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Melanie A. Mason, Anne C. Russ, Ryan T. Tierney, and Jamie L. Mansell

Islets of Langerhans. 2 , 3 Once the β cells are destroyed, the pancreas no longer produces insulin, which is a vital hormone responsible for maintenance of blood glucose levels. 3 Insulin is needed for intracellular transport of glucose into various tissues (e.g., muscle, adipose), which allows for

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Randall L. Wilber and Robert J. Moffatt

Ten trained male runners performed a treadmill exercise test at 80% VO2max under two experimental conditions, carbohydrate (CHO, 7% carbohydrate) and placebo (P), to determine the effect of carbohydrate ingestion on endurance performance (treadmill run time), blood glucose concentration, respiratory exchange ratio (RER), and subjective ratings of perceived exertion (RPE). Treatment order was randomized and counterbalanced and test solutions were administered double-blind. Ingestion took place 5 min preexercise (250 ml) and at 15-min intervals during exercise (125 ml). Performance was enhanced by 29.4% (p ~ 0.05) during CHO (115 ±25 min) compared to P (92 ± 27 min). Blood glucose concentration was significantly greater during CHO (5.6 ± 0.9 mM) relative to P (5.0 ±0.7 mM). There was a significant increase in mean RER following CHO ingestion (.94±.01) compared to P (.90±.01). Average RPE was significantly less during CHO (14.5±2.3) relative to P (15.4±2.4). These data suggest that time to exhaustion of high-intensity treadmill exercise is delayed as a result of carbohydrate ingestion and that this effect is mediated by favorable alterations in blood glucose concentration and substrate utilization.

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Robert A. Robergs, Susie B. McMinn, Cristine Mermier, Guy Leadbetter III, Brent Ruby, and Chris Quinn

This study was conducted to compare blood glucose and glucoregulatory hormone responses to the ingestion of solid and liquid carbohydrate (CHO) during prolonged cycling, followed by 30 min of isokinetic cycling. Eight male cyclists randomly completed three cycling trials (LC = liquid CHO, SCE = solid CHO with water equal to LC, SCA = solid CHO + ad libitum water). Each subject cycled for 120 min at 65% of VO2max with CHO ingestion (0.6 g CHO/kg/hr) at 0, 30, 60, 90, and 120 min. Subjects then completed a 30-min maximal isokinetic ride at 90 rpm. There was no significant (p < .05) difference between the trials for plasma glucose, insulin, glucagon, glycerol, lactate, RER, HR, VO2 RPE, and total work performed during the isokinetic ride. However, serum glucose was significantly lower in the SCE and SCA trials compared to LC at 80 min. The ingestion of a solid food containing CHO. protein, and fat with added water produced similar blood glucose, metabolic, glucoregulatory hormone, and exercise performance responses to those seen with the ingestion of liquid CHO.

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Joel B. Mitchell, Paul C. DiLauro, Francis X. Pizza, and Daniel L. Cavender

The purpose of this study was to determine the effect of a high vs. a low preexercise carbohydrate (CHO) diet on performance during multiple sets of resistance exercise. Eleven resistance-trained males performed cycle ergometry to deplete quadriceps muscle glycogen stores, followed by 48 hr of a high (HICHO) or a low (LOCHO) CHO diet. Subjects then performed five sets each of squats, leg presses, and knee extensions (resistance = 15 RM) to failure. Blood samples were taken before and during exercise for determination of glucose and lactate (LA). No differences in performance (repetitions X weight lifted) were observed (HICHO = 15,975±1,381 and LOCHO = 15,723±1,231 kg). Blood glucose was significantly higher after exercise for HICHO compared to LOCHO (HICHO = 4.8 ± 0.2 vs. LOCHO = 3.9 ± 0.2 mmol·L−1). No differences in LA accumulation were observed. The data indicated that preexercise CHO status did not affect resistance exercise performance. Further, the differences in blood glucose and the similarity in LA responses suggest that glycolysis was maintained in the LOCHO condition, and there may have been an increased reliance on blood glucose when preexercise CHO status was low.

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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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Penelope M. Warwick

The purpose of the study was to investigate thermic and glycemic responses to conventional meals with and without prior low-intensity exercise. Fourteen healthy volunteers (7 men, 7 women) undertook 4 treatments, 2 bread and 2 pasta meals, either with (E) or without (NE) prior exercise (a 45-min treadmill walk). Meals provided 58 g carbohydrate and 2360 kJ. Energy expenditure and blood-glucose concentrations were measured before and for 3 h after the meals. The thermic effect of food (TEF) was lower after pasta (121 ± 32 kJ/3 h) than after bread (154 ± 62 kJ/3 h), P = 0.009, but was not affected by exercise. Glycemic responses were lower after E (155 ± 113 mmol·L−1 ·3 h−1) than NE (199 ± 97 mmol·L−1 · 3 h−1) after pasta (P = 0.020) but not after bread. TEF was lower after pasta than bread but was not affected by prior low-intensity exercise. The effects of exercise on glycemic responses to meals were inconsistent.

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Jie Kang, Robert J. Robertson, Bart G. Denys, Sergio G. DaSilva, Paul Visich, Richard R. Suminski, Alan C. Utter, Fredric L. Goss, and Kenneth F. Metz

This investigation determined whether carbohydrate ingestion during prolonged moderate-intensity exercise enhanced endurance performance when the exercise was preceded by carbohydrate supercompensation. Seven male trained cyclists performed two trials at an initial power output corresponding to 71 ± 1 % of their peak oxygen consumption. During the trials, subjects ingested either a 6% glucose/sucrose (C) solution or an equal volume of artificially flavored and sweetened placebo (P) every 20 min throughout exercise. Both C and P were preceded by a 6-day carbohydrate supercompensation procedure in which subjects undertook a depletion-taper exercise sequence in conjunction with a moderate- and high-carbohydrate diet regimen. Statistical analysis of time to exhaustion, plasma glucose concentration, carbohydrate oxidation rate, fat oxidation rate, and plasma glycerol concentration indicated that in spite of a carbohydrate supercompensation procedure administered prior to exercise, carbohydrate ingestion during exercise can exert an additional ergogenic effect by preventing a decline in blood glucose levels and maintaining carbohydrate oxidation during the later stages of moderate-intensity exercise.

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Joel B. Mitchell, James R. Rowe, Meena Shah, James J. Barbee, Austen M Watkins, Chad Stephens, and Steve Simmons

To examine the effect of prior exercise on the postprandial lipid response to a high-carbohydrate meal in normal-weight (NW = BMI h25) and overweight (OW = BMI ≥25) women (age 18–25), 10 NW and 10 OW participants completed 2 conditions separated by 1 month. In the morning, the day after control (CT = no exercise) or exercise conditions (EX = 60 min cycling at 60% VO2peak), participants consumed a high-carbohydrate meal (80% CHO, 15% protein, 5% fat; 75 kJ/kg BM) followed by 6 hr of hourly blood sampling. Blood was analyzed for triglycerides (TG), blood glucose (BG), and insulin (IN). TG levels over the 6-hr period were lower in NW than OW (p = .021) and lower in EX than in CT (p = .006). Area under the curve (AUC) for TG was lower in NW than OW (p = .016) and EX than CT (p = .003). There were nonsignificant tendencies for reduced BG over time (p = .053) and AUC (p = .083), and IN AUC was lower in EX than in CT (p = .040) for both groups and lower in NW than in OW (p = .039). Prior exercise improved TG levels after a high-carbohydrate meal in both groups, and OW women demonstrated a greater postprandial lipemic response than NW regardless of condition. There were tendencies for improved glucose removal with prior exercise in NW vs. OW. Acute exercise can improve postprandial TG responses and might also improve postprandial BG and IN after a large meal in NW and OW young women.

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Michael C. Riddell, Oded Bar-Or, Beatriz V. Ayub, Randolph E. Calvert, and George J.F. Heigenhauser

There are currently no guidelines regarding the carbohydrate (CHO) dosage required to prevent exercise-induced hypoglycemia in children with insulin-dependent diabetes mellitus (IDDM). To prevent hypoglycemia by matching glucose ingestion with total-CHO utilization, 20 adolescents with IDDM attended 2 trials: control (CT; drinking water) and glucose (GT; drinking 6-8% glucose). Participants performed 60 min of moderate-intensity cycling 100 min after insulin injection and breakfast. CT's total-CHO utilization during exercise was determined using indirect calorimetry. In GT, participants ingested glucose in the amount equal to total CHO utilization in the CT. A total of 9 participants had BG <4.0 mmol/L in CT compared to 3 in GT (p < .05). In conclusion, glucose ingestion equal to total-CHO utilization attenuates the drop in blood glucose and reduces the likelihood of hypoglycemia during exercise in adolescents with IDDM.

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Jennifer M. Sacheck, Helen M. Rasmussen, Meghan M. Hall, Tamar Kafka, Jeffrey B. Blumberg, and Christina D. Economos

To investigate the association between pregame snacks varying in macronutrient content and exercise intensity, physiological stress, and fatigue in young soccer players. One hour before a 50-min soccer game, children (n = 79; 9.1 ± 0.8 y) were randomly assigned to consume a raisin-, peanut-butter-, or cereal-based snack. Body mass index, blood glucose, and salivary measures of stress (cortisol and immunoglobulin A-IgA) were measured pre- and post-game. Exercise intensity was measured by accelerometry. Self-administered questionnaires were used to assess diet quality and fatigue. Analysis of covariance was used to examine the relationship between pregame snacks and biochemical outcomes. Postgame glucose and cortisol increased [12.9 ± 21.3 mg/dL (p < .001) and 0.04 ± 0.10 μg/dL (p < .05), respectively] and IgA decreased −2.3 ± 9.6 μg/mL; p < .001) from pregame values. The pregame snack was not associated with exercise intensity or post-game outcome; however, children consuming the cereal-based (high-sugar and high-glycemic index (GI)) snack exercised more intensely than the 2 lower-GI snack groups (p < .05). Children who consumed the high-sugar, high-GI snack also reported more symptoms of fatigue (p < .05). A high-sugar, high-GI pregame snack was associated with exercise intensity and fatigue but not changes in blood sugar or stress biomarkers following a soccer game in children.