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.
Ian Rollo and Clyde Williams
Joanne L. Fallowfield and Clyde Williams
The present study examined the influence of ingesting 3.0 g CHO ·
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.
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.
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.
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.
Stephen H. Wong, Clyde Williams, and Neville Adams
This randomized, double-blind study examined the effects of rehydration per se and rehydration plus carbohydrate (CHO) ingestion during recovery (REC) on subsequent endurance running capacity. Nine men ran at 70% V̇O2max on a level treadmill for 90 min (Tl) on two occasions, followed by a 4 hour REC and a further exhaustive run at the same speed (T2). During the first 3 hours of REC, subjects drank either a 6.9% CHO-electrolyte solution (CE) or a CHO- and electrolyte-free sweetened placebo (PL) every 30 min. Volumes prescribed were 200% of the fluid lost after Tl. but the actual volume of fluid ingested during the REC ranged from 113–200% and 88.5–200% of the body mass lost for the CE and PL trials (NS). However, positive fluid balance was found in both trials after REC. During T2. run time was 24.3 ± 4.4 min longer in the CE trial (69.3 ± 5.5 vs. 45.0 ± 4.2 min; p < .05). Higher blood glucose concentrations were observed throughout REC in the CE trial. These results suggest that ingesting a CHO-electrolyte solution is more effective in restoring endurance capacity compared to the same large volume of placebo, even though complete rehydration was achieved in both trials.
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 (
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.
Tzai-Li Li, Ching-Ling Wu, Michael Gleeson, and Clyde Williams
The purpose of this study was to determine the effect of pre-exercise high carbohydrate meals with high glycemic index (HGI) or low glycemic index (LGI) on blood leukocyte redistribution during subsequent endurance exercise. Eight male subjects performed a 90-min run on a treadmill at 70% VO2max 3 h after ingesting an isocaloric HGI or LGI meal with GI values of 77 and 37, respectively. Blood counts of leukocytes, and neutrophils and the neutrophil/lymphocyte ratio were significantly lower in LGI than HGI at 90 min of exercise (P < 0.05). The plasma glucose concentrations were significantly higher in LGI than HGI between 15 min and 45 min of exercise. There were, however, no differences in plasma cortisol, growth hormone, and interleukin-6 concentrations between trials. Thus, the GI of a pre-exercise meal influences leukocyte trafficking and plasma glucose but has limited effects on circulating stress hormone and cytokine responses to exercise.