Search

Diet can significantly influence athletic performance, but recent research developments have substantially changed our understanding of sport and exercise nutrition. Athletes adopt various nutritional strategies in training and competition in the pursuit of success. The aim of training is to promote changes in the structure and function of muscle and other tissues by selective modulation of protein synthesis and breakdown in response to the training stimulus. This process is affected by the availability of essential amino acids in the post-exercise period. Athletes have been encouraged to eat diets high in carbohydrate, but low-carbohydrate diets up-regulate the capacity of muscle for fat oxidation, potentially sparing the limited carbohydrate stores. Such diets, however, do not enhance endurance performance. It is not yet known whether the increased capacity for fat oxidation that results from training in a carbohydrate-deficient state can promote loss of body fat. Preventing excessive fluid deficits will maintain exercise capacity, and ensuring adequate hydration status can also reduce subjective perception of effort. This latter effect may be important in encouraging exercise participation and promoting adherence to exercise programmes. Dietary supplement use is popular in sport, and a few supplements may improve performance in specific exercise tasks. Athletes must be cautious, however, not to contravene the doping regulations. There is an increasing recognition of the role of the brain in determining exercise performance: various nutritional strategies have been proposed, but with limited success. Nutrition strategies developed for use by athletes can also be used to achieve functional benefits in other populations. [ABSTRACT FROM PUBLISHER]

The change in blood and plasma volume following ingestion of glucose solutions of varying concentrations was estimated in twelve healthy male volunteers. Subjects consumed, within a 5 min period, 600 ml of a solution containing 0, 2, 5 or 10 % glucose with osmolalities of 0 (sd 0), 111 (sd 1), 266 (sd 7) and 565 (sd 5) mOsm/kg, respectively. Blood samples were collected over the course of 1 h after ingestion at intervals of 10 min. After ingestion of the 2 % glucose solution, plasma volume increased from baseline levels at 20 min. Plasma volume decreased from baseline levels at 10 and 60 min after ingestion of the 10 % glucose solution. Heart rate was elevated at 10 and 60 min after ingestion of the 10 % glucose solution and decreased at 30 and 40 min after ingestion of the 2 % glucose solution relative to the average heart rate recorded before drinking. It is concluded that ingestion of hypertonic, energy-dense glucose solutions results in a decrease in plasma and extracellular fluid volume, most likely due to the net secretion of water into the intestinal lumen. [ABSTRACT FROM PUBLISHER]

Sweat evaporation can be a key thermoregulatory mechanism and it causes a loss of water from all compartments of the body. Hypohydration can also develop with restricted fluid intake or with intake of diuretics. Hypohydration can affect physical and/or mental performance and/or have implications for dietary recommendations. A variety of different types and modes of exercise performance can be influenced by hydration state. Reviews of the published literature are currently most conclusive for endurance exercise. Dehydration equivalent to 2% body mass loss during exercise in a hot environment (31–32°C) impairs endurance performance, but when the exercise is performed in a temperate environment (20–21°C) a 2% body mass loss appears to have a lesser and inconsequential effect. In cold environments a body mass loss >2% may be tolerable for endurance exercise. There is a less conclusive picture as to the effects of hypohydration on other types of physical performance, including strength and power activities, team sports and the skills component of many sports, and for mental performance. A number of physiological mechanisms are responsible for the effects observed. Fluid consumption can be used to attenuate the development of a water deficit or to correct it. The composition and temperature of a drink and the volume and rate of its consumption can all influence the physiological responses to ingestion and can impact on exercise performance. [ABSTRACT FROM PUBLISHER]

Presents a study that investigated the sodium and water loss during and replacement after exercise-induced volume depletion. Methodology used in the study; How the need to replace electrolytes after volume depletion is linked to the loss of electrolytes in sweat; Significance of adding sodium to fluids ingested after exercise-induced volume depletion in the restoration and maintenance of whole body fluid balance.

Muscle-wasting in chronic kidney disease (CKD) arises from several factors including sedentary behaviour and metabolic acidosis. Exercise is potentially beneficial but might worsen acidosis through exercise-induced lactic acidosis. We studied the chronic effects of exercise in CKD stage 4-5 patients (brisk walking, 30 min, 5 times/week), and non-exercising controls; each group receiving standard oral bicarbonate (STD), or additional bicarbonate (XS) (Total n = 26; Exercising + STD n = 9; Exercising +XS n = 6; Control + STD n = 8; Control + XS n = 3). Blood and vastus lateralis biopsies were drawn at baseline and 6 months. The rise in blood lactate in submaximal treadmill tests was suppressed in the Exercising + XS group. After 6 months, intramuscular free amino acids (including the branched chain amino acids) in the Exercising + STD group showed a striking chronic depletion. This did not occur in the Exercising + XS group. The effect in Exercising + XS patients was accompanied by reduced transcription of ubiquitin E3-ligase MuRF1 which activates proteolysis via the ubiquitin-proteasome pathway. Other anabolic indicators (Akt activation and suppression of the 14 kDa actin catabolic marker) were unaffected in Exercising + XS patients. Possibly because of this, overall suppression of myofibrillar proteolysis (3-methylhistidine output) was not observed. It is suggested that alkali effects in exercisers arose by countering exercise-induced acidosis. Whether further anabolic effects are attainable on combining alkali with enhanced exercise (e.g. resistance exercise) merits further investigation. [ABSTRACT FROM AUTHOR]

The aims of this study were to determine the effect of cold (4°C) and thermoneutral (37°C) beverages on thermoregulation and performance in the heat and to explore sensory factors associated with ingesting a cold stimulus. Seven males (age 32.8 ± 6.1 years, [Vdot]O2peak 59.4 ± 6.6 ml · kg-1 · min-1) completed cold, thermoneutral, and thermoneutral + ice trials in randomized order. Participants cycled for 90 min at 65%[Vdot]O2peak followed by a 15-min performance test at 28°C and 70% relative humidity. They ingested 2.3 ml · kg-1 of a 7.4% carbohydrate-electrolyte solution every 10 min during the 90-min steady-state exercise including 30 ml ice puree every 5 min in the ice trial. Absolute changes in skin temperature (0.22 ± 1.1°C vs. 1.14 ± 0.9°C; P = 0.02), mean body temperature (1.2 ± 0.3 vs. 1.6 ± 0.3°C; P = 0.03), and heat storage were lower across the 90-min exercise bout for the cold compared with the thermoneutral trial. Significant improvements (4.9 ± 2.4%, P < 0.01) in performance were observed with cold but no significant differences were detected with ice. Consumption of cold beverages during prolonged exercise in the heat improves body temperature measures and performance. Consumption of ice did not reveal a sensory response, but requires further study. Beverages consumed by athletes exercising in the heat should perhaps be cold for performance and safety reasons. [ABSTRACT FROM AUTHOR]

Following a 2.0 +/- 0.1% body mass loss induced by intermittent exercise in the heat, seven male volunteers ingested either a carbohydrate-electrolyte solution (CE) or skimmed milk (M) in a volume equal to 150% of body mass loss. At the end of the 3 h recovery period, subjects were essentially in positive fluid balance on trial M (191 +/- 162 mL), and euhydrated on trial CE (-135 +/- 392 mL) despite being in negative sodium balance on both trials and negative potassium balance on trial CE. This difference of 326 +/- 354 mL or 0.4% body mass approached significance (P = 0.051). Subjects ingested 137 +/- 15 and 113 +/- 12 g of CHO during the CE and M trials, respectively, as well as 75 +/- 8 g of protein during the M trial. At the end of the 3 h recovery period, an exercise capacity test was completed at 61% VO(2peak) in warm (35.3 +/- 0.5 degrees C), humid (63 +/- 2%) conditions. HR (P = 0.020) and rectal temperature (P = 0.045) were higher on trial M, but no difference in exercise time to exhaustion was observed between trials (39.6 +/- 7.3 min vs. 39.7 +/- 8.1 min on trials CE and M, respectively). The results of the present study suggest that milk can be an effective post-exercise rehydration drink, with subjects remaining in net positive fluid balance throughout the recovery period. Despite the effect on fluid retention, exercise capacity was not different between skimmed milk and a commercially available carbohydrate-electrolyte drink 4 h following exercise/heat-induced body mass loss. [ABSTRACT FROM AUTHOR]

The article discusses the risk of undertaking fasting among athletes, official support staff and spectators. Fasting is assumed risky for athletes who disregard guidelines for optimum nutrition before, during or after exercise. Athletes are prohibited to undertake fasting during extreme exercise in a stressful environment. A personal strategy crafted by a professional trainer should be followed by athletes who need fasting during competition.

Muscle cramp is a temporary but intense and painful involuntary contraction of skeletal muscle that can occur in many different situations. The causes of, and cures for, the cramps that occur during or soon after exercise remain uncertain, although there is evidence that some cases may be associated with disturbances of water and salt balance, while others appear to involve sustained abnormal spinal reflex activity secondary to fatigue of the affected muscles. Evidence in favour of a role for dyshydration comes largely from medical records obtained in large industrial settings, although it is supported by one large-scale intervention trial and by field trials involving small numbers of athletes. Cramp is notoriously unpredictable, making laboratory studies difficult, but experimental models involving electrical stimulation or intense voluntary contractions of small muscles held in a shortened position can induce cramp in many, although not all, individuals. These studies show that dehydration has no effect on the stimulation frequency required to initiate cramping and confirm a role for spinal pathways, but their relevance to the spontaneous cramps that occur during exercise is questionable. There is a long history of folk remedies for treatment or prevention of cramps; some may reduce the likelihood of some forms of cramping and reduce its intensity and duration, but none are consistently effective. It seems likely that there are different types of cramp that are initiated by different mechanisms; if this is the case, the search for a single strategy for prevention or treatment is unlikely to succeed.

The 2019 International Amateur Athletics Federation Track-and-Field World Championships will take place in Qatar in the Middle East. The 2020 Summer Olympics will take place in Tokyo, Japan. It is quite likely that these events may set the record for hottest competitions in the recorded history of both the Track-and-Field World Championships and Olympic Games. Given the extreme heat in which track-and-field athletes will need to train and compete for these games, the importance of hydration is amplified more than in previous years. The diverse nature of track-and-field events, training programs, and individuality of athletes taking part inevitably means that fluid needs will be highly variable. Track-and-field events can be classified as low, moderate, or high risk for dehydration based on typical training and competition scenarios, fluid availability, and anticipated sweat losses. This paper reviews the risks of dehydration and potential consequences to performance in track-and-field events. The authors also discuss strategies for mitigating the risk of dehydration.

The use of dietary supplements is widespread among athletes in all sports and at all levels of competition, as it is in the general population. For the athlete training at the limits of what is sustainable, or for those seeking a shortcut to achieving their aims, supplements offer the prospect of bridging the gap between success and failure. Surveys show, however, that this is often not an informed choice and that the knowledge level among consumers is often low and that they are often influenced in their decisions by individuals with an equally inadequate understanding of the issues at stake. Supplement use may do more harm than good, unless it is based on a sound analysis of the evidence. Where a deficiency of an essential nutrient has been established by appropriate investigations, supplementation can provide a rapid and effective correction of the problem. Supplements can also provide a convenient and time-efficient solution to achieving the necessary intake of key nutrients such as protein and carbohydrate. Athletes contemplating the use of supplements should consider the potential for both positive and negative outcomes. Some ergogenic supplements may be of benefit to some athletes in some specific contexts, but many are less effective than is claimed. Some may be harmful to health of performance and some may contain agents prohibited by anti-doping regulations. Athletes should make informed choices that maximize the benefits while minimizing the risks.

Previous investigations have suggested that exercise at intensities greater than 70% maximal oxygen uptake (VO2max) reduces gastric emptying rate during exercise, but little is known about the effect of exercise intensity on gastric emptying in the postexercise period. To examine this, 8 healthy participants completed 3 experimental trials that included 30 min of rest (R), low-intensity (L; 33% of peak power output) exercise, or high-intensity (H; 10 × 1 min at peak power output followed by 2 min rest) exercise. Thirty minutes after completion of exercise, participants ingested 595 ml of a 5% glucose solution, and gastric emptying rate was assessed via the double-sampling gastric aspiration method for 60 min. No differences (p > .05) were observed in emptying characteristics for total stomach volume or test meal volume between the trials, and the quantity of glucose delivered to the intestine did not differ between trials (p > .05). Half-emptying times did not differ (p = .902) between trials and amounted to 22 ± 9, 22 ± 9, and 22 ± 7 min (M ± SD) during the R, L, and H trials, respectively. These results suggest that exercise has little effect on postexercise gastric emptying rate of a glucose solution.

Purpose: This study examined the effects of sodium chloride and potassium chloride supplementation during 48-h severe energy restriction on exercise capacity in the heat., Methods: Nine males completed three 48-h trials: adequate energy intake (100 % requirement), adequate electrolyte intake (CON); restricted energy intake (33 % requirement), adequate electrolyte intake (ER-E); and restricted energy intake (33 % requirement), restricted electrolyte intake (ER-P). At 48 h, cycling exercise capacity at 60 % VO2 peak was determined in the heat (35.2 °C; 61.5 % relative humidity)., Results: Body mass loss during the 48 h was greater during ER-P [2.16 (0.36) kg] than ER-E [1.43 (0.47) kg; P < 0.01] and CON [0.39 (0.68) kg; P < 0.001], as well as greater during ER-E than CON (P < 0.01). Plasma volume decreased during ER-P (P < 0.001), but not ER-E or CON. Exercise capacity was greater during CON [73.6 (13.5) min] and ER-E [67.0 (17.2) min] than ER-P [56.5 (13.1) min; P < 0.01], but was not different between CON and ER-E (P = 0.237). Heart rate during exercise was lower during CON and ER-E than ER-P (P < 0.05)., Conclusions: These results demonstrate that supplementation of sodium chloride and potassium chloride during energy restriction attenuated the reduction in exercise capacity that occurred with energy restriction alone. Supplementation maintained plasma volume at pre-trial levels and consequently prevented the increased heart rate observed with energy restriction alone. These results suggest that water and electrolyte imbalances associated with dietary energy and electrolyte restriction might contribute to reduced exercise capacity in the heat.

Heat stress and exercise increase water loss from the body, primarily in the form of sweat. For some occupational groups, including miners, construction workers in hot climates, soldiers, and some athletes, daily water losses can reach 10-12 L. These losses must be replaced on a daily basis to maintain functional capacity. Both hyperhydration and hypohydration will, if sufficiently severe, impair all aspects of physiological function. Tests of strength and power are largely unaffected by dehydration of up to about 2%-4% of body mass. However, decrements in the performance of endurance tests may occur at these levels, especially in warm environments. Body water deficits, if sufficiently severe, also have adverse effects on measures of mood and on some elements of cognitive function and result in an increased subjective rating of the perception of effort. Beverages consumed during exercise can provide carbohydrates and electrolytes that may be beneficial in some situations; however, drinking in volumes required to match sweat loss may cause gastrointestinal discomfort that will generally impair performance., (© The Author(s) 2015. Published by Oxford University Press on behalf of the International Life Sciences Institute. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Studies to assess water intake have been undertaken in many countries around the world. Some of these have been large-scale studies, whereas others have used a small number of subjects. These studies provide an emerging picture of water and/or fluid consumption in different populations around the world. Studies of this nature have also formed the basis of a number of recommendations published by different organizations, including the US Institute of Medicine and the European Food Safety Authority. The results of these intake studies indicate substantial differences in water and/or fluid intake in different populations, which have translated into different intake recommendations., (© 2012 International Life Sciences Institute.)

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% VO2max in cool conditions (10°C, n = 12) or 60% VO2max 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.

Objective: This study investigated the effect of the osmolality and carbohydrate content of drinks on their rehydration effectiveness after exercise-induced dehydration., Methods: Six healthy male volunteers were dehydrated by 1.9+/-0.1% of body mass by intermittent cycle ergometer exercise in the heat before ingesting one of three solutions with different carbohydrate contents and osmolalities over a period of 1h. Thirty minutes after the cessation of exercise, subjects drank a volume that amounted to 150% (130-150, median [range]) of their body mass loss. Drinks contained 25 mmol/L Na(+) and 0%, 2%, or 10% glucose with osmolalities of (mean+/-SD) 79+/-4, 193+/-5, and 667+/-12 mosm/kg, respectively. Blood and urine samples were collected before exercise, after exercise, and 0, 1, 2, 3, 4, and 6h after the end of the rehydration period., Results: Significantly more of the ingested fluid was retained in the 10% trial (46+/-9%) than in the 0% trial (27+/-13%), with 40+/-14% retained in the 2% trial. Subjects remained euhydrated for 1h longer in the 10% glucose trial than in the 2% glucose trial. In the 2% glucose trial, plasma volume was elevated immediately after and 1h after rehydration., Conclusion: This study suggests that, following the rehydration protocol used, hypertonic glucose-sodium drinks may be more effective at restoring and maintaining hydration status after sweat loss than more dilute solutions when the sodium concentration is comparable.

Sweat evaporation can be a key thermoregulatory mechanism and it causes a loss of water from all compartments of the body. Hypohydration can also develop with restricted fluid intake or with intake of diuretics. Hypohydration can affect physical and/or mental performance and/or have implications for dietary recommendations. A variety of different types and modes of exercise performance can be influenced by hydration state. Reviews of the published literature are currently most conclusive for endurance exercise. Dehydration equivalent to 2% body mass loss during exercise in a hot environment (31-32 degrees C) impairs endurance performance, but when the exercise is performed in a temperate environment (20-21 degrees C) a 2% body mass loss appears to have a lesser and inconsequential effect. In cold environments a body mass loss >2% may be tolerable for endurance exercise. There is a less conclusive picture as to the effects of hypohydration on other types of physical performance, including strength and power activities, team sports and the skills component of many sports, and for mental performance. A number of physiological mechanisms are responsible for the effects observed. Fluid consumption can be used to attenuate the development of a water deficit or to correct it. The composition and temperature of a drink and the volume and rate of its consumption can all influence the physiological responses to ingestion and can impact on exercise performance.

Purpose: To investigate the effect of drink temperature on cycling capacity in the heat., Methods: On two separate trials, eight males cycled at 66 +/- 2% VO2peak (mean +/- SD) to exhaustion in hot (35.0 +/- 0.2 degrees C) and humid (60 +/- 1%) environments. Participants ingested three 300-mL aliquots of either a cold (4 degrees C) or a warm (37 degrees C) drink during 30 min of seated rest before exercise and 100 mL of the same drink every 10 min during exercise. Rectal and skin temperatures, heart rate, and sweat rate were recorded. Ratings of thermal sensation and perceived exertion were assessed., Results: Exercise time was longer (P < 0.001) with the cold drink (63.8 +/- 4.3 min) than with the warm drink (52.0 +/- 4.1 min). Rectal temperature fell by 0.5 +/- 0.1 degrees C (P < 0.001) at the end of the resting period after ingestion of the cold drinks. There was no effect of drink temperature on mean skin temperature at rest (P = 0.870), but mean skin temperature was lower from 20 min during exercise with ingestion of the cold drink than with the warm drink (P < 0.05). Heart rate was lower before exercise and for the first 35 min of exercise with ingestion of the cold drink than with the warm drink (P < 0.05). Drink temperature influenced sweat rate (1.22 +/- 0.34 and 1.40 +/- 0.41 L x h(-1) for the cold and the warm drink, respectively; P < 0.05). Ratings of thermal sensation and perceived exertion (P < 0.01) during exercise were lower when the cold drink was ingested., Conclusion: Compared with a drink at 37 degrees C, the ingestion of a cold drink before and during exercise in the heat reduced physiological strain (reduced heat accumulation) during exercise, leading to an improved endurance capacity (23 +/- 6%).

To investigate how differing moderate sodium chloride concentrations affect rehydration after exercise and subsequent exercise capacity, eight males lost 1.98 +/- 0.1% body mass exercising in the heat, then consumed one of four drinks in a volume equivalent to 150% of mass loss. Drinks were identical except for sodium chloride content (1 +/- 1, 31 +/- 1, 40 +/- 1, 50 +/- 1 mmol/l). After 4 h recovery subjects cycled for 5 min at 70% VO(2peak) then at 95% VO(2peak) until volitional fatigue. Urine output was inversely related to sodium intake: more was produced with the 1 than the 40 and 50 mmol/l drinks (P < 0.01). Time to exhaustion in the exercise capacity test was not different between treatments (P = 0.883). The addition of 40 or 50 mmol/l of sodium chloride to a rehydration beverage reduced subsequent urine output, thereby providing more effective rehydration than a sodium-free drink. This did not, however, result in improved performance 4 h after the end of the rehydration period.

In this study, we examined thermoregulatory responses to ingestion of separate aliquots of drinks at different temperatures during low-intensity exercise in conditions of moderate heat stress. Eight men cycled at 50% (s = 3) of their peak oxygen uptake (VO2peak) for 90 min (dry bulb temperature: 25.3 degrees C, s = 0.5; relative humidity: 60%, s = 5). Four 400-ml aliquots of flavoured water at 10 degrees C (cold), 37 degrees C (warm) or 50 degrees C (hot) were ingested after 30, 45, 60, and 75 min of exercise. Immediately after the 90 min of exercise, participants cycled at 95% VO2peak to exhaustion to assess exercise capacity. There were no differences between trials in rectal temperature at the end of the 90 min of exercise (cold: 38.11 degrees C, s = 0.30; warm: 38.10 degrees C, s = 0.33; hot: 38.21 degrees C, s = 0.30; P = 0.765). Mean skin temperature between 30 and 90 min tended to be influenced by drink temperature (cold: 34.49 degrees C, s = 0.64; warm: 34.53 degrees C, s = 0.69; hot: 34.71 degrees C, s = 0.48; P = 0.091). Mean heart rate from 30 to 90 min was higher in the hot trial (129 beats . min(-1), s = 7; P < 0.05) than on the cold (124 beats . min(-1), s = 9) and warm trials (126 beats . min(-1), s = 8). Ratings of thermal sensation were higher on the hot trial than on the cold trial at 35 and 50 min (P < 0.05). Exercise capacity was similar between trials (P = 0.963). The heat load and debt induced by periodic drinking resulted in similar body temperatures during low-intensity exercise in conditions of moderate heat stress due to appropriate thermoregulatory reflexes.

Objective: The effects of fluid intake during prolonged exercise have been extensively studied but at present there exists little information on the effects of milk-based drinks on the response to prolonged exercise. Thus, the purpose of this study was to investigate the effects of milk-based drinks on exercise capacity., Methods: Eight healthy males (age 24 +/- 4 y, height 1.76 +/- 0.04 m, mass 68.9 +/- 9.5 kg, body fat 12.5 +/- 2.4%, peak oxygen consumption 4.3 +/- 0.6 L/min) exercised to volitional exhaustion at 70% peak oxygen consumption on four occasions. Subjects ingested 1.5 mL/kg body mass of plain water, a carbohydrate-electrolyte solution, low-fat (0.1%) milk, or low-fat (0.1%) milk with added glucose before and every 10 min during exercise. The effect of the drink on exercise capacity and the cardiovascular, metabolic, and thermoregulatory responses to prolonged exercise were examined., Results: Exercise time to exhaustion was not significantly influenced by the drink ingested (P = 0.19), but there was a tendency for subjects to exercise longer when the carbohydrate-electrolyte (110.6, range 82.0-222.7 min), milk (103.3, range 85.7-228.5 min), or milk plus glucose (102.8, range 74.3-167.1 min) was ingested compared with water (93.3, range 82.4-192.3 min). The solution ingested did not influence the cardiovascular, metabolic, or thermoregulatory response to exercise., Conclusion: The results of this study suggest that although the low-fat milk-based fluids did not enhance exercise capacity over that seen with the ingestion of plain water, the effect was comparable to that observed with a carbohydrate-electrolyte beverage.

There is little information on the nutritional habits of female football players at any level of the game. There is also a shortage of information on the nutrition and hydration strategies that players should adopt. In general, differences in nutritional needs between males and females are smaller than differences between individuals, so that principles developed for male players also apply to women. There is a need to address energy balance and body composition: prolonged energy deficits cannot be sustained without harm to health and performance. Published reports show mean carbohydrate intakes for female players of about 5 g/kg/day, and this seems to be too low to sustain consistent intensive training. The timing of protein intake may be as important as the amounts consumed, provided that the total intake is adequate. Dehydration adversely affects skill and stamina in women as it does in men, so an individualised hydration strategy should be developed. The prevalence of iron deficiency in women generally is high, but it seems to be alarmingly high in female players. All players should adopt dietary habits that ensure adequate iron intake. Football training seems to increase bone mass in the weight-bearing limbs, with positive implications for bone health in later life, but some players may be at risk from inadequate calcium dietary intake.

Hydration status is not easily measured, but acute changes in hydration status are often estimated from body mass change. Changes in body mass are also often used as a proxy measure for sweat losses. There are, however, several sources of error that may give rise to misleading results, and our aim in this paper is to quantify these potential errors. Respiratory water losses can be substantial during hard work in dry environments. Mass loss also results from substrate oxidation, but this generates water of oxidation which is added to the body water pool, thus dissociating changes in body mass and hydration status: fat oxidation actually results in a net gain in body mass as the mass of carbon dioxide generated is less than the mass of oxygen consumed. Water stored with muscle glycogen is presumed to be made available as endogenous carbohydrate stores are oxidized. Fluid ingestion and sweat loss complicate the picture by altering body water distribution. Loss of hypotonic sweat results in increased osmolality of body fluids. Urine and faecal losses can be measured easily, but changes in the water content of the bladder and the gastrointestinal tract cannot. Body mass change is not always a reliable measure of changes in hydration status and substantial loss of mass may occur without an effective net negative fluid balance.

The marathon poses a considerable physical challenge for athletes of all levels. When combined with high heat and humidity, not only is performance potentially compromised, but health and well-being are also at risk. There are well recognised effects of heat and hydration status on the cardiovascular and thermoregulatory systems that can account for the decreased performance and increased sensation of effort that are experienced when competing in the heat. Elevated exercise heart rate and core temperature at the same absolute exercise intensity are commonly reported. Dehydration occurring during exercise in the heat and results in reductions in stroke volume, cardiac output and blood pressure, as well as a marked decline in blood flow to the working muscles. Recent work suggests that hyperthermia may have a direct affect on the CNS and the brain may contribute to fatigue during prolonged exercise in a warm environment. At present, evidence supports a significant role of catecholaminergic neurotransmission, but there are a number of metabolic and circulatory perturbations occurring within the brain that may also be important in the fatigue process.

The diverse nature of the athletic events, together with the varied training programmes and individuality of athletes taking part, inevitably means that fluid needs are highly variable--between athletes, perhaps between training and competition, and with differing environmental conditions and degree of training and heat acclimatization. There are limited data from athletics on all aspects of fluid balance, but wherever possible we have focused on this information to draw conclusions. When appropriate, euhydration will best be ensured by consuming 6-8 ml . kg body mass(-1) of a sodium-containing fluid, or sodium-free fluid together with food, about 2 h before exercise. The individual sweat responses are so variable that athletes should assess their own individual sweat losses to determine if these are likely to be a cause for concern. The volume of drink that is consumed should never be so much that an athlete gains mass over an event, unless perhaps there is evidence that they began in a hypohydrated state. This may be a particular concern in the field events and multi-event disciplines when competition can be spread over a number of hours and when there are significant rest periods between activities.

Athletics is a popular sport among young people. To maintain health and optimize growth and athletic performance, young athletes need to consume an appropriate diet. Unfortunately, the dietary intake of many young athletes follows population trends rather than public health or sports nutrition recommendations. To optimize performance in some disciplines, young athletes may strive to achieve a lower body weight or body fat content and this may increase their risk for delayed growth and maturation, amenorrhoea, reduced bone density, and eating disorders. Although many of the sports nutrition principles identified for adults are similar to those for young athletes, there are some important differences. These include a higher metabolic cost of locomotion and preferential fat oxidation in young athletes during exercise. Young athletes, particularity children, are at a thermoregulatory disadvantage due to a higher surface area to weight ratio, a slower acclimatization, and lower sweating rate. An appropriate dietary intake rather than use of supplements (except when clinically indicated) is recommended to ensure young athletes participate fully and safely in athletics.

The high metabolic rates sustained by soccer players during training and match-play cause sweat to be produced in both warm and temperate environments. There is limited published information available on the effects of this sweat loss on performance in soccer. However, this limited information, 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 to the effects in these other activities. Therefore, the generalization that a body mass reduction equivalent to 2% should be the acceptable limit of sweat losses seems reasonable. This amount, or more, of sweat loss reflected in body mass loss is a common experience for some players. Sodium is the main electrolyte lost in sweat and the available data indicate considerable variability in sodium losses between players due to differences in sweating rate and sweat electrolyte concentration. Additionally, the extent of sodium loss is such that its replacement will be warranted for some of these players during training sessions and matches. Although soccer 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 nutritional strategy.

The use of alcohol is often intimately associated with sport. As well as providing a source of energy, alcohol (ethanol) has metabolic, cardiovascular, thermoregulatory, and neuromuscular actions that may affect exercise performance. Strength is minimally affected, and performance impairments depend on the dose of alcohol and subject habituation to alcohol intake, exercise duration, environmental conditions, and other factors. Central nervous system function is impaired at high doses, resulting in decrements in cognitive function and motor skill, as well as behavioral changes that may have adverse effects on performance. Effects may persist for hours after intoxication.

Seven active men were recruited to examine changes in the serum concentration of S100beta, a proposed peripheral marker of blood-brain barrier permeability, following prolonged exercise in temperate (T) and warm (W) conditions. Subjects were seated immersed to the neck in water at 35.0 (0.1) degrees C (T) or 39.0 (0.1) degrees C (W) for 30 min. Subjects then entered a room maintained at either 18.3 (1.8) degrees C (T) or 35.0 (0.3) degrees C (W) and completed 60 min of cycle exercise at 60% peak oxygen uptake. Serum S100beta concentration was elevated after exercise in the W trial (+0.12 (0.10) microg/l; P = 0.02) but not after the T trial (P = 0.238). Water immersion and exercise elevated core temperature by 2.1 (0.5) degrees C to 39.5 (0.3) degrees C at the end of exercise in the W trial compared with a 0.9 (0.2) degrees C increase during the T trial (P < 0.001). Weighted mean skin temperature was higher throughout the W trial compared with the T trial (P < 0.001). Heart rate (P < 0.001) and blood glucose (P < 0.001) and lactate (P < 0.001) concentrations were elevated to a greater extent during exercise in the W trial than in the T trial. Ratings of perceived exertion (P < 0.001) and thermal comfort (P < 0.001) were markedly higher throughout the W trial than in the T trial. The results of this study demonstrate that serum S100beta was elevated after water immersion and prolonged exercise in a warm environment, suggesting that blood-brain barrier permeability may be altered.

Eight males were recruited to examine the effect of branched-chain amino acid (BCAA) supplementation on exercise capacity in a glycogen-depleted state in a warm environment. Following a exercise and dietary regimen designed to reduce glycogen availability, subjects returned to the laboratory the following morning and remained seated for 2 h, before cycling to volitional exhaustion at 50% VO2 peak in a warm environment [30.0 (0.2) degrees C; mean (SD)]. Four 250 ml aliquots of a 12 g l(-1) BCAA solution or placebo were ingested at 30 min intervals prior to exercise, with an additional 150 ml consumed every 15 min throughout exercise. BCAA ingestion had no effect on exercise capacity [placebo 103.9 (26.9) min; BCAA 111.0 (29.2) min; P = 0.129). No difference in heart rate (P = 0.345), core temperature (P = 0.628), or weighted mean skin temperature (P = 0.114) was apparent between trials. Ingestion of the BCAA solution produced a marked increase in plasma BCAA immediately prior to exercise [+ 1126 (158) micromol l(-1); P < 0.001) with this difference maintained throughout. Consequently, a significant reduction in the plasma concentration ratio of free tryptophan to BCAA was observed during the BCAA trial when compared to the placebo (P < 0.001). Plasma ammonia concentration was significantly elevated during exercise throughout the BCAA trial (P < 0.001), with no change from rest apparent during the placebo trial (P = 0.608). Blood glucose (P = 0.114) and lactate (P = 0.836) concentrations were not different between trials. Ingestion of a BCAA solution prior to, and during, prolonged exercise in glycogen-depleted subjects did not influence exercise capacity in a warm environment.