Fluid and electrolyte needs for preparation and recovery from training and competition

Isolate Whey Protein Promotes Fluid Balance and Endurance Capacity Better Than Isolate Casein and Carbohydrate-Electrolyte Solution in a Warm, Humid Environment

Protein ingestion is known to enhance post-exercise hydration. Whether the type of protein (i.e., whey, casein) can alter this response is unknown. Accordingly, this study aimed to compare the effects of the addition of milk-derived whey isolate or casein protein to carbohydrate-electrolyte (CE) drinks on post-exercise rehydration and endurance capacity. Thirty male soldiers (age: 24 ± 2.1 y; VO2max: 49.3 ± 4.7 mL/kg/min) were recruited. Upon losing ~2.2% of body mass by running in warm and humid conditions (32.3 °C, 76% relative humidity [RH]), participants ingested either a CE solution (66 g/L carbohydrate [CHO]), or CE plus isolate whey protein (CEW, 44 g/L CHO, 22 g/L isolate whey), or CE plus isolate casein protein (CEC, 44 g/L CHO, 22 g/L isolate casein) beverage in a volume equal to 150% of body mass loss. At the end of the 3 h rehydration period, a positive fluid balance was higher with CEW (0.22 L) compared to CEC (0.19 L) and CE (0.12 L). Overall mean fluid retention was higher in CEW (80.35%) compared with the CE (76.67%) and CEC trials (78.65%). The time of the endurance capacity test [Cooper 2.4 km (1.5 miles) run test] was significantly higher in CEC (14.25 ± 1.58 min) and CE [(12.90 ± 1.01 min; (p = 0.035)] than in CEW [(11.40 ± 1.41 min); (p = 0.001)]. The findings of this study indicate that the inclusion of isolate whey protein in a CE solution yields superior outcomes in terms of rehydration and enhanced endurance capacity, as compared to consuming the CE solution alone or in conjunction with isolate casein protein.

Tracking Health, Performance and Recovery in Athletes Using Machine Learning

Training and competitive periods can temporarily impair the performance of an athlete. This disruption can be short- or long-term, lasting up to several days. We analyzed the health indicators of 3661 athletes during an in-depth medical examination. At the time of inclusion in the study, the athletes were healthy. Instrumental examinations (fluorography, ultrasound examination of the abdominal cavity and pelvic organs, echocardiography, electrocardiography, and stress testing “to failure”), laboratory examinations (general urinalysis and biochemical and general clinical blood analysis), and examinations by specialists (ophthalmologist, otolaryngologist, surgeon, cardiologist, neurologist, dentist, gynecologist (women), endocrinologist, and therapist) were performed. This study analyzed the significance of determining the indicators involved in the implementation of the “catabolism” and “anabolism” phenotypes using the random forest and multinomial logistic regression machine learning methods. The use of decision forest and multinomial regression models made it possible to identify the most significant indicators of blood and urine biochemistry for the analysis of phenotypes as a characterization of the effectiveness of recovery processes in the post-competitive period in athletes. We found that the parameters of muscle metabolism, such as aspartate aminotransferase, creatine kinase, lactate dehydrogenase, and alanine aminotransferase levels, and the parameters of the ornithine cycle, such as creatinine, urea acid, and urea levels, made the most significant contribution to the classification of two types of metabolism: catabolism and anabolism.

Effects of carbohydrate-electrolyte dissolved alkaline electrolyzed water on physiological responses during exercise under heat stress in physically active men

Purpose

This study investigated the effects of 1400 mL intake of alkaline electrolyzed water (AEW) or purified water (PW) into which carbohydrate-electrolyte (CE) was dissolved on improving physiological responses during exercise under heat stress.

Methods

This double-blinded, crossover randomized controlled trial included 10 male participants who completed two exercise trials in a hot environment (35 °C, ambient temperature, and 50% relative humidity) after consuming CE-dissolved PW (P-CE) or CE-dissolved AEW (A-CE). The exercise trial consisted of running for 30 min on a treadmill (at an intensity corresponding to 65% of heart rate reserve adjusted for heat stress conditions) and repeated sprint cycling (10 × 7-s maximal sprint cycling), with a 35-min rest interval between the two exercises, followed by a 30-min post-exercise recovery period. Before and after running, and after cycling, the participants drank P-CE (hydrogen concentration of 0 ppm, pH 3.8) or A-CE (0.3 ppm, pH 4.1). Blood samples were obtained before, during (rest interval between running and cycling), and post-exercise.

Results

Repeated sprint performance and oxidative stress response did not differ between the P-CE and A-CE trials. A-CE consumption significantly attenuated the increase in blood lactate concentration during the running exercise but not during repeated sprint cycling under heat stress conditions.

Conclusion

Our findings suggested that A-CE did not significantly affect repeated sprint performance; however, the attenuated elevation in blood lactate by A-CE ingestion implies a partial enhancement of endurance performance during submaximal exercise under heat stress.

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A-CE did not enhance repeated sprint performance in a hot environment.

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A-CE failed to decrease oxidative damage induced by exercise in a hot environment.

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Blood lactate response during submaximal running was attenuated by drinking A-CE.

Influence of Peak Menstrual Cycle Hormonal Changes on Restoration of Fluid Balance After Induced Dehydration

The present study examined the impact of hormonal differences between late follicular (LF) and midluteal (ML) phases on restoration of fluid balance following dehydration. Ten eumenorrheic female participants were dehydrated by 2% of their body mass through overnight fluid restriction followed by exercise-heat stress. Trials were undertaken during the LF (between Days 10 and 13 of the menstrual cycle) and ML phases (between Days 18 and 23 of the menstrual cycle) with one phase repeated to assess reliability of observations. Following dehydration, participants ingested a volume equivalent to 100% of mass loss of a commercially available sports drink in four equal volumes over 30 min. Mean serum values for steroid hormones during the ML (estradiol [E2]: 92 ± 11 pg/ml, progesterone: 19 ± 4 ng/ml) and LF (estradiol [E2]: 232 ± 64 pg/ml, progesterone: 3 ± 2 ng/ml) were significantly different between phases. Urine tests confirmed no luteinizing hormone surge evident during LF trials. There was no effect of menstrual cycle phase on cumulative urine volume during the 3-hr rehydration period (ML: 630 [197-935] ml, LF: 649 [180-845] ml) with percentage of fluid retained being 47% (33-85)% on ML and 46% (37-89)% on LF (p = .29). There was no association between the progesterone:estradiol ratio and fluid retained in either phase. Net fluid balance, urine osmolality, and thirst intensity were not different between phases. No differences in sodium (ML: -61 [-36 to -131] mmol, LF: -73 [-5 to -118] mmol; p = .45) or potassium (ML: -36 [-11 to -80] mmol, LF: -30 [-19 to -89] mmol; p = .96) balance were observed. Fluid replacement after dehydration does not appear to be affected by normal hormonal fluctuations during the menstrual cycle in eumenorrheic young women.

Dietary Macronutrient and Micronutrient Intake over a 7-Day Period in Female Varsity Ice Hockey Players

This study examined the energy, macronutrient, and micronutrient intakes of female ice hockey players over a 7-d period including game, practice, and rest days. Twenty-three female varsity players (19.0 ± 1.1 yr, 167.1 ± 6.5 cm, 67.0 ± 8.0 kg) volunteered for the study. Average total daily energy expenditure (TDEE) was estimated over the 7-day period. Average 7-day energy intake (EI) and TDEE were 2354 ± 353 and 2304 ± 204 kcal. The majority (n = 19) of athletes had an EI ≥ 90% of their estimated TDEE. Macronutrient intake was 52% carbohydrate (CHO), 32% fat, and 16% protein of total EI, although CHO intake was slightly below recommendations (5 g/kg BM/d) on game and practice (4.8 ± 1.4 and 4.5 g/kg BM/d) days. Game day EI was greater than practice and rest days. Recommended micronutrient intakes were not met by most athletes for iron, calcium, vitamin D, and potassium, and intakes were similar between game, practice, and rest days. In summary, the average EI for female varsity ice hockey players appeared adequate to meet their energy needs over a weekly cycle of game, practice, and rest days. However, these female athletes would benefit from increasing CHO intake on game and practice days and selecting foods that are rich in vitamins and minerals.

Comparisons of isomaltulose, sucrose, and mixture of glucose and fructose ingestions on postexercise hydration state in young men

PURPOSE

Isomaltulose is a low glycemic and insulinaemic carbohydrate available as a constituent in sports drink. However, it remains unclear whether postexercise rehydration achieved by isomaltulose drink ingestion alone differs as compared to other carbohydrates.

METHODS

Thirteen young men performed intermittent exercise in the heat (35 °C and relative humidity 40%) to induce a state of hypohydration as defined by a 2% loss in body mass. Thereafter, participants were rehydrated by ingesting drinks equal to the volume of body mass loss with either a mixture of 3.25% glucose and 3.25% fructose, 6.5% sucrose (SUC), or 6.5% isomaltulose (ISO) within the first 30 min of a 3-h recovery. The change in plasma volume (ΔPV) from pre-exercise baseline, blood glucose, and plasma insulin concentration were assessed every 30-min.

RESULTS

ΔPV was lower in ISO as compared to SUC until 90 min of the recovery (all P ≤ 0.038) with no difference thereafter (all P ≥ 0.391). The ΔPV were paralleled by concomitant changes in blood glucose levels that were greater in ISO as compared to other drinks after 90 min of the recovery (all P ≤ 0.035). Plasma insulin secretion, which potentially enhances renal sodium reabsorption and fluid retention, did not differ between the trials (interaction, P = 0.653). ISO induced a greater net fluid volume retention as compared to SUC (P = 0.010).

CONCLUSION

We showed that rehydration with an isomaltulose drink following exercise-heat stress induces comparable recovery of PV and a greater net fluid retention as compared to other drinks, albeit this response is delayed. The delayed water transport along with glucose absorption may modulate this response. This trial was registered in 25th Sep 2019 at https://www.umin.ac.jp/ as UMIN000038099. (249/250).

Efficacy of Ingesting an Oral Rehydration Solution after Exercise on Fluid Balance and Endurance Performance

This study investigated the efficacy of ingesting an oral rehydration solution (DD) that has a high electrolyte concentration after exercise on fluid balance and cycling performance in comparison with a sports drink (SD) and water (WA). Nine healthy males aged 24 ± 2 years (mean ± SD), with peak oxygen uptake (VO₂ peak) 55 ± 6 mL·kg⁻¹·min⁻¹ completed three experimental trials in a randomised manner ingesting WA, SD (carbohydrates: 62 g·L⁻¹, sodium: 31 ± 3 mmol·L⁻¹) or DD (carbohydrates: 33 g·L⁻¹, sodium: 60 ± 3 mmol·L⁻¹). On all trials, fluid was ingested during 75 min cycling at 65% VO₂ peak (temperature: 30.4 ± 0.3 °C, relative humidity: 76 ± 1%, simulated wind speed: 8.0 ± 0.6 m·s⁻¹) and during 2 h of recovery (temperature: 23.0 ± 1.0 °C, relative humidity: 67 ± 2%), with the total volume equivalent to 150% of sweat loss during the ride. A 45 min pre-load cycling time trial at a 65% VO₂ peak followed by a 20 km time trial was conducted after a further 3 h of recovery. Fluid retention was higher with DD (30 ± 15%) than WA (−4 ± 19%; p < 0.001) and SD (10 ± 15%; p = 0.002). Mean ratings of palatability were similar among drinks (WA: 4.25 ± 2.60; SD: 5.61 ± 1.79; DD: 5.40 ± 1.58; p = 0.33). Although time trial performance was similar across all three trials (WA: 2365 ± 321 s; SD: 2252 ± 174 s; DD: 2268 ± 184 s; p = 0.65), the completion time was faster in eight participants with SD and seven participants with DD than with WA. Comparing SD with DD, completion time was reduced in five participants and increased in four participants. DD was more effective at restoring the fluid deficit during recovery from exercise than SD and WA without compromising the drink’s palatability with increased sodium concentration. Most individuals demonstrated better endurance exercise time trial performance with DD and SD than with WA.

Association of Copeptin, a Surrogate Marker of Arginine Vasopressin, with Decreased Kidney Function in Sugarcane Workers in Guatemala

BACKGROUND

Vasopressin is elevated in response to heat and dehydration and has been postulated to have a role in the chronic kidney disease of unknown origin being observed in Central America. The aims of this study were to examine whether the vasopressin pathway, as measured by copeptin, is associated with the presence of kidney dysfunction, and to examine whether higher fluid intake is associated with lower circulating copeptin and thereby preserves kidney health among sugarcane workers exposed to hot conditions.

METHODS

Utilizing a longitudinal study of 105 workers in Guatemala, we examined relationships between hydration indices, plasma copeptin concentrations, and kidney function markers at 3 times during the 6-month harvest. We also examined whether baseline copeptin concentrations increased the odds of developing an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2.

RESULTS

Copeptin concentrations were positively associated with serum creatinine (β 1.41, 95% CI 0.88-2.03) and negatively associated with eGFR (β -1.07, 95% CI -1.43 to -0.70). In addition, as workers improved their hydration (measured by increases in fluid balance), copeptin concentrations were reduced, and this reduction was associated with an improvement in kidney function.

CONCLUSIONS

Results suggest that copeptin should be studied as a potential prognostic biomarker.

Pre-Exercise Rehydration Attenuates Central Fatigability during 2-Min Maximum Voluntary Contraction in Hyperthermia

Background and objectives: Hyperthermia with dehydration alters several brain structure volumes, mainly by changing plasma osmolality, thus strongly affecting neural functions (cognitive and motor). Here, we aimed to examine whether the prevention of significant dehydration caused by passively induced whole-body hyperthermia attenuates peripheral and/or central fatigability during a sustained 2-min isometric maximal voluntary contraction (MVC). Materials and Methods: Ten healthy and physically active adult men (21 ± 1 years of age) performed an isometric MVC of the knee extensors for 2 min (2-min MVC) under control (CON) conditions, after passive lower-body heating that induced severe whole-body hyperthermia (HT, T_re > 39 °C) with dehydration (HT-D) and after HT with rehydration (HT-RH). Results: In the HT-D trial, the subjects lost 0.94 ± 0.15 kg (1.33% ± 0.13%) of their body weight; in the HT-RH trial, their body weight increased by 0.1 ± 0.42 kg (0.1% ± 0.58%). After lower-body heating, the HT-RH trial (vs. HT-D trial) was accompanied by a significantly lower physiological stress index (6.77 ± 0.98 vs. 7.40 ± 1.46, respectively), heart rate (47.8 ± 9.8 vs. 60.8 ± 13.2 b min⁻¹, respectively), and systolic blood pressure (−12.52 ± 5.1 vs. +2.3 ± 6.4, respectively). During 2-min MVC, hyperthermia (HT-D; HT-RH) resulted in greater central fatigability compared with the CON trial. The voluntary activation of exercising muscles was less depressed in the HT-RH trial compared with the HT-D trial. Over the exercise period, electrically (involuntary) induced torque decreased less in the HT-D trial than in the CON and HT-RH trials. Conclusions: Our results suggest that pre-exercise rehydration might have the immediate positive effect of reducing physiological thermal strain, thus attenuating central fatigability even when exercise is performed during severe (T_re > 39 °C) HT, induced by passive warming of the lower body.

Examining the Influence of Exercise Intensity and Hydration on Gastrointestinal Temperature in Collegiate Football Players

DeMartini-Nolan, JK, Martschinske, JL, Casa, DJ, Lopez, RM, Stearns, RL, Ganio, MS, and Coris, E. Examining the influence of exercise intensity and hydration on gastrointestinal temperature in collegiate football players. J Strength Cond Res 32(10): 2888-2896, 2018-Debate exists regarding the influence of intensity and hydration on body temperature during American football. The purpose of this study was to observe body core temperature responses with changes in intensity and hydration. Twenty-nine male football players (age = 21 ± 1 year, height = 187 ± 9 cm, mass = 110.1 ± 23.5 kg, body mass index [BMI] = 31.3 ± 5.0, and body surface area [BSA] = 2.34 ± 0.27 m) participated in 8 days of practice in a warm environment (wet bulb globe temperature: 29.6 ± 1.6° C). Participants were identified as starters (S; n = 12) or nonstarters (n = 17) and linemen (L; n = 14) or nonlinemen (NL; n = 15). Variables of interest included core body temperature (T), hydration status, and physical performance characteristics as measured by a global positioning system. Intensity measures of average heart rate (138 ± 9 bpm), low-velocity movement (4.2 ± 1.7%), high-velocity movement (0.6 ± 0.6%), and average velocity (0.36 ± 0.10 m·s) accounted for 42% of the variability observed in T (38.32 ± 0.34° C, r = 0.65, p = 0.01). Hydration measures (percent body mass loss = -1.56 ± 0.80%, urine specific gravity [Usg] = 1.025 ± 0.006, and urine color [Ucol] = 6 ± 1) did not add to the prediction of T (p = 0.83). Metrics of exercise intensity accounted for 39% of the variability observed in maximum T (38.83 ± 0.42° C, r = 0.62, p = 0.02). Hydration measures did not add to this prediction (p = 0.40). Low-velocity movement, high-velocity movement, average velocity, BMI, and BSA were significantly different (p = 0.002, p < 0.001, p = 0.02, p < 0.001, p < 0.001, respectively) between L vs. NL. Heart rate and T were not different between L and NL (p > 0.05). Exercise intensity primarily accounted for the rise in core body temperature. Although L spent less time at higher velocities, T was similar to NL, suggesting that differences in BMI and BSA added to thermoregulatory strain.

Urine Specific Gravity as a Practical Marker for Identifying Suboptimal Fluid Intake of Runners ∼12-hr Postexercise

The legitimacy of urine specific gravity (USG) as a stand-alone measure to detect hydration status has recently been challenged. As an alternative to hydration status, the purpose of this study was to determine the diagnostic capability of using the traditional USG marker of >1.020 to detect insufficient recovery fluid consumption with consideration for moderate versus high sweat losses (2.00-2.99 or >3% body mass, respectively). Adequate recovery fluid intake was operationally defined as ≥100% beverage fluid intake plus food water from one or two meals and a snack. Runners (n = 59) provided 132 samples from five previous investigations in which USG was assessed 10-14 hr after 60-90 min runs in temperate-to-hot environments. Samples were collected after a meal (n = 58) and after waking (n = 74). When sweat losses exceeded 3% body mass (n = 60), the relationship between fluid replacement percentage and USG increased from r = -.55 to -.70. Correct diagnostic decision improved from 66.6 to 83.3%, and receiver operating characteristic area under the curve increased the diagnostic accuracy score from 0.76 to approaching excellent (0.86). Artifacts of significant prerun hyperhydration (eight of 15 samples has USG <1.005) may explain false positive diagnoses, while almost all (84%) cases of false positives were found when sweat losses were <3.0% of body mass. Evidence from this study suggests that euhydrated runners experiencing significant sweat losses who fail to reach adequate recovery fluid intake levels can be identified by USG irrespective of acute meal and fluid intake ∼12-hr postrun.

Nutritional Peak Week and Competition Day Strategies of Competitive Natural Bodybuilders

Bodybuilders utilize peaking strategies in a bid to fine-tune their aesthetics for competition day. The most prevalent peaking strategies utilized by natural bodybuilders are unreported in the current literature. Eighty-one (M-59, F-22) natural bodybuilders were recruited from competitions during the 2016 and 2017 British Natural Bodybuilder Federation seasons. Competitors completed a 34-item questionnaire designed to investigate peaking and contest day strategies. The questionnaire listed commonly utilized peaking strategies and provided additional space for qualitative information. Analysis of the data indicated that carbohydrate (CHO), water, and sodium manipulation were the most commonly utilized peaking strategies. The consumption of high glycemic index CHO was the most common competition day strategy. Only 6.2% of competitors reported following their regular diet the week prior to competition. The CHO manipulation strategies followed were similar to classical CHO loading, whereby bodybuilders attempt to maximize muscle glycogen concentrations. Furthermore, bodybuilders attempted to remove superfluous water by exploiting the diuretic/polyuria effect associated with water loading/restriction. The potentially deleterious effects of peaking on bodybuilders' health is considered and the efficacy of these strategies to enhance appearance is discussed. The findings of the present investigation are likely to be of interest to bodybuilders and their coaches.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Heart rate variability responses to acute and repeated postexercise sauna in trained cyclists

Short- to medium-term (i.e., 4-14 days) heating protocols induce physiological adaptations including improved cardiac autonomic modulations, as assessed using heart rate variability, which may contribute to greater exercise performance. Whether similar cardiac autonomic changes occur during an intense heating protocol (sauna) reported to increase plasma volume in athletes remains to be confirmed. This study examined changes in heart rate and its variability during a single extreme heat (sauna) exposure and repeated exposures in athletes. Six well-trained male cyclists undertook sauna bathing (30 min, 87 °C, 11% relative humidity) immediately after normal training over 10 consecutive days. Heart rate recordings were obtained during each sauna bout. Heart rate and its variability (natural logarithm of root mean square of successive differences, lnRMSSD) were analysed during 10-min periods within the first bout, and changes in heart rate and lnRMSSD were analysed during each bout via magnitude-based inferences. During the first sauna bout, heart rate was almost certainly increased (∼32%, effect size 1.68) and lnRMSSD was almost certainly reduced (∼62%, effect size -5.21) from the first to the last 10-min period, indicating reduced parasympathetic and (or) enhanced sympathetic modulations. Acute exposure to extreme heat stress via sauna produced alterations in heart rate and cardiac autonomic modulations with successive postexercise heat exposures producing unclear changes over a 10-day period. The physiological benefits of intense heating via sauna on cardiac control in athletes remain to be elucidated.

Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration

Hypohydration, or a body water deficit, is a common occurrence in athletes and recreational exercisers following the completion of an exercise session. For those who will undertake a further exercise session that day, it is important to replace water losses to avoid beginning the next exercise session hypohydrated and the potential detrimental effects on performance that this may lead to. The aim of this review is to provide an overview of the research related to factors that may affect postexercise rehydration. Research in this area has focused on the volume of fluid to be ingested, the rate of fluid ingestion, and fluid composition. Volume replacement during recovery should exceed that lost during exercise to allow for ongoing water loss; however, ingestion of large volumes of plain water results in a prompt diuresis, effectively preventing longer-term maintenance of water balance. Addition of sodium to a rehydration solution is beneficial for maintenance of fluid balance due to its effect on extracellular fluid osmolality and volume. The addition of macronutrients such as carbohydrate and protein can promote maintenance of hydration by influencing absorption and distribution of ingested water, which in turn effects extracellular fluid osmolality and volume. Alcohol is commonly consumed in the postexercise period and may influence postexercise rehydration, as will the coingestion of food. Future research in this area should focus on providing information related to optimal rates of fluid ingestion, advisable solutions to ingest during different duration recovery periods, and confirmation of mechanistic explanations for the observations outlined.

Fluid, energy and nutrient recovery via ad libitum intake of different fluids and food

INTRODUCTION

This study compared the effects of ad libitum consumption of different beverages and foods on fluid retention and nutrient intake following exercise.

METHODS

Ten endurance trained males (mean±SD; Age=25.3±4.9years, VO₂max=63.0±7.2mL·kg·min^-1) performed four trials employing a counterbalanced, crossover design. Following 60min of exercise (matched for energy expenditure and fluid loss) participants consumed either water (W1 and W2), a sports drink (Powerade® (P)) or a milk-based liquid meal supplement (Sustagen Sport® (SS)) over a four hour recovery period. Additionally, participants had access to snack foods on two occasions within the first 2h of recovery on all trials. All beverages and food were consumed ad libitum. Total nutrient intake, urine volume, USG, body weight as well as subjective measures of gastrointestinal tolerance and thirst were obtained hourly. Plasma osmolality was measured pre, post, 1 and 4h after exercise.

RESULTS

Total fluid volume ingested from food and beverages in W1 (2.28±0.42L) and P (2.82±0.80L) trials were significantly greater than SS (1.94±0.54L). Total urine output was not different between trials (W1=644±202mL, W2=602±352mL, P=879±751mL, SS=466±129mL). No significant differences in net body weight change was observed between trials (W1=0.01±0.28kg, W2=0.08±0.30kg, P=-0.02±0.24kg, SS=-0.05±0.24kg). Total energy intake was higher on P (10,179±1484kJ) and SS (10,577±2210kJ) compared to both water trials (W1=7826±888kJ, W2=7578±1112kJ).

CONCLUSION

With the co-ingestion of food, fluid restoration following exercise is tightly regulated and not influenced by the choice of either water, a carbohydrate-electrolyte (sports drink) or a milk-based beverage.

Recurrent nightly ketosis after prolonged exercise in type 1 diabetes - the need for glycogen replacement strategies. Case report and review of literature

Exercise in diabetes patients has many benefits but also several risks, of which hypoglycemia is most often discussed. We present a case with recurrent keto-acidosis post-exercise, in which we hypothesize that glycogen replacement strategies were insufficient. Our experience in this case and review of the literature emphasize the importance of discussing glycogen replacement strategies with your diabetic athletes.

Physical Activity and Beverage Consumption among Adolescents

This study assessed the relationship between physical activity and beverage consumption among adolescents with a population based cross-sectional survey was carried out in the Balearic Islands, Spain (n = 1988; 12-17 years old). Body composition, educational and income level, physical activity (PA), and beverage consumption and energy intake were assessed. Sixty-two percent of adolescents engaged in >300 min/week of PA. Boys were more active than girls, younger adolescents were more active than older counterparts, low parental income was associated with physical inactivity, and time spent watching TV (including, TV, Internet or handheld cellular devices) was inversely associated with PA practice. The average beverage intake of the studied adolescents was 0.9 L/day, higher in boys than in girls. Beverage intake was positively associated with PA practice, and the highest amount of energy intake from beverages was observed in active boys and girls. Most of the studied adolescent population met the PA recommendations. Gender, age, parental income, and time spent watching TV were significant determinants of PA. Type and amount of beverages drunk varied according to gender and PA, and general daily total beverage intake was lower than recommended adequate fluid intake. PA behavior should be considered when analyzing beverage consumption in adolescents.

Effects of protein addition to carbohydrate-electrolyte solutions on postexercise rehydration

Background/Objective

This study aimed to examine the effects of the addition of whey or casein protein, the two major proteins in milk, to carbohydrate-electrolyte (CE) solutions on postexercise rehydration.

Methods

Ten young men aged 20.7 ± 1.4 years with an average VO_2max of 60.7 mL/kg/min ran for 60 minutes at 65% VO_2max on three occasions followed by 4 hours' recovery. During recovery, the participants consumed either CE solution with 66 g/L carbohydrate (CHO), or CE plus whey protein solution (CW trial, 44 g/L CHO, 22 g/L whey), or CE plus casein protein solution (CC trial, 44 g/L CHO, 22 g/L casein); the solutions were matched for energy and electrolyte content.

Results

The participants lost 2.36 ± 0.32% of their pre-exercise body weight after the exercise. Total urine output after recovery was greater in the CE and CC trials than CW trial (CE vs. CW vs. CC: 1184 ± 378 mL vs. 1005 ± 214 mL vs. 1256 ± 413 mL; p < 0.05). Fluid retention after ingestion of CW solution was greater than CE and CC solutions (CE vs. CW vs. CC: 46.9 ± 16.5% vs. 54.9 ± 9.2% vs. 45.8 ± 17.3%; p < 0.05). Lower urine specific gravity and urine osmolality were observed by the end of recovery in the CE trial compared with CW trial (p < 0.05). No difference was found in the changes in plasma volume in all trials.

Conclusion

These results suggest that during the 4 hours' recovery after a 60-minute run, the CW solution was more effective for rehydration compared with the CE or CC solution.

Performance Enhancing Diets and the PRISE Protocol to Optimize Athletic Performance

The training regimens of modern-day athletes have evolved from the sole emphasis on a single fitness component (e.g., endurance athlete or resistance/strength athlete) to an integrative, multimode approach encompassing all four of the major fitness components: resistance (R), interval sprints (I), stretching (S), and endurance (E) training. Athletes rarely, if ever, focus their training on only one mode of exercise but instead routinely engage in a multimode training program. In addition, timed-daily protein (P) intake has become a hallmark for all athletes. Recent studies, including from our laboratory, have validated the effectiveness of this multimode paradigm (RISE) and protein-feeding regimen, which we have collectively termed PRISE. Unfortunately, sports nutrition recommendations and guidelines have lagged behind the PRISE integrative nutrition and training model and therefore limit an athletes' ability to succeed. Thus, it is the purpose of this review to provide a clearly defined roadmap linking specific performance enhancing diets (PEDs) with each PRISE component to facilitate optimal nourishment and ultimately optimal athletic performance.

Consumo alimentar e condições de trabalho no corte manual de cana de açúcar no estado de São Paulo1

Objetivo Descrever as condições de trabalho e aspectos relacionados à alimentação do trabalhador no corte manual de cana para contribuir para desenvolver políticas públicas de vigilância e atenção integral em Saúde do Trabalhador. Métodos Foram utilizados a observação direta do trabalho no campo em colheita no estado de São Paulo e aplicado questionário semi-estruturado a um grupo de 40 cortadores manuais de cana migrantes procedentes do estado do Ceará, durante 15 dias da safra 2007/2008. Aspectos sócio-demográficos, consumo de água, reposição eletrolítica, alimentação e aspectos culturais, pausas, dores e a jornada de trabalho foram registrados. Resultados Os trabalhadores ingerem de 5 a 10 litros de água/dia e a diluição dos repositores eletrolíticos foi inferior à adequada. A alimentação durante a safra não garantia a segurança alimentar e nutricional. A alimentação foi monótona, conservada e consumida em temperatura inadequada, e incompatível com os hábitos culturais, gerando desperdício e redução do consumo alimentar. Os trabalhadores relataram dores e câimbras no decorrer da jornada. As pausas para descanso foram insuficientes. O pagamento pela quantidade de produção, o processo de trabalho e as práticas de pagamento foram considerados determinantes da situação de precariedade ampla a que estes trabalhadores estavam submetidos. O trabalho no corte manual de cana é extenuante e o pagamento por produção pode ser um agravante para a saúde, pois implica na redução das pausas para descanso. A alimentação e hidratação corretas poderiam minimizar o desgaste e as dores durante o trabalho.

Effect of sauna-based heat acclimation on plasma volume and heart rate variability

PURPOSE

We investigated the effect of post-exercise sauna bathing on plasma volume (PV) expansion and whether such responses can be tracked by changes in heart rate (HR)-based measures.

METHODS

Seven, well-trained male cyclists were monitored for 35 consecutive days (17 days baseline training, 10 days training plus sauna, 8 days training). Sauna exposure consisted of 30 min (87 °C, 11 % relative humidity) immediately following normal training. Capillary blood samples were collected while resting seated to assess PV changes. HR (HRwake) and vagal-related HR variability (natural logarithm of square root mean squared differences of successive R-R intervals, ln rMSSDwake) were assessed daily upon waking. A sub-maximal cycle test (5 min at 125 W) was performed on days 1, 8, 15, 22, 25, 29, and 35 and HR recovery (HRR60s) and ln rMSSDpostex were assessed post-exercise. Effects were examined using magnitude-based inferences.

RESULTS

Compared with baseline, sauna resulted in: (1) peak PV expansion after four exposures with a likely large increase [+17.8 % (90 % confidence limits, 7.4; 29.2)]; (2) reduction of HRwake by a trivial-to-moderate amount [-10.2 % (-15.9; -4.0)]; (3) trivial-to-small changes for ln rMSSDwake [4.3 % (1.9; 6.8)] and ln rMSSDpostex [-2.4 % (-9.1; 4.9)]; and (4) a likely moderate decrease in HRR60s [-15.6 % (-30.9; 3.0)]. Correlations between individual changes in PV and HR measures were all unclear.

CONCLUSIONS

Sauna bathing following normal training largely expanded PV in well-trained cyclists after just four exposures. The utility of HR and HRV indices for tracking changes in PV was uncertain. Future studies will clarify mechanisms and performance benefits of post-training sauna bathing.

Effect of milk consumption on rehydration in youth following exercise in the heat

Low-fat milk is thought to be an effective postexercise rehydration beverage in adults; however, little is known about milk’s rehydration ability in children after exercising in the heat. This study tested the hypothesis that because of its electrolyte and protein content, skim milk (SM) would be more effective than both water (W) and a carbohydrate/electrolyte solution (CES) in replacing body fluid losses in children following exercise in the heat. Thirty-eight (19 females) heat-acclimated pre- to early pubertal (PEP, aged 7–11 years) and mid- to late-pubertal (MLP, aged 14–17 years) children performed 3 sessions in 34.5 °C, 47.3% relative humidity, consisting of 2 × 20-min cycling bouts at 60% peak oxygen uptake followed by consumption of either W, CES, or SM. Each beverage was consumed immediately after exercise in a volume equal to 100% of their body mass loss during exercise. Urine samples were collected before, during, and after exercise, as well as the 2-h period following beverage consumption. On average, children dehydrated 1.3% ± 0.4%. Children ingested 0.40 ± 0.11 L (PEP) and 0.74 ± 0.20 L (MLP) of fluid. The fraction of the ingested beverage retained at 2 h of recovery was greater with SM (74% ± 18%) than W (47% ± 26%) and CES (59% ± 20%, p < 0.001 for both), and greater in CES than W (p < 0.001). All participants were in a hypohydrated state after 2 h of recovery, following the pattern SM < CES < W. In both PEP and MLP children, SM is more effective than W and CES at replacing fluid losses that occur during exercise in the heat.

Postexercise rehydration: potassium-rich drinks versus water and a sports drink

Fluid retention, thirst quenching, tolerance, and palatability of different drinks were assessed. On 4 different days, 12 healthy, physically active volunteers (24.4 ± 3.2 years old, 74.75 ± 11.36 kg body mass (mean ± S.D)), were dehydrated to 2.10% ± 0.24% body mass by exercising in an environmental chamber (32.0 ± 0.4 °C dry bulb, 53.8 ± 5.2% relative humidity). Each day they drank 1 of 4 beverages in random order: fresh coconut water (FCW), bottled water (W), sports drink (SD), or potassium-rich drink (NEW); volume was 120% of weight loss. Urine was collected and perceptions self-reported for 3 h. Urine output was higher (p < 0.05) for W (894 ± 178 mL) than SD (605 ± 297 mL) and NEW (599 ± 254 mL). FCW (686 ± 250 mL) was not different from any other drink (p > 0.05). Fluid retention was higher for SD than W (68.2% ± 13.0% vs. 51.3% ± 12.6%, p = 0.013), but not for FCW and NEW (62.5% ± 15.4% and 65.9% ± 15.4%, p > 0.05). All beverages were palatable and well tolerated; none maintained a positive net fluid balance after 3 h, but deficit was greater in W versus SD (p = 0.001). FCW scored higher for sweetness (p = 0.03). Thirst increased immediately after exercise but returned to baseline after drinking a small volume (p < 0.0005). In conclusion, additional potassium in FCW and NEW did not result in additional rehydration benefits over those already found in a conventional sports drink with sodium.

Cardiac parasympathetic reactivation following exercise: implications for training prescription

The objective of exercise training is to initiate desirable physiological adaptations that ultimately enhance physical work capacity. Optimal training prescription requires an individualized approach, with an appropriate balance of training stimulus and recovery and optimal periodization. Recovery from exercise involves integrated physiological responses. The cardiovascular system plays a fundamental role in facilitating many of these responses, including thermoregulation and delivery/removal of nutrients and waste products. As a marker of cardiovascular recovery, cardiac parasympathetic reactivation following a training session is highly individualized. It appears to parallel the acute/intermediate recovery of the thermoregulatory and vascular systems, as described by the supercompensation theory. The physiological mechanisms underlying cardiac parasympathetic reactivation are not completely understood. However, changes in cardiac autonomic activity may provide a proxy measure of the changes in autonomic input into organs and (by default) the blood flow requirements to restore homeostasis. Metaboreflex stimulation (e.g. muscle and blood acidosis) is likely a key determinant of parasympathetic reactivation in the short term (0-90 min post-exercise), whereas baroreflex stimulation (e.g. exercise-induced changes in plasma volume) probably mediates parasympathetic reactivation in the intermediate term (1-48 h post-exercise). Cardiac parasympathetic reactivation does not appear to coincide with the recovery of all physiological systems (e.g. energy stores or the neuromuscular system). However, this may reflect the limited data currently available on parasympathetic reactivation following strength/resistance-based exercise of variable intensity. In this review, we quantitatively analyse post-exercise cardiac parasympathetic reactivation in athletes and healthy individuals following aerobic exercise, with respect to exercise intensity and duration, and fitness/training status. Our results demonstrate that the time required for complete cardiac autonomic recovery after a single aerobic-based training session is up to 24 h following low-intensity exercise, 24-48 h following threshold-intensity exercise and at least 48 h following high-intensity exercise. Based on limited data, exercise duration is unlikely to be the greatest determinant of cardiac parasympathetic reactivation. Cardiac autonomic recovery occurs more rapidly in individuals with greater aerobic fitness. Our data lend support to the concept that in conjunction with daily training logs, data on cardiac parasympathetic activity are useful for individualizing training programmes. In the final sections of this review, we provide recommendations for structuring training microcycles with reference to cardiac parasympathetic recovery kinetics. Ultimately, coaches should structure training programmes tailored to the unique recovery kinetics of each individual.

An amino acid-electrolyte beverage may increase cellular rehydration relative to carbohydrate-electrolyte and flavored water beverages

BACKGROUND

In cases of dehydration exceeding a 2% loss of body weight, athletic performance can be significantly compromised. Carbohydrate and/or electrolyte containing beverages have been effective for rehydration and recovery of performance, yet amino acid containing beverages remain unexamined. Therefore, the purpose of this study is to compare the rehydration capabilities of an electrolyte-carbohydrate (EC), electrolyte-branched chain amino acid (EA), and flavored water (FW) beverages.

METHODS

Twenty men (n = 10; 26.7 ± 4.8 years; 174.3 ± 6.4 cm; 74.2 ± 10.9 kg) and women (n = 10; 27.1 ± 4.7 years; 175.3 ± 7.9 cm; 71.0 ± 6.5 kg) participated in this crossover study. For each trial, subjects were dehydrated, provided one of three random beverages, and monitored for the following three hours. Measurements were collected prior to and immediately after dehydration and 4 hours after dehydration (3 hours after rehydration) (AE = -2.5 ± 0.55%; CE = -2.2 ± 0.43%; FW = -2.5 ± 0.62%). Measurements collected at each time point were urine volume, urine specific gravity, drink volume, and fluid retention.

RESULTS

No significant differences (p > 0.05) existed between beverages for urine volume, drink volume, or fluid retention for any time-point. Treatment x time interactions existed for urine specific gravity (USG) (p < 0.05). Post hoc analysis revealed differences occurred between the FW and EA beverages (p = 0.003) and between the EC and EA beverages (p = 0.007) at 4 hours after rehydration. Wherein, EA USG returned to baseline at 4 hours post-dehydration (mean difference from pre to 4 hours post-dehydration = -0.0002; p > 0.05) while both EC (-0.0067) and FW (-0.0051) continued to produce dilute urine and failed to return to baseline at the same time-point (p < 0.05).

CONCLUSION

Because no differences existed for fluid retention, urine or drink volume at any time point, yet USG returned to baseline during the EA trial, an EA supplement may enhance cellular rehydration rate compared to an EC or FW beverage in healthy men and women after acute dehydration of around 2% body mass loss.

Validity and reliability of a field technique for sweat Na+ and K+ analysis during exercise in a hot-humid environment

This study compared a field versus reference laboratory technique for extracting (syringe vs. centrifuge) and analyzing sweat [Na⁺] and [K⁺] (compact Horiba B‐722 and B‐731, HORIBA vs. ion chromatography, HPLC) collected with regional absorbent patches during exercise in a hot‐humid environment. Sweat samples were collected from seven anatomical sites on 30 athletes during 1‐h cycling in a heat chamber (33°C, 67% rh). Ten minutes into exercise, skin was cleaned/dried and two sweat patches were applied per anatomical site. After removal, one patch per site was centrifuged and sweat was analyzed with HORIBA in the heat chamber (CENTRIFUGE HORIBA) versus HPLC (CENTRIFUGE HPLC). Sweat from the second patch per site was extracted using a 5‐mL syringe and analyzed with HORIBA in the heat chamber (SYRINGE HORIBA) versus HPLC (SYRINGE HPLC). CENTRIFUGE HORIBA, SYRINGE HPLC, and SYRINGE HORIBA were highly related to CENTRIFUGE HPLC ([Na⁺]: ICC = 0.96, 0.94, and 0.93, respectively; [K⁺]: ICC = 0.87, 0.92, and 0.84, respectively), while mean differences from CENTRIFUGE HPLC were small but usually significant ([Na⁺]: 4.7 ± 7.9 mEql/L, −2.5 ± 9.3 mEq/L, 4.0 ± 10.9 mEq/L (all P < 0.001), respectively; [K⁺]: 0.44 ± 0.52 mEq/L (P < 0.001), 0.01 ± 0.49 mEq/L (P = 0.77), 0.50 ± 0.48 mEq/L (P < 0.001), respectively). On the basis of typical error of the measurement results, sweat [Na⁺] and [K⁺] obtained with SYRINGE HORIBA falls within ±15.4 mEq/L and ±0.68 mEq/L, respectively, of CENTRIFUGE HPLC 95% of the time. The field (SYRINGE HORIBA) method of extracting and analyzing sweat from regional absorbent patches may be useful in obtaining sweat [Na⁺] when rapid estimates in a hot‐humid field setting are needed.

This study compared a field versus reference laboratory technique for extracting (SYRINGE vs. CENTRIFUGE) and analyzing sweat [Na⁺] and [K⁺] (compact HORIBA B‐722 and B‐731 versus ion chromatography, HPLC) collected with regional absorbent patches during exercise in a hot‐humid environment. The HORIBA analyzers provided highly reliable test‐retest and day‐to‐day measurements of sweat [Na⁺] and [K⁺]. The 95% limit of agreement between the SYRINGE HORIBA field technique and the reference laboratory‐based CENTRIFUGE HPLC technique was ±15.4 mEq/L and ±0.68 mEq/L for [Na⁺] and [K⁺], respectively; which may be acceptable in a field‐testing context, when simply aiming to estimate electrolyte losses for the purpose of identifying athletes/workers at greater risk for large electrolyte losses.

Novel hydration assessment techniques employing thirst and a water intake challenge in healthy men

Exploring novel hydration indices is important because no human biomarker has been shown to be incontrovertibly valid in all life situations. The present investigation was designed to identify inexpensive, nontechnical methods to use when self-assessing hydration status. This investigation evaluated the validity and efficacy of 2 novel techniques (i.e., thirst sensation and urine volume) to assess hydration state of 29 active men (mean ± SD; age, 23 ± 4 years; body mass, 76.02 ± 11.94 kg) at rest. Eight combinations of 4 water challenges (4.8, 9.3, 11.0, or 14 mL·kg−1) and 2 hydration states (mildly hypohydrated (HY), –2.0%; euhydrated (EU), –0.2% body mass) were employed. First, thirst was linearly related to body water loss, and ratings of thirst distinguished HY from EU (p < 0.001) subsequent to 19 h of controlled food and fluid intake. Second, measurements of urine volume 60 min after consuming a water bolus (11.0 or 14 mL·kg−1) were strongly and inversely correlated with entering hydration state, assessed by urine specific gravity (r2 = 0.76, p < 0.0001) and urine osmolality (r2 = 0.77, p < 0.0001). We concluded that healthy men can employ simple measurements of morning thirst sensation and urine volume to identify the presence of mild hypohydration and to guide fluid replacement. These 2 techniques are relevant because HY (–2% body mass) is the approximate threshold for the onset of thirst, reduced endurance exercise performance, and decrements of working memory and mood.

Effects of different protocols of hydration on cardiorespiratory parameters during exercise and recovery

INTRODUCTION

Hydration plays a key role in the physiological maintenance required by exercise.

OBJECTIVE

To evaluate the behavior of heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, pulse oxygen saturation (SpO2) and respiratory rate (RR) of young people during and after prolonged physical exercise, with and without the intake of water or isotonic solution.

METHOD

31 young individuals (21.63 ± 1.86 years) were subjected to a four-step protocol with a 48-hour interval between each step, namely: i) a test to determine the incremental load used in subsequent steps, ii) a control protocol without hydration (CP), iii) an experimental protocol with water intake (PE1), iv) an experimental protocol with ingestion of isotonic (PE2). The protocols consisted of 10 min rest, 90 min of exercise on a treadmill at 60% of VO2peak and 60 min of recovery. The parameters HR, SBP, DBP, RR and SPO2 were measured at rest, at 30, 60 and 90 min of exercise, with the exception of RR; and at 1, 3, 5, 7, 10, 20, 30, 40, 50 and 60 min of recovery. The two-factor analysis of variance for repeated measures model was used for analysis (p<0.05).

RESULTS

There was a moment effect for all variables in exercise (p<0.001), however, no effect was observed between the protocols (SBP, p=0.998; DBP, p=0.897; SpO2, p=0.077, HR=0.281) and in the interaction moment and protocol (SBP, p=0.058; DBP, p=0.191 and SpO2, p=0.510, HR=0.496). In recovery there was also a moment effect for all variables analyzed (p<0.001). There was no effect among protocols for SBP (p=0.986), DBP (p=0.536) and RR (p=0.539), however in the SpO2 (p=0.001) and HR (p=0.033) variables, effects were observed between the protocols. Regarding the moment and protocol interaction, an effect was observed for HR (SBP, p=0.431; DBP, p=0.086; SpO2, p=0.445, RR, p=0.147, HR, p=0.022).

CONCLUSION

For the type of exercise performed, both the water and the isotonic solution influenced the behavior of cardiorespiratory parameters, and independent of the type of hydration given the behavior of the parameters studied was similar.

Effect of varying the concentrations of carbohydrate and milk protein in rehydration solutions ingested after exercise in the heat

The present study investigated the relationship between the milk protein content of a rehydration solution and fluid balance after exercise-induced dehydration. On three occasions, eight healthy males were dehydrated to an identical degree of body mass loss (BML, approximately 1·8 %) by intermittent cycling in the heat, rehydrating with 150 % of their BML over 1 h with either a 60 g/l carbohydrate solution (C), a 40 g/l carbohydrate, 20 g/l milk protein solution (CP20) or a 20 g/l carbohydrate, 40 g/l milk protein solution (CP40). Urine samples were collected pre-exercise, post-exercise, post-rehydration and for a further 4 h. Subjects produced less urine after ingesting the CP20 or CP40 drink compared with the C drink (P< 0·01), and at the end of the study, more of the CP20 (59 (sd 12) %) and CP40 (64 (sd 6) %) drinks had been retained compared with the C drink (46 (sd 9) %) (P< 0·01). At the end of the study, whole-body net fluid balance was more negative for trial C ( − 470 (sd 154) ml) compared with both trials CP20 ( − 181 (sd 280) ml) and CP40 ( − 107 (sd 126) ml) (P< 0·01). At 2 and 3 h after drink ingestion, urine osmolality was greater for trials CP20 and CP40 compared with trial C (P< 0·05). The present study further demonstrates that after exercise-induced dehydration, a carbohydrate–milk protein solution is better retained than a carbohydrate solution. The results also suggest that high concentrations of milk protein are not more beneficial in terms of fluid retention than low concentrations of milk protein following exercise-induced dehydration.

Whey protein addition to a carbohydrate-electrolyte rehydration solution ingested after exercise in the heat

CONTEXT

Many active people finish exercise hypohydrated, so effective rehydration after exercise is an important consideration.

OBJECTIVE

To determine the effects of a rehydration solution containing whey protein isolate on fluid balance after exercise-induced dehydration.

DESIGN

Randomized controlled clinical trial.

SETTING

University research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twelve healthy men (age = 21 ± 1 years, height = 1.82 ± 0.08 m, mass = 82.71 ± 10.31 kg) participated.

INTERVENTION(S)

Participants reduced body mass by 1.86% ± 0.07% after intermittent exercise in the heat and rehydrated with a volume of drink in liters equivalent to 1.5 times their body mass loss in kilograms of a solution of either 65 g/L carbohydrate (trial C) or 50 g/L carbohydrate and 15 g/L whey protein isolate (trial CPl. Solutions were matched for energy density and electrolyte content. Urine samples were collected before and after exercise and for 4 hours after rehydration.

MAIN OUTCOME MEASURE(S)

We measured urine volume, drink retention, net fluid balance, urine osmolality, and subjective responses. Drink retention was calculated as the difference between the volume of drink ingested and urine produced. Net fluid balance was calculated from fluid gained through drink ingestion and fluid lost through sweat and urine production.

RESULTS

Total cumulative urine output after rehydration was not different between trial C (1173 ± 481 mL) and trial CP (1180 ± 330 mL) (F(1) = 0.002, P = .96), and drink retention during the study also was not different between trial C (50% ± 18%) and trial CP (49% ± 13%) (t(11) = -0.159, P =.88). At the end of the study, net fluid balance was negative compared with baseline for trial C (-432 ± 436 mL) (t(11) = 3.433, P = .03) and trial CP (-432 ± 302 mL) (t(11) = 4.958, P = .003).

CONCLUSIONS

When matched for energy density and electrolyte content, a solution of carbohydrate and whey protein isolate neither increased nor decreased rehydration compared with a solution of carbohydrate.

Hydration status, fluid intake, and electrolyte losses in youth soccer players

The purpose of the study was to determine the hydration status, fluid intake, and electrolyte losses of 21 male professional youth soccer players (age 17.1 ± 0.7 y) training in a cool environment. Pretraining and posttraining measurements of body mass, urine (freezing-point osmolality method), and sweat concentration (flame-emission spectroscopy) were collected. Fourteen players were found to be hypohydrated before training. The amount of fluid lost due to exercise equated to a 1.7% loss in body mass, which equated to a gross dehydration loss of 0.5%. Overall, the soccer players replaced 46% ± 88% of sweat loss during training, and only 4 remained hypohydrated after training. No significant correlations between sweat loss and sweat concentrations of Na+ (r = -.11, P = .67) or K+ (r = .14, P = .58) were found, but there was a significant correlation with Mg2+ (r = -.58, P < .009). This study found large variability in pretraining hydration status that the players were able to rehydrate during the training sessions. However, given the numbers starting training in a hypohydrated state, adequate hydration status before training should be considered by youth players, coaches, and sports-science support staff.

Hydration: special issues for playing football in warm and hot environments

The high metabolic rates and body temperatures sustained by football players during training and matches causes sweating--particularly when in warm or hot environments. There is limited published data on the effects of this sweat loss on football performance. The limited information available, together with knowledge of the effects of sweat loss in other sports with skill components as well as endurance and sprint components, suggests that the effects of sweating will be similar as in these other activities. Therefore, the generalization that, on average, a body mass reduction equivalent to 2% should be the acceptable limit of sweat losses seems reasonable. This magnitude and more, of sweat loss is a common occurrence for some players. Sodium is the main electrolyte lost in sweat but there is large variability in sodium losses between players. However, the extent of sodium losses in some players may be such that its replacement is warranted for these players. Although football is a team sport, the great individual variability in sweat and electrolyte losses of players in the same training session or match dictates that individual monitoring to determine individual water and electrolyte requirements should be an essential part of a player's nutrition strategy.

Hydration status of rugby league players during home match play throughout the 2008 Super League season

The hydration status of rugby league players during competitive home match play was assessed throughout the 2008 Super League season. Fourteen players from 2 Super League clubs were monitored (72 observations). On arrival, 2 h prior to kick off, following normal prematch routines, players’ body mass were measured following a urine void. Prematch fluid intake, urine output, and osmolality were assessed until kick off, with additional measurements at half time. Fluid intake was also monitored during match play for club B only, and final measurements of variables were made at the end of the match. Mean body mass loss per match was 1.28 ± 0.7 kg (club A, 1.15 kg; club B, 1.40 kg), which would equate to an average level of dehydration of 1.31% (mass loss, assumed to be water loss, expressed as a percentage of body mass), with considerable intra-individual coefficient of variation (CV, 47%). Mean fluid intake for club B was 0.64 ± 0.5 L during match play, while fluid loss was 2.0 ± 0.7 L, with considerable intra-individual CV (51% and 34%, respectively). Mean urine osmolality was 396 ± 252 mosm·kg−1 on arrival, 237 ± 177 mosm·kg−1 prematch, 315 ± 133 mosm·kg−1 at half time, and 489 ± 150 mosm·kg−1 postmatch. Body mass losses were primarily a consequence of body fluid losses not being completely balanced by fluid intake. Furthermore, these data show that there is large inter- and intra-individual variability of hydration across matches, highlighting the need for future assessment of individual relevance.

Effect of milk protein addition to a carbohydrate–electrolyte rehydration solution ingested after exercise in the heat

The present study examined the effects of milk protein on rehydration after exercise in the heat, via the comparison of energy- and electrolyte content-matched carbohydrate and carbohydrate–milk protein solutions. Eight male subjects lost 1·9 (sd 0·2) % of their body mass by intermittent exercise in the heat and rehydrated with 150 % of their body mass loss with either a 65 g/l carbohydrate solution (trial C) or a 40 g/l carbohydrate, 25 g/l milk protein solution (trial CP). Urine samples were collected before and after exercise and for 4 h after rehydration. Total cumulative urine output after rehydration was greater for trial C (1212 (sd 310) ml) than for trial CP (931 (sd 254) ml) (P < 0·05), and total fluid retention over the study was greater after ingestion of drink CP (55 (sd 12) %) than that after ingestion of drink C (43 (sd 15) %) (P < 0·05). At the end of the study period, whole body net fluid balance (P < 0·05) was less negative for trial CP ( − 0·26 (sd 0·27) litres) than for trial C ( − 0·52 (sd 0·30) litres), and although net negative for both the trials, it was only significantly negative after ingestion of drink C (P < 0·05). The results of the present study suggest that when matched for energy density and fat content, as well as for Na and K concentration, and when ingested after exercise-induced dehydration, a carbohydrate–milk protein solution is better retained than a carbohydrate solution. These results suggest that gram-for-gram, milk protein is more effective at augmenting fluid retention than carbohydrate.

Fatigue management in the preparation of Olympic athletes

Fatigue is often a consequence of physical training and the effective management of fatigue by the coach and athlete is essential in optimizing adaptation and performance. In this paper, we explore a range of practical and contemporary methods of fatigue management for Olympic athletes. We assesses the scientific merit of methods for monitoring fatigue, including self-assessment of training load, self-scored questionnaires, and the usefulness of saliva and blood diagnostic markers for indicating fatigued and under-recovered athletes, effective nutrition and hydration strategies for optimizing recovery and short-term recovery methods. We conclude that well-accepted methods such as sufficient nutrition, hydration, and rest appear to be the most effective strategies for optimizing recovery in Olympic athletes.

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.