Modificado em 31 Outubro 2012

Physical signs of dehydration in the elderly.Shimizu M, Kinoshita K, Hattori K, Ota Y, Kanai T, Kobayashi H, Tokuda Y.Intern Med (Tokyo) 2012;51(10):1207-10.

It is widely recognised that dehydration is a common condition in the elderly and that it is a frequent cause of hospitalization among older people, in spite of efforts by caregivers to prevent its development. Successful prevention strategies will require early identification of individuals at increased risk, which in turn means that knowledge of simple but reliable signs of mild dehydration is required. In this study, various physical signs were examined as clinical signs of dehydration in elderly. In this study, 27 consecutive elderly patients who were admitted to the Department of Medicine were evaluated. Based on a definition of dehydration as a calculated serum osmolality of more than 295 mOsm/kg, 9 patients were classified as dehydrated (mean osmolality of 310 mOsmol/kg) and 18 as non-dehydrated (mean osmolality of 279 mOsmol/kg). All patients were observed for physical signs of dehydration: decreased consciousness level; dry axilla; dry mouth; sunken eyes; decreased skin turgor; delayed capillary refill time. Blood and urine chemistry analyses were also compared between the two groups. For the physical signs, dry axilla had moderate sensitivity (44%) and good specificity (89%) to detect dehydration. Sunken eyes and delayed capillary refill time also showed relatively good specificity (83%). As expected, the mean serum sodium concentration in the dehydrated group (146 mmol/l) was higher (p<0.01) than that in the non-dehydrated group (134 mmol/l). During the hospitalization, 44% of patients in the dehydrated group died, while 17% in the non-dehydrated group died. The authors concluded that physical signs of dehydration in elderly showed relatively good specificity but poor sensitivity. They suggested that evaluation of the axillary moisture could help assess dehydration in situations where laboratory analysis was not available. Although the number of subjects in the study was small, these preliminary results help raise the awareness of the need for careful observation of vulnerable elderly individuals.

Beverage carbohydrate concentration influences the intermittent endurance capacity of adolescent team games players during prolonged intermittent running.

Phillips SM, Turner AP, Sanderson MF, Sproule J.: European Journal of Applied Physiology, Março 2012, 112(3):1107-16.

This study investigated the influence of consuming a 2, 6, and 10% carbohydrate-electrolyte (CHO-E) solution on the intermittent endurance capacity and sprint performance of adolescent team games players. Seven participants (five males and two females; mean age 13.3 ± 0.5 years, height 1.71 ± 0.05 m, body mass (BM) 62.0 ± 6.3 kg) performed three trials separated by 3-7 days. In each trial, they completed four 15-min periods of part A of the Loughborough Intermittent Shuttle Test (LIST) followed by an intermittent run to exhaustion (part B). Participants consumed 5 ml kg(-1) BM of the solution during the 5-min pre-exercise period, and a further 2 ml kg(-1) BM every 15 min during part A of the LIST. Intermittent endurance capacity increased by 34% with ingestion of the 6% CHO-E solution compared with the 10% solution (5.5 ± 0.8 vs. 4.1 ± 1.5 min, P < 0.05), equating to a distance of 931 ± 172 versus 706 ± 272 m (P < 0.05). There was no significant difference between the 2% (4.8 ± 1.2 min) and 6% (P = 0.10) or the 2 and 10% solutions (P = 0.09). Carbohydrate concentration did not significantly influence mean 15-m sprint time (P = 0.38). These results suggest that the carbohydrate concentration of an ingested solution influences the intermittent endurance capacity of adolescent team games players with a 6% solution significantly more effective than a 10% solution.

Carbohydrate gel ingestion significantly improves the intermittent endurance capacity, but not sprint performance, of adolescent team games players during a simulated team games protocol.

Phillips SM, Turner AP, Sanderson MF, Sproule J.: European Journal of Applied Physiology, Março 2012, 112(3):1133-41

The aim of this study was to investigate the influence of ingesting a carbohydrate (CHO) gel on the intermittent endurance capacity and sprint performance of adolescent team games players. Eleven participants [mean age 13.5 ± 0.7 years, height 1.72 ± 0.08 m, body mass (BM) 62.1 ± 9.4 kg] performed two trials separated by 3-7 days. In each trial, they completed four 15 min periods of part A of the Loughborough Intermittent Shuttle Test (LIST), followed by an intermittent run to exhaustion (part B). In the 5 min pre-exercise, participants consumed 0.818 mL kg(-1) BM of a CHO or a non-CHO placebo gel, and a further 0.327 mL kg(-1) BM every 15 min during part A of the LIST (38.0 ± 5.5 g CHO h(-1) in the CHO trial). Intermittent endurance capacity was increased by 21.1% during part B when the CHO gel was ingested (4.6 ± 2.0 vs. 3.8 ± 2.4 min, P < 0.05, r = 0.67), with distance covered in part B significantly greater in the CHO trial (787 ± 319 vs. 669 ± 424 m, P < 0.05, r = 0.57). Gel ingestion did not significantly influence mean 15 m sprint time (P = 0.34), peak sprint time (P = 0.81), or heart rate (P = 0.66). Ingestion of a CHO gel significantly increases the intermittent endurance capacity of adolescent team games players during a simulated team games protocol.

Fluid intake and changes in limb volumes in male ultra-marathoners: does fluid overload lead to peripheral oedema?

Bracher A, Knechtle B, Gnädinger M, Bürge J, Rüst CA, Knechtle P, Rosemann T.: European Journal of Applied Physiology, Março 2012, 112(3):991-1003.

An increase in body mass due to oedema has been previously described. The aim of this study was to investigate a potential association between both fluid and electrolyte intake and the formation of peripheral oedemas. Fluid and electrolyte intakes and the changes in limb volumes in 50 male 100-km ultra-marathoners were measured. Pre- and post-race serum sodium concentration ([Na(+)]), serum aldosterone concentration, serum copeptin concentration, serum and urine osmolality and body mass were determined. Fluid intake, renal function parameters and urinary output, as well as the changes of volume in the extremities, were measured. The changes of volume in the limbs were measured using plethysmography. Serum [Na(+)] increased by 1.6%; body mass decreased by 1.9 kg. Serum copeptin and aldosterone concentrations were increased. The change in serum copeptin concentration and the change in serum [Na(+)] correlated positively; the change in serum [Na(+)] and body mass correlated negatively. A mean fluid intake of 0.58 L/h was positively related to running speed and negatively to post-race serum [Na(+)]. Total fluid intake was positively related to the changes in both arm and lower leg volumes. Running speed was positively associated with the changes in arm and lower leg volumes; race time was related to the changes in serum copeptin or aldosterone concentrations. To conclude, fluid intake was related to the changes in limb volumes, where athletes with an increased fluid intake developed an increase in limb volumes.

Exercise and dehydration: A possible role of inner ear in balance control disorder.

Lion A, Bosser G, Gauchard GC, Djaballah K, Mallié JP, Perrin PP.: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology

201012 20(6):1196-202 . Balance Control and Motor Performance (EPM), UFR STAPS, Henri Poincaré University, Nancy-University, 54600 Villers-lès-Nancy, France; National Institute for Health and Medical Research (INSERM), UMR 954, Faculty of Medicine, 54505 Vandoeuvre-lès-Nancy, France.

To study the effect of exercise and dehydration on the postural sensory-motor strategies, 10 sportsmen performed a 45min-exercise on a cycle ergometer at intensity just below the ventilatory threshold without fluid intake. They performed, before, immediately and 20min after exercise, a sensory organization test to evaluate balance control in six different sensory situations, that combine three visual conditions (eyes open, eyes closed and sway-referenced visual surround motion) with two platform conditions (stable platform, sway-referenced platform motion). Blood samples were collected before and after exercise. Exercise induced a mild dehydration, characterized by body mass loss and increase in proteinemia. Postural performances decreased immediately after exercise, mainly in the standard situation (eyes open, stable visual surround and platform) and when only the vestibular cue was reliable (eyes closed and sway-referenced platform). Moreover, the decreased use of vestibular input was correlated with the dehydration level. Finally, postural performances normalized 20min after exercise. Even though muscular fatigue could explain the decrease in postural performances, vestibular fluid modifications may also be involved by its influence on the intralabyrinthine homeostasis, lowering thus the contribution of vestibular information on balance control.

Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes

J McGarvey, Thompson, C Hanna, T D Noakes, J Stewart , D Speedy: Br J Sports Med 2010;44:716-719.

Objective To investigate the diagnostic accuracy of commonly used signs of dehydration in marathon runners.

Design The diagnostic accuracy of 5 clinical signs/symptoms thought to indicate dehydration (altered skin turgor, dry oral mucous membranes, sunken eyes, an inability to spit and the sensation of thirst) was assessed by comparing the presence of these markers with the criterion standard of body weight change over a marathon footrace.

Setting 2006 Auckland Marathon

Participants 606 competitors in the full marathon Assessment: Body weight was measured before and immediately after the marathon. The 5 clinical signs/symptoms were assessed immediately after the marathon.

Main outcome measures Diagnostic accuracy of clinical signs/symptoms to detect dehydration greater than 3% of body weight.

Results 606 complete data sets were obtained. 3 clinical signs were associated with greater percentage weight loss: sunken eyes (mean percentage weight loss with symptom 2.6% (standard deviation 1.5), without 2.3% (1.5)); decreased skin turgor (with 3.0% (1.4), without 2.3% (1.5)) and the sensation of thirst (with 2.5% (1.5), without 2.3% (1.5)). The ability to spit and dry oral mucous membranes were unrelated to percentage weight loss. No signs/symptoms showed acceptably high validity for detecting a weight loss equal to or greater than 3% of body weight.

Conclusions The 5 parameters (decreased skin turgor, sensation of thirst, sunken eyes, inability to spit and dry mucous membranes) tested in this study did not precisely identify runners with total weight loss.3% at the end of a marathon.

The incidence of exercise-associated hyponatraemia in the London marathon

Courtney Kipps, Sanjay Sharma, Dan Tunstall Pedo. Br J Sports Med 2011, 45:11-19.

Background Exercise-associated hyponatraemia (EAH) is a potentially fatal cause of collapse in endurance exercise. It is understood to be a dilutional hyponatraemia caused by an increase of total body water relative to the amount of exchangeable sodium stores. Fourteen runners presented to one London hospital with symptomatic EAH several hours after finishing the 2003 London Marathon, and more recently, a young male runner died from the complications of severe EAH after crossing the finish line of the London Marathon.

Objectives To determine the incidence of EAH in runners in the London Marathon.

Methods Volunteers were recruited at race registration where they were weighed, had blood tests and completed a demographic and experience questionnaire. Weights, blood tests and a fluid intake questionnaire were repeated after the finish. Blood was analysed on-site using hand-held i-STAT blood analysers.

Results Of the 88 volunteers, 11 (12.5%) developed asymptomatic hyponatraemia (serum sodium 128–134 mmol/l). They consumed more fluid (p<0.001) and gained more weight (p<0.001) than did those without hyponatraemia.

Conclusions A significant proportion (12.5%) of healthy volunteers developed asymptomatic hyponatraemia running a marathon in cool conditions. On average, these runners consumed more fluid and gained more weight than did non-hyponatraemic runners, although fluid intake was not related to weight gain in this study. Four of the 11 hyponatraemic runners lost weight over the course of the marathon, strengthening the case for an additional factor, such as inappropriate antidiuretic hormone release during exercise, in the development of EAH.

Water ingestion improves performance compared with mouth rinse in dehydrated subjects. Arnaoutis, G, SA Kavouras, I Christaki, LS Sidossis . Medicine and Science in Sports and Exercise, 44(1), 175-179 2012,

It is well recognised that the ingestion of carbohydrate-electrolyte sports drinks can enhance performance of endurance exercise and can also have some other benefits such as a reduction in core temperature, in heart rate and in the perception of effort in exercise that is not continued to exhaustion. These effects were generally attributed to an effect of the increased availability of the ingested carbohydrate as a fuel for the working muscles and action of the water and sodium to balance the losses in sweat and maintain the blood volume. That picture changed a few years ago with the publication of a study that showed that simply rinsing the mouth with a carbohydrate drink that was then expectorated without swallowing was also effective in improving exercise performance. The interpretation of this observation was that receptors in the mouth responded to the presence of carbohydrate and signalled to the brain that carbohydrate was on its way.

We know that there are also receptors in the mouth and pharynx that respond to water ingestion and can even meter the amount consumed. This raises the obvious question as to whether rinsing the mouth with plain water – rather than with a carbohydrate-containing solution – has any effect on exercise performance or on the physiological and psychological responses to exercise. This paper addressed that question by requiring ten healthy trained male cyclists to complete three time-to-exhaustion cycling tests at 75% of their maximum power output after being dehydrated by 2% of their total body weight. Dehydration was induced by a 2-h moderate-intensity exercise (70% of maximum HR), which included 30-min intervals alternating between jogging and cycling in the heat (31°C). All subjects repeated the protocol in random order on three separate occasions: a) mouth rinse with 25 mL of plain water before and every 5 min of the trial (MR), b) ingestion of 25 mL of plain water before and every 5 min (DR), and c) control (CON), where no fluids were provided. Time to exhaustion was longer in the DR trial than on MR and CON trials (Mean ± SEM: 21.9 ± 1.2 vs 18.7 ± 1.3 and 17.7 ± 1.1 min, respectively; P < 0.05). There were no differences in heart rate responses, maximum blood lactate concentration, or the subjective rating of effort between the three trials. Based on these results, the authors concluded that ingestion of even a small amount of water increased exercise time in dehydrated subjects possibly through activation of pharyngeal receptors, but that simply rinsing the mouth with water had no significant effects. It remains to be seen, though, whether a longer exercise period would show similar responses.

Effect of Dilute CHO Beverages on Performance in Cool and Warm Environments. Watson P, Shirreffs SM, Maughan RJ

44(2):336-43, 2012 PURPOSE: The efficacy of drinks containing low concentrations of CHO (2%-6%) on physical performance in cool and warm environments was evaluated. METHODS: In two separate but related studies, 24 healthy males completed a familiarization trial and four trials to volitional exhaustion (TTE) at 70% V?O2max in cool conditions (10°C, n = 12) or 60% V?O2max in a warm environment (30°C, n = 12). Subjects ingested 0%, 2%, 4%, or 6% CHO solutions (sucrose, glucose, and fructose in a ratio of 50:25:25) immediately before exercise and every 10 min during exercise. RESULTS: TTE in 10°C was 102.6 ± 33.9, 109.2 ± 33.9, 121.0 ± 25.7, and 122.4 ± 29.9 min in the 0%, 2%, 4%, and 6% trials, respectively (P = 0.012). Compared with the 0% trial, TTE was longer in the 4% (P = 0.032, effect size (ES) = 0.72) and 6% (P = 0.044, ES = 0.66) trials. In addition, TTE was longer in the 6% trial than in the 2% trial (P = 0.025). TTE was also significantly influenced by drink CHO content at 30°C (0% = 94.5 ± 24.5 min, 2% = 104.1 ± 20.1 min, 4% = 105.5 ± 26.7 min, 6% = 112.0 ± 28.7 min; P = 0.046). No differences in TTE were apparent between the 0% and the 2% or 4% trials, but TTE was longer in the 6% trial compared with the placebo (P = 0.045, ES = 0.62). HR, core temperature, or rates of substrate oxidation were not affected by drink CHO content. CONCLUSIONS: These results demonstrate significant improvements in exercise capacity over the placebo trial when 4% and 6% CHO solutions were ingested at 10°C and a 6% CHO drink was ingested at 30°C.

Voluntary fluid intake in the cold. Mears SA, Shirreffs SM

British journal of sports medicine 45(15):A1-2 2011 Dez When exercising in a cold environment, fluid losses can occur via sweat, cold induced diuresis and respiration but failure to replace lost fluid is common in the cold due to a blunted thirst response (Kenefick et al. Med Sci Sports Exerc 2004;36;1528-34). This study assessed voluntary fluid intake and measures of hydration status following moderate intensity exercise in the cold. Ten healthy males (age 22±2 years, mass 67.8±7.0 kg, height 1.77±0.06 m, VO(2peak) 60.5±8.9 ml.kg.min(-1)) completed two trials following familiarisation separated by 7-14 days. In each trial, subjects sat for 30 min before cycling at 70% VO(2peak) for 60 min in either 25.0±0.1°C, 50.8±1.5% RH (warm) or 0.4±1.0°C, 68.8±7.5% RH (cold). Subjects then sat for 120 min at 22.2±1.2°C, 50.5±8.0% RH. Ad libitum drinking was allowed during the exercise and recovery periods. Urine volume, body mass, serum osmolality and Na and K concentrations and sensations of thirst were measured at baseline, postexercise and after 60 and 120 min of the recovery period. Sweat loss was lower in the cold trial (0.48±0.15 l vs 0.96±0.18 l) (p0.05). Postexercise serum osmolality was higher compared to baseline in the cold (292±2 vs 287±3 mOsm.kg(-1), p<0.0001) and warm trials (288±5 vs 285±4 mOsm.kg(-1); p=0.048). Voluntary fluid intake was less in the cold environment, however in both the warm and cold environment, ad libitum fluid intake, combined with fluid losses, resulted in similar changes in body mass.

Unilateral fluid absorption and effects on peak power after ingestion of commercially available hypotonic, isotonic, and hypertonic sports drinks. Rowlands DS, Bonetti DL, Hopkins WG

International journal of sport nutrition and exercise metabolism 21(6):480-91, 2011 Dez School of Sport and Exercise, Massey University, Wellington, New Zealand.

Isotonic sports drinks are often consumed to offset the effects of dehydration and improve endurance performance, but hypotonic drinks may be more advantageous. The purpose of the study was to compare absorption and effects on performance of a commercially available hypotonic sports drink (Mizone Rapid: 3.9% carbohydrate [CHO], 218 mOsmol/kg) with those of an isotonic drink (PowerAde: 7.6% CHO, 281 mOsmol/ kg), a hypertonic drink (Gatorade: 6% CHO, 327 mOsmol/kg), and a noncaloric placebo (8 mOsmol/kg). In a crossover, 11 cyclists consumed each drink on separate days at 250 ml/15 min during a 2-hr preload ride at 55% peak power followed by an incremental test to exhaustion. Small to moderate increases in deuterium oxide enrichment in the preload were observed with Mizone Rapid relative to PowerAde, Gatorade, and placebo (differences of 88, 45, and 42 parts per million, respectively; 90% confidence limits ±28). Serum osmolality was moderately lower with Mizone Rapid than with PowerAde and Gatorade (-1.9, -2.4; mOsmol/L; ±1.2 mOsmol/L) but not clearly different vs. placebo. Plasma volume reduction was small to moderate with Mizone Rapid, PowerAde, and Gatorade relative to placebo (-1.9%, -2.5%, -2.9%; ± 2.5%). Gut comfort was highest with Mizone Rapid but clearly different (8.4% ± 4.8%) only vs PowerAde. Peak power was highest with Mizone Rapid (380 W) vs. placebo and other drinks (1.2-3.0%; 99% confidence limits ±4.7%), but differences were inconclusive with reference to the smallest important effect (~1.2%). The outcomes are consistent with fastest fluid absorption with the hypotonic sports drink. Further research should determine whether the effect has a meaningful impact on performance.

Oral salt supplementation and long-distance exercise. Lehance C, Rodriguez de la Cruz C, Counet L, Seideil L, Bury T

British journal of sports medicine 45(15):A6, 2011 Dez During long-distance exercise, it can become difficult to continue to provide good nutrition support. The aim was to evaluate the potential of sausage "Saucisport" (water: 71%, proteins: 17%, carbohydrates: 3%, fat: 6%, other: 3%) to maintain metabolic balance and performance during long-distance exercise. 10 male long-distance runners (mean ± SD: age 34±14 y, height 177±6 cm, weight 71±6 kg, VO(2max) 56±8 ml/min/kg) performed two sessions on treadmill (4 h at 65-70% VO(2 max)). These two exercises were separated by 10 days. Subjects were randomised to receive "standard" or oral salt supplementation. During rectangular test, different parameters were recorded every hour (T0, T1, T2, T3, T4) and 1 h postexercise (T5): ventilation, respiratory quotient, oxygen consumption, heart rate, insulin, glucose and free fatty acids. Analysis of respiratory and cardiovascular parameters did not show any difference between salt and sugar supplementation, although in general the values observed in sweet supplementation are slightly higher than those in salt supplementation. Evolution of insulin during the stress test was comparable in both types of supplementation. Blood glucose values were higher after 3 h (p = 0.036) and 4 h (p = 0.014) of effort under "standard" supplementation, but were not different at the end of the exercise test. Our study shows that the sausage Saucisport® does not alter the physiological parameters, metabolic balance or performance during long-distance exercise.

Fluid balance and sodium losses during indoor tennis match play. Lott MJ, Galloway SD

International journal of sport nutrition and exercise metabolism 21(6):492-500, 2011 DezSchool of Sport, University of Stirling, Stirling, Scotland.This study assessed fluid balance, sodium losses, and effort intensity during indoor tennis match play (17 ± 2 °C, 42% ± 9% relative humidity) over a mean match duration of 68.1 ± 12.8 min in 16 male tennis players. Ad libitum fluid intake was recorded throughout the match. Sweat loss from change in nude body mass; sweat electrolyte content from patches applied to the forearm, calf, and thigh, and back of each player; and electrolyte balance derived from sweat, urine, and daily food-intake analysis were measured. Effort intensity was assessed from on-court heart rate compared with data obtained during a maximal treadmill test. Sweat rate (M ± SD) was 1.1 ± 0.4 L/hr, and fluid-ingestion rate was 1.0 ± 0.6 L/hr (replacing 93% ± 47% of fluid lost), resulting in only a small mean loss in body mass of 0.15% ± 0.74%. Large interindividual variabilities in sweat rate (range 0.3-2.0 L/hr) and fluid intake (range 0.31-2.52 L/hr) were noted. Whole-body sweat sodium concentration was 38 ± 12 mmol/L, and total sodium losses during match play were 1.1 ± 0.4 g (range 0.5-1.8 g). Daily sodium intake was 2.8 ± 1.1 g. Indoor match play largely consisted of low-intensity exercise below ventilatory threshold (mean match heart rate was 138 ± 24 beats/min). This study shows that in moderate indoor temperature conditions players ingest sufficient fluid to replace sweat losses. However, the wide range in data obtained highlights the need for individualized fluid-replacement guidance.

Hydration status of nursing home residents in Taiwan: a cross-sectional study.

AIM: To investigate fluid intake, dehydration and the key factors affecting nursing home residents' fluid intake and dehydration. BACKGROUND: Inadequate fluid intake is a common problem in nursing homes, but related studies on risk factors of inadequate fluid intake and dehydration in nursing homes have seldom been explored in detail in nursing research. METHODS: A cross-sectional design was developed and implemented. The sample was composed of 111 residents from nursing homes in Kaohsiung, Taiwan. Data of demographic characteristics, activities of daily living, and modes of feeding were collected and tested for association with hydration status. Laboratory data on hydration status were also collected. Data was collected from October to December 2005. RESULTS: Average daily fluid intake of the residents was 2083 mL. Forty-five per cent of the residents had a daily fluid intake that was less than their estimated requirements. Seventeen per cent of the residents had a blood urea nitrogen/creatinine ratio that was higher than 20. Mode of feeding and a diagnosis of dementia were the significant predictors of daily fluid intake and contributed to 28.8% of the total variance in daily fluid intake. Age, gender and a diagnosis of heart disease were the significant predictors of blood urea nitrogen/creatinine ratio, contributing to 17.0% of the total variance in the ratio. CONCLUSION: The nursing home residents in our study, especially females or those fed orally, had a comparatively higher prevalence of inadequate fluid intake. It is important to assess periodically the hydration status of nursing home residents and adjust their fluid intake accordingly.

Do ultra-runners in a 24-h run really dehydrate?

Knechtle B, Wirth A, Knechtle P, Rosemann T, Senn O.. Ir J Med Sci. 2011 Mar;180(1):129-34. Epub 2010 May 30.

Changes in hydration status of soccer players competing in the 2008 European Championship.

The incidence of exercise-associated hyponatraemia in the London marathon (Jan 2011)

Head Hair Reduces Sweat Rate During Exercise Under the Sun - Int J Sports Med 2010; 31(11): 779-783

Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes

J McGarvey, Thompson, C Hanna, T D Noakes, J Stewart , D Speedy: Br J Sports Med 2010;44:716-719.

Objective To investigate the diagnostic accuracy of commonly used signs of dehydration in marathon runners.

Design The diagnostic accuracy of 5 clinical signs/symptoms thought to indicate dehydration (altered skin turgor, dry oral mucous membranes, sunken eyes, an inability to spit and the sensation of thirst) was assessed by comparing the presence of these markers with the criterion standard of body weight change over a marathon footrace.

Setting 2006 Auckland Marathon

Participants 606 competitors in the full marathon Assessment: Body weight was measured before and immediately after the marathon. The 5 clinical signs/symptoms were assessed immediately after the marathon.

Main outcome measures Diagnostic accuracy of clinical signs/symptoms to detect dehydration greater than 3% of body weight.

Results 606 complete data sets were obtained. 3 clinical signs were associated with greater percentage weight loss: sunken eyes (mean percentage weight loss with symptom 2.6% (standard deviation 1.5), without 2.3% (1.5)); decreased skin turgor (with 3.0% (1.4), without 2.3% (1.5)) and the sensation of thirst (with 2.5% (1.5), without 2.3% (1.5)). The ability to spit and dry oral mucous membranes were unrelated to percentage weight loss. No signs/symptoms showed acceptably high validity for detecting a weight loss equal to or greater than 3% of body weight.

Conclusions The 5 parameters (decreased skin turgor, sensation of thirst, sunken eyes, inability to spit and dry mucous membranes) tested in this study did not precisely identify runners with total weight loss.3% at the end of a marathon.

The incidence of exercise-associated hyponatraemia in the London marathon

Courtney Kipps, Sanjay Sharma, Dan Tunstall Pedo. Br J Sports Med 2011, 45:11-19.

Background Exercise-associated hyponatraemia (EAH) is a potentially fatal cause of collapse in endurance exercise. It is understood to be a dilutional hyponatraemia caused by an increase of total body water relative to the amount of exchangeable sodium stores. Fourteen runners presented to one London hospital with symptomatic EAH several hours after finishing the 2003 London Marathon, and more recently, a young male runner died from the complications of severe EAH after crossing the finish line of the London Marathon.

Objectives To determine the incidence of EAH in runners in the London Marathon.

Methods Volunteers were recruited at race registration where they were weighed, had blood tests and completed a demographic and experience questionnaire. Weights, blood tests and a fluid intake questionnaire were repeated after the finish. Blood was analysed on-site using hand-held i-STAT blood analysers.

Results Of the 88 volunteers, 11 (12.5%) developed asymptomatic hyponatraemia (serum sodium 128–134 mmol/l). They consumed more fluid (p<0.001) and gained more weight (p<0.001) than did those without hyponatraemia.

Conclusions A significant proportion (12.5%) of healthy volunteers developed asymptomatic hyponatraemia running a marathon in cool conditions. On average, these runners consumed more fluid and gained more weight than did non-hyponatraemic runners, although fluid intake was not related to weight gain in this study. Four of the 11 hyponatraemic runners lost weight over the course of the marathon, strengthening the case for an additional factor, such as inappropriate antidiuretic hormone release during exercise, in the development of EAH.

Ingesting a 6% carbohydrate-electrolyte solution improves endurance capacity, but not sprint performance, during intermittent, high-intensity shuttle running in adolescent team games players aged 12-14 years.

Phillips SM, Turner AP, Gray S, Sanderson MF, Sproule J.: European journal of applied physiology, 2010-07 109(5):811-21. Department of Physical Education, Sport and Leisure Studies, University of Edinburgh, St Leonards Land, Holyrood Road, Edinburgh, EH8 8AQ, UK.

The main aim of this study was to investigate the influence of consuming a 6% carbohydrate-electrolyte (CHO-E) solution on the intermittent, high-intensity endurance performance and capacity of adolescent team games players. Fifteen participants (mean age 12.7 +/- 0.8 years) performed two trials separated by 3-7 days. In each trial, they completed 60 min of exercise composed of four 15-min periods of part A of the Loughborough Intermittent Shuttle Test, followed by an intermittent run to exhaustion (part B). In a double-blind, randomised, counterbalanced fashion participants consumed either the 6% CHO-E solution or a non-carbohydrate (CHO) placebo (5 ml kg(-1) BM) during the 5 min pre-trial and after each 15-min period of part A (2 ml kg(-1) BM). Time to fatigue was increased by 24.4% during part B when CHO was ingested (5.1 +/- 1.8 vs. 4.1 +/- 1.6 min, P < 0.05), with distance covered in part B also significantly greater in the CHO trial (851 +/- 365 vs. 694 +/- 278 m, P < 0.05). No significant between-trials differences were observed for mean 15-m sprint time (P = 0.35), peak sprint time (P = 0.77), or heart rate (P = 0.08) during part A. These results demonstrate, for the first time, that ingestion of a CHO-E solution significantly improves the intermittent, high-intensity endurance running capacity of adolescent team games players during an exercise protocol designed to simulate the physiological demands of team games.

Thermoregulation, pacing and fluid balance during mass participation distance running in a warm and humid environment.

Lee JK, Nio AQ, Lim CL, Teo EY, Byrne C.: European journal of applied physiology, 2010-07 109(5):887-98. Military Physiology Laboratory, Defence Medical and Environmental Research Institute, DSO National Laboratories, 27 Medical Drive, #09-01, Singapore, 117510, Singapore.

Deep body temperature (T(c)), pacing strategy and fluid balance were investigated during a 21-km road race in a warm and humid environment. Thirty-one males (age 25.3 +/- 3.2 years; maximal oxygen uptake 59.1 +/- 4.2 ml kg(-1) min(-1)) volunteered for this study. Continuous T(c) responses were obtained in 25 runners. Research stations at approximately 3-km intervals permitted accurate assessment of split times and fluid intake. Environmental conditions averaged 26.4 degrees C dry bulb temperature and 81% relative humidity. Peak T(c) was 39.8 +/- 0.5 (38.5-40.7) degrees C with 24 runners achieving T(c) > 39.0 degrees C, 17 runners > or = 39.5 degrees C, and 10 runners > or = 40.0 degrees C. In 12 runners attaining peak T(c) > or = 39.8 degrees C, running speed did not differ significantly when T(c) was below or above this threshold (208 +/- 15 cf. 205 +/- 24 m min(-1); P = 0.532). Running velocity was the main significant predictor variable of T(c) at 21 km (R(2) = 0.42, P or = 39.8 degrees C) and normothermic runners (T(c) < 39.8 degrees C) up to 11.8 km. A reverse J-shaped pacing profile characterised by a marked reduction in running speed after 6.9 km and evidence of an end-spurt in 16 runners was observed. Variables relating to fluid balance were not associated with any T(c) parameters or pacing. We conclude that hyperthermia, defined by a deep body temperature greater than 39.5 degrees C, is common in trained individuals undertaking outdoor distance running in environmental heat, without evidence of fatigue or heat illness.

Effect of milk-based carbohydrate-protein supplement timing on the attenuation of exercise-induced muscle damage

Emma Cockburn, Emma Stevenson, Philip R. Hayes, Paula Robson-Ansley, and Glyn Howatson: Appl. Physiol. Nutr. Metab. 35(3): 270–277 (2010).

Exercise-induced muscle damage (EIMD) leads to decrements in muscle performance and increases in intramuscular enzymes measured in the plasma, and to delayed onset of muscle soreness (DOMS), partly due to the activation of degradative pathways. It has been shown that milk-based carbohydrate-protein (CHO-P) can limit changes in markers of EIMD, possibly by attenuating protein degradation and (or) increasing protein synthesis. However, the timing of supplementation has received limited attention, and this may alter the response. This study examined the effects of acute milk-based CHO-P supplementation timing on the attenuation of EIMD. Four independent matched groups of 8 healthy males consumed milk-based CHO-P before (PRE), immediately after (POST), or 24 h after (TWENTY-FOUR) muscle-damaging exercise. Active DOMS, isokinetic muscle performance, reactive strength index (RSI), and creatine kinase (CK) were assessed immediately before and 24, 48, and 72 h after EIMD. POST and TWENTY-FOUR demonstrated a benefit in limiting changes in active DOMS, peak torque, and RSI over 48 h, compared with PRE. PRE showed a possible benefit in reducing increases in CK over 48 h and limiting changes in other variables over 72 h. Consuming milk-based CHO-P after muscle-damaging exercise is more beneficial in attenuating decreases in muscle performance and increases in active DOMS at 48 h than ingestion prior to exercise.

On-ice sweat rate, voluntary fluid intake, and sodium balance during practice in male junior ice hockey players drinking water or a carbohydrate-electrolyte solution.

Palmer MS, Logan HM, Spriet LL.: Applied Physiology, Nutrition, and Metabolism, 2010, 35(3):328-35 Language: eng Country: Canada Department of Human Health and Nutritional Sciences, University of Guelph, ON N1G 2W1, Canada.

This study evaluated the repeatability of hydration and sweat measurements taken during on-ice hockey practices with players drinking only water, and determined whether having only a carbohydrate-electrolyte solution (CES) to drink during practices decreased fluid intake or affected other hydration and (or) sweat measures. All testing was conducted on elite players of an Ontario Hockey League team (+/-SE; mean age, 17.6 +/- 0.3 years; mean height, 182.9 +/- 1.4 cm; mean body mass, 83.0 +/- 1.7 kg). Players were studied 3 times over the course of 6 weekly on-ice practices (+/-SE; mean playing time, 1.58 +/- 0.07 h; mean temperature, 11.4 +/- 0.8 degrees C; mean relative humidity, 52% +/- 3%). There was strong repeatability of the measured hydration and sweat parameters between 2 similar on-ice practices when players drank only water. Limiting the players to drinking only a CES (as opposed to water) did not decrease fluid intake during practice (+/-SE; mean CES intake, 0.72 +/- 0.07 L.h-1 vs. mean water intake, 0.82 +/- 0.08 L.h-1) or affect sweat rate (1.5 +/- 0.1 L.h-1 vs. 1.5 +/- 0.1 L.h-1), sweat sodium concentration (72.4 +/- 5.6 mmol.L-1 vs. 73.0 +/- 4.4 mmol.L-1), or percent body mass loss (1.1% +/- 0.2% vs. 0.9% +/- 0.2%). Drinking a CES also improved sodium balance (-2.1 +/- 0.2 g.h-1 vs. -2.6 +/- 0.3 g.h-1) and provided the players with a significant carbohydrate (43 +/- 4 g.h-1 vs. 0 +/- 0 g.h-1) during practice. In summary, a single field sweat test during similar on-ice hockey practices in male junior hockey players is sufficient to evaluate fluid and electrolyte balance. Also, a CES does not affect voluntary fluid intake during practice, compared with water, in these players. The CES provided some salt to offset the salt lost in sweat, and carbohydrate, which may help maintain physical and mental performance in the later stages of practice.

Beneficial effects of ice ingestion as a precooling strategy on 40-km cycling time-trial performance.

Ihsan M, Landers G, Brearley M, Peeling P.: International Journal of Sports Physiology and Performance

201006 5(2):140-51 .School of Sport Science, Exercise and Health, University of Western Australia, Crawley, WA, Australia.

Purpose: The effect of crushed ice ingestion as a precooling method on 40-km cycling time trial (CTT) performance was investigated. Methods: Seven trained male subjects underwent a familiarization trial and two experimental CTT which were preceded by 30 min of either crushed ice ingestion (ICE) or tap water (CON) consumption amounting to 6.8 g x kg(-1) body mass. The CTT required athletes to complete 1200 kJ of work on a wind-braked cycle ergometer. During the CTT, gastrointestinal (Tgi) and skin (Tsk) temperatures, cycling time, power output, heart rate (HR), blood lactate (BLa), ratings of perceived exertion (RPE) and thermal sensation (RPTS) were measured at set intervals of work. Results: Precooling lowered the Tgi after ICE significantly more than CON (36.74 +/- 0.67 degrees C vs 37.27 +/- 0.24 degrees C, P .05). The CTT completion time was 6.5% faster in ICE when compared with CON (ICE: 5011 +/- 810 s, CON: 5359 +/- 820 s, P < .05). Conclusions: Crushed ice ingestion was effective in lowering Tgi and improving subsequent 40-km cycling time trial performance. The mechanisms for this enhanced exercise performance remain to be clarified.

Increase of total body water with decrease of body mass while running 100 km nonstop--formation of edema?

Knechtle B, Wirth A, Knechtle P, Rosemann T.: Research Quarterly for Exercise and Sport, 2009, 80(3):593-603 . St. Gallen Health Center, St. Gallen, Switzerland.

We investigated whether ultraendurance runners in a 100-km run suffer a decrease of body mass and whether this loss consists of fat mass, skeletal muscle mass, or total body water. Male ultrarunners were measured pre- and postrace to determine body mass, fat mass, and skeletal muscle mass by using the anthropometric method. In addition, bioelectrical impedance analysis was used to determine total body water, and urinary (urinary specific gravity) and hematological parameters (hematocrit and plasma sodium) were measured in order to determine hydration status. Body mass decreased by 1.6 kg (p < .01), fat mass by 0.4 kg (p < .01), and skeletal muscle mass by 0.7 kg (p < .01), whereas total body water increased by 0.8 L (p < .05). Hematocrit and plasma sodium decreased significantly (p < .01), whereas plasma urea and urinary specific gravity (USG) increased significantly (p < .01). The decrease of 2.2% body mass and a USG of 1.020 refer to a minimal dehydration. Our athletes seem to have been relatively overhydrated (increase in total body water and plasma sodium) and dehydrated (decrease in body mass and increase in USG) during the race, as evidenced by the increased total body water and the fact that plasma sodium and hematocrit were lower postrace than prerace. The change of body mass was associated with the change of total body water (p < .05), and we presume the development of.

Can changes in body mass and total body water accurately predict hyponatremia after a 161-km running race?

Lebus DK, Casazza GA, Hoffman MD, Van Loan MD.: Clinical Journal of Sport Medicine , 2010, 20(3):193-9 . Sports Medicine Program, University of California Davis Medical Center, Sacramento, California, USA.

Objectives: To relate changes in body mass, total body water (TBW), extracellular fluid (ECF), and serum sodium concentration ([Na]) from a 161-km ultramarathon to finish time and incidence of hyponatremia. Design: Observational. Setting:: The 2008 Rio Del Lago 100-Mile (161-km) Endurance Run in Granite Bay, California. Participants: Forty-five runners. MAIN OUTCOME MEASUREMENTS: Pre-race and post-race body mass, TBW, ECF, and serum [Na]. Results: Body mass and serum [Na] significantly decreased 2% to 3% (P < 0.001) from pre-race to post-race, but TBW and ECF were unchanged. Significant relationships were observed between finish time and percentage change in body mass (r = 0.36; P = 0.01), TBW (r = 0.50; P = 0.007), and ECF (r = 0.61; P = 0.003). No associations were found between post-race serum [Na] and percentage change in body mass (r = -0.04; P = 0.94) or finish time (r = 0.5; P = 0.77). Hyponatremia (serum [Na] < 135 mmol/L) was present among 51.2% of finishers. Logistic regression prediction equation including pre-race TBW and percentage changes in TBW and ECF had an 87.5% concordance with the classification of hyponatremia. Conclusions: Hyponatremia occurred in over half of the 161-km ultramarathon finishers but was not predicted by change in body mass. The combination of pre-race TBW and percentage changes in TBW and ECF explained 87.5% of the variation in the incidence of hyponatremia. CLINICAL SIGNIFICANCE: Exercise-associated hyponatremia can occur simultaneously with dehydration and cannot be predicted by weight checks at races.

Effect of various carbohydrate-electrolyte fluids on cycling performance and maximal voluntary contraction.

Ganio MS, Klau JF, Lee EC, Yeargin SW, McDermott BP, Buyckx M, Maresh CM, Armstrong LE.: International Journal of Sport Nutrition and Exercise Metabolism, 2010, 20(2):104-14. Human Performance Laboratory, University of Connecticut, Storrs, CT, USA.

The purpose of this study was to compare the effects of a carbohydrate-electrolyte plus caffeine, carnitine, taurine, and B vitamins solution (CE+) and a carbohydrate-electrolyte-only solution (CE) vs. a placebo solution (PLA) on cycling performance and maximal voluntary contraction (MVC). In a randomized, double-blind, crossover, repeated-measures design, 14 male cyclists (M +/- SD age 27 +/- 6 yr, VO2max 60.4 +/- 6.8 ml x kg-1 x min(-1)) cycled for 120 min submaximally (alternating 61% +/- 5% and 75% +/- 5% VO2max) and then completed a 15-min performance trial (PT). Participants ingested CE+, CE, or PLA before (6 ml/kg) and every 15 min during exercise (3 ml/kg). MVC was measured as a single-leg isometric extension (70 degree knee flexion) before (pre) and after (post) exercise. Rating of perceived exertion (RPE) was measured throughout. Total work accumulated (KJ) during PT was greater (p < .05) in CE+ (233 +/- 34) than PLA (205 +/- 52) but not in CE (225 +/- 39) vs. PLA. MVC (N) declined (p < .001) from pre to post in PLA (988 +/- 213 to 851 +/- 191) and CE (970 +/- 172 to 870 +/- 163) but not in CE+ (953 +/- 171 to 904 +/- 208). At Minutes 60, 90, 105, and 120 RPE was lower in CE+ (14 +/- 2, 14 +/- 2, 12 +/- 1, 15 +/- 2) than in PLA (14 +/- 2, 15 +/- 2, 14 +/- 2, 16 +/- 2; p < .001). CE+ resulted in greater total work than PLA. CE+, but not PLA or CE, attenuated pre-to-post MVC declines. Performance increases during CE+ may have been influenced by lower RPE and greater preservation of leg strength during exercise in part as a result of the hypothesized effects of CE+ on the central nervous system and skeletal muscle.

Glycemic index and endurance performance.

Donaldson CM, Perry TL, Rose MC.: International Journal of Sport Nutrition and Exercise Metabolism,

2010, 20(2):154-65. States Dept. of Human Nutrition, University of Otago, Dunedin, New Zealand.

The aim of this review is to provide an up-to-date summary of the evidence surrounding glycemic index (GI) and endurance performance. Athletes are commonly instructed to consume low-GI (LGI) carbohydrate (CHO) before exercise, but this recommendation appears to be based on the results of only a few studies, whereas others have found that the GI of CHO ingested before exercise has no impact on performance. Only 1 study was designed to directly investigate the impact of the GI of CHO ingested during exercise on endurance performance. Although the results indicate that GI is not as important as consuming CHO itself, more Research in this area is clearly needed. Initial Research investigating the impact of GI on postexercise recovery indicated consuming high-GI (HGI) CHO increased muscle glycogen resynthesis. However, recent studies indicate an interaction between LGI CHO and fat oxidation, which may play a role in enhancing performance in subsequent exercise. Despite the fact that the relationship between GI and sporting performance has been a topic of Research for more than 15 yr, there is no consensus on whether consuming CHO of differing GI improves endurance performance. Until further well-designed Research is carried out, athletes are encouraged to follow standard recommendations for CHO consumption and let practical issues and individual experience dictate the use of HGI or LGI meals and supplements before, during, and after exercise.

An isocaloric glucose-fructose beverage's effect on simulated 100-km cycling performance compared with a glucose-only beverage.

Triplett D, Doyle JA, Rupp JC, Benardot D.: International Journal of Sport Nutrition and Exercise Metabolism, 2010, 20(2):122-31. Dept. of Kinesiology and Health, Georgia State University, Atlanta, GA.

A number of recent Research studies have demonstrated that providing glucose and fructose together in a beverage consumed during exercise results in significantly higher oxidation rates of exogenous carbohydrate (CHO) than consuming glucose alone. However, there is insufficient evidence to determine whether the increased exogenous CHO oxidation improves endurance performance. The purpose of this study was to determine whether consuming a beverage containing glucose and fructose (GF) would result in improved cycling performance compared with an isocaloric glucose-only beverage (G). Nine male competitive cyclists (32.6 +/- 5.8 years, peak oxygen uptake 61.5 +/- 7.9 ml x kg(-1) x min(-1)) completed a familiarization trial and then 2 simulated 100-km cycling time trials on an electronically braked Lode cycle ergometer separated by 5-7 d. During the randomly ordered experimental trials, participants received 36 g of CHO of either G or GF in 250 ml of water every 15 min. All 9 participants completed the 100-km time trial significantly faster when they received the GF beverage than with G (204.0 +/- 23.7 vs. 220.6 +/- 36.6 min; p = .023). There was no difference at any time point between trials for blood glucose or for blood lactate. Total CHO oxidation increased significantly from rest during exercise but was not statistically significant between the GF and G trials, although there was a trend for CHO oxidation to be higher with GF in the latter stages of the time trial. Consumption of a CHO beverage containing glucose and fructose results in improved 100-km cycling performance compared with an isocaloric glucose-only beverage.

Influence of beverage temperature on exercise performance in the heat: a systematic review.

Burdon CA, O'Connor HT, Gifford JA, Shirreffs SM.: International Journal ofSsport Nutrition and Exercise Metabolism, 2010, 20(2):166-74. States Discipline of Exercise and Sport Science, University of Sydney, Sydney, Australia.

PURPOSE: Increased core temperature (T(c)), impaired cardiovascular function, and dehydration contribute to fatigue during prolonged exercise in the heat. Although many studies have examined mechanisms addressing these factors, few have investigated the effect of cold beverage temperature on thermoregulation and exercise performance in the heat. METHODS: Citations from MEDLINE (Ovid), Sport Discus (EBSCOhost), AUSPORT and AusportMed (Informit), Web of Science, and SCOPUS were identified from the earliest record until September 2008 using the search terms: drink temperature, beverage temperature, fluid temperature, water temperature, and cold fluid combined with body temperature and thermoregulation. To be included, studies needed to assess core or rectal temperature during exercise in moderate or hot environmental conditions. After quality rating was completed by two reviewers, the difference in mean Tc and exercise performance was calculated. RESULTS: Ten studies meeting search inclusion criteria were available for analysis. Three were excluded because sufficient detail or statistical data were not reported. A meta-analysis was not performed because the studies were deemed too different to group. Three of the remaining 7 studies found modulated T(c) with cold beverage consumption, and from the 4 that conducted exercise performance tests, performance improved by 10% with cold fluids. CONCLUSION: Cold fluid may attenuate T(c) rise and improve exercise performance in the heat; however, study findings are mixed. Research using well-trained athletes and fluid-ingestion protocols replicating competition scenarios is required. Potential sensory effects of cold fluid in maintaining motivation also need to be assessed as a mechanism underpinning improved performance.

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

Godek SF, Bartolozzi AR, Peduzzi C, Heinerichs S, Garvin E, Sugarman E, Burkholder R.: Journal of Athletic Training, 2010 Mar-Apr 45(2):128-35. Chester University, West Chester, PA 19383, USA.

Hypothesis: 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 and 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.

Yeargin SW, Casa DJ, Judelson DA, McDermott BP, Ganio MS, Lee EC, Lopez RM, Stearns RL, Anderson JM, Armstrong LE, Kraemer WJ, Maresh CM.: Journal of Athletic Training, 2010 Mar-Apr 45(2):136-46. Indiana State University, Terre Haute, IN 47809, USA.

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 and 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.

Influence of hydration on physiological function and performance during trail running in the heat.

Casa DJ, Stearns RL, Lopez RM, Ganio MS, McDermott BP, Walker Yeargin S, Yamamoto LM, Mazerolle SM, Roti MW, Armstrong LE, Maresh CM.: Journal of Athletic Training, 2010 Mar-Apr 45(2):147-56. Department of Kinesiology, University of Connecticut, Storrs, CT 06269-1110, USA.

Context: Authors of most field studies have not observed decrements in physiologic function and performance with increases in dehydration, although authors of well-controlled laboratory studies have consistently reported this relationship. Investigators in these field studies did not control exercise intensity, a known modulator of body core temperature. Objective: To directly examine the effect of moderate water deficit on the physiologic responses to various exercise intensities in a warm outdoor setting. Design: Semirandomized, crossover design. Setting: Field setting. Patients or Other Participants: Seventeen distance runners (9 men, 8 women; age = 27 +/- 7 years, height = 171 +/- 9 cm, mass = 64.2 +/- 9.0 kg, body fat = 14.6% +/- 5.5%). Intervention (s): Participants completed four 12-km runs (consisting of three 4-km loops) in the heat (average wet bulb globe temperature = 26.5 degrees C): (1) a hydrated, race trial (HYR), (2) a dehydrated, race trial (DYR), (3) a hydrated, submaximal trial (HYS), and (4) a dehydrated, submaximal trial (DYS). Main Outcome Measure(s): For DYR and DYS trials, dehydration was measured by body mass loss. In the submaximal trials, participants ran at a moderate pace that was matched by having them speed up or slow down based on pace feedback provided by researchers. Intestinal temperature was recorded using ingestible thermistors, and participants wore heart rate monitors to measure heart rate. Results: Body mass loss in relation to a 3-day baseline was greater for the DYR (-4.30% +/- 1.25%) and DYS trials (-4.59% +/- 1.32%) than for the HYR (-2.05% +/- 1.09%) and HYS (-2.0% +/- 1.24%) trials postrun (P < .001). Participants ran faster for the HYR (53.15 +/- 6.05 minutes) than for the DYR (55.7 +/- 7.45 minutes; P .05). Intestinal temperature immediately postrun was greater for DYR than for HYR (P < .05), the only significant difference. Intestinal temperature was greater for DYS than for HYS postloop 2, postrun, and at 10 and 20 minutes postrun (all: P < .001). Intestinal temperature and heart rate were 0.22 degrees C and 6 beats/min higher, respectively, for every additional 1% body mass loss during the DYS trial compared with the HYS trial. Conclusions : A small decrement in hydration status impaired physiologic function and performance while trail running in the heat.

Maintained total body water content and serum sodium concentrations despite body mass loss in female ultra-runners drinking ad libitum during a 100 km race.

Knechtle B, Senn O, Imoberdorf R, Joleska I, Wirth A, Knechtle P, Rosemann T.: Asia Pacific Journal of Clinical Nutrition, 2010 19(1):83-90. Facharzt FMH fur Allgemeinmedizin, Gesundheitszentrum St. Gallen, Vadianstrasse 26, 9001 St. Gallen, Switzerland.

We investigated in 11 female ultra-runners during a 100 km ultra-run, the association between fluid intake and prevalence of exercise-associated hyponatremia in a cross-sectional study. Athletes drank ad libitum and recorded their fluid intake. They competed at 8.0 (1.0) km/h and finished within 762 (91) min. Fluid intake was 4.1 (1.3) L during the race, equal to 0.3 (0.1) L/h. Body mass decreased by 1.5 kg (p< 0.01); pre race body mass was related to speed in the race (r = -0.78, p< 0.05); and change (Delta) in body mass was not associated with speed in the race. Change in body mass was positively (r = 0.70; p< 0.05), and Delta urinary specific gravity negatively (r = -0.67; p< 0.05), correlated to Delta percent total body water. Changes in body mass were not related to fluid intake during the race. Fluid intake was not correlated to running speed and showed no association with either Delta percent total body water nor Delta [Na] in plasma. Fluid intake showed no relationship with both Delta haematocrit and Delta plasma volume. No exercise-associated hyponatremia occurred. Female ultra- runners consuming fluids ad libitum during the race experienced no fluid overload, and ad libitum drinking protects against exercise-associated hyponatremia. The reported higher incidence of exercise-associated hyponatremia in women is not really a gender effect but due to women being more prone to overdrink.

The effects of progressive dehydration on strength and power: is there a dose response?

Hayes LD, Morse CI.: European Journal of Applied Physiology, 2010, 108(4):701-7. Department of Exercise and Sports Science, Manchester Metropolitan University, Hassall Road, Alsager, ST7 2HL, UK.

This study examined the effect of exercise- and heat-induced dehydration on strength, jump capacity and neuromuscular function. Twelve recreationally active males completed six resistance exercise bouts (baseline and after each 5 exposure sessions) in an increasing state of hypohydration obtained by repeated heat exposure and exercise sessions (5 periods of 20 min jogging at up to approximately 80% age predicted heart rate maximum at 48.5 +/- 0.48 degrees C, relative humidity 50 +/- 4%). Relative to starting values, body mass decreased 1.0 +/- 0.5, 1.9 +/- 0.7, 2.6 +/- 0.8, 3.3 +/- 0.9 and 3.9 +/- 1.0% after exposure 1, 2, 3, 4 and 5, respectively. However, plasma volume remained constant. No significant differences existed amongst trials in vertical jump height, electromyography data or isokinetic leg extension at a rate of 120 degrees s(-1). Isometric leg extensions were significantly reduced (P < 0.05) after the first (1% body mass loss) and subsequent exposures in comparison to baseline. Isokinetic leg extensions at a rate of 30 degrees s(-1) were significantly reduced after the third (2.6% body mass loss) and subsequent exposures compared with baseline. No dose response was identified in any of the tested variables yet a threshold was observed in isometric and isokinetic strength at 30 degrees s(-1). In conclusion, dehydration caused by jogging in the heat had no effect on vertical jumping or isokinetic leg extensions at a rate of 120 degrees s(-1). Alternatively, exercise-induced dehydration was detrimental to isometric and isokinetic leg extensions at a rate of 30 degrees s(-1), suggesting the force-velocity relationship in hypohydration merits further research.

Carbohydrate exerts a mild influence on fluid retention following exercise-induced dehydration.

Osterberg KL, Pallardy SE, Johnson RJ, Horswill CA.: Journal of Applied Physiology, 2010, 108(2):245-50. Gatorade Sports Science Institute, Barrington, IL 60010, USA.

Rapid and complete rehydration, or restoration of fluid spaces, is important when acute illness or excessive sweating has compromised hydration status. Many studies have investigated the effects of graded concentrations of sodium and other electrolytes in rehydration solutions; however, no study to date has determined the effect of carbohydrate on fluid retention when electrolyte concentrations are held constant. The Purpose of this study was to determine the effect of graded levels of carbohydrate on fluid retention following exercise-induced dehydration. Fifteen heat-acclimatized men exercised in the heat for 90 min with no fluid to induce 2-3% dehydration. After a 30-min equilibration period, they received, over the course of 60 min, one of five test beverages equal to 100% of the acute change in body mass. The experimental beverages consisted of a flavored placebo with no electrolytes (P), placebo with electrolytes (P + E), 3%, 6%, and 12% carbohydrate solutions with electrolytes. All beverages contained the same type and concentration of electrolytes (18 meq/l Na(+), 3 meq/l K(+), 11 meq/l Cl(-)). Subjects voided their bladders at 60, 90, 120, 180, and 240 min, and urine specific gravity and urine volume were measured. Blood samples were taken before exercise and 30, 90, 180, and 240 min following exercise and were analyzed for glucose, sodium, hemoglobin, hematocrit, renin, aldosterone, and osmolality. Body mass was measured before and after exercise and a final body mass was taken at 240 min. There were no differences in percent dehydration, sweat loss, or fluid intake between trials. Fluid retention was significantly greater for all carbohydrate beverages compared with P (66.3 +/- 14.4%). P + E (71.8 +/- 9.9%) was not different from water, 3% (75.4 +/- 7.8%) or 6% (75.4 +/- 16.4%) but was significantly less than 12% (82.4 +/- 9.2%) retention of the ingested fluid. No difference was found between the carbohydrate beverages. Carbohydrate at the levels measured exerts a mild influence on fluid retention in postexercise recovery.

Acute effects of chocolate milk and a commercial recovery beverage on postexercise recovery indices and endurance cycling performance.

Pritchett K, Bishop P, Pritchett R, Green M, Katica C.: Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquée, Nutrition et Métabolisme, 2009, 34(6):1017-22. Department of Health, Human Performance, and Nutrition, Central Washington University, Ellensburg, WA 98926, USA.

To maximize training quality, athletes have sought nutritional supplements that optimize recovery. This study compared chocolate milk (CHOC) with a carbohydrate replacement beverage (CRB) as a recovery aid after intense exercise, regarding performance and muscle damage markers in trained cyclists. Ten regional-level cyclists and triathletes (maximal oxygen uptake 55.2 +/- 7.2 mL.kg(-1).min(-1)) completed a high-intensity intermittent exercise protocol, then 15-18 h later performed a performance trial at 85% of maximal oxygen uptake to exhaustion. Participants consumed 1.0 g carbohydrate.kg-1.h-1 of a randomly assigned isocaloric beverage (CHOC or CRB) after the first high-intensity intermittent exercise session. The same protocol was repeated 1 week later with the other beverage. A 1-way repeated measures analysis of variance revealed no significant difference (p = 0.91) between trials for time to exhaustion at 85% of maximal oxygen uptake (CHOC 13 +/- 10.2 min, CRB 13.5 +/- 8.9 min). The change in creatine kinase (CK) was significantly (p < 0.05) greater in the CRB trial than in the CHOC trial (increase CHOC 27.9 +/- 134.8 U.L(-1), CRB 211.9 +/- 192.5 U.L(-1)), with differences not significant for CK levels before the second exercise session (CHOC 394.8 +/- 166.1 U.L(-1), CRB 489.1 +/- 264.4 U.L(-1)) between the 2 trials. These findings indicate no difference between CHOC and this commercial beverage as potential recovery aids for cyclists between intense workouts.

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

Volpe SL, Poule KA, Bland EG.: Journal of Athletic Training, 2009: 44(6):624-9. University of Pennsylvania, Division of Biobehavioral and Health Sciences, School of Nursing, Claire M. Fagin Hall, 418 Curie Boulevard, Philadelphia, PA 19104-4217, USA.

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 result(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). A greater percentage of men (47%) than women (28%) were hypohydrated (chi(2) = 8.33, 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.

Effect of ingesting a honey-sweetened beverage on soccer performance and exercise-induced cytokine response.

Abbey EL, Rankin JW.: International Journal of Sport Nutrition and Exercise Metabolism, 2009 19(6):659-72. Dept. of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0430, USA.

Purpose: This study compared the effect of a honey-sweetened beverage with those of a commercial sports drink and a placebo on performance and inflammatory response to a 90-min soccer simulation. Methods: Ten experienced male soccer players randomly performed 3 trials (honey [H], sports drink , and placebo [P]), consuming the beverage before and during halftime for a total of 1.0 g/kg carbohydrate for H and S. Performance measures included 5 sets (T1-T5) of a high-intensity run and agility and ball-shooting tests followed by a final progressive shuttle-run (PSR) test to exhaustion. Blood samples were drawn pretest, posttest (B2), and 1 hr posttest (B3) for markers of inflammation, oxygen radical absorbance capacity (ORAC), and hormone response. Results: T2-T5 were significantly slower than T1 (p < .05), and a decrease in PSR time was observed from baseline (-22.9%) for all treatments. No significant effect of the interventions was observed for any performance measures. Plasma IL-1ra levels increased posttest for all treatments (65.5% S, 63.9% P, and 25.8% H), but H was significantly less than S at posttest and P at B3. Other cytokines and ORAC increased at B2 (548% IL-6, 514% IL-10, 15% ORAC) with no difference by treatment. Conclusion: Acute ingestion of honey and a carbohydrate sports drink before and during a soccer-simulation test did not improve performance, although honey attenuated a rise in IL-1ra. Ingestion of carbohydrate and/ or antioxidant-containing beverages at frequencies typical of a regulation match may not be beneficial for trained soccer players.

Influence of ingesting a carbohydrate-electrolyte solution before and during a 1-hr running performance test.

Rollo I, Williams C.: International Journal of Sport Nutrition and Exercise Metabolism, 2009, 19(6):645-58. School of Sport and Exercise Sciences, Loughborough University, Loughborough, UK.

The aim of this study was to investigate the influence of ingesting a carbohydrate-electrolyte solution (CHO-E) on performance during a 1-hr treadmill run. Eight male endurance-trained runners (age 31 +/- 8 yr, M +/- SD) completed three 1-hr performance runs separated by 1 wk. The study used a double-blind placebo (PLA) controlled design. On 2 occasions (P1, P2) runners consumed a placebo solution, 8 ml/kg body mass (BM), 30 min before and 2 ml/kg BM at 15-min intervals throughout the 1-hr run. On a separate occasion they consumed the same quantity of a 6.4% CHO-E solution (C). Total distances covered for P1, P2, and C trials were 13,685 +/- 1,116 m, 13,715 +/- 1,143 m, and 14,046 +/- 1,104 m, respectively. Although there was no difference between the 2 PLA trials (p > .05), the distance covered during the C trial was significantly greater than in either PLA trial (p < .05). CHO ingestion resulted in a higher blood glucose concentration only at the onset of exercise (p < .05) compared with the PLA trials. Blood lactate, respiratory-exchange ratio, and CHO oxidation were similar in all 3 trials. In conclusion, ingestion of a 6.4% CHO-E solution before and during exercise was associated with improved running performance in runners compared with the ingestion of a color- and taste-matched placebo.

Physiological and performance effects of glycerol hyperhydration and rehydration.

van Rosendal SP, Osborne MA, Fassett RG, Coombes JS

.   Nutrition reviews. (12):690-705, 2009.

The University of Queensland, School of Human Movement Studies, Brisbane, Queensland, Australia. Studies have shown that beverages containing glycerol can enhance and maintain hydration status and may improve endurance exercise performance by attenuating adverse physiological changes associated with dehydration. Improvements to performance include increased endurance time to exhaustion by up to 24%, or a 5% increase in power or work. However, some studies have found no performance benefits during either prolonged exercise or specific skill and agility tests. In studies that have shown benefits, the improvements have been associated with thermoregulatory and cardiovascular changes. These include increased plasma volume and sweat rates, as well as reduced core temperature and ratings of perceived exertion. In a very small number of subjects, glycerol consumption has been associated with side-effects including nausea, gastrointestinal discomfort, dizziness, and headaches. In summary, while glycerol and fluid ingestion results in hyperhydration, the documented benefits to exercise performance remain inconsistent.

Hazards of ultra-marathon running in the Scottish Highlands: exercise-associated hyponatraemia. Cuthill, J. A., Ellis, C., Inglis, A.: Intensive Care Unit, Glasgow Royal Infirmary, Glasgow, UK. Emergency medicine journal : EMJ, 26(12):906-7, 2009. The case histories are presented of four athletes taking part in a 95-mile ultra-endurance foot race in Scotland who were hospitalised after developing exercise-associated hyponatraemia and rhabdomyolysis. Exercise-associated hyponatraemia is relatively uncommon in temperate climates. Risk factors disposing to this disorder are discussed. Exercise-associated hyponatraemia is thought to be due to overconsumption of hypotonic fluid with other associated pathophysiology including an inability to suppress fully antidiuretic hormone during exercise or to mobilise adequate sodium from osmotically inactive internal stores. Non-specific symptoms make this disorder difficult to diagnose on site without the assistance of serum sodium measurement, but any delay in treatment of patients with encephalopathy can prove fatal. Mainstays of treatment include fluid restriction, hypertonic saline, loop diuretics and mannitol.