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Xiaocai Shi, William Bartoli, Mary Horn and Robert Murray

Eight healthy subjects, aged 39.0 ± 2.4 years, consumed four 6% carbohydrate-electrolyte solutions containing either one (glucose or fructose) or two transportable carbohydrates in single (glucose + fructose) or bound (sucrose) forms. Solution osmolalities ranged from 250 to 434 mOsm/kg H2O. The test solutions were ingested at rest in the amount of 6 ml/kg of body weight at a temperature of 12 °C. Gastric emptying rate was measured by repeated aspirations via a nasogastric tube using the modified George double-sampling technique. The intragastric temperature was determined by a temperature probe attached to the nasogastric tube. There were no significant differences in gastric emptying rates and gastric volumes among the solutions. Intragastric temperature dropped from 36.5 °C to 23.3±3 °C immediately after beverage ingestion but recovered to above 30 °C within 5 min. These data suggest that the gastric emptying rate of the specified beverages is not affected by the number and type of carbohydrates or by solution osmolalities within the tested range. Within 5 min after ingestion, cold beverages are warmed to above 30 °C in the stomach. This infers that the effect of cold solution temperature on gastric emptying rate is likely to be small and transitory.

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Robert Murray, William Bartoli, John Stofan, Mary Horn and Dennis Eddy

The purpose of this study was to determine the effects of repeated ingestion of drinks containing varying concentrations of carbohydrate on gastric emptying rate during steady-state exercise. On five separate occasions, 14 subjects cycled for 90 min at an average power output of 151 ± 2 W. At 15-min intervals, subjects ingested 227 ± 3 ml of either water, 4% carbohydrate (CHO), 6% CHO, or 8% CHO. Gastric volume was determined prior to each drink and at 90 min using the modified double-sampling technique. Gross gastric volumes were significantly greater and mean gastric emptying rates and the percentage of ingested beverage emptied from the stomach were significantly less for 8% CHO. These data indicate that repeated ingestion of an 8% CHO beverage during exercise significantly reduces gastric emptying rate, whereas lower concentrations of carbohydrate do not. In addition, beverage osmolality is not as important as beverage energy content in influencing gastric emptying rate at these carbohydrate concentrations.

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Gethin H. Evans, Phillip Watson, Susan M. Shirreffs and Ronald J. Maughan

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

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Jennifer Rogers, Robert W. Summers and G. Patrick Lambert

The purpose of this study was to determine if lowering carbohydrate (CHO) concentration in a sport drink influences gastric emptying, intestinal absorption, or performance during cycle ergometry (85 min, 60% VO2peak). Five subjects (25 ± 1 y, 61.5 ± 2.1 mL · kg−1 · min−1 VO2peak) ingested a 3% CHO, 6% CHO, or a water placebo (WP) beverage during exercise. Gastric emptying was determined by repeated double sampling and intestinal absorption by segmental perfusion. Total solute absorption and plasma glucose was greater for 6% CHO; however, neither gastric emptying, intestinal water absorption, or 3-mi time trial performance (7:58 ± 0:33 min, 8:13 ± 0:25 min, and 8:25 ± 0:29 min, respectively, for 6% CHO, 3% CHO, and WP) differed among solutions. These results indicate lowering the CHO concentration of a sport drink from 6% CHO does not enhance gastric emptying, intestinal water absorption, or time trial performance, but reduces CHO and total solute absorption.

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Nicholas Gant, John B. Leiper and Clyde Williams

This study examined gastric emptying, core temperature, and sprint performance during prolonged intermittent shuttle running in 30 °C when ingesting a carbohydrate-electrolyte solution (CES) or favored water (FW). Nine male soccer players performed 60 min of shuttle running, ingesting fluid before exercise and every 15 min during exercise. Gastric emptying was measured using a double-sampling aspiration technique, and intestinal temperature was monitored via ingested capsules. There were no differences between trials in the total fluid volume emptied from the stomach during each exercise period (P = 0.054). The volume emptied every 15 min was 244 ± 67 mL in the CES trial and 273 ± 66 mL in the FW trial. Intestinal temperature was higher during exercise in the CES trial (P = 0.004), and cumulative sprint time was shorter (P = 0.037). Sprint performance was enhanced by the ingestion of a CES, which resulted in elevated core temperatures, and the rate of gastric emptying remained similar between solutions.

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Robert Murray, William P. Bartoli, Dennis E. Eddy and Mary K. Horn

The purpose of this study was to compare the gastric emptying rates (GER) of water, a 6% carbohydrate (CHO) beverage, and a 20% CHO beverage and to contrast those rates against the rate at which deuterium oxide in the drinks accumulated in plasma (DAR) following beverage ingestion. Ten subjects (8 males, 2 females) cycled at 60% VO2max for 70 min; at 13 min, the subjects ingested 400 ml of one of the beverages. The GER and DAR of water and 6% CHO were similar, while GER and DAR were both significantly slowed by ingestion of 20% CHO. Although there was a significant correlation (r = .63, p < .05) between GER and DAR, only 40% of the variation in DAR could be accounted for by variation in GER. These data support the contention that DAR is partially determined by GER, with differences in the rate of fluid absorption across the intestine and other factors accounting for the remaining variation in DAR.

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Kevin J. Cole, Peter W. Grandjean, Richard J. Sobszak and Joel B. Mitchell

This study examined the effects of serial feedings of different carbohydrate (CHO) solutions on plasma volume, gastric emptying (GE), and performance during prolonged cycling exercise. Solutions containing 6 g% glucose-sucrose (CHO-6GS), 83 g% high fructose com syrup (CHO-8HF), 6.3 g% high fructose corn syrup + 2 g% glucose polymer (CHO-8HP), and a water placebo (WP) were compared. Ten trained male cyclists performed four cycling trials consisting of 105 min at 70% VQ2max followed by a 15-min all-out, self-paced performance ride. Every 15 min the men consumed one of the four test solutions. Blood samples were taken before, during, and after exercise to determine blood glucose and plasma volume changes. There were no significant differences in performance, GE, or plasma volume changes between trials. Blood glucose was significantly elevated at the 105-min timepoint in all CHO trials when compared to WP. The CHO-8HF and CHO-8HP drinks resulted in a significantly higher delivery of CHO to the intestine. Higher rates of CHO oxidation during the steady-state ride were observed only with the CHO-6GS drink.

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Jeffrey J. Zachwieja, David L. Costill, Glenn C. Beard, Robert A. Robergs, David D. Pascoe and Dawn E. Anderson

To determine the effect of a carbonated carbohydrate (CHO) drink on gastric function and exercise performance, eight male cyclists completed four 120- min bouts of cycling. Each bout consisted of a 105-min ride at 70% VO2max followed by a 15-min self-paced performance ride. During each trial, one of four test solutions was ingested: carbonated CHO (C-10%), noncarbonated CHO (NC-10%), carbonated non-CHO (C), and noncarbonated non-CHO (NC). Following the performance ride, the subjects had their stomach contents removed by aspiration. There were no significant differences in gastric emptying (GE) except for Trial C-10%, which averaged 13.3% less than NC. However, there was no difference in the perception of gastrointestinal comfort between this trial and any other. Average power output during the performance ride was not significantly different between carbonated and noncarbonated trials, or between CHO-fed and no-CHO trials; however, the subjects worked at a greater intensity when fed CHO. Finally, acid base status did not change when a carbonated drink was ingested. This indicates that adding carbonation to a sport drink does not significantly alter gastric function, the perception of GI comfort, or exercise performance.

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Jeffrey J. Zachwieja, David L. Costill, Jeffrey J. Widrick, Dawn E. Anderson and Glenn K. McConell

The intent of this study was to determine whether adding carbonation to either water or a low calorie sport drink would affect gastric emptying (GE). Fifteen subjects rode for 20 minutes on a cycle ergometer at 55% of max VO2. After 5 minutes of exercise, the subjects ingested 5.5 mllkg body weight of a test solution: water (W), carbonated water (CW), and a low calorie sport drink in both a carbonated (C2C) and noncarbonated (2C) form. At the end of each ride, the stomach was emptied through gastric aspiration. The results indicate that carbonation has no effect on GE. However, the type of drink did have an effect on GE, as both 2C and C2C emptied from the stomach at a slower rate than either W or CW. Subjective ratings of gastrointestinal comfort were similar for both carbonated and noncarbonated forms, and at no time did the subjects report discomfort. The results were independent of the exercise challenge, as exercise intensity, heart rate, and ratings of perceived exertion did not differ between experimental trials. It is concluded that carbonation does not affect the GE characteristics of a drink taken during submaximal exercise, but the flavoring system of the low calorie beverage decreased the rate of GE by as much as 25% when compared to water.

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David J. Clayton, Gethin H. Evans and Lewis J. James

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.