boiler room were recruited for this study. The subjects were initially assessed with a health examination and body composition assessment before sailing. In order to compare the within-subject differences before and after heat exposure, the index-related heat exposure was collected before and after a routine 5-h work shift and 7-day sailing. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), a useful marker of oxidative DNA damage was the measurement by liquid chromatography/tandem mass spectrometry. The median of the change in urinary 8-OHdG was 0.78 μg/g creatinine, as the urinary 8-OHdG after sailing was significantly higher than before sailing (p < 0.01). The urinary 8-OHdG was significantly decreased in heat-acclimated boiler tenders. Oxidative DNA damage was significantly decreased in heat-acclimated subjects. Urinary 8-OHdG can be used as a biomarker to assess the effect of heat stress as a result of occupational exposure to extremely high heat conditions.

Efeito de suplemento hidroeletrolítico na hidratação de jogadores juniores de futebol

O estado de hidratação de jogadores sub-18 de um time de futebol foi avaliado após a ingestão de suplemento hidroeletrolítico mais aceito em teste afetivo. A aceitação de três suplementos elaborados foi avaliada por meio de teste afetivo em laboratório. O estudo foi realizado com nove jogadores de futebol, do sexo masculino, submetidos a 80 minutos de treinamento, com a ingestão de 900mL de suplemento hidroeletrolítico comercial (controle) ou suplemento mais aceito no teste sensorial e 300mL de água. Para avaliação do estado de hidratação foram determinados o tempo de movimentação, a intensidade do exercício, a densidade de urina, o peso corporal, a perda de peso corporal, a porcentagem de perda de peso corporal, o grau de hidratação e a taxa de sudorese. A bebida com 8% de carboidrato teve melhor aceitação. A intensidade de exercício dos jogadores foi maior no dia de ingestão da bebida teste em comparação ao dia de ingestão da bebida controle, já o tempo de movimentação em relação à bebida teste foi significativamente menor do que a bebida controle (p = 0,008). A perda de peso, o grau de desidratação e a taxa de sudorese dos atletas com ingestão da bebida teste foram maiores quando comparadas à ingestão da bebida controle. Os atletas concluíram a partida mais desidratados com a ingestão de bebida teste; contudo, o limite de 2% de perda de peso corporal não foi ultrapassado. A intensidade do exercício (de leve a moderada) e as condições climáticas (temperatura mais baixa e umidade relativa do ar mais elevada) no dia da ingestão da bebida controle podem ter favorecido os melhores resultados de capacidade de hidratação da bebida comercial.

Gastrointestinal temperature trends in football linemen during physical exertion under heat stress

CONTEXT

Exertional heat stroke is the third leading cause of death in US athletes. Elevations in core temperature in the digestive tract (TGI) have correlated with core temperature and are possible indicators of those at increased risk of heat stroke.

OBJECTIVE

The primary objective was to compare a.m. vs. p.m. TGI variation in collegiate football linemen during intense "two-a-day" preseason practice. A secondary objective was to compare longitudinal TGI in offensive and defensive linemen.

DESIGN

Cross-sectional observational study.

SETTING

Division I Intercollegiate Athletics Football Program.

INTERVENTIONS

TGI was monitored during consecutive preseason sessions.

MAIN OUTCOME MEASUREMENTS

TGI, heat illness, weight changes, environmental stress, and subjective symptoms.

RESULTS

Mean TGI were 37.8°C and 38.3°C during a.m. and p.m. practices, respectively. The a.m. practices revealed higher TGI gain (1.8°C) compared to p.m. (1.4°C). The p.m. practices had higher maximum TGI than a.m. practices (39.1°C versus 38.8, P=0.0001). Mean time to maximum temperature (Tmax) was 1 hr and 30 min for a.m. and 1 hr and 22 min for p.m. practices. Offensive linemen trended toward higher mean TGI than defensive players (38.0°C vs. 36.7°C, P = 0.069). The rate of rise in TGI was significantly greater in a.m. practices. A decrease in rate of TGI rise was seen from the first to last a.m. practices of the week (P = 0.004).

CONCLUSION

Significant TGI elevations in asymptomatic athletes are common in extreme heat during football practice. Intense a.m. practices in full gear result in higher net temperature gain and rate of temperature gain than p.m. practices. Offensive linemen trended toward higher TGI than defensive linemen. As players acclimatized, a decrease in the rate of TGI increase was appreciable, particularly in a.m. practices. Appreciating cumulative heat stress and variations in heat stress related to scheduling of practice is critical.

Water, hydration, and health

This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Sweat rates, sweat sodium concentrations, and sodium losses in 3 groups of professional football players

CONTEXT

Sweat sodium losses have never been reported in a large cohort of American football players.

OBJECTIVE

To compare sweat rates (SwtRs), sweat sodium concentrations (SwtNa(+)), and sodium losses in 3 groups of players (backs and receivers [BK], linebackers and quarterbacks [LB/QB], and linemen [LM]) to determine if positional differences and, therefore, size differences exist.

DESIGN

Observational study.

SETTING

Data were collected during practices in the second week of 2 consecutive training camps. The wet bulb globe temperature was 78.5 degrees F +/- 3.5 degrees F (25.9 degrees C +/- 1.9 degrees C).

PATIENTS OR OTHER PARTICIPANTS

Eighteen BK, 12 LB/QB, and 14 LM volunteered.

INTERVENTION(S)

Sterile sweat patches were applied to the right forearm after the skin was appropriately cleaned. The patches were removed during practice, placed in sterile tubes, centrifuged, frozen, and later analyzed by flame photometry.

MAIN OUTCOME MEASURE(S)

Sweat rate, SwtNa(+), and sodium loss. We calculated SwtR by change in mass adjusted for urine produced and fluids consumed divided by practice time in hours.

RESULTS

Other than age, physical characteristics were different among groups (P < .001). The SwtR was different among groups (F(2,41) = 7.3, P = .002). It was lower in BK (1.42 +/- 0.45 L/h) than in LB/QB (1.98 +/- 0.49 L/h) (P < .05) and LM (2.16 +/- 0.75 L/h) (P < .01), but we found no differences between SwtRs for LB/QB and LM. The SwtNa(+) was not different among groups (BK = 50 +/- 16 mEq/L, LB/QB = 48.2 +/- 23 mEq/L, and LM = 52.8 +/- 25 mEq/L) and ranged from 15 to 99 mEq/L. Sweat sodium losses ranged from 642 mg/h to 6.7 g/h, and findings for group comparisons approached significance (P = .06). On days when players practiced 4.5 hours, calculated sodium losses ranged from 2.3 to 30 g/d.

CONCLUSIONS

The BK sweated at lower rates than did the midsized LB/QB and large LM, but LB/QB sweated similarly to LM. Sweat sodium concentration and daily sodium losses ranged considerably. Heavy, salty sweaters require increased dietary consumption of sodium during preseason.

Fluid consumption and sweating in National Football League and collegiate football players with different access to fluids during practice

CONTEXT

Considerable controversy regarding fluid replacement during exercise currently exists.

OBJECTIVE

To compare fluid turnover between National Football League (NFL) players who have constant fluid access and collegiate football players who replace fluids during water breaks in practices.

DESIGN

Observational study.

SETTING

Respective preseason training camps of 1 National Collegiate Athletic Association Division II (DII) football team and 1 NFL football team. Both morning and afternoon practices for DII players were 2.25 hours in length, and NFL players practiced for 2.25 hours in the morning and 1 hour in the afternoon. Environmental conditions did not differ.

PATIENTS OR OTHER PARTICIPANTS

Eight NFL players (4 linemen, 4 backs) and 8 physically matched DII players (4 linemen, 4 backs) participated.

INTERVENTION(S)

All players drank fluids only from their predetermined individual containers. The NFL players could consume both water and sports drinks, and the DII players could only consume water.

MAIN OUTCOME MEASURE(S)

We measured fluid consumption, sweat rate, total sweat loss, and percentage of sweat loss replaced. Sweat rate was calculated as change in mass adjusted for fluids consumed and urine produced.

RESULTS

Mean sweat rate was not different between NFL (2.1 +/- 0.25 L/h) and DII (1.8 +/- 0.15 L/h) players (F(1,12) = 2, P = .18) but was different between linemen (2.3 +/- 0.2 L/h) and backs (1.6 +/- 0.2 L/h) (t(14) = 3.14, P = .007). We found no differences between NFL and DII players in terms of percentage of weight loss (t(7) = -0.03, P = .98) or rate of fluid consumption (t(7) = -0.76, P = .47). Daily sweat loss was greater in DII (8.0 +/- 2.0 L) than in NFL (6.4 +/- 2.1 L) players (t(7) = -3, P = .02), and fluid consumed was also greater in DII (5.0 +/- 1.5 L) than in NFL (4.0 +/- 1.1 L) players (t(7) = -2.8, P = .026). We found a correlation between sweat loss and fluids consumed (r = 0.79, P < .001).

CONCLUSIONS

During preseason practices, the DII players drinking water at water breaks replaced the same volume of fluid (66% of weight lost) as NFL players with constant access to both water and sports drinks.

Thermoregulatory responses and hydration practices in heat-acclimatized adolescents during preseason high school football

CONTEXT

Previous researchers have not investigated the thermoregulatory responses to multiple consecutive days of American football in adolescents.

OBJECTIVE

To examine the thermoregulatory and hydration responses of high school players during formal preseason football practices.

DESIGN

Observational study.

SETTING

Players practiced outdoors in late August once per day on days 1 through 5, twice per day on days 6 and 7, and once per day on days 8 through 10. Maximum wet bulb globe temperature averaged 23 +/- 4 degrees C.

PATIENTS OR OTHER PARTICIPANTS

Twenty-five heat-acclimatized adolescent boys (age = 15 +/- 1 years, height = 180 +/- 8 cm, mass = 81.4 +/- 15.8 kg, body fat = 12 +/- 5%, Tanner stage = 4 +/- 1).

MAIN OUTCOME MEASURE(S)

We observed participants within and across preseason practices of football. Measures included gastrointestinal temperature (T(GI)), urine osmolality, sweat rate, forearm sweat composition, fluid consumption, testosterone to cortisol ratio, perceptual measures of thirst, perceptual measures of thermal sensation, a modified Environmental Symptoms Questionnaire, and knowledge questionnaires assessing the participants' understanding of heat illnesses and hydration. Results were analyzed for differences across time and were compared between younger (14-15 years, n = 13) and older (16-17 years, n = 12) participants.

RESULTS

Maximum daily T(GI) values remained less than 40 degrees C and were correlated with maximum wet bulb globe temperature (r = 0.59, P = .009). Average urine osmolality indicated that participants generally experienced minimal to moderate hypohydration before (881 +/- 285 mOsmol/kg) and after (856 +/- 259 mOsmol/kg) each practice as a result of replacing approximately two-thirds of their sweat losses during exercise but inadequately rehydrating between practices. Age did not affect most variables; however, sweat rate was lower in younger participants (0.6 +/- 0.2 L/h) than in older participants (0.8 +/- 0.1 L/h) (F(1,18) = 8.774, P = .008).

CONCLUSIONS

Previously heat-acclimatized adolescent boys (T(GI) < 40 degrees C) can safely complete the initial days of preseason football practice in moderate environmental conditions using well-designed practice guidelines. Adolescent boys replaced most sweat lost during practice but remained mildly hypohydrated throughout data collection, indicating inadequate hydration habits when they were not at practice.

Efeito do nível de condicionamento físico e da hidratação oral sobre a homeostase hídrica em exercício aeróbico

Objetivou-se avaliar a influência do nível de condicionamento físico no estado de hidratação e a eficácia do consumo de 3mL de água/kg de peso corporal para manter a eu-hidratação de indivíduos atletas ou ativos saudáveis. Foram avaliados 15 atletas {VO2máx 68 ± 5,4mL (kg.min)-1} e 15 sujeitos ativos {VO2máx 50,3 ± 6,3mL(kg.min)-1} saudáveis do sexo masculino. O estado de hidratação foi diagnosticado por meio do monitoramento do peso corporal, da gravidade específica da urina e do hematócrito durante 80 minutos de corrida em esteira. Foram consumidos, durante a atividade, 3mL de água/kg de peso corporal. As condições ambientais do teste foram de 21,9 ± 1,5°C e 89,2 ± 5,6% de umidade relativa do ar (URA) para os atletas e 21,8 ± 1,6°C e 93,2 ± 3,5% URA para os ativos. O percentual médio de desidratação e a perda de peso relativa foram significativamente maiores nos atletas (2,15 ± 0,7% e 1,3 ± 0,5kg), comparados aos ativos (1,03 ± 0,7% e 0,74 ± 0,43kg), respectivamente. A gravidade específica da urina aumentou significativamente apenas nos atletas, enquanto o hematócrito não variou significativamente entre os grupos. Considerando as condições de teste, conclui-se que o nível de condicionamento mais alto permitiu menor estado de hidratação e que, embora a perda hídrica não tenha atingido níveis críticos, a estratégia de hidratação utilizada (3mL de água/kg de peso corporal) não foi suficiente para manter os avaliados completamente eu-hidratados.

Estimation of prepractice hydration status of National Collegiate Athletic Association Division I athletes

CONTEXT

To our knowledge, no one has compared the prepractice hydration status of male and female National Collegiate Athletic Association (NCAA) Division I athletes or has studied the effects of the menstrual cycle phase on women's prepractice hydration status.

OBJECTIVE

To report prepractice hydration status of collegiate athletes and determine the factors that might influence that status.

DESIGN

Cross-sectional, descriptive study.

SETTING

University sports team practices.

PATIENTS OR OTHER PARTICIPANTS

Participants included 138 male and 125 female athletes (age = 19.9 + or - 1.3 years, height = 165.8 + or - 42.9 cm, mass = 77.4 + or - 17.5 kg) from an NCAA Division I New England university.

INTERVENTION(S)

One spontaneously voided (spot) urine sample was collected from each participant before his or her team practice and was measured 2 times.

MAIN OUTCOME MEASURE(S)

A refractometer was used to analyze the amount of light that passed through a small drop of urine and assess urine specific gravity. Fluid intake and menstrual history for women were also collected. Three hydration-status groups were defined based on the American College of Sports Medicine and National Athletic Trainers' Association criteria: (1) euhydrated, which was urine specific gravity less than 1.020; (2) hypohydrated, from 1.020 to 1.029; and (3) significantly hypohydrated, equal to or more than 1.030.

RESULTS

Thirteen percent of student-athletes appeared significantly hypohydrated, with a mean urine specific gravity of 1.031 + or - 0.002 (chi(2) = 12.12, P < .05); 53% appeared hypohydrated, with a mean urine specific gravity of 1.024 + or - 0.003 (chi(2) = 12.12, P < .05); and 34% appeared euhydrated, with a mean urine specific gravity of 1.012 + or - 0.005 (chi(2) = 0.03, P > .05). A greater percentage of men (47%) than women (28%) were hypohydrated (chi(2) = 8.33, P < .05). In women, no difference was evident between the luteal and follicular phases of their menstrual cycles (chi(2) = 0.02, P > .05).

CONCLUSIONS

Before activity, athletes were hypohydrated at different levels. A greater percentage of men than women were hypohydrated. Menstrual cycle phase did not appear to affect hydration in women.

Sweat rate, salt loss, and fluid intake during an intense on-ice practice in elite Canadian male junior hockey players

Previous research in many sports suggests that losing ~1%–2% body mass through sweating impairs athletic performance. Elite-level hockey involves high-intensity bursts of skating, arena temperatures are >10 °C, and players wear protective equipment, all of which promote sweating. This study examined the pre-practice hydration, on-ice fluid intake, and sweat and sodium losses of 44 candidates for Canada’s junior men’s hockey team (mean ± SE age, 18.4 ± 0.1 y; height, 184.8 ± 0.9 cm; mass, 89.9 ± 1.1 kg). Players were studied in groups of 10–12 during 4 intense 1 h practices (13.9 °C, 66% relative humidity) on 1 day. Hydration status was estimated by measuring urine specific gravity (USG). Sweat rate was calculated from body mass changes and fluid intake. Sweat sodium concentration ([Na]) was analyzed in forehead sweat patch samples and used with sweat rate to estimate sodium loss. Over 50% of players began practice mildly hypohydrated (USG > 1.020). Sweat rate during practice was 1.8 ± 0.1 L·h–1 and players replaced 58% (1.0 ± 0.1 L·h–1) of the sweat lost. Body mass loss averaged 0.8% ± 0.1%, but 1/3 of players lost more than 1%. Sweat [Na] was 54.2 ± 2.4 mmol·L–1 and sodium loss averaged 2.26 ± 0.17 g during practice. Players drank only water during practice and replaced no sodium. In summary, elite junior hockey players incurred large sweat and sodium losses during an intense practice, but 2/3 of players drank enough to minimize body mass loss. However, 1/3 of players lost more than 1% body mass despite ready access to fluid and numerous drinking opportunities from the coaches.

Sweat rates and fluid turnover in professional football players: a comparison of National Football League linemen and backs

CONTEXT

Many National Football League (NFL) teams practice 2 times per day over consecutive days in a hot and humid environment. Large body surface area (BSA) and use of protective equipment result in high sweat rates and total sweat loss in these football players.

OBJECTIVE

To compare sweat rate, sweat loss, fluid consumption, and weight loss between NFL linemen and backs during preseason practices.

DESIGN

Between-groups design.

SETTING

Preseason training camp with wet bulb globe temperature between 19 degrees C and 25 degrees C.

PATIENTS OR OTHER PARTICIPANTS

Eight linemen and 4 backs and receivers participated.

MAIN OUTCOME MEASURE(S)

Data were collected during both practice sessions on 2 separate days during the first week of August. Sweat rate was calculated as change in mass adjusted for all fluids consumed between prepractice and postpractice body mass measurements and the urine produced during practice divided by the length of the practice session. Gross daily sweat losses also were calculated.

RESULTS

Height, mass, and BSA were higher in linemen than in backs. Sweat rate was also higher in linemen (2385 +/- 520 mL/h) than in backs (1410 +/- 660 mL/h, P < .001), as was the total volume of sweat lost during both practices in 1 day (6870 +/- 1034 mL/d versus 4110 +/- 2287 mL/d, P = .014). Compared with backs, linemen consumed more fluids during practice (2030 +/- 849 mL versus 1179 +/- 753 mL, P = .025) but produced less urine (53 +/- 73 mL versus 163 +/- 141 mL, P = .018). There was no difference in postpractice weight loss (linemen = -1.15 +/- 0.83%, backs = -1.06 +/- 0.76%).

CONCLUSIONS

Linemen sweated at higher rates, lost larger volumes of sweat, consumed more fluids, and produced less urine during practice compared with the physically smaller backs, but they did not lose a greater percentage of body weight. Sodium losses could be considerable in NFL players during the preseason because of high daily sweat losses in backs and in linemen.

Heat-related illness in athletes

Heat stroke in athletes is entirely preventable. Exertional heat illness is generally the result of increased heat production and impaired dissipation of heat. It should be treated aggressively to avoid life-threatening complications. The continuum of heat illness includes mild disease (heat edema, heat rash, heat cramps, heat syncope), heat exhaustion, and the most severe form, potentially life-threatening heat stroke. Heat exhaustion typically presents with dizziness, malaise, nausea, and vomiting, or excessive fatigue with accompanying mild temperature elevations. The condition can progress to heat stroke without treatment. Heat stroke is the most severe form of heat illness and is characterized by core temperature >104 degrees F with mental status changes. Recognition of an athlete with heat illness in its early stages and initiation of treatment will prevent morbidity and mortality from heat stroke. Risk factors for heat illness include dehydration, obesity, concurrent febrile illness, alcohol consumption, extremes of age, sickle cell trait, and supplement use. Proper education of coaches and athletes, identification of high-risk athletes, concentration on preventative hydration, acclimatization techniques, and appropriate monitoring of athletes for heat-related events are important ways to prevent heat stroke. Treatment of heat illness focuses on rapid cooling. Heat illness is commonly seen by sideline medical staff, especially during the late spring and summer months when temperature and humidity are high. This review presents a comprehensive list of heat illnesses with a focus on sideline treatments and prevention of heat illness for the team medical staff.

Evidence-Based Approach to Lingering Hydration Questions

Studies related to fundamental hydration issues have required clinicians to re-examine certain practices and concepts. The ingestion of substances such as creatine, caffeine, and glycerol has been questioned in regards to safety and hydration status. Reports of overdrinking (hyponatremia) also have brought into question the practices of drinking appropriate fluid amounts and the role that fluid-electrolyte balance has in the etiology of heat illnesses such as heat cramps. This article offers a fresh perspective on timely topics related to hydration, fluid balance, and exercise in the heat.