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Influence of Ingesting a Carbohydrate-Electrolyte Solution before and during a 1-hr Running Performance Test

Ian Rollo and Clyde Williams

The aim of this study was to investigate the influence of ingesting a carbohydrate-electrolyte solution (CHO-E) on performance during a 1-hr treadmill run. Eight male endurance-trained runners (age 31 ± 8 yr, M ± SD) completed three 1-hr performance runs separated by 1 wk. The study used a double-blind placebo (PLA) controlled design. On 2 occasions (P1, P2) runners consumed a placebo solution, 8 ml/kg body mass (BM), 30 min before and 2 ml/kg BM at 15-min intervals throughout the 1-hr run. On a separate occasion they consumed the same quantity of a 6.4% CHO-E solution (C). Total distances covered for P1, P2, and C trials were 13,685 ± 1,116 m, 13,715 ± 1,143 m, and 14,046 ± 1,104 m, respectively. Although there was no difference between the 2 PLA trials (p > .05), the distance covered during the C trial was significantly greater than in either PLA trial (p < .05). CHO ingestion resulted in a higher blood glucose concentration only at the onset of exercise (p < .05) compared with the PLA trials. Blood lactate, respiratory-exchange ratio, and CHO oxidation were similar in all 3 trials. In conclusion, ingestion of a 6.4% CHO-E solution before and during exercise was associated with improved running performance in runners compared with the ingestion of a color- and taste-matched placebo.

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The Metabolic Responses to High Carbohydrate Meals with Different Glycemic Indices Consumed during Recovery from Prolonged Strenuous Exercise

Emma Stevenson, Clyde Williams, and Helen Biscoe

This study investigated the metabolic responses to high glycemic index (HGI) or low glycemic index (LGI) meals consumed during recovery from prolonged exercise. Eight male, trained athletes undertook 2 trials. Following an overnight fast, subjects completed a 90-min run at 70% VO2max. Meals were provided 30 min and 2 h following cessation of exercise. The plasma glucose responses to both meals were greater in the HGI trial compared to the LGI trial (P < 0.05). Following breakfast, there were no differences in the serum insulin concentrations between the trials; however, following lunch, concentrations were higher in the HGI trial compared to the LGI trial (P < 0.05). This suggests that the glycemic index of the carbohydrates consumed during the immediate post-exercise period might not be important as long as sufficient carbohydrate is consumed. The high insulin concentrations following a HGI meal later in the recovery period could facilitate further muscle glycogen resynthesis.

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A Low Glycemic Index Meal before Exercise Improves Endurance Running Capacity in Men

Ching-Lin Wu and Clyde Williams

This study investigated the effects of ingesting a low (LGI) or high (HGI) glyce-mic index carbohydrate (CHO) meal 3 h prior to exercise on endurance running capacity. Eight male recreational runners undertook two trials (LGI or HGI) which were randomized and separated by 7 d. After an overnight fast (12 h) the subjects ingested either a LGI or HGI meal 3 h prior to running at 70% VO2max until exhaustion. The meals contained 2 g/kg body mass CHO and were isocaloric and iso-macronutrient with calculated GI values 77 and 37 for the HGI and LGI respectively. The run times for the LGI and HGI trials were 108.8 ± 4.1 min and 101.4 ± 5.2 min respectively (P = 0.038). Fat oxidation rates were higher during exercise after the LGI meal than after the HGI meal (P < 0.05). In summary, ingestion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal.

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The Influence of a High Carbohydrate Intake during Recovery from Prolonged, Constant-Pace Running

Joanne L. Fallowfield and Clyde Williams

The present study examined the influence of ingesting 3.0 g CHO · kg 1 body mass ⋅ 2  hr 1 after prolonged exercise on recovery and running capacity 4 hr later. Nine men and 8 women completed two trials in a counterbalanced design. Each trial consisted of a 90-min run on a level treadmill at 70% VO 2 max ( R t ) followed by 4 hr recovery (REC) and a further exhaustive run at 70% VO 2 max (R2). During REC, subjects ingested either two feedings of a 6.9% glucose-polymer (GP) solution (D trial) or two feedings of a 19.3% GP solution (C trial). There were no differences in mean (±SE) R 2 run times between the C and D trials or between the male and female subjects. More stable blood glucose concentrations were maintained during REC in the C trial, such that blood glucose was elevated in the C trial in comparison with the D trial after 210 min of REC. It was concluded that increasing postexercise carbohydrate intake from 1.0 to 3.0 g CHO ⋅ Kg 1 body mass 2  hr 1 does not improve endurance capacity 1 hr later.

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Carbohydrate Intake and Recovery from Prolonged Exercise

Joanne L. Fallowfield and Clyde Williams

The influence of increased carbohydrate intake on endurance capacity was investigated following a bout of prolonged exercise and 22.5 hrs of recovery. Sixteen male subjects were divided into two matched groups, which were then randomly assigned to either a control (C) or a carbohydrate (CHO) condition. Both groups ran at 70% VO2max on a level treadmill for 90 min or until volitional fatigue, whichever came first (T1), and 22.5 hours later they ran at the same % VO2max for as long as possible to assess endurance capacity (T2). During the recovery, the carbohydrate intake of the CHO group was increased from 5.8 (±0.5) to 8.8 (±0.1) g kg-1 BW. This was achieved by supplementing their normal diet with a 16.5% glucose-polymer solution. An isocaloric diet was prescribed for the C group, in which additional energy was provided in the form of fat and protein. Run times over T1 did not differ between the groups. However, over T2 the run time of the C group was reduced by 15.57 min (p<0.05), whereas those in the CHO group were able to match their T1 performance. Blood glucose remained stable throughout Tl and T2 in both groups. In contrast, blood lactate, plasma FFA, glycerol, ammonia, and urea increased. Thus, a high carbohydrate diet restored endurance capacity within 22.5 hrs whereas an isocaloric diet without additional carbohydrate did not.

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Improved Recovery from Prolonged Exercise Following the Consumption of Low Glycemic Index Carbohydrate Meals

Emma Stevenson, Clyde Williams, Gareth McComb, and Christopher Oram

This study examined the effects of the glycemic index (GI) of post-exercise carbohydrate (CHO) intake on endurance capacity the following day. Nine active males participated in 2 trials. On day 1, subjects ran for 90 min at 70% VO2max (R1). Thereafter, they were supplied with either a high GI (HGI) or low GI (LGI) CHO diet which provided 8 g CHO/kg body mass (BM). On day 2, after an overnight fast, subjects ran to exhaustion at 70% VO2max (R2). Time to exhaustion during R2 was longer in the LGI trial (108.9 ± 7.4 min) than in the HGI trial (96.9 ± 4.8 min) (P < 0.05). Fat oxidation rates and free fatty acid concentrations were higher in the LGI trial than the HGI trial (P < 0.05). The results suggest that the increased endurance capacity was largely a consequence of the increased fat oxidation following the LGI recovery diet.

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Gastric Emptying of Fluids during Variable-Intensity Running in the Heat

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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The Influence of Carbohydrate Mouth Rinse on Self-Selected Speeds during a 30-min Treadmill Run

Ian Rollo, Clyde Williams, Nicholas Gant, and Maria Nute

The purpose of this study was to examine the influences of a carbohydrate (CHO) mouth rinse on self-selected running speeds during a 30-min treadmill run. Ten endurance-trained men performed 2 trials, each involving a 10-min warm-up at 60% VO2max followed by a 30-min run. The run was performed on an automated treadmill that allowed the spontaneous selection of speeds without manual input. Participants were asked to run at speeds that equated to a rating of perceived exertion of 15, mouth rinsing with either a 6% CHO or taste-matched placebo (PLA) solution. In addition to recording self-selected speeds and total distance covered the authors assessed the runners’ subjective feelings. The total distance covered was greater during the CHO than during the PLA trial (p < .05). Faster speeds selected during the first 5 min of exercise corresponded with enhanced feelings of pleasure when mouth rinsing with the CHO solution. Mouth rinsing with a CHO solution increased total distance covered during a self-selected 30-min run in comparison with mouth rinsing with a color- and tastematched placebo.

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The Effect of Carbohydrate-Electrolyte Beverage Drinking Strategy on 10-Mile Running Performance

Ian Rollo, Lewis James, Louise Croft, and Clyde Williams

The purpose of the current study was to investigate the influence of ingesting a carbohydrate-electrolyte (CHO-E) beverage ad libitum or as a prescribed volume on 10-mile run performance and gastrointestinal (GI) discomfort. Nine male recreational runners completed the 10-mile run under the following 3 conditions: no drinking (ND; 0 ml, 0 g CHO), ad libitum drinking (AD; 315 ± 123 ml, 19 ± 7 g CHO), and prescribed drinking (PD; 1,055 ± 90 ml, 64 ± 5 g CHO). During the AD and PD trials, drinks were provided on completion of Miles 2, 4, 6, and 8. Running performance, speed (km/hr), and 10-mile run time were assessed using a global positioning satellite system. The runners’ ratings of perceived exertion and GI comfort were recorded on completion of each lap of the 10-mile run. There was a significant difference (p < .10) in performance times for the 10-mile race for the ND, AD, and PD trials, which were 72:05 ± 3:36, 71:14 ± 3:35, and 72:12 ± 3.53 min:s, respectively (p = .094). Ratings of GI comfort were reduced during the PD trial in comparison with both AD and ND trials. In conclusion, runners unaccustomed to habitually drinking CHO-E beverages during training improved their 10-mile race performance with AD drinking a CHO-E beverage, in comparison with drinking a prescribed volume of the same beverage or no drinking.

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The Influence of Ingesting a Carbohydrate-Electrolyte Beverage during 4 Hours of Recovery on Subsequent Endurance Capacity

Joanne L. Fallowfield, Clyde Williams, and Rabindar Singh

Recovery from prolonged exercise involves both rehydration and replenishment of endogenous carbohydrate stores. The present study examined the influence of ingesting a carbohydrate-electrolyte (CE) solution following prolonged running, on exercise capacity 4 hr later. Twelve men and 4 women were divided into two matched groups, which were randomly assigned to either a control (P) or a carbohydrate (CHO) condition. Both groups ran at 70% of maximal oxygen uptake ( VO 2 max ) on a level treadmill for 90 min or until volitional fatigue (R,), and they ran at the same % VO 2 max to exhaustion 4 hr later to assess endurance capacity ( R 2 ). The CHO group ingested a 6.9% CE solution providing 1.0 g CHO · kg body weight−1 immediately post-R, and again 2 hr later. The P group ingested equal volumes of a placebo solution. Run times (mean ± SEM) for Rj did not differ between the groups (P 86.3 ± 3.8 min; CHO 87.5 ± 2.5 min). The CHO group ran 22.2 (±3.5) min longer than the P group during R 2 (P 39.8 ± 6.1 min; CHO 62.0 ± 6.2 min) (p < .05). Thus, ingesting a 6.9% carbohydrate-electrolyte beverage following prolonged, constant-pace running improves endurance capacity 4 hr later.