The purpose of this study was to examine the gastric emptying and rehydration effects of hypotonic and hypertonic glucose-electrolyte drinks after exercise-induced dehydration. Eight healthy males lost ~1.8% body mass by intermittent cycling and rehydrated (150% of body mass loss) with a hypotonic 2% (2% trial) or a hypertonic 10% (10% trial) glucose-electrolyte drink over 60 min. Blood and urine samples were taken at preexercise, postexercise, and 60, 120, 180, and 240 min postexercise. Gastric and test drink volume were determined 15, 30, 45, 60, 90, and 120 min postexercise. At the end of the gastric sampling period 0.3% (2% trial) and 42.1% (10% trial; p < .001) of the drinks remained in the stomach. Plasma volume was lower (p < .01) and serum osmolality was greater (p < .001) at 60 and 120 min during the 10% trial. At 240 min, 52% (2% trial) and 64% (10% trial; p < .001) of the drinks were retained. Net fluid balance was greater from 120 min during the 10% trial (p < .001). When net fluid balance was corrected for the volume of fluid in the stomach, it was greater at 60 and 120 min during the 2% trial (p < .001). These results suggest that the reduced urine output following ingestion of a hypertonic rehydration drink might be mediated by a slower rate of gastric emptying, but the slow gastric emptying of such solutions makes rehydration efficiency difficult to determine in the hours immediately after drinking, compromising the calculation of net fluid balance.
David J. Clayton, Gethin H. Evans and Lewis J. James
Sandra luliano, Geraldine Naughton, Greg Collier and John Carlson
Thirty-two elite junior athletes in two age categories, older than or equal to IS years old (O15) (8 females and 9 males) and less than 15 years old (U15) (8 females and 7 males), performed a laboratory-based duathlon (run-ride-run). At the completion of the event, significant body mass losses were recorded for all groups. Compared with the other three groups, the O15 males lost body mass at a greater absolute rate (1.26 ±0.06 kg ⋅ hr−1 vs. a mean of 0.62 ±0.11 kg ⋅ hr−1 for the other three groups) and a greater relative rate (1.95 ± 0.10% BM ⋅ hr−1 vs. a mean of 1.23 ± 0.19 %BM ⋅ hr−1 for the other three groups) (p < .05). No differences were observed between groups for fluid consumption. Subjects consumed more fluid (p < .05) during the cycle phase and postevent than preevenl or during the run phases. Results indicated that the athletes' fluid intake practices were insufficient to maintain adequate hydration during the simulated event.
Susan M. Shirreffs, Luis F. Aragon-Vargas, Mhairi Keil, Thomas D. Love and Sian Phillips
To determine the effectiveness of 3 commonly used beverages in restoring fluid and electrolyte balance, 8 volunteers dehydrated by 1.94% ± 0.17% of body mass by intermittent exercise in the heat, then ingested a carbohydrate-electrolyte solution (Gatorade), carbonated water/apple-juice mixture (Apfelschorle), and San Benedetto mineral water in a volume equal to 150% body-mass loss. These drinks are all are perceived to be effective rehydration solutions, and their effectiveness was compared with the rehydration effectiveness of Evian mineral water, which is not perceived in this way by athletes. Four hours after rehydration, the subjects were in a significantly lower hydration status than the pretrial situation on trials with Apfelschorle (–365 ± 319 mL, P = 0.030), Evian (–529 ± 319 mL, P < 0.0005), and San Benedetto (–401 ± 353 mL, P = 0.016) but were in the same hydration status as before the dehydrating exercise on Gatorade (–201 ± 388 mL, P = 0.549). Sodium balance was negative on all trials throughout the study; only with Apfelschorle did subjects remain in positive potassium balance. In this scenario, recovery of fluid balance can only be achieved when significant, albeit insufficient, quantities of sodium are ingested after exercise. There is a limited range of commercially available products that have a composition sufficient to achieve this, even though the public thinks that some of the traditional drinks are effective for this purpose.
Gethin H. Evans, Jennifer Miller, Sophie Whiteley and Lewis J. James
The purpose of this study was to examine the efficacy of water and a 50 mmol/L NaCl solution on postexercise rehydration when a standard meal was consumed during rehydration. Eight healthy participants took part in two experimental trials during which they lost 1.5 ± 0.4% of initial body mass via intermittent exercise in the heat. Participants then rehydrated over a 60-min period with water or a 50 mmol/L NaCl solution in a volume equivalent to 150% of their body mass loss during exercise. In addition, a standard meal was ingested during this time which was equivalent to 30% of participants predicted daily energy expenditure. Urine samples were collected before and after exercise and for 3 hr after rehydration. Cumulative urine volume (981 ± 458 ml and 577 ± 345 mL; p = .035) was greater, while percentage fluid retained (50 ± 20% and 70 ± 21%; p = .017) was lower during the water compared with the NaCl trial respectively. A high degree of variability in results was observed with one participant producing 28% more urine and others ranging from 18–83% reduction in urine output during the NaCl trial. The results of this study suggest that after exercise induced dehydration, the ingestion of a 50 mmol/L NaCl solution leads to greater fluid retention compared with water, even when a meal is consumed postexercise. Furthermore, ingestion of plain water may be effective for maintenance of fluid balance when food is consumed in the rehydration period.
Hamish A.B. Reid, Nicholas C. Dennison, Jonathan Quayle and Tom Preston
Meeting the energy demands of prolonged arduous expeditions and endurance sport may be a significant barrier to success. Expedition rowing is associated with high levels of body-mass loss, reflecting the challenge of meeting energy expenditure in this exacting environment.
To use the doubly labeled water (DLW) technique to calculate the total energy expenditure (TEE) and body-composition changes of two 28-y-old healthy male athletes during a 50-d continuous and unsupported row around Great Britain.
A measured dose of DLW was taken at the start of 2 separate study periods (days 5–19 and 34–48) followed by sequential urine collection, which was analyzed on return to land.
Mean TEE was 15.3 MJ/d: athlete 1, 16.4 MJ/d; athlete 2, 14.9 MJ/d. Athlete 1 lost 11.2 kg and athlete 2 lost 14.9 kg of body mass during the row. Average energy provision was 19.1 MJ per 24-h ration pack.
These results highlight the difficulty of maintaining energy balance during expedition rowing. A starvation state was observed despite dietary provision in excess of estimated energy expenditure, indicating that nutritional strategy rather than caloric availability was at fault. The authors recommend that future expeditions prioritize thorough testing and the individualization of rations to ensure that they are both palatable and practical during the weeks to months at sea.
Ben Desbrow, Daniel Murray and Michael Leveritt
To investigate the effect of manipulating the alcohol and sodium content of beer on fluid restoration following exercise.
Seven male volunteers exercised on a cycle ergometer until 1.96 ± 0.25% body mass (mean± SD) was lost. Participants were then randomly allocated a different beer to consume on four separate occasions. Drinks included a low-alcohol beer (2.3% ABV; LightBeer), a low-alcohol beer with 25 mmol×L−1 of added sodium (LightBeer+25), a full-strength beer (4.8% ABV; Beer), or a full-strength beer with 25 mmol×L−1 of added sodium (Beer+25). Volumes consumed were equivalent to 150% of body mass loss during exercise and were consumed over a 1h period. Body mass and urine samples were obtained before and hourly for 4 hr after beverage consumption.
Significantly enhanced net fluid balance was achieved following the LightBeer+25 trial (–1.02 ± 0.35 kg) compared with the Beer (–1.59 ± 0.32 kg) and Beer+25 (–1.64 ± 0.28 kg) treatments. Accumulated urine output was significantly lower in the LightBeer+25 trial (1477 ± 485 ml) compared with the Beer+25 (2101 ± 482 ml) and Beer (2175 ± 372 ml) trials.
A low alcohol beer with added sodium offers a potential compromise between a beverage with high social acceptance and one which avoids the exacerbated fluid losses observed when consuming full strength beer.
George Wilson, Neil Chester, Martin Eubank, Ben Crighton, Barry Drust, James P. Morton and Graeme L. Close
Professional jockeys are unique among weight-making athletes, as they are often required to make weight daily and, in many cases, all year-round. Common methods employed by jockeys include dehydration, severe calorie restriction, and sporadic eating, all of which have adverse health effects. In contrast, this article outlines a structured diet and exercise plan, employed by a 22-yr-old professional National Hunt jockey in an attempt to reduce weight from 70.3 to 62.6 kg, that does not rely on any of the aforementioned techniques. Before the intervention, the client’s typical daily energy intake was 8.2 MJ (42% carbohydrate [CHO], 36% fat, 22% protein) consumed in 2 meals only. During the 9-wk intervention, daily energy intake was approximately equivalent to resting metabolic rate, which the athlete consumed as 6 meals per day (7.6 MJ, 46% CHO, 19% fat, 36% protein). This change in frequency and composition of energy intake combined with structured exercise resulted in a total body-mass loss of 8 kg, corresponding to reductions in body fat from 14.5% to 9%. No form of intentional dehydration occurred throughout this period, and mean urine osmolality was 285 mOsm/kg (SD 115 mOsm/kg). In addition, positive changes in mood scores (BRUMS scale) also occurred. The client was now able to ride light for the first time in his career without dehydrating, thereby challenging the cultural practices inherent in the sport.
Lewis J. James and Susan M. Shirreffs
Weight categorized athletes use a variety of techniques to induce rapid weight loss (RWL) in the days leading up to weigh in. This study examined the fluid and electrolyte balance responses to 24-hr fluid restriction (FR), energy restriction (ER) and fluid and energy restriction (F+ER) compared with a control trial (C), which are commonly used techniques to induce RWL in weight category sports. Twelve subjects (six male, six female) received adequate energy and water (C) intake, adequate energy and restricted water (~10% of C; FR) intake, restricted energy (~25% of C) and adequate water (ER) intake or restricted energy (~25% of C) and restricted (~10% of C) water intake (F+ER) in a randomized counterbalanced order. Subjects visited the laboratory at 0 hr, 12 hr, and 24 hr for blood and urine sample collection. Total body mass loss was 0.33% (C), 1.88% (FR), 1.97% (ER), and 2.44% (F+ER). Plasma volume was reduced at 24 hr during FR, ER, and F+ER, while serum osmolality was increased at 24 hr for FR and F+ER and was greater at 24 hr for FR compared with all other trials. Negative balances of sodium, potassium, and chloride developed during ER and F+ER but not during C and FR. These results demonstrate that 24 hr fluid and/or energy restriction significantly reduces body mass and plasma volume, but has a disparate effect on serum osmolality, resulting in hypertonic hypohydration during FR and isotonic hypohydration during ER. These findings might be explained by the difference in electrolyte balance between the trials.
Ben Desbrow, Danielle Cecchin, Ashleigh Jones, Gary Grant, Chris Irwin and Michael Leveritt
The addition of 25 mmol·L−1 sodium to low alcohol (2.3% ABV) beer has been shown to enhance post exercise fluid retention compared with full strength (4.8% ABV) beer with and without electrolyte modification. This investigation explored the effect of further manipulations to the alcohol and sodium content of beer on fluid restoration following exercise. Twelve male volunteers lost 2.03 ± 0.19% body mass (mean ± SD) using cycling-based exercise. Participants were then randomly allocated a different beer to consume on four separate occasions. Drinks included low alcohol beer with 25 mmol·L−1 of added sodium [LightBeer+25], low alcohol beer with 50 mmol·L−1 of added sodium [LightBeer+50], midstrength beer (3.5% ABV) [Mid] or midstrength beer with 25 mmolL−1 of added sodium [Mid+25]. Total drink volumes in each trial were equivalent to 150% of body mass loss during exercise, consumed over a 1h period. Body mass, urine samples and regulatory hormones were obtained before and 4 hr after beverage consumption. Total urine output was significantly lower in the LightBeer+50 trial (1450 ± 183 ml) compared with the LightBeer+25 (1796 ± 284 ml), Mid+25 (1786 ± 373 ml) and Mid (1986 ± 304 ml) trials (allp < .05). This resulted in significantly higher net body mass following the LightBeer+50 trial (-0.97 ± 0.17kg) compared with all other beverages (LightBeer+25 (-1.30 ± 0.24 kg), Mid+25 (-1.38 ± 0.33 kg) and Mid (-1.58 ± 0.29 kg), all p < .05). No significant changes to aldosterone or vasopressin were associated with different drink treatments. The electrolyte concentration of low alcohol beer appears to have more significant impact on post exercise fluid retention than small changes in alcohol content.
Nicholas Gant, Ajmol Ali and Andrew Foskett
Carbohydrate and caffeine are known to independently improve certain aspects of athletic performance. However, less is understood about physiological and performance outcomes when these compounds are coingested in a rehydration and carbohydrate-replacement strategy. The aim of this study was to examine the influence of adding a moderate dose of caffeine to a carbohydrate solution during prolonged soccer activity. Fifteen male soccer players performed two 90-min intermittent shuttle-running trials. They ingested a carbohydrate-electrolyte solution (CON) providing a total of 1.8 g/kg body mass (BM) of carbohydrate or a similar solution with added caffeine (CAF; 3.7 mg/kg BM). Solutions were ingested 1 hr before exercise and every 15 min during the protocol. Soccer passing skill and countermovement-jump height (CMJ) were quantified before exercise and regularly during exercise. Sprinting performance, heart rate, blood lactate concentration (La) and the subjective experiences of participants were measured routinely. Mean 15-m sprint time was faster during CAF (p = .04); over the final 15 min of exercise mean sprint times were CAF 2.48 ± 0.15 s vs. CON 2.59 ± 0.2 s. Explosive leg power (CMJ) was improved during CAF (52.9 ± 5.8 vs. CON 51.7 ± 5.7 cm, p = .03). Heart rate was elevated throughout CAF, and ratings of pleasure were significantly enhanced. There were no significant differences in passing skill, rating of perceived exertion, La, or body-mass losses between trials. The addition of caffeine to the carbohydrate-electrolyte solution improved sprinting performance, countermovement jumping, and the subjective experiences of players. Caffeine appeared to offset the fatigue-induced decline in self-selected components of performance.