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James A. Lang, Carl V. Gisolfi, and G. Patrick Lambert

The purpose of this study was to determine the effects of exercise intensity on active and passive intestinal glucose absorption. Eight trained runners (age = 23 ± 2 y; VO2max = 62.1 ± 5.8 mL · kg−1 · min−1) performed a 1 h resting experiment and three 1 h treadmill experiments at 30, 50, or 70% VO2max in a thermoneutral environment. Immediately prior to each experiment, euhydrated subjects ingested a solution containing two non-metabolizable glucose analogs, 3-O-methyl-D-glucose (3MG; actively absorbed; 5 g) and D-xylose (passively absorbed; 5 g). During the following 5 h, all urine was collected and the amount of 3MG and D-xylose in the urine was determined. Using repeated measures ANOVA, a significant (P < 0.05) reduction in urinary excretion of each carbohydrate was observed at 70% VO2max compared to the other intensities suggesting that both active and passive intestinal absorption of glucose may be reduced during prolonged running at this intensity.

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Alan J. Ryan, Amy E. Navarre, and Carl V. Gisolfi

These studies were done to determine the effect of carbonation and carbohydrate content on either gastric emptying or ad libitum drinking during treadmill exercise in the heat. Four test drinks were used: a 6% carbohydrate, noncarbonated; a 6% carbohydrate, carbonated; a 10% carbohydrate, noncarbonated; and a 10% carbohydrate, carbonated drink. For gastric emptying studies, subjects completed four 1-hr treadmill runs in the heat. They were given 400 mL of test drink at 0 rnin and 200 mL at 15, 30, and 45 min of exercise. For ad libitum drinking studies, subjects completed four 2-hr treadmill runs in the heat. Gastric residual volumes were similar during the four 1-hr runs. During the 2-hr runs, ad libitum drinking of the four beverages was also similar. Mean values for sweat rate, percentage of body weight lost, and percentage of fluid replaced by ad libitum drinking were similar for the four trials. Similar changes in heart rate, rectal temperature, and ratings of perceived exertion were also observed during the four 2-hr treadmill runs. We conclude that the presence of carbonation in a carbohydrate drink did not have a significant effect on either gastric emptying or ad libitum drinking.

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G. Patrick Lambert, Timothy L. Bleiler, Ray-Tai Chang, Alan K. Johnson, and Carl V. Gisolfi

Eight male runners performed four 2-hr treadmill runs at 65% ~ 0 , m a x in the heat (35"C, 15-20% RH). A different beverage was offered each trial and subjects drank ad libitum for 2 min every 20 min. The beverages were, 6% carbohydrate (CHO) solution (NC 6), 6% carbonated-CHO solution (C 6), 10% CHO solution (NC 10), and 10% carbonated-CHO solution (C 10). NC 6 and C 6 contained 4% sucrose and 2% glucose. NC 10 and C 10 contained high fructose corn syrup. Subjects drank more NC 6 than C 6. Fluid consumption was not different among other trials. During all trials, volume consumed and %ΔPV declined while heart rate and rectal temperature increased (p<0.05). No significant differences occurred between beverages for these variables. Percent body weight lost was greater (p<0.05) for the C 10 trial compared to the NC 6 trial. Neither sweat rate, percent fluid replaced, plasma [Na+], [K+], osmolality, percent of drink volume emptied from the stomach, or glucose concentration differed among trials. Plasma [K+] and osmolality increased (p<0.05) over time. Ratings of fullness and thirst were not different among beverages, although both perceptions increased (p<0.05) with time. It is concluded that (a) carbonation decreased the consumption of the 6% CHO beverage; (b) fluid homeostasis and thermoregulation were unaffected by the solutions ingested; and (c) fluid consumption decreased with time, while ratings of fullness and thirst increased.

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Rachel D. Smetanka, C. Patrick Lambert, Robert Murray, Dennis Eddy, Mary Horn, and Carl V. Gisolfi

Abdominal cramping, nausea, diarrhea, and GI bleeding are often reported in long-distance runners. This study set out to determine the effects of prolonged (2-4 hrs) exercise and NSAID ingestion on gastric and intestinal permeability during the first 5 hrs following the 1996 Chicago Marathon. Thirty-four healthy volunteers (20 M, 14 F; ages 30-50) completed the race and ingested the test solution (5 g sucrose, 5 g lactulose, 2 g rhamnose, in 40 ml water) within 10-15 min. The urinary excretion ratio of lactulose/rhamnose was used to assess small intestine permeability; sucrose excretion was used to evaluate gastric impairment. There were no significant differences for mean training mileage, postrace rectal temperature, and percent dehydration between runners who ingested NSAIDs and those who did not. In all, 75% of subjects reported aspirin or ibuprofen ingestion before or during the race. Runners who ingested ibuprofen had significant elevations in urinary lactulose excretion and lactulose/rhamnose ratio, whereas those who ingested aspirin or who did not ingest either NSAID had no significant differences in urinary excretion of lactulose, rhamnose, sucrose, or lactulose/rhamnose ratio compared to resting controls. Thirteen of the 26 NSAID users and 4 of the 8 non-users reported GI symptoms. It is concluded that (a) ibuprofen but not aspirin ingestion during prolonged exercise may increase gastrointestinal permeability and lead to GI symptoms, and (b) prolonged exercise alone can produce GI symptoms.

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Robert A. Oppliger, Scott A. Magnes, LeRoy A. Popowski, and Carl V. Gisolfi

To reduce the adverse consequences of exertion-related and acute intentional dehydration research has focused on monitoring hydration status. This investigation: 1) compared sensitivity of urine specific gravity (Usg), urine osmolality (Uosm) and a criterion measurement of hydration, plasma osmolality (Posm), at progressive stages of acute hypertonic dehydration and 2) using a medical decision model, determined whether Usg or Uosm accurately reflected hydra-tion status compared to Posm among 51 subjects tested throughout the day. Incremental changes in Posm were observed as subjects dehydrated by 5% of body weight and rehydrated while Usg and Uosm showed delayed dehydration-related changes. Using the medical decision model, sensitivity and specificity were not significant at selected cut-offs for Usg and Uosm. At the most accurate cut-off values, 1.015 and 1.020 for Usg and 700 mosm/kg and 800 mosm/kg for Uosm, only 65% of the athletes were correctly classified using Usg and 63% using Uosm. Posm, Usg, and Uosm appear sensitive to incremental changes in acute hypertonic dehydration, however, the misclassified outcomes for Usg and Uosm raise concerns. Research focused on elucidating the factors affecting accurate assessment of hydration status appears warranted.