The effects of consuming carbohydrate-electrolyte beverages on gastric emptying and fluid absorption during and following exercise

Carbohydrate or Electrolyte Rehydration Recovers Plasma Volume but Not Post-immersion Performance Compared to Water After Immersion Diuresis

INTRODUCTION

We tested the hypothesis that a carbohydrate (CHO: 6.5%) or carbohydrate-electrolyte (CHO + E: 6.5% + 50 mmol/L NaCl) drink would better recover plasma volume (PV) and exercise performance compared to water (H2O) after immersion diuresis.

METHODS

Twelve men (24 ± 2 years; 82.4 ± 15.5 kg; and V̇O2max: 49.8 ± 5.1 mL · kg-1 · min-1) completed four experimental visits: a no-immersion control (CON) and three 4-h cold-water (18.0 °C) immersion trials (H2O, CHO, and CHO + E) followed by exercise in a warm environment (30 °C, 50% relative humidity). The exercise was a 60-minute loaded march (20.4 kg; 55% VO2max) followed by a 10-minute intermittent running protocol. After immersion, subjects were rehydrated with 100% of body mass loss from immersion diuresis during the ruck march. PV is reported as a percent change after immersion, after the ruck march, and after the intermittent running protocol. The intermittent running protocol distance provided an index of exercise performance. Data are reported as mean ± SD.

RESULTS

After immersion, body mass loss was 2.3 ± 0.7%, 2.3 ± 0.5%, and 2.3 ± 0.6% for H2O, CHO, and CHO + E. PV loss after immersion was 19.8 ± 8.5% in H2O, 18.2 ± 7.0% in CHO, and 13.9 ± 9.3% in CHO + E, which was reduced after the ruck march to 14.7 ± 4.7% (P = .13) in H2O, 8.8 ± 8.3% (P < .01) in CHO, and 4.4 ± 10.9% (P = .02) in CHO + E. The intermittent running protocol distance was 1.4 ± 0.1 km in CON, 1.4 ± 0.2 km in H2O, 1.4 ± 0.1 km in CHO, and 1.4 ± 0.2 km in CHO + E (P = .28).

CONCLUSIONS

Although CHO and CHO + E better restored PV after immersion, post-immersion exercise performance was not augmented compared to H2O, highlighting that fluid replacement following immersion diuresis should focus on restoring volume lost rather than fluid constituents.

Health Claims for Sports Drinks-Analytical Assessmentaccording to European Food Safety Authority's Scientific Opinion

In Europe, sports food supplements (SSFs) are subject to specific laws and regulations. Up to 70% of athletes are highly influenced by the information on the label or the advertisement of the SSF, which often does not correspond to the scientific evidence, such as health claims. The aim is to analyze such claims relating to sports drinks (SDs) in commercial messages. To this end, an observational and cross-sectional study was conducted based on the analysis of the content and degree of adequacy of the health claims indicated on the labelling or technical data sheet of the SDs with those established by the European legislation in force according to the European Food Safety Authority (EFSA). The SSFs were searched for via Amazon and Google Shopping. A total of 114 health claims were evaluated. No claim fully conformed with the recommendations. A total of 14 claims (n = 13 products) almost conformed to the recommendations; they were "Maintain endurance level in exercises requiring prolonged endurance", "Improve water absorption during physical exercise", and "Improved physical performance during high intensity, high duration physical exercise in trained adults", representing 12.3% of the total (n = 114). The vast majority of the claims identified indicated an unproven cause-effect and should be modified or eliminated, which amounts to food fraud towards the consumer.

Partial and Complete Fluid Replacement Maintains Exercise Performance in a Warm Environment Following Prolonged Cold-Water Immersion

ABSTRACT

Wheelock, CE, Stooks, J, Schwob, J, Hess, HW, Pryor, RR, and Hostler, D. Partial and complete fluid replacement maintains exercise performance in a warm environment following prolonged cold-water immersion. J Strength Cond Res 38(2): 290-296, 2024-Special warfare operators may be exposed to prolonged immersion before beginning a land-based mission. This immersion will result in substantial hypohydration because of diuresis. This study tested the hypothesis that both partial and full postimmersion rehydration would maintain performance during exercise in the heat. Seven men (23 ± 2 years; V̇o2max: 50.8 ± 5.3 ml·kg-1·min-1) completed a control trial (CON) without prior immersion and 3 immersion (18.0°C) trials without rehydration (NO) or with partial (HALF) or full (FULL) rehydration. After immersion, subjects completed a 60-minute weighted ruck march (20.4 kg; 5.6 kph) and a 15-minute intermittent exercise protocol (iEPT) in a warm environment (30.0°C and 50.0% relative humidity). The primary outcome was distance (km) covered during the iEPT. A priori statistical significance was set to p ≤ 0.05. Immersion resulted in 2.3 ± 0.4% loss of body mass in all immersion trials (p < 0.01). Distance covered during the first 13-minute interval run portion of iEPT was reduced in the NO rehydration trial (1.59 ± 0.18 km) compared with all other conditions (CON: 1.88 ± 0.18 km, p = 0.03; HALF: 1.80 ± 0.18 km, p < 0.01; FULL: 1.86 ± 0.28 km, p = 0.01). During the final 2 minutes of the iEPT, distance in the NO rehydration trial (0.31 ± 0.07 km) was reduced compared with the FULL rehydration trial (0.37 ± 0.07 km; p < 0.01) but not compared with CON (0.35 ± 0.07 km; p = 0.09) or HALF (0.35 ± 0.07 km; p = 0.08). Both partial and full postimmersion fluid replacement maintained intermittent exercise performance and should be applied as rehydration strategies.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Fructose: A New Variable to Consider in SIADH and the Hyponatremia Associated With Long-Distance Running?

Fructose has recently been proposed to stimulate vasopressin secretion in humans. Fructose-induced vasopressin secretion is not only postulated to result from ingestion of fructose-containing drinks but may also occur from endogenous fructose production via activation of the polyol pathway. This raises the question of whether fructose might be involved in some cases of vasopressin-induced hyponatremia, especially in situations where the cause is not fully known such as in the syndrome of inappropriate secretion of diuretic hormone (SIADH) and exercise-associated hyponatremia, which has been observed in marathon runners. Here we discuss the new science of fructose and vasopressin, and how it may play a role in some of these conditions, as well as in the complications associated with rapid treatment (such as the osmotic demyelination syndrome). Studies to test the role of fructose could provide new pathophysiologic insights as well as novel potential treatment strategies for these common conditions.

Cultural differences in hydration practices among physically active individuals: a narrative review

It is well-established that appropriate hydration practices are essential in promoting health and optimizing performance and recovery. However, evidence-based hydration guidelines may not be adopted due to cultural differences across countries, such as religious beliefs, traditions, preferences, and beverage availability. Examples of hydration practices influenced by culture include beer consumption after sports in Western countries, consumption of sugarcane juice in India and Ramadan fasting among Muslims. For most cultural hydration practices, there is limited scientific evidence on their effects on rehydration, exercise performance, and recovery. Despite possible benefits of various hydration practices on exercise performance and recovery, they are inconsistent with current evidence-based hydration recommendations. More research on the impacts of cultural hydration differences on physiology, performance, and recovery is warranted to allow evidence-based guidelines and advisories.

Abbreviations: ABV: alcohol by volume, ACSM: American College of Sports Medicine, NATA: National Athletic Trainers’ Association, ROS: reactive oxygen species, TCM: Traditional Chinese Medicine

Does the Nutritional Composition of Dairy Milk Based Recovery Beverages Influence Post-exercise Gastrointestinal and Immune Status, and Subsequent Markers of Recovery Optimisation in Response to High Intensity Interval Exercise?

This study aimed to determine the effects of flavored dairy milk based recovery beverages of different nutrition compositions on markers of gastrointestinal and immune status, and subsequent recovery optimisation markers. After completing 2 h high intensity interval running, participants (n = 9) consumed a whole food dairy milk recovery beverage (CM, 1.2 g/kg body mass (BM) carbohydrate and 0.4 g/kg BM protein) or a dairy milk based supplement beverage (MBSB, 2.2 g/kg BM carbohydrate and 0.8 g/kg BM protein) in a randomized crossover design. Venous blood samples, body mass, body water, and breath samples were collected, and gastrointestinal symptoms (GIS) were measured, pre- and post-exercise, and during recovery. Muscle biopsies were performed at 0 and 2 h of recovery. The following morning, participants returned to the laboratory to assess performance outcomes. In the recovery period, carbohydrate malabsorption (breath H2 peak: 49 vs. 24 ppm) occurred on MBSB compared to CM, with a trend toward greater gut discomfort. No difference in gastrointestinal integrity (i.e., I-FABP and sCD14) or immune response (i.e., circulating leukocyte trafficking, bacterially-stimulated neutrophil degranulation, and systemic inflammatory profile) markers were observed between CM and MBSB. Neither trial achieved a positive rate of muscle glycogen resynthesis [-25.8 (35.5) mmol/kg dw/h]. Both trials increased phosphorylation of intramuscular signaling proteins. Greater fluid retention (total body water: 86.9 vs. 81.9%) occurred on MBSB compared to CM. Performance outcomes did not differ between trials. The greater nutrient composition of MBSB induced greater gastrointestinal functional disturbance, did not prevent the post-exercise reduction in neutrophil function, and did not support greater overall acute recovery.

Tolerance to Central Hypovolemia Is Greater Following Caffeinated Coffee Consumption in Habituated Users

We investigated the influence of caffeinated coffee consumption on cardiovascular responses and tolerance to central hypovolemia in individuals habituated to caffeine. Thirteen participants completed three trials, consuming caffeinated coffee, decaffeinated coffee or water before exposure to central hypovolemia via lower body negative pressure (LBNP) to pre syncope. Tolerance to central hypovolemia was quantified as cumulative stress index (CSI: LBNP level multiplied by time; mmHg × min). Prior to the consumption of caffeinated coffee, decaffeinated coffee, and water, heart rate (HR: 62 ± 10, 63 ± 9 and 61 ± 8 BPM, respectively), stroke volume (SV: 103 ± 23, 103 ± 17 and 102 ± 18 mL/beat, respectively), and total peripheral resistance (TPR: 14.2 ± 3.0, 14.0 ± 3.0, and 14.3 ± 2.7 mmHg/L/min, respectively), were not different between trials (all P > 0.05). Mean arterial pressure (MAP) increased following consumption of all drinks (Post Drink) (Caffeinated coffee: from 86 ± 8 to 97 ± 7; Decaffeinated coffee: from 88 ± 10 to 94 ± 7; and Water: from 87 ± 10 to 96 ± 6 mmHg; all P = 0.0001) but was not different between trials (P = 0.247). During LBNP, HR increased (P = 0.000) while SV decreased (P = 0.000) relative to post drink values and TPR as unchanged (P = 0.109). HR, SV, and TPR were not different between trials (all P > 0.05). MAP decreased at pre syncope in all trials (60 ± 5, 60 ± 7, and 61 ± 6 mmHg; P < 0.001). LBNP tolerance was greater following caffeinated coffee (914 ± 309 mmHg × min) relative to decaffeinated coffee and water (723 ± 336 and 769 ± 337 mmHg × min, respectively, both P < 0.05). Tolerance to central hypovolemia was greater following consumption of caffeinated coffee in habituated users.

Fluid type influences acute hydration and muscle performance recovery in human subjects

Background

Exercise and heat trigger dehydration and an increase in extracellular fluid osmolality, leading to deficits in exercise performance and thermoregulation. Evidence from previous studies supports the potential for deep-ocean mineral water to improve recovery of exercise performance post-exercise. We therefore wished to determine whether acute rehydration and muscle strength recovery was enhanced by deep-ocean mineral water following a dehydrating exercise, compared to a sports drink or mountain spring water. We hypothesized that muscle strength would decrease as a result of dehydrating exercise, and that recovery of muscle strength and hydration would depend on the type of rehydrating fluid.

Methods

Using a counterbalanced, crossover study design, female (n = 8) and male (n = 9) participants performed a dehydrating exercise protocol under heat stress until achieving 3% body mass loss. Participants rehydrated with either deep-ocean mineral water (Deep), mountain spring water (Spring), or a carbohydrate-based sports drink (Sports) at a volume equal to the volume of fluid loss. We measured relative hydration using salivary osmolality (S_osm) and muscle strength using peak torque from a leg extension maneuver.

Results

S_osm significantly increased (p < 0.0001) with loss of body mass during the dehydrating exercise protocol. Males took less time (90.0 ± 18.3 min; P < 0.0034) to reach 3% body mass loss when compared to females (127.1 ± 20.0 min). We used a mono-exponential model to fit the return of S_osm to baseline values during the rehydrating phase. Whether fitting stimulated or unstimulated S_osm, male and female participants receiving Deep as the hydrating fluid exhibited the most rapid return to baseline S_osm (p < 0.0001) regardless of the fit parameter. Males compared to females generated more peak torque (p = 0.0005) at baseline (308.3 ± 56.7 Nm vs 172.8 ± 40.8 Nm, respectively) and immediately following 3% body mass loss (276.3 ± 39.5 Nm vs 153.5 ± 35.9 Nm). Participants experienced a loss. We also identified a significant effect of rehydrating fluid and sex on post-rehydration peak torque (p < 0.0117).

Conclusion

We conclude that deep-ocean mineral water positively affected hydration recovery after dehydrating exercise, and that it may also be beneficial for muscle strength recovery, although this, as well as the influence of sex, needs to be further examined by future research.

Trial registration

clincialtrials.gov PRS, NCT02486224. Registered 08 June 2015.

Repeated High-Intensity Cycling Performance Is Unaffected by Timing of Carbohydrate Ingestion

Shei, R-J, Paris, HL, Beck, CP, Chapman, RF, and Mickleborough, TD. Repeated high-intensity cycling performance is unaffected by timing of carbohydrate ingestion. J Strength Cond Res 32(8): 2243-2249, 2018-To determine whether carbohydrate (CHO) feeding taken immediately before, early, or late in a series of high-intensity cycling exercises affected cycling performance. A total of 16 trained, male cyclists (>6 hours postprandial) performed 3-, 4-km cycling time trials (TT1, TT2, and TT3) separated by 15 minutes of active recovery on 4 separate occasions. Carbohydrate feeding (80 g) was given either before TT1 (PRE1), before TT2 (PRE2), before TT3 (PRE3), or not at all (control, CTL). Treatment order was randomized. Sweet placebo was given before the other TTs. Blood glucose (BG) concentration was measured before each trial. Mean power output (Pmean) and time to completion (TTC) were recorded. Pmean was higher in TT1 compared with TT2 (p = 0.001) and TT3 (p = 0.004) in all conditions, but no differences were observed between treatments. Time to completion was lower in TT1 compared with TT2 (p = 0.01), but no other differences in TTC (within or between treatments) were observed. Within CTL and PRE1, BG did not differ between TT1, TT2, and TT3. In PRE2, BG was significantly higher in TT2 compared with TT1 (p = 0.006), in TT3 compared with TT1 (p = 0.001), and in TT3 compared with TT2 (p = 0.01). In PRE3, BG was significantly higher in TT3 compared with TT1 and TT2 (p = 0.001 for both). Given that performance was not influenced by the timing of CHO ingestion, athletes engaging in repeated, high-intensity cycling exercise do not need to ingest CHO before- or between-exercise bouts; furthermore, athletes should refrain from ingesting CHO between bouts if they wish to avoid a rise in BG.

Timing of post-resistance exercise nutrient ingestion: effects on gastric emptying and glucose and amino acid responses in humans

This study examined the effects of post-resistance exercise protein ingestion timing on the rate of gastric emptying (GE) and blood glucose (BG) and plasma branched-chain amino acid (BCAA) responses. In all, eleven healthy participants randomly ingested 400 ml of a nutrient-rich drink containing 12 g carbohydrates and 20 g protein at rest (Con), at 5 min (post-exercise (PE)-5) or at 30 min (PE-30) after a single bout of strenuous resistance exercises. The first and second sets comprised ten repetitions at 50 % of each participant's one-repetition maximum (1RM). The third, fourth and fifth sets comprised ten repetitions at 75 % of 1RM, and the sixth set involved repeated repetitions until exhaustion. Following ingestion of the nutrient-rich drink, we assessed the GE rate using 13C-sodium acetate breath test and evaluated two parameters according to the T max-calc (time when the recovery per hour is maximised), which is a standard analytical method, and T 1/2 (time when the total cumulative dose of [13CO2] reaches one-half). T max-calc and T 1/2 were slower for the PE-5 condition than for either the PE-30 or Con condition (T max-calc; Con: 53 (sd 7) min, PE-5: 83 (sd 16) min, PE-30: 62 (sd 9) min, T 1/2; Con: 91 (sd 7) min, PE-5: 113 (sd 21) min, PE-30: 91 (sd 11) min, P<0·05). BG and BCAA responses were also slower for the PE-5 condition than for either the PE-30 or Con condition. Ingesting nutrients immediately after strenuous resistance exercise acutely delayed GE, which affected BG and plasma BCAA levels in blood circulation.

The effect of endurance exercise on intestinal integrity in well-trained healthy men

Exercise is one of the external factors associated with impairment of intestinal integrity, possibly leading to increased permeability and altered absorption. Here, we aimed to examine to what extent endurance exercise in the glycogen‐depleted state can affect intestinal permeability toward small molecules and protein‐derived peptides in relation to markers of intestinal function. Eleven well‐trained male volunteers (27 ± 4 years) ingested 40 g of casein protein and a lactulose/rhamnose (L/R) solution after an overnight fast in resting conditions (control) and after completing a dual – glycogen depletion and endurance – exercise protocol (first protocol execution). The entire procedure was repeated 1 week later (second protocol execution). Intestinal permeability was measured as L/R ratio in 5 h urine and 1 h plasma. Five‐hour urine excretion of betacasomorphin‐7 (BCM7), postprandial plasma amino acid levels, plasma fatty acid binding protein 2 (FABP‐2), serum pre‐haptoglobin 2 (preHP2), plasma glucagon‐like peptide 2 (GLP2), serum calprotectin, and dipeptidylpeptidase‐4 (DPP4) activity were studied as markers for excretion, intestinal functioning and recovery, inflammation, and BCM7 breakdown activity, respectively. BCM7 levels in urine were increased following the dual exercise protocol, in the first as well as the second protocol execution, whereas 1 h‐plasma L/R ratio was increased only following the first exercise protocol execution. FABP2, preHP2, and GLP2 were not changed after exercise, whereas calprotectin increased. Plasma citrulline levels following casein ingestion (iAUC) did not increase after exercise, as opposed to resting conditions. Endurance exercise in the glycogen depleted state resulted in a clear increase of BCM7 accumulation in urine, independent of DPP4 activity and intestinal permeability. Therefore, strenuous exercise could have an effect on the amount of food‐derived bioactive peptides crossing the epithelial barrier. The health consequence of increased passage needs more in depth studies.

Timing of postexercise carbohydrate-protein supplementation: roles of gastrointestinal blood flow and mucosal cell damage on gastric emptying in humans

It is well known that protein ingestion immediately after exercise greatly stimulates muscle protein synthesis during the postexercise recovery phase. However, immediately after strenuous exercise, the gastrointestinal (GI) mucosa is frequently injured by hypoperfusion in the organ/tissue, possibly resulting in impaired GI function (e.g., gastric emptying; GE). The aim of this study was to examine the effect of GI blood flow on the GE rate. Eight healthy young subjects performed an intermittent supramaximal cycling exercise for 30 min, which consisted of a 120% V̇o_2peak for 20 s, followed by 20 W for 40 s. The subjects ingested 300 ml of a nutrient drink containing carbohydrate-protein at either 5 min postexercise in one trial (PE-5) or 30 min postexercise in another trial (PE-30). In the control trial (Con), the subjects ingested the same drink without exercise. The celiac artery blood flow (CABF) and superior mesenteric artery blood flow (SMABF) and GE rate were assessed by ultrasonography. Before drink ingestion in PE-5, CABF significantly decreased from baseline, whereas in PE-30, it returned to baseline. Following drink ingestion in PE-5, CABF did not change from baseline, but it significantly increased in PE-30 and Con. SMABF increased significantly later in PE-5 than in PE-30 and Con. The GE rate was consistently slower in PE-5 than in PE-30 and Con. In conclusion, the CABF response after exercise seems to modulate the subsequent GE rate and SMABF response.NEW & NOTEWORTHY A carbohydrate-protein drink was ingested at either 5 min (i.e., profoundly decreased celiac artery blood flow; CABF) or 30 min (i.e., already recovered CABF) postexercise. In the 5-min postexercise trial, the gastric emptying (GE) rate and superior mesenteric artery blood flow (SMABF) response were slower than those in the 30-min postexercise trial. The GE rate and SMABF response may be altered depending on the postexercise CABF response.

Methodological and metabolic considerations in the study of caffeine-containing energy drinks

Caffeine-containing energy drinks are popular and widely available beverages. Despite large increases in consumption, studies documenting the nutritional, metabolic, and health implications of these beverages are limited. This review provides some important methodological considerations in the examination of these drinks and highlights their potential impact on the gastrointestinal system, liver, and metabolic health. The gastrointestinal system is important as it comes into contact with the highest concentration of energy drink ingredients and initiates a chain of events to communicate with peripheral tissues. Although energy drinks have diverse compositions, including taurine, ginseng, and carnitine, the most metabolically deleterious ingredients appear to be simple sugars (such as glucose and fructose) and caffeine. In combination, these last two ingredients have the greatest metabolic impact and potential influence on overall health.

Optimal composition of fluid-replacement beverages

The objective of this article is to provide a review of the fundamental aspects of body fluid balance and the physiological consequences of water imbalances, as well as discuss considerations for the optimal composition of a fluid replacement beverage across a broad range of applications. Early pioneering research involving fluid replacement in persons suffering from diarrheal disease and in military, occupational, and athlete populations incurring exercise- and/or heat-induced sweat losses has provided much of the insight regarding basic principles on beverage palatability, voluntary fluid intake, fluid absorption, and fluid retention. We review this work and also discuss more recent advances in the understanding of fluid replacement as it applies to various populations (military, athletes, occupational, men, women, children, and older adults) and situations (pathophysiological factors, spaceflight, bed rest, long plane flights, heat stress, altitude/cold exposure, and recreational exercise). We discuss how beverage carbohydrate and electrolytes impact fluid replacement. We also discuss nutrients and compounds that are often included in fluid-replacement beverages to augment physiological functions unrelated to hydration, such as the provision of energy. The optimal composition of a fluid-replacement beverage depends upon the source of the fluid loss, whether from sweat, urine, respiration, or diarrhea/vomiting. It is also apparent that the optimal fluid-replacement beverage is one that is customized according to specific physiological needs, environmental conditions, desired benefits, and individual characteristics and taste preferences.

The effects of ingestion of sugarcane juice and commercial sports drinks on cycling performance of athletes in comparison to plain water

PURPOSE

Sugarcane juice (ScJ) is a natural drink popular in most tropical Asian regions. However, research on its effect in enhancing sports performance is limited. The present investigation was to study the effect of sugarcane juice on exercise metabolism and sport performance of athletes in comparison to a commercially available sports drinks.

METHODS

Fifteen male athletes (18-25 yrs) were asked to cycle until volitional exhaustion at 70% VO2 max on three different trials viz. plain water (PW), sports drink (SpD) and ScJ. In each trial 3ml/kg/BW of 6 % of carbohydrate (CHO) fluid was given at every 20 min interval of exercise and a blood sample was taken to measure the hematological parameters. During recovery 200 ml of 9% CHO fluid was given and blood sample was drawn at 5, 10, 15 min of recovery.

RESULTS

Ingestion of sugarcane juice showed significant increase (P<0.05) in blood glucose levels during and after exercise compared to SpD and PW. However, no significant difference was found between PW, SpD and ScJ for total exercise time, heart rate, blood lactate and plasma volume.

CONCLUSION

ScJ may be equally effective as SpD and PW during exercise in a comfortable environment (<30°C) and a more effective rehydration drink than SpD and PW in post exercise as it enhances muscle glycogen resynthesis.

Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation

There is a growing body of research on the influence of ingesting carbohydrate-electrolyte solutions immediately prior to and during prolonged intermittent, high-intensity exercise (team games exercise) designed to replicate field-based team games. This review presents the current body of knowledge in this area, and identifies avenues of further research. Almost all early work supported the ingestion of carbohydrate-electrolyte solutions during prolonged intermittent exercise, but was subject to methodological limitations. A key concern was the use of exercise protocols characterized by prolonged periods at the same exercise intensity, the lack of maximal- or high-intensity work components and long periods of seated recovery, which failed to replicate the activity pattern or physiological demand of team games exercise. The advent of protocols specifically designed to replicate the demands of field-based team games enabled a more externally valid assessment of the influence of carbohydrate ingestion during this form of exercise. Once again, the research overwhelmingly supports carbohydrate ingestion immediately prior to and during team games exercise for improving time to exhaustion during intermittent running. While the external validity of exhaustive exercise at fixed prescribed intensities as an assessment of exercise capacity during team games may appear questionable, these assessments should perhaps not be viewed as exhaustive exercise tests per se, but as indicators of the ability to maintain high-intensity exercise, which is a recognized marker of performance and fatigue during field-based team games. Possible mechanisms of exercise capacity enhancement include sparing of muscle glycogen, glycogen resynthesis during low-intensity exercise periods and attenuated effort perception during exercise. Most research fails to show improvements in sprint performance during team games exercise with carbohydrate ingestion, perhaps due to the lack of influence of carbohydrate on sprint performance when endogenous muscle glycogen concentration remains above a critical threshold of ∼200  mmol/kg dry weight. Despite the increasing number of publications in this area, few studies have attempted to drive the research base forward by investigating potential modulators of carbohydrate efficacy during team games exercise, preventing the formulation of optimal carbohydrate intake guidelines. Potential modulators may be different from those during prolonged steady-state exercise due to the constantly changing exercise intensity and frequency, duration and intensity of rest intervals, potential for team games exercise to slow the rate of gastric emptying and the restricted access to carbohydrate-electrolyte solutions during many team games. This review highlights fluid volume, carbohydrate concentration, carbohydrate composition and solution osmolality; the glycaemic index of pre-exercise meals; fluid and carbohydrate ingestion patterns; fluid temperature; carbohydrate mouthwashes; carbohydrate supplementation in different ambient temperatures; and investigation of all of these areas in different subject populations as important avenues for future research to enable a more comprehensive understanding of carbohydrate ingestion during team games exercise.

Relevância da temperatura e do esvaziamento gástrico de líquidos consumidos por praticantes de atividade física

A prática de atividade física implica alterações da homeostase hidroeletrolítica, que podem trazer impactos adversos ao desempenho do indivíduo e, talvez, à saúde, caso os líquidos corporais perdidos no suor são sejam suficientemente repostos. A eficiência da hidratação depende também do esvaziamento gástrico, que, por sua vez, é influenciado por vários fatores, dentre os quais a temperatura da solução ingerida. Este estudo objetiva analisar criticamente os procedimentos de reposição de líquidos adotados por praticantes de atividade física e discutir como o efeito da temperatura do líquido sobre o esvaziamento gástrico influencia esse comportamento de hidratação. Verificou-se que estudos relacionados ao tema apresentavam resultados conflituosos, que se devem, provavelmente, aos diferentes procedimentos metodológicos utilizados. Em condições de exercício, são insuficientes os trabalhos que avaliam a temperatura do líquido no trato gastrintestinal. Durante o repouso, observa-se que os efeitos de temperaturas extremas, considerando o tempo total de esvaziamento gástrico, não são significantes, uma vez que a temperatura intragástrica após a ingestão da bebida normaliza-se rapidamente. Contudo, existem evidências científicas claras de que o consumo de bebidas geladas aumenta o esvaziamento gástrico nos primeiros minutos após a ingestão. Este fato deve ser melhor estudado, quando associado a outros fatores pré-competição, como o estado psicológico do atleta. Entretanto, baixas temperaturas melhoram a palatabilidade da solução, implicando maior ação de hidratação pelos atletas, diminuindo o risco de desidratação. Os efeitos da baixa temperatura sobre o esvaziamento gástrico não são determinantes, tendo a reposição de líquidos fatores de intervenção mais relevantes do que a temperatura.

Effect of beverage glucose and sodium content on fluid delivery

BACKGROUND

Rapid fluid delivery from ingested beverages is the goal of oral rehydration solutions (ORS) and sports drinks.

OBJECTIVE

The aim of the present study was to investigate the effects of increasing carbohydrate and sodium content upon fluid delivery using a deuterium oxide (D2O) tracer.

DESIGN

Twenty healthy male subjects were divided into two groups of 10, the first group was a carbohydrate group (CHO) and the second a sodium group (Na). The CHO group ingested four different drinks with a stepped increase of 3% glucose from 0% to 9% while sodium concentration was 20 mmol/L. The Na group ingested four drinks with a stepped increase of 20 mmol/L from 0 mmol/L to 60 mmol/l while glucose concentration was 6%. All beverages contained 3 g of D2O. Subjects remained seated for two hours after ingestion of the experimental beverage, with blood taken every 5 min in the first hour and every 10 min in the second hour.

RESULTS

Including 3% glucose in the beverage led to a significantly greater AUC 60 min (19640 ± 1252 δ per thousand vs. VSMOW.60 min) than all trials. No carbohydrate (18381 ± 1198 δ per thousand vs. VSMOW.60 min) had a greater AUC 60 min than a 6% (16088 ± 1359 δ per thousand vs. VSMOW.60 min) and 9% beverage (13134 ± 1115 δ per thousand vs. VSMOW.60 min); the 6% beverage had a significantly greater AUC 60 min than the 9% beverage. There was no difference in fluid delivery between the different sodium beverages.

CONCLUSION

In conclusion the present study showed that when carbohydrate concentration in an ingested beverage was increased above 6% fluid delivery was compromised. However, increasing the amount of sodium (0-60 mmol/L) in a 6% glucose beverage did not lead to increases in fluid delivery.

Body weight changes and voluntary fluid intakes of beach volleyball players during an official tournament

The aim of this study was to calculate sweat rates (measured by weight changes), voluntary fluid intakes, and fluid balance of beach volleyball players during a tournament. Data was collected during the 3 days of the tournament for male players (n=47) age M=26.17 (S.D.=5.12) years old. Participants were weighed before the warm up and they reweighed immediately after the game. The differences in body weight were calculated in grams. The voluntary fluid intake of players during the game was also recorded by observers, whose inter and intra reliability were evaluated (inter r=.89 and intra reliability r=.93). Fifty matches took place with a M=42.2min duration per match. A wide individual variation appeared in fluid intake and sweat loss. The calculated average sweat rate, fluid intake rate and fluid balance of players during each match were M=1440ml, M=731ml and M=-0.8%, respectively. Air temperature ranged from 26 degrees to 38 degrees C (M=33.58 degrees C, S.D.=2.8) and humidity from 42% to 75% (M=56.04%, S.D.=8.7) and both were measured in each day of tournament, at the beginning and at the end of each game. Although players' dehydration (-0.8%) was of mild level, it was more or less the same as it was reported in other team sports studies. ANOVA did not prove differences between elite and non-elite athletes in sweat loss and fluid intake (p>.01). Sweat rate was associated only with humidity (r=.99, p<.01) and with fluid intake (r=.315, p<.05). The athletes should be aware of the great significance of fluids and to intake greater quantities in order to prevent weight loss and at the same time loss of vital elements that would cause their performance to decline.

Thermoregulation during Exercise in the Heat

As a result of the inefficiency of metabolic transfer, >75% of the energy that is generated by skeletal muscle substrate oxidation is liberated as heat. During exercise, several powerful physiological mechanisms of heat loss are activated to prevent an excessive rise in body core temperature. However, a hot and humid environment can significantly add to the challenge that physical exercise imposes on the human thermoregulatory system, as heat exchange between body and environment is substantially impaired under these conditions. This can lead to serious performance decrements and an increased risk of developing heat illness. Fortunately, there are a number of strategies that athletes can use to prevent and/or reduce the dangers that are associated with exercise in the heat. In this regard, heat acclimatisation and nutritional intervention seem to be most effective. During heat acclimatisation, the temperature thresholds for both cutaneous vasodilation and the onset of sweating are lowered, which, in combination with plasma volume expansion, improve cardiovascular stability. Effective nutritional interventions include the optimisation of hydration status by the use of fluid replacement beverages. The latter should contain moderate amounts of glucose and sodium, which improve both water absorption and retention.

Ambient-temperature beverages are consumed at a rate similar to chilled water in heat-exposed workers

Palatability of beverages has been shown to influence drinking patterns and hydration. Cool beverages are known to enhance palatability; however, situations exist in which cooling is not possible. The purpose of this study was to determine the palatability of a variety of flavors of ambient temperature beverages. Ten healthy males performed two work trials in a temperature-controlled environment (WBGT = 30 degrees C; wet = 25 degrees C, dry = 40 degrees C, globe = 41 degrees C). In one trial, the subjects had only chilled water to drink. In the second trial the subjects drank their choice (any or all) of five ambient temperature beverages (water, fruit punch, lemon-lime, orange, and cola). Repeated measures ANOVA showed no difference in absolute or relative fluid consumption between the two trials (chilled = 1730 +/- 316 mL and 21 +/- 5 mL/kg; ambient [all five beverages combined] = 1510 +/- 219 mL and 19 +/- 4 mL/kg). There was no difference in the rate of fluid consumption between the two trials (608 +/- 88 mL/30 min and 674 +/- 82 mL/30 min, p > 0.05). Additionally, when combining all ambient-temperature, flavored beverages, consumption was significantly greater than that of ambient temperature water (1245 +/- 206 vs. 255 +/- 86 mL, p < 0.05). These findings demonstrate that providing ambient temperature beverages in a hot condition results in fluid consumption values similar to chilled water. These findings are relevant to industry in that there may be times when workers are at risk for heat-related illness due to dehydration and chilled beverages are not available. By providing flavored beverages, fluid consumption may be maintained and degree of heat-illness may be lessened.

The effects of ad libitum fluid ingestion on fluid balance during alpine skiing in recreational skiers

The aim of this study was to assess the influence of ad libitum water ingestion, using a back-mounted hydration system (BMHS), on fluid balance during alpine skiing. Fourteen skiers skied on two different days. On one day, seven skiers ingested water during skiing via the BMHS and the other seven skiers refrained from fluid ingestion during skiing until the midday break (NW trial). On the second day, the trials were reversed. Results indicated that when skiers used the BMHS they drank significantly more water than during the NW trials (2.0 +/- 0.9 vs. 0.78 +/- 0.4 litres). However, skiers drank significantly more at the midday break during the NW trials than during the BMHS trials (0.78 +/- 0.4 vs. 0.4 +/- 0.2 litres). Percent change in plasma volume was less during the BMHS trials than during the NW trials (-0.1 +/- 5.3 vs. -4.9 +/- 5.2%), urine osmolality was maintained in the BMHS trials but rose from 295 +/- 80 to 818 +/- 168 mOsm . kg(-1) at midday during the NW trials, and body mass loss was minimized during the BMHS trials compared with the NW trials (0.4 +/- 0.4 vs. 1.1 +/- 0.2 kg). Skiers reported that they felt significantly better when they ingested water during the BMHS trials. In conclusion, a back-mounted hydration system allowed the skiers to maintain hydration status.

[Scintigraphic study of gastric emptying of rehydration drinks in athletes]

This study aims to evaluate how rehydration beverage ingestion influences gastric emptying rate (in cycle ergometer) at rest and during exercise at 70 % of maximal oxygen consumption (VO2max).

MATERIAL AND METHOD

26 well-trained cyclists performed a preliminary maximal test until exhaustion to evaluate their VO2max, and two submaximal exercise tests at 70 % of their mode-specific VO2max. Each test was separated by one week. During the two submaximal tests, cyclists consumed 200 ml of a 99mTc-DTPA labeled rehydration beverage (A or B) and scintigraphy determinations were performed at rest. After, exercise was initiated for 60 minutes with an intake rate of 200 ml every 15 minutes, making gastric serial scintigraphy determinations. The difference regarding chemical composition between A and B drinks resides in the fact that drink A contains a smaller load in carbohydrates (10.3 g/100 ml versus 15.2 g/100 ml of B), proteins in form of serum milk and antioxidants in form of fruit juice. Both contain ions and vitamins.

RESULTS

at rest, gastric count number was significantly reduced (p > 0.000) from 0 to 25 minutes for both A and B beverage. At the end of exercise (60 min), there was greater gastric retention for B beverage than for A, this difference being statistically significant (p < 0.031).

CONCLUSIONS

The A beverage, a rehydration drink on the market with protein and antioxidants with fruit juice content, has a faster gastric emptying rate than the B sport beverage.

Effect of ambience on food intake and food choice

Eating takes place in a context of environmental stimuli known as ambience. Various external factors such as social and physical surroundings, including the presence of other people and sound, temperature, smell, color, time, and distraction affect food intake and food choice. Food variables such as the temperature, smell, and color of the food also influence food intake and choice differently. However, the influence of ambience on nutritional health is not fully understood. This review summarizes the research on ambient influences on food intake and food choice. The literature suggests that there are major influences of ambience on eating behavior and that the magnitude of the effect of ambience may be underestimated. Changes in intake can be detected with different levels of the number of people present, food accessibility, eating locations, food color, ambient temperatures and lighting, and temperature of foods, smell of food, time of consumption, and ambient sounds. It is suggested that the manipulation of these ambient factors as a whole or individually may be used therapeutically to alter food intake and that more attention needs to be paid to ambience in nutrition-related research.

Recommendations for treatment of hyponatraemia at endurance events

This review focuses on possible pathophysiology of exercise-associated hyponatraemia and its implication on evaluation and treatment of collapsed athletes during endurance events. Rehydration guidelines and field care have traditionally been based on the belief that endurance events create a state of significant fluid deficit in athletes, which must be corrected by liberal hydration. Beliefs in the necessity of liberal hydration may have contributed to cases of hyponatraemia. Assumptions that fluid loss accounts for the entire weight loss during exercise and that fluid ingestion is the only source of water gain during exercise may lead to an overestimation of the degree of volume depletion and the amount of fluid needed for replacement. Increasing evidence suggests that hyponatraemic athletes are fluid overloaded; ingestion of large amount of hypotonic fluid in combination with inappropriate or inadequate physiological responses leads to excessive retention of free fluid. Risk factors include hot weather, female sex, slower finishing time, and possibly the use of nonsteroidal anti-inflammatory medications. Symptoms of hyponatraemia can be subtle and can mimic those of other exercise-related illnesses, thereby complicating its diagnosis and leading to possible inappropriate treatment. Most athletes who collapse at the finish line experience exercise-associated collapse, a benign and transient form of postural hypotension that can be treated simply by continued ambulation after finishing or elevation of legs while in a supine position for those who cannot walk. Care providers should consider the use of intravenous hydration with normal saline carefully since it is not needed by most collapsed athletes and may worsen the condition of patients with unsuspected hyponatraemia. Historic information and clinical signs of volume depletion should be elicited prior to its use. Most hyponatraemic athletes will recover uneventfully with careful observation while awaiting spontaneous diuresis. Use of hypertonic saline should be reserved for patients with severe symptoms. Moderate consumption of carbohydrate-electrolyte solution during exercise may allow the maintenance of adequate hydration and the prevention of hyponatraemia.

ENVIRONMENTAL FACTORS THAT INCREASE THE FOOD INTAKE AND CONSUMPTION VOLUME OF UNKNOWING CONSUMERS

Package size, plate shape, lighting, socializing, and variety are only a few of the environmental factors that can influence the consumption volume of food far more than most people realize. Although such environmental factors appear unrelated, they generally influence consumption volume by inhibiting consumption monitoring and by suggesting alternative consumption norms. For researchers, this review suggests that redirecting the focus of investigations to the psychological mechanisms behind consumption will raise the profile and impact of research. For health professionals, this review underscores how small structural changes in personal environments can reduce the unknowing overconsumption of food.

Heat Illness in Athletes

In 1980, 1700 people died during a prolonged heat wave in a region under-prepared for heat illness prevention. Dramatically underreported, heat-related pathology contributes to significant morbidity as well as occasional mortality in athletic, elderly, paediatric and disabled populations. Among US high school athletes, heat illness is the third leading cause of death. Significant risk factors for heat illness include dehydration, hot and humid climate, obesity, low physical fitness, lack of acclimatisation, previous history of heat stroke, sleep deprivation, medications (especially diuretics or antidepressants), sweat gland dysfunction, and upper respiratory or gastrointestinal illness. Many of these risk factors can be addressed with education and awareness of patients at risk. Dehydration, with fluid loss occasionally as high as 6-10% of bodyweight, appears to be one of the most common risk factors for heat illness in patients exercising in the heat. Core body temperature has been shown to rise an additional 0.15-0.2 degrees C for every 1% of bodyweight lost to dehydration during exercise. Identifying athletes at risk, limiting environmental exposure, and monitoring closely for signs and symptoms are all important components of preventing heat illness. However, monitoring hydration status and early intervention may be the most important factors in preventing severe heat illness.

Gastric emptying and fluid availability after ingestion of glucose and soy protein hydrolysate solutions in man

The double sampling gastric aspiration method was used to measure the effect of energy content on the rate of gastric emptying of glucose and soy protein hydrolysate solutions. The net rate of absorption of water from these solutions was assessed using deuterium oxide as a tracer for water. Six healthy male subjects were each studied on four separate occasions using a test drink volume of 600 ml. The half emptying times (t 1/2, median (range)) of the iso-energetic soy protein hydrolysate (6P, 60 g l(-1), 36 (14-39) min) and glucose (7G, 70 g l(-1), 25 (19-29) min) solutions were similar. These two solutions (6P, 7G) delivered energy to the small intestine at similar rates, and resulted in similar rates of accumulation of the deuterium tracer in the circulation. The dilute glucose solution (LG, 23 g l(-1)) was emptied faster (t 1/2 13 (11-19) min) and resulted in a faster rate of tracer accumulation in the circulation than any of the other solutions, including the iso-osmotic soy protein solution (LG 311 +/- 5 mosmol kg(-1), 6P 321 +/- 24 mosmol kg(-1)). The concentrated soy protein hydrolysate solution (12P, 120 g l(-1)) emptied more slowly (t 1/2 80 (44-120) min) than the more dilute solutions. The rate of energy delivery to the small intestine from 12P was similar to that from 6P for the first 50 min after ingestion, and similar to that from 7G at all sample points. These results indicate that the iso-energetic solutions of glucose and soy protein hydrolysate used in this study are emptied from the stomach at similar rates and result in similar rates of fluid availability after ingestion.

Fluid and electrolyte balance in ultra-endurance sport

It is well known that fluid and electrolyte balance are critical to optimal exercise performance and, moreover, health maintenance. Most research conducted on extreme sporting endeavour (>3 hours) is based on case studies and studies involving small numbers of individuals. Ultra-endurance sportsmen and women typically do not meet their fluid needs during exercise. However, successful athletes exercising over several consecutive days come close to meeting fluid needs. It is important to try to account for all factors influencing bodyweight changes, in addition to fluid loss, and all sources of water input. Increasing ambient temperature and humidity can increase the rate of sweating by up to approximately 1 L/h. Depending on individual variation, exercise type and particularly intensity, sweat rates can vary from extremely low values to more than 3 L/h. Over-hydration, although not frequently observed, can also present problems, as can inappropriate fluid composition. Over-hydrating or meeting fluid needs during very long-lasting exercise in the heat with low or negligible sodium intake can result in reduced performance and, not infrequently, hyponatraemia. Thus, with large rates of fluid ingestion, even measured just to meet fluid needs, sodium intake is vital and an increased beverage concentration [30 to 50 mmol/L (1.7 to 2.9 g NaCl/L) may be beneficial. If insufficient fluids are taken during exercise, sodium is necessary in the recovery period to reduce the urinary output and increase the rate of restoration of fluid balance. Carbohydrate inclusion in a beverage can affect the net rate of water assimilation and is also important to supplement endogenous reserves as a substrate for exercising muscles during ultra-endurance activity. To enhance water absorption, glucose and/or glucose-containing carbohydrates (e.g. sucrose, maltose) at concentrations of 3 to 5% weight/volume are recommended. Carbohydrate concentrations above this may be advantageous in terms of glucose oxidation and maintaining exercise intensity, but will be of no added advantage and, if hyperosmotic, will actually reduce the net rate of water absorption. The rate of fluid loss may exceed the capacity of the gastrointestinal tract to assimilate fluids. Gastric emptying, in particular, may be below the rate of fluid loss, and therefore, individual tolerance may dictate the maximum rate of fluid intake. There is large individual variation in gastric emptying rate and tolerance to larger volumes. Training to drink during exercise is recommended and may enhance tolerance.

Gastric emptying of a carbohydrate-electrolyte drink during a soccer match

PURPOSE

To investigate the effect on gastric emptying of intermittent exercise at varying intensities such as occurs during a soccer match.

METHODS

We compared the emptying rate of a carbohydrate-electrolyte (CE) drink during two 15-min periods of a competitive 5-a-side indoor soccer match separated by 10 min and during two 15-min periods of low-intensity walking exercise. Seven healthy male subjects, all of whom regularly played soccer, completed the study. Exercise intensity on each trial was calculated from heart rate recordings. Subjects ingested 500 mL of the CE drink immediately before starting each exercise period. Before and after completing each 15-min exercise period, the gastric contents were aspirated and the volume recorded. Ambient room temperature ranged from 16-22 degrees C and humidity ranged from 57-72% on both trials.

RESULTS

Mean +/- SD heart rate was higher during the Soccer trial than during the Walking trial at all time points. Exercise intensity was calculated to be 54 +/- 23% and 63 +/- 20% VO2max, respectively, for the first and second periods of exercise on the Soccer trial and 13 +/- 9% and 12 +/- 11% VO2max, respectively, for the first and second periods of exercise on the Walking trial. During the first 15-min period of exercise, a greater (median (range)) volume of the CE drink was emptied from the stomach on the Walking trial (247 mL (102-361 mL)) than on the Soccer trial (84 mL (17-230 mL); P = 0.022). In the second exercise period, however, gastric emptying rates were not different (P = 0.16) between the Walking trial (247 mL (104-363 mL)) and Soccer trial (148 mL (17-293 mL)).

CONCLUSION

As indicated by heart rate, the overall exercise intensity of an indoor soccer match appears to be moderate. The pattern of activity during a match is intermittent with periods of low level activity punctuated by short bursts of high-intensity sprinting. The present study demonstrates that the intensity of activity during this type of exercise is sufficient to slow gastric emptying.

Effect of intermittent high-intensity exercise on gastric emptying in man

PURPOSE

The effect on gastric emptying of brief intermittent high-intensity sprints and a moderate-intensity steady-state cycle exercise was studied.

METHODS

Eight healthy male subjects were each studied at rest (R), during steady-state exercise at a constant power output corresponding to 66% of their VO(2max) (C66), during intermittent high-intensity exercise at a power output averaging 66% of their VO(2max) (I66), and during intermittent high-intensity exercise at a power output averaging 75% of their VO(2max) (I75). Gastric emptying was measured using the double-sampling gastric aspiration technique. Subjects ingested 600 mL of a 6% carbohydrate-electrolyte solution immediately before exercise or seated rest.

RESULTS

The volume of test solution in the stomach was less at all time points on trial I66 than on trial I75 (P = 0.023). The rate of gastric emptying, expressed as the median (range) time (minutes) taken to empty half the test meal volume (t(1/2)), was not different on trials R (20 (7--30)) and C66 (21 (7--49)), and was faster than on trial I75 (62 (27--100); P = 0.003 and P = 0.005, respectively). Median t(1/2) was faster on trial R than on trial I66 (30 (15--74) min; P = 0.019), but no difference was detected between C66 and I66 or between I66 and I75. However, over the initial 30 min period after ingestion, the median (range) volume of test drink delivered to the duodenum was faster (P < 0.01) on trials R (387 (296--541) mL) and C66 (389 (165--584) mL) than on trials I66 (331 (191--494) mL) or I75 (249 (79-335) mL).

CONCLUSION

The data demonstrate that gastric emptying of liquids is slowed during brief intermittent high-intensity exercise compared with rest or steady-state moderate exercise.

Intestinal fluid absorption during exercise: role of sport drink osmolality and [Na+]

The purpose of this study was to evaluate the effects of modifying the osmolality and [Na+] of orally ingested rehydration beverages during exercise on intestinal absorption in the duodenum and upper jejunum. Six subjects randomly ingested (23 mL.kg-1 BW) the following 6% carbohydrate solutions with and without Na+ during 85-min of cycle exercise (65% VO2 peak) in a cool (22 degrees C, 40% RH) environment: a) 0 Na+, 245 mOsm.kg-1; b) 20 mEq Na+, 283 mOsm.kg-1; c) 20 mEq Na+, 169 mOsm.kg-1; d) 50 mEq Na+, 275 mOsm.kg-1; and e) 50 mEq Na+, 176 mOsm.kg-1. To alter solution osmolality and maintain carbohydrate concentration constant, glucose, sucrose, fructose, and maltodextrin were used in different combinations. Nasogastric and multilumen tubes were fluoroscopically placed in the stomach and intestine, respectively, to simultaneously determine gastric emptying and intestinal absorption as previously described (Lambert et al., Int. J. Sports Med.17:48, 1996). Gastric emptying was not different among solutions and averaged 13 +/- 0.5 mL.min-1. Net fluid absorption was not different among beverages nor between duodenum and jejunum (x = 10.8 +/- 1.6 and 7.9 +/- 1.1 mL.cm-1.h-1, respectively). Mean osmolality increased significantly (P < 0.05) from the duodenum to the jejunum (242 +/- 6 and 293 +/- 7 mOsm.kg-1, respectively) but did not differ among solutions. These data provide evidence that a hypotonic 6% carbohydrate beverage with 50 mEq.L-1 Na+ did not enhance intestinal fluid absorption or attenuate the decline in plasma volume during exercise more than an isotonic carbohydrate-electrolyte solution or a hypotonic carbohydrate solution without sodium.

Impact of beverage acceptability on fluid intake during exercise

These two studies investigated the impact of beverage acceptability on voluntary fluid intake during exercise and the subsequent impact of exercise on the perception and liking of beverages. In Experiment 1, 49 triathletes and runners first tasted an array of 10 commercially available flavors of a 6% carbohydrate-electrolyte drink (CE) and water (W) to determine the most-acceptable flavor (M) and least-acceptable flavor (L) for each subject. Subjects were subsequently given M, L, or W ad libitum during 180 min of exercise. Drink acceptability was again measured after 90 and 180 min of exercise. Drink intake was measured at 15-min intervals. Intake of M was significantly greater than L and W throughout the first 75 min and significantly greater than W throughout the entire exercise period. In Experiment 2, subjects were given M+W, or L+W, in a two-bottle procedure. Voluntary intake of M and L exceeded W by 318% and 233%, respectively. An unexpected finding was a strong interaction between drink acceptability and exercise state. The acceptability of L increased substantially from sedentary to exercise conditions. These data demonstrated that the flavored, sweetened beverages used in this study, substantially increased voluntary fluid intake over W.

The thermophysiology of uncompensable heat stress. Physiological manipulations and individual characteristics

In many athletic and occupational settings, the wearing of protective clothing in warm or hot environments creates conditions of uncompensable heat stress where the body is unable to maintain a thermal steady state. Therefore, special precautions must be taken to minimise the threat of thermal injury. Assuming that manipulations known to reduce thermoregulatory strain during compensable heat stress would be equally effective in an uncompensable heat stress environment is not valid. In this review, we discuss the impact of hydration status, aerobic fitness, endurance training, heat acclimation, gender, menstrual cycle, oral contraceptive use, body composition and circadian rhythm on heat tolerance while wearing protective clothing in hot environments. The most effective countermeasure is ensuring that the individual is adequately hydrated both before and throughout the exercise or work session. In contrast, neither short term aerobic training or heat acclimation significantly improve exercise-heat tolerance during uncompensable heat stress. While short term aerobic training is relatively ineffective, long term improvements in physical fitness appear to provide some degree of protection. Individuals with higher proportions of body fat have a lower heat tolerance because of a reduced capacity to store heat. Women not using oral contraceptives are at a thermoregulatory disadvantage during the luteal phase of the menstrual cycle. The use of oral contraceptives eliminates any differences in heat tolerance throughout the menstrual cycle but tolerance is reduced during the quasi-follicular phase compared with non-users. Diurnal variations in resting core temperature do not appear to influence tolerance to uncompensable heat stress.

The effectiveness of commercially available sports drinks

The purpose of this review is to evaluate the effectiveness of commercially available sports drinks by answering the questions: (i) will consuming a sports drink be beneficial to performance? and (ii) do different sports drinks vary in their effectiveness? To answer these questions we have considered the composition of commercially available sports drinks, examined the rationale for using them, and critically reviewed the vast number of studies that have investigated the effectiveness of sports drinks on performance. The focus is on the drinks that contain low carbohydrate concentrations (<10%) and are marketed for general consumption before and during exercise rather than those with carbohydrate concentrations >10%, which are intended for carbohydrate loading. Our conclusions are 3-fold. First, because of variations in drink composition and research design, much of the sports drinks research from the past cannot be applied directly to the effectiveness of currently available sports drinks. Secondly, in studies where a practical protocol has been used along with a currently available sports beverage, there is evidence to suggest that consuming a sports drinks will improve performance compared with consuming a placebo beverage. Finally, there is little evidence that any one sports drink is superior to any of the other beverages on the market.

Investigation of the side pain "stitch" induced by running after fluid ingestion

PURPOSE

Text books attribute the side pain "stitch" during exercise to changes in blood flow to the viscera, but the little available research favors stretching of visceral ligaments. We therefore induced and modified stitch experimentally to investigate its cause and possible treatments.

METHODS

Ten active healthy young men reported the intensity of stitch during sessions of intermittent exercise after drinking either no fluid (control) or a body-mass-adjusted volume (14 mL x kg(-1)) of each of four fluids: water, Exceed, decarbonated Coca-Cola, and a hypertonic solution of the nonabsorbable sugar lactulose. Each exercise session consisted of five 5-min bouts of hard running on a treadmill, with 10-min rests between each bout. In another experiment, seven subjects reported the effect of several physical maneuvers on stitch during exercise after drinking decarbonated Coca-Cola.

RESULTS

Stitch developed to a similar intensity with all fluids during the first two bouts of running; thereafter, stitch declined only with Exceed, reaching the intensity with no fluid by the last two bouts. Bending forward while tightening abdominal muscles, tightening a belt around the waist, or breathing through pursed lips with increased lung volume alleviated stitch within seconds, but attempting to relax abdominal muscles or increasing the impact of foot strike had little effect.

CONCLUSIONS

Our observations cannot be explained readily by mechanisms involving digestion-induced changes in blood flow but are consistent with the notion that stitch arises when the fluid-engorged gut tugs on visceral ligaments.

Effect of beverage osmolality on intestinal fluid absorption during exercise

To determine how osmolality of an orally ingested fluid-replacement beverage would alter intestinal fluid absorption from the duodenum and/or jejunum during 85 min of cycle exercise (63.3 +/- 0.9% peak O2 uptake) in a cool environment (22 degreesC), seven subjects (5 men, 2 women, peak O2 uptake = 54.5 +/- 3.8 ml . kg-1 . min-1) participated in four experiments separated by 1 wk in which they ingested a water placebo (WP) or one of three 6% carbohydrate (CHO) beverages formulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH2O. CHO solutions also contained 17-18 meq Na+ and 3.2 meq K+. Nasogastric and multilumen tubes were fluoroscopically positioned in the gastric antrum and duodenojejunum, respectively. Subjects ingested a total of 23 ml/kg body mass of the test solution, 20% (370 +/- 9 ml) of this volume 5 min before exercise and 10% (185 +/- 4 ml) every 10 min thereafter. By using the rate of gastric emptying as the rate of intestinal perfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl, and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 cm). There were no differences (P > 0.05) in gastric emptying (mean 18.1 +/- 1.3 ml/min) or total fluid absorption (802 +/- 109, 650 +/- 52, 674 +/- 62, and 633 +/- 74 ml . 50 cm-1 . h-1 for WP, hypo-, iso-, and hypertonic solutions, respectively) among beverages; but WP was absorbed faster (P < 0.05) from the duodenum than in the jejunum. Of the total volume of fluid ingested, 82 +/- 14, 74 +/- 6, 76 +/- 5, and 68 +/- 7% were absorbed for WP, hypo-, iso-, and hypertonic beverages, respectively. There were no differences in urine production or percent change in plasma volume among solutions. We conclude that total fluid absorption of 6% CHO-electrolyte beverages from the duodenojejunum during exercise, within the osmotic range studied, is not different from WP.

Fluid replacement needs of well-trained male and female athletes during indoor and outdoor steady state running

Twelve male and six female well-trained middle distance athletes performed a series of six one hour runs at 75% VO2 peak pace under similar environmental states indoors (treadmill) and outdoors (track). Running was undertaken in control (C, no fluid), followed by water (W) and sports drink (SD) treatments, with each run separated by a one week interval. Both fluid treatments were supplied in volumes equivalent to individual body mass (fluid) losses incurred in the respective indoor and outdoor C treatments. Haemodynamic (plasma volume), physiological (heart rate and body temperature) and blood chemistry (blood lactate and glucose) measures were analysed as pre to post run changes (delta values). During the respective indoor and outdoor C treatments, males demonstrated approximately a twofold change in body mass (fluid) losses (delta 1.81 +/- 0.10 kg and 2.06 +/- 0.13 kg) compared with females (delta 0.93 +/- 0.11 kg and 1.32 +/- 0.12 kg) (all p<0.05). These losses resulted in almost a twofold fluid replacement need relative to body mass during the running phases of respective indoor and outdoor W and SD treatments in males compared with females (all p<0.05). Both W and SD treatments were effective in minimising the pre to post run disturbances in plasma volume, heart rate, body temperature and blood lactate, while SD treatment resulted in enhanced blood glucose changes. The results suggest gender specific differences in fluid replacement needs during steady state running, which need to be incorporated into fluid replacement strategies to compensate for the demands of training and competition in middle distance athletic events.

Treatments affecting fluid and electrolyte status during exercise

A number of feeding and management practices, dietary electrolyte supplements, and medications may affect fluid and electrolyte status in resting and exercising horses. The contents of the gastrointestinal tract of the equine athlete, unlike its human counterpart, are responsible for more than 10% of body weight. Although ingesta traditionally has been considered dead weight for the sprinting horse, it is a valuable reservoir of fluid and electrolytes that may be used during endurance exercise. Numerous strategies for hyperhydration of the equine athlete and for replacement of fluid and electrolytes lost via sweating were developed in preparation for competing in the hot and humid climate of the 1996 Olympic Games in Atlanta. These strategies have implications for all equine athletes. Medications, including sodium bicarbonate, furosemide, and acetazolamide commonly are used to enhance performance by either buffering alterations in fluid and electrolyte homeostasis or by ameliorating the effects of other conditions that may limit performance.