Carbohydrate-electrolyte Drink Research Articles

CrossRef Listing of Deleted DOIs

A paucity of literature exists with regard to research on nutrition for the pediatric athlete. This lack of research makes the development of specific nutritional recommendations for young athletes problematic. This issue is made difficult by the macro- and micronutrient intake required for growth and development in conjunction with that required for sports. Exogenous carbohydrate drinks could be considered for the young athlete engaged in both endurance exercise and high-intensity exercise. Monitoring of the energy intake during resistance training in the pediatric athlete needs to be considered, as there is evidence to suggest that energy deficits may occur. If decrements in exercise performance are noted, then serum ferritin and hemoglobin concentrations should be monitored, as nonanemic iron deficiency is prevalent in the pediatric athlete. The pediatric athlete exercising in the heat is susceptible to voluntary dehydration and evidence exists to suggest that a carbohydrate-electrolyte drink will abolish this phenomenon.

Variable versus constant power strategies during cycling time-trials: Prediction of time savings using an up-to-date mathematical model

Swain (1997) employed the mathematical model of Di Prampero et al. (1979) to predict that, for cycling time-trials, the optimal pacing strategy is to vary power in parallel with the changes experienced in gradient and wind speed. We used a more up-to-date mathematical model with validated coefficients (Martin et al., 1998) to quantify the time savings that would result from such optimization of pacing strategy. A hypothetical cyclist (mass = 70 kg) and bicycle (mass = 10 kg) were studied under varying hypothetical wind velocities (−10 to 10 m · s−1), gradients (−10 to 10%), and pacing strategies. Mean rider power outputs of 164, 289, and 394 W were chosen to mirror baseline performances studied previously. The three race scenarios were: (i) a 10-km time-trial with alternating 1-km sections of 10% and −10% gradient; (ii) a 40-km time-trial with alternating 5-km sections of 4.4 and −4.4 m · s−1 wind (Swain, 1997); and (iii) the 40-km time-trial delimited by Jeukendrup and Martin (2001). Varying a mean power of 289 W by ± 10% during Swain's (1997) hilly and windy courses resulted in time savings of 126 and 51 s, respectively. Time savings for most race scenarios were greater than those suggested by Swain (1997). For a mean power of 289 W over the “standard” 40-km time-trial, a time saving of 26 s was observed with a power variability of 10%. The largest time savings were found for the hypothetical riders with the lowest mean power output who could vary power to the greatest extent. Our findings confirm that time savings are possible in cycling time-trials if the rider varies power in parallel with hill gradient and wind direction. With a more recent mathematical model, we found slightly greater time savings than those reported by Swain (1997). These time savings compared favourably with the predicted benefits of interventions such as altitude training or ingestion of carbohydrate-electrolyte drinks. Nevertheless, the extent to which such power output variations can be tolerated by a cyclist during a time-trial is still unclear.

Physiological Strain and Perceptual Differences during Repeated-bout Exercise in the Heat

One of the biggest challenges facing numerous young athletes is attempting to train or perform safely and effectively in the heat. An even greater performance challenge and clinical risk for incurring heat injury is encountered when a young athlete has to train or compete again soon on the same day, following a prior heat exposure and strenuous exercise session or competition. PURPOSE: To test the hypothesis that young athletes will experience an increase in physiological strain and related ratings of perceptual discomfort during a second identical exercise bout (compared to the first) in the heat, with a one-hour recovery period (21°C) in between bouts, even when maintaining adequate hydration (6% carbohydrate-electrolyte drink; [Na+]: 21.1 mmoH-1). METHODS: 24 healthy, young soccer players (6 boys, 6 girls 12–13 y: 12.6 ± 0.5 y, 161.8 ± 7.5cm, 49.9 ± 7.9 kg, BMI: 18.6 ± 2.2; 6 boys, 6 girls 16–17 y: 16.5 ± 0.5y, 166.0 ± 8.0 cm, 61.0 ± 8.6 kg, BMI: 21.8 ± 2.0) each completed two 80-min intermittent exercise (treadmill: 60% VO2max; cycle ergometer: 40% VO2max) sessions in the heat (33°C; relative humidity: 48.9 ± 6.0%) on the same day. RESULTS: Sweat loss incurred during each bout (B) of exercise was similar within each age group (12–13 yB1: 943.6 ± 237.1 ml, B2: 955.5 ± 250.3 ml; 16–17yB1: 1382.2 ± 480.7 ml, B2: 1373.1 ± 472.2 ml). Area under the curve (AUC) was not statistically different (p>0.05) between exercise bouts for core body temperature (12–13 y B1 peak: 38.6 ± 0.4°C, B2: 38.4 ± 0.2°C; 16–17y B1 peak: 38.8 ± 0.7°C, B2: 38.7 ± 0.6°C), physiological strain index (PSI) (12–13 yB1 peak: 7.9 ± 0.9, B2: 7.5 ± 0.7; 16–17 yB1 peak: 8.1 ± 1.5,B2: 7.9 ± 1.4), or thermal sensation for any age/gender sub-group or for all subjects combined. However, rating of perceived exertion AUC for all subjects combined was higher (p=0.0002) during B2 (B1 peak: 15.3 ± 2.0; B2: 16.2 ± 2.2), with the biggest difference shown in the older boys. Notably, 4 subjects experienced a consistently higher core temperature and PSI throughout exercise B2 compared to B1. CONCLUSION: With fit, young athletes, one hour of cool-down and rehydration, following 80 min of exercise in the heat, is insufficient time to avert greater perception of effort, and for some, greater physiological strain, during a subsequent identical exercise bout. Supported by Gatorade Sports Science Institute

A Carbohydrate-Electrolyte Drink Attenuates Decline In Blood Sodium During Prolonged Exercise In The Heat

PURPOSE: To determine rate of change in blood sodium with the consumption of fluid with or without electrolytes during continuous mo derate-intensity cycling exercise in the heat. METHODS: In a randomized design, seven adult male endurance athletes (33 ± 6 y, 177 ± 10 cm, 76 ± 8 kg, 56 ± 7 ml/kg/min) completed 3h of cycling at 55% of peak VO2in the heat (WBGT=28.3 ± 1.6°C), during which they consumed either a carbohydrate drink (C, 6% CHO) or carbohydrate-electrolyte beverage (CE, 6% CHO, 36 mmol/L Na+, 10 mmol/L K+, 1 mmol/L Ca++, 0.75 mmol/L Mg++, and 11 mmol/L Cl-) in equal volume. Drinks were consumed every 15 minutes equivalent to the rate of fluid loss determined in a preliminary trial. Whole venous blood sodium (b[Na]) was analyzed at baseline, 15 min, and then at 30 min intervals on a clinical electrolyte analyzer (IL GEM 3000), and plasma volume (PV) changes were determined from Hct and Hgb measures. Sweat loss was determined by body mass change, and sweat [Na] by the regional skin patch technique, corrected to whole body values. ANOVA and linear regression of b[Na] scatter were used to determine decline during different treatments. RESULTS: Fluid intake (FI) was 3.8 ± 1.4 L, and mean sweat rates were 1.1 ±0.3 L/h, resulting in gross sweat loss (GSL) of 3.2 ± 0.8 L in 3h. No differences existed in GSL across treatments. Total sweat sodium loss (volume x concentration) was 143 ± 64 mmol versus 155 ± 66 mmol (C vs. CE, P=0.58), with sodium intake (CE) being 138.6 ± 50.4 mmol. Blood sodium declined from 140.0 ± 1.0 to 135.5 ± 1.4 mmol/L (C) and 139.9 ± 1.4 to 137.6 ± 2.0 mmol/L (CE) over 3h. Absolute Ab[Na] from start ofexercisewas-4.3±2.1 mmol for C and −2.3 ± 1.6 mmol for CE (P=0.04). Slopes (Ab[Na] per unit time) differed significantly (C vs. CE, P=0.002), with predicted decline being −1.7 (C) and −0.8 mmol/L/h (CE). Mean APV with C was −12.8 ± 8.0% compared to −7.4 ± 5.0% for CE (P=0.05). CONCLUSIONS: Carbohydrate-electrolyte beverage intake closely matching sweat loss attenuated the decline in blood sodium and maintained PV better compared to a carbohydrate beverage not containing electrolytes during prolonged exercise in the heat.

The use of recovery methods post‐exercise

Competitive soccer engages many of the body's systems to a major extent. The musculoskeletal, nervous, immune and metabolic systems are stressed to a point where recovery strategies post‐exercise become influential in preparing for the next match. Intense activity at a 7-day training camp causes participants to experience lowered concentrations of non-killer cells and T-helper cells. Two consecutive games in 24 h produce disturbances in the testosterone – cortisol ratio. When competitive schedules are congested, the recovery process should be optimized for performance capabilities to be restored to normal as soon as possible. There is evidence that glycogen stores are reduced near to depletion at the end of a soccer game and that a diet high in carbohydrates can aid recovery. Water alone is not the best means of restoring body fluids, since carbohydrate-electrolyte drinks display better intestinal absorption and reduce urine output. Some relief from muscle soreness may be achieved by means of a warm-down. Deep-water running regimens can replace conventional physical training in the days after competition. Massage, cryotherapy and alternative therapies have not been shown to be consistently effective. It is concluded that optimizing recovery post‐exercise depends on a combination of factors that incorporate a consideration of individual differences and lifestyle factors. The procedures to facilitate recovery processes should start immediately the game or training finishes. Match administrators and tournament planners should consider the stressful consequences for players in periods of congested fixtures and alleviate the physiological strain as far as possible by allowing 72 h between competitive games. This frequency of competition is unlikely to be sustainable in the long term.

Fluid Ingestion Attenuates The Decline In Vo2max Associated With Cardiovascular Drift

Cardiovascular drift (CV drift), characterized by the progressive rise in heart rate (HR) and fall in stroke volume (SV) during prolonged moderate-intensity exercise, is a well established phenomenon, but its effects on maximal oxygen uptake (VO2max) are not clear. PURPOSE To determine whether manipulation of CV drift by altering duration of exercise and fluid ingestion is associated with corresponding changes in VO2max. METHODS CV drift was measured in 11 moderately-trained men (age=26±5 yr, VO2max=57.8±6.7 ml/kg/min) as they cycled for either 60 min with no fluid (60NF), 120 min with no fluid (120NF), or 120 min while ingesting a 7% carbohydrate-electrolyte drink to replace sweat losses (120F). A control trial of 15 min with no fluid (15NF) also was conducted in order to assess VO2max before CV drift occurred. All exercise was performed at 60% VO2max in 30°C, 40% relative humidity, and wind speed ∼2.5 m/s. After submaximal exercise, without cessation of cycling, subjects began a continuous incremental-test to exhaustion to measure VO2max. RESULTS Subjects became 2.3%, 3.7%, and 0.7% dehydrated in 60NF, 120NF and 120F, respectively. Compared to 15NF, SV decline was not significant in 60NF (6 ml, 4.6%) but was in 120NF (16 ml, 13.8%, p < 0.05). Fluid ingestion (120F) significantly reduced the decline in SV to 3 ml (2.1%) compared to 120NF (p < 0.05). Compared to 15NF, VO2max was not decreased in 60NF (−1.2%), but was lower in 120NF by 5.1 ml/min/kg (−8.7%, p < 0.05). Fluid ingestion (120F) significantly reduced the decline in VO2max 1.3 ml/min/kg (−1.9%) compared to 120NF (p < 0.05). Changes in VO2max were significantly correlated with changes in SV and HR after 15 min during submaximal exercise (r=.62 and .47, SEE=5.8 and 6.6, respectively, p < 0.05). CONCLUSION Manipulation of CV drift by altering exercise duration and fluid ingestion is associated with proportional changes in VO2max. The results provide support for the hypothesis that, under these conditions, CV drift causes reduced VO2max.

The Effect of Intermittent High-Intensity Running on Gastric Emptying of Fluids in Man

This study examined the effect of variable-intensity shuttle running on gastric emptying of a carbohydrate-free placebo (Plac) drink and of a 6.4% carbohydrate-electrolyte (CHO) sports drink. We compared the volume of test drink emptied during two 15-min periods of walking exercise (WE) with that during two 15-min periods of the Loughborough Intermittent Shuttle Test (LIST). Gastric emptying was measured on the four trials using a double-sampling aspiration technique in eight healthy males after ingestion of a 420 +/- 49 mL and a 168 +/- 20 mL bolus of the appropriate test drink at the start of the first and second exercise period, respectively. During the initial 15 min of exercise, the mean (+/-SD) volume of Plac (124 +/- 95 mL) and CHO (71 +/- 43 mL) drink emptied was similar between the two LIST trials, but the volume of Plac (227 +/- 85 mL) and CHO (159 +/- 63 mL) drinks emptied on the WE trials was greater than for the respective test drinks on the LIST trials. Similar volumes of test drinks were emptied on all trials (P = 0.20) during the second 15 min of exercise. Over the 30 min of each trial, the exercise intensity of the LIST reduced the volume of the Plac (211 +/- 108 mL) and CHO (208 +/- 83 mL) drink emptied compared with that on the WE trial for the Plac (396 +/- 74 mL) and CHO (293 +/- 73 mL) drink, respectively. The exercise intensity of the LIST is sufficient to slow gastric emptying of carbohydrate and noncarbohydrate containing drinks compared with walking. Dilute carbohydrate-electrolyte drinks empty at about the same rate as carbohydrate-free beverages during variable-intensity running.

Short‐term effects of aerobic exercise on executive processes and emotional reactivity

The effect of individual bouts of aerobic exercise on young adults’ performance of an executive processing task (The Paced Auditory Serial Addition Test, PASAT) and on ratings of emotion and workload (NASA‐Task Load Index, TLX) was assessed in two experiments. In Experiment 1, nine men completed two test sessions during which the PASAT and the TLX were administered prior to and following a 40‐minute bout of cycling. A cold medication (Phenergan VC) was administered prior to exercise in one session; a placebo was given in the other session. PASAT performance increased following exercise, both after the ingestion of the cold medication and following the placebo. TLX ratings changed with practice but were not influenced by exercise. In Experiment 2, 10 women performed the PASAT and provided TLX ratings prior to and following four 120‐minute sessions of cycling and a control session. Participants were given one of three carbohydrate electrolyte drinks or a placebo drink prior to, during, and following cycling. PASAT performance improved significantly following exercise regardless of the type of drink ingested. Exercise did not influence TLX ratings. The results of these experiments add to a growing literature that demonstrates the facilitative effects of acute aerobic exercise on working memory and attentional processes.

Erosive Effect of a New Sports Drink on Dental Enamel during Exercise

To compare the potential erosive effect of a prototype carbohydrate-electrolyte drink (PCE) with a neutral control (water) and a commercially available carbohydrate-electrolyte drink (CCE) during exercise. : Nineteen healthy adults (male, N = 16; female, N = 3) took part in this single blind, three-way crossover study. Subjects were given each of the three drinks according to a randomization schedule, approximately balanced for first-order carryover effects. At the beginning of each of the three study periods, the volunteers were fitted with an intraoral appliance containing two human enamel blocks. During each study period, volunteers exercised for 75 min.d(-1) (5 repetitions of 15 min of exercise, with 5-min rests between exercise repetitions), 5 d.wk(-1) for 3 wk. Each day, drink aliquots of 200 mL were consumed during a 5-min period before exercise and after every 15-min bout of exercise, followed by a final 400-mL aliquot ingested over a 10-min period: a total of 1400 mL per study day. Dental erosion was measured as tissue loss from the enamel blocks by profilometry at the end of each study period. Water, PCE, and CCE produced 0.138 microm (SD 0.090 microm), 0.138 microm (SD 0.038 microm), and 4.238 microm (SD 3.872 microm) of enamel loss, respectively. A Wilcoxon t statistic showed a significant statistical difference between the PCE and CCE drinks (P < 0.001), whereas no significant difference could be detected between the PCE drink and water (P = 0.740). The PCE solution showed minimal erosion compared with the commercially available drink, and was statistically indistinguishable from water under the conditions of this study. Use of CE solutions formulated to minimize erosion during exercise may provide significant dental benefits.

Nutrition for the pediatric athlete.

A paucity of literature exists with regard to research on nutrition for the pediatric athlete. This lack of research makes the development of specific nutritional recommendations for young athletes problematic. This issue is made difficult by the macro- and micronutrient intake required for growth and development in conjunction with that required for sports. Exogenous carbohydrate drinks could be considered for the young athlete engaged in both endurance exercise and high-intensity exercise. Monitoring of the energy intake during resistance training in the pediatric athlete needs to be considered, as there is evidence to suggest that energy deficits may occur. If decrements in exercise performance are noted, then serum ferritin and hemoglobin concentrations should be monitored, as nonanemic iron deficiency is prevalent in the pediatric athlete. The pediatric athlete exercising in the heat is susceptible to voluntary dehydration and evidence exists to suggest that a carbohydrate-electrolyte drink will abolish this phenomenon.

Effect of Post-Exercise Supplement Consumption on Adaptations to Resistance Training

Objective: Athletes are interested in nutritional manipulations that may enhance lean tissue gains stimulated by resistance training. Some research demonstrates that acute consumption of food containing protein causes superior muscle protein synthesis compared to isoenergetic foods without protein. This benefit has not been verified in longer-term training studies. We compared body composition and muscle function responses to resistance training in males who consumed a carbohydrate or a multi-macronutrient beverage following each training session.Methods: Nineteen, untrained men (18–25 years) consumed either a milk (MILK) or a carbohydrate-electrolyte (CHO) drink immediately following each workout during a 10 week resistance training program. Muscle strength (1RM for seven exercises), body composition (DXA scan), fasted, resting concentrations of serum total and free testosterone, cortisol, IGF-1, and resting energy expenditure (REE) were measured prior to and at the end of training.Results: Resistance training caused an increase (44 ± 4%, p < 0.001) in muscular strength for all subjects. The training program reduced percent body fat (8%, p < 0.05, −0.9 ± 0.5 kg) and increased fat-free soft tissue (FFST) mass (2%, 1.2 ± 0.3 kg, p < 0.01). MILK tended to increase body weight and FFST mass (p=0.10 and p=0.13, respectively) compared to CHO. Resting total and free testosterone concentrations decreased from baseline values in all subjects (16.7%, 11%, respectively, p < 0.05). Significant changes in fasting IGF-1, cortisol, and REE across training were not observed for either group.Conclusion: Post-resistance exercise consumption of MILK and CHO caused similar adaptations to resistance training. It is possible that a more prolonged training with supplementation period would expand the trend for greater FFST gains in MILK.

Effect of Endurox on Exercise Time to Fatigue, Recovery, and Recovery Exercise Performance

1176 Endurox claims to increase fat metabolism, raise anaerobic threshold, and improve recovery measured by heart rate and lactate. Good scientific research by Cheuvront et al (1999) and Plowman et al (1999) does not support the claims made by Endurox on endurance performance. Both of these studies analyzed a submax endurance task, but did not look at a recovery exercise bout. PURPOSE: To analyze exercise time to fatigue, recovery, and a recovery exercise bout with an Endurox supplement in comparison to a carbohydrate-electrolyte drink (PowerAde) and a Placebo. METHODS: Three trials (Endurox, PowerAde, Placebo) on a cycle ergometer were conducted in double blind random order. 18 recreationally active subjects (9 males, 9 females) between 20–40 years of age participated. The drinks were administered pre, during, and immediately after initial exercise to fatigue. The initial exercise was 45 minutes at 65% intensity, followed by two minute increments until fatigue. This was followed by 15 minutes of rest, and then another incremental ride to fatigue (recovery bout). VO2, HR, RER, lactate, glucose, RPE, sweat loss, Ve, and time to fatigue were measured. RESULTS: The Endurox (50.8 min) trial had significantly less time to fatigue than the PowerAde (51.9 min) trial and the Placebo trial (52.0 min) for the initial exercise bout, and slightly less (non-significant) time to fatigue during the recovery bout. No significant differences in lactate, RPE, VO2, Ve, RER, and glucose were found. Interestingly, sweat loss was significantly less during the Endurox trial (1353 ml), compared to the Placebo (1472 ml) and PowerAde (1540 ml) trials. Heart rate tended to be higher during the latter portion of the initial exercise bout for the Endurox trial compared to the other two trials, and was significantly higher (146.7 bpm) than the Placebo trial (138.5 bpm), but not the PowerAde trial (142.5 bpm) at minute 35 of the initial exercise bout. Lactate and HR during the recovery bout were not significantly different. CONCLUSIONS: Endurox has no performance benefit and may even have a performance decrement during incremental exercise to fatigue compared to a Placebo and PowerAde. The reduced time to fatigue may be related to reduced thermoregulation, since HR was higher and Sweat loss was reduced.

THE EFFECT OF INTERMITTENT HIGH-INTENSITY RUNNING ON THE RATE OF GASTRIC EMPTYING IN MAN

PURPOSE The aim of this study was to examine the effect of variable-intensity shuttle running exercise on the gastric emptying rate of a carbohydrate-free placebo (P) drink and of a 6.4% carbohydrate-electrolyte (CHO) sports drink. METHOD We compared the volume of test drink emptied in 8 healthy males during two 15 min periods of low intensity walking exercise (WE) and during two 15 min periods of a shuttle running test (LIST) that simulates the activity pattern of soccer. Gastric emptying was measured on the four trials using a modification of the double sampling aspiration technique following ingestion of a body mass adjusted volume of the appropriate test drink. On each trial, subjects ingested 420 ± 49 ml (5 ml/kg) of test drink immediately before starting the first 15 min of exercise and 167 ± 18 ml (2 ml/kg) was ingested before the second exercise bout. RESULTS During the initial 15 min of exercise, the volume of P (124 ± 95 ml) and CHO (71 ± 43 ml) drinks emptied was similar for the two LIST trials, but the volume of P (227 ± 85 ml) and CHO (159 ± 63 ml) drinks emptied on the WE trials was greater than for the respective test drinks on the LIST trials (p < 0.05). Similar volumes of test drinks were emptied on all trials (p = 0.20) during the second 15 min of exercise. Over the 30 min of each trial, the exercise intensity of the LIST reduced the volume of the P (211 ± 108 ml) and CHO (208 ± 83 ml) drink emptied from the stomach compared with that on the WE trial for the P (396 ± 74 ml; p < 0.001) and CHO (293 ± 73 ml; p < 0.05) drink respectively. CONCLUSIONS The data demonstrate that the exercise intensity of the LIST is sufficient to slow gastric emptying of both carbohydrate and non-carbohydrate containing drinks compared to low-intensity walking. Dilute carbohydrate-electrolyte drinks are emptied at about the same rate as carbohydrate-free beverages during variable-intensity running.

EFFECTS OF SPORTS DRINK WITH B VITAMINS ON PERFORMANCE DURING CYCLING

B vitamins regulate energy metabolism by modulating the synthesis and degradation of substrates. Whether Vitamin B3, B6, and B12 added to a carbohydrate-electrolyte (CE) drink effects physiological responses during exercise is not clear. PURPOSE: To examine if ingestion of 8%CE with B vitamins (CE8-B) alters physiological responses or exercise performance during prolonged, high-intensity cycling. METHODS: During a 95 min cycling bout at 80%VO2max, 12 trained cyclists ingested a water placebo (P), 6%CE (CE6), or CE8-B. The volume of fluid ingested was 400 ml prior to cycling, 3.5 ml/kg body weight every 20 min during cycling, and ad libitum during 30 min recovery. CE8-B contained 12.7, 1.7, and 8.9 mg/L of B3, B6 and B12, respectively. Relative fluid uptake was assessed by the appearance of deuterium oxide [D2O] in plasma. Beverage palatability was examined using a Visual Analogue Scale. RESULTS: Mean (± SD) work completed (kJ/kg BW) during a 15 min performance ride was significantly greater (p < 0.02) by 7% with CE6 and CE8-B (3.19 ± 0.16) compared to P (2.97 ± 0.19). There were no differences in carbohydrate oxidation, heart rate, %Δ plasma volume, blood lactate, [D2O], electrolytes, or perceived exertion among beverages. Blood glucose was significantly lower with P (3.9 ± 0.2 mmol/L) at 95 min compared to both CE drinks (4.4 ± 0.2 mmol/L). During recovery, a greater volume of CE8-B (487 ± 102 ml) was ingested (p < 0.05) compared to P (188 ± 65 ml) but not different from 6%CE (389 ± 55 ml). Subjects rated P significantly lower on good taste, acceptability, and higher on bitterness compared to CE6 and CE8-B. CONCLUSION: Ingestion of CE8-B was palatable, had no effect on relative fluid uptake or substrate oxidation during cycling, and improved performance compared to P. Supported by The Coca Cola Company

Exogenous carbohydrate oxidation from drinks ingested during prolonged exercise in a cold environment in humans.

Six healthy male volunteers performed four rides to exhaustion on a cycle ergometer at approximately 80% of maximal oxygen consumption. Subjects ingested a bolus volume of fluid (7.14 ml/kg) immediately before exercise and additional fluid volumes (1.43 ml/kg) every 10 min during exercise. The fluids ingested were either a flavored water control or glucose-electrolyte beverages with glucose concentrations of 2, 6, or 12%. The beverages were labeled with [U-(13)C]glucose (99.2%: 0.05 g/l). Exercise capacity was not different (P = 0.13) between trials; median (range) exercise time was 83.52 (79.85--89.68), 103.19 (78.82--108.22), 100.37 (80.60--124.07), and 94.76 (76.78--114.25) min in the 0, 2, 6, and 12% trials, respectively. The oxidation of exogenous glucose in each 15-min period was significantly lower in the 2% trial (P = 0.02) than in the 6 and 12% trials where oxidation rates were between 0.5 and 0.7 g/min. No difference in endogenous glucose oxidation was observed between trials (P = 0.71). These findings indicate that the oxidation of exogenous glucose during exercise of this intensity and duration in a cold environment is similar to that observed in warmer conditions. Thus a low oxidation of exogenous substrate is unlikely to be a factor limiting the effectiveness of carbohydrate-electrolyte drink ingestion on exercise capacity in a cold environment.

Improving cycling performance: how should we spend our time and money.

Cycling performance is dependent on physiological factors which influence mechanical power production and mechanical and environmental factors that affect power demand. The purpose of this review was to summarize these factors and to rank them in order of importance. We used a model by Martin et al. to express all performance changes as changes in 40 km time trial performance. We modelled the performance of riders with different ability ranging from novice to elite cyclists. Training is a first and most obvious way to improve power production and was predicted to have the potential to improve 40 km time trial performance by 1 to 10% (1 to 7 minutes). The model also predicts that altitude training per se can cause a further improvement of 23 to 34 seconds. Carbohydrate-electrolyte drinks may decrease 40 km time by 32 to 42 seconds. Relatively low doses of caffeine may improve 40 km time trial performance by 55 to 84 seconds. Another way of improving time trial performance is by reducing the power demand of riding at a certain velocity. Riding with hands on the brake hoods would improve aerodynamics and increase performance time by approximately 5 to 7 minutes and riding with hands on the handlebar drops would increase performance time by 2 to 3 minutes compared with a baseline position (elbows on time trail handle bars). Conversely, riding with a carefully optimised position could decrease performance time by 2 to 2.5 minutes. An aerodynamic frame saved the modelled riders 1:17 to 1:44 min:sec. Furthermore, compared with a conventional wheel set, an aerodynamic wheel set may improve time trial performance time by 60 to 82 seconds. From the analysis in this article it becomes clear that novice cyclists can benefit more from the suggested alterations in position, equipment, nutrition and training compared with elite cyclists. Training seems to be the most important factor, but sometimes large improvements can be made by relatively small changes in body position. More expensive options of performance improvement include altitude training and modifications of equipment (light and aerodynamic bicycle and wheels). Depending on the availability of time and financial resources cyclists have to make decisions about how to achieve their performance improvements. The data presented here may provide a guideline to help make such decisions.

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 180min of exercise. Drink acceptability was again measured after 90 and 180min of exercise. Drink intake was measured at 15-min intervals. Intake of M was significantly greater than L and W throughout the first 75min 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 effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment

A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO 2max ) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45 - 0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12 - 0.47 litres). The ambient temperature was 30.2 - 0.6°C (mean - s ), with a relative humidity of 71 - 1% and an air speed of approximately 0.7 m.s -1 on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly ( P ≪ 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly ( P ≪ 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear.

Effect of a carbohydrate-electrolyte drink on endurance capacity during prolonged intermittent high intensity running.

OBJECTIVE: To examine the effect of a carbohydrate-electrolyte solution on endurance capacity during prolonged intermittent running. METHODS: Nine subjects (eight men and one woman) ran to exhaustion on a motorised...

Factors influencing the restoration of fluid and electrolyte balance after exercise in the heat.

Maintenance of fluid balance is a major concern for all athletes competing in events held in hot climates. This paper reviews recent work relating to optimisation of fluid replacement after...