The effect of a carbohydrate-arginine supplement on postexercise muscle glycogen storage was investigated. Twelve well-trained cyclists rode for 2 hr on two separate occasions to deplete theirmuscle glycogen stores. At 0, l, 2, and 3 hr after each exercise bout, the subjects ingested either a carbohydrate (CHO) supplement (1 g carbohydrate/kg body weight) or a carbohydrate-arginine (CHO/AA) supplement (1 g carbohydrate/kg body mass and 0.08 g arginine-hydrochloride/kg body weight). No difference in rate of glycogen storage was found between the CHO/AA and CHO treatments, although significance was approached. There were also no differences in plasma glucose, insulin, or blood lactate responses between treatments. Postexercise carbohydrate oxidation during the CHO/AA treatment was significantly reduced compared to the CHO treatment. These results suggest that the addition of arginine to a CHO supplement reduces the rate of CHO oxidation postexercise and therefore may increase the availability of glucose for muscle glycogen storage during recovery.
Ben B. Yaspelkis III and John L. lvy
Jean-Marc Foricher, Nathalie Boisseau, Nathalie S. Ville, Phanélie M. Berthon, Dominique Bentué-Ferrer, Arlette Gratas-Delamarche and Paul Delamarche
To examine hormonal and metabolic effects of an oral challenge in glucose (≈ 16 g), 15 prepubertal girls performed a 30-min ergocycle test at 60% of Wmax. Among them, 8 ingested an oral glucose challenge between 2 and 3 min after the beginning of the exercise whereas the other 7 girls received no fluid intake. Plasma glucose is influenced by the oral challenge, as the values obtained at the 15th and 30th min are higher than those of the control group. Plasma FFA, catecholamines, and insulin are not significantly modified by the oral challenge. Therefore, it seems that a challenge in glucose at the beginning of a prolonged exercise could avoid a fall in plasma glucose.
Isaiah Trice and Emily M. Haymes
In this study a double-blind design was used to determine the effect of caffeine on time to exhaustion and on associated metabolic and circulatory measures. Eight male subjects ingested either caffeine (5 mg/kg body weight) or a placebo 1 hr prior to exercise at 85-90% of maximum workload. Subjects were encouraged to complete three 30-min intermittent cycling periods at 70 rpm with 5 min rest between each. The exercise was terminated when the subject failed to complete three 30-min periods or failed to maintain 70 rpm for at least 15 s consecutively. Serum free fatty acids, glycerol, blood glucose, lactate, perceived exertion, heart rate, and
Andrew C. Morris, Ira Jacobs, Tom M. McLellan, Abbey Klugerman, Lawrence C.H. Wang and Jiri Zamecnik
The purpose of this study was to examine the effects of ginseng extract ingestion on physiological responses to intense exercise. Subjects performed a control ride (CN) on a cycle ergometer, followed by placebo (PL) and ginseng (GS) treatments. Ginseng was ingested as 8 or 16 mg/kg body weight daily for 7 days prior to trial GS. Venous blood was sampled for FFA, lactate, and glucose analyses. Due to similar findings for both dose groups, the subjects were considered as one group. Lactate, FFA,
John L. Ivy, Peter T. Res, Robert C. Sprague and Matthew O. Widzer
Increasing the plasma glucose and insulin concentrations during prolonged variable intensity exercise by supplementing with carbohydrate has been found to spare muscle glycogen and increase aerobic endurance. Furthermore, the addition of protein to a carbohydrate supplement will enhance the insulin response of a carbohydrate supplement. The purpose of the present study was to compare the effects of a carbohydrate and a carbohydrate-protein supplement on aerobic endurance performance. Nine trained cyclists exercised on 3 separate occasions at intensities that varied between 45% and 75% VO2max for 3 h and then at 85% VO2max until fatigued. Supplements (200 ml) were provided every 20 min and consisted of placebo, a 7.75% carbohydrate solution, and a 7.75% carbohydrate / 1.94% protein solution. Treatments were administered using a double-blind randomized design. Carbohydrate supplementation significantly increased time to exhaustion (carbohydrate 19.7 ± 4.6 min vs. placebo 12.7 ± 3.1 min), while the addition of protein enhanced the effect of the carbohydrate supplement (carbohydrate-protein 26.9 ± 4.5 min, p < .05). Blood glucose and plasma insulin levels were elevated above placebo during carbohydrate and carbohydrate-protein supplementation, but no differences were found between the carbohydrate and carbohydrate-protein treatments. In summary, we found that the addition of protein to a carbohydrate supplement enhanced aerobic endurance performance above that which occurred with carbohydrate alone, but the reason for this improvement in performance was not evident.
Roy L.P.G. Jentjens and Asker E. Jeukendrup
Vanadium compounds have been shown to have insulin-like properties in rats and non-insulin-dependent diabetic humans. The purpose of the present study was to examine whether the effects of acute and short-term administration of vanadyl sulphate (VS) on insulin sensitivity also exist in healthy active individuals. Five male and 2 female participants (age: 24.9 ± 1.5 years; height: 176.1 ± 2.9 cm; body mass: 70.1 ± 2.9 kg) underwent 3 oral glucose tolerance tests (OGTT). The first OGTT was performed to obtain a baseline index of insulin sensitivity (ISI). On the night preceding the second OGTT, participants ingested 100 mg of VS, and the acute effects of VS on ISI were examined. For the next 6 days, participants were instructed to ingest 50 mg of VS twice daily, and a final OGTT was performed on day 7 to determine the short-term effects of VS on ISI. No differences were found in fasting plasma glucose and insulin concentrations after VS administration. Furthermore, ISI after 1 day and 7 days of VS administration was not different compared with baseline ISI (4.8±0.1 vs. 4.7±0.1 vs. 4.7 ± 0.1, respectively). These results demonstrate that there are no acute and short-term effects of VS administration on insulin sensitivity in healthy humans.
Karen Van Proeyen, Monique Ramaekers, Ivo Pischel and Peter Hespel
The purpose of this study was to investigate the effect of Opuntia ficus-indica (OFI) cladode and fruit-skin extract on blood glucose and plasma insulin increments due to high-dose carbohydrate ingestion, before and after exercise. Healthy, physically active men (n = 6; 21.0 ± 1.6 years, 78.1 ± 6.0 kg) participated in a doubleblind placebo-controlled crossover study involving 2 experimental sessions. In each session, the subjects successively underwent an oral glucose tolerance test at rest (OGTTR), a 30-min cycling bout at ~75% VO2max, and another OGTT after exercise (OGTTEX). They received capsules containing either 1,000 mg OFI or placebo (PL) 30 min before and immediately after the OGTTR. Blood samples were collected before (t 0) and at 30-min intervals after ingestion of 75 g glucose for determination of blood glucose and serum insulin. In OGTTEX an additional 75-g oral glucose bolus was administered at t 60. In OGTTR, OFI administration reduced the area under the glucose curve (AUCGLUC) by 26%, mainly due to lower blood glucose levels at t 30 and t 60 (p < .05). Furthermore, a higher serum insulin concentration was noted after OFI intake at baseline and at t 30 (p < .05). In OGTTEX, blood glucose at t 60 was ~10% lower in OFI than in PL, which resulted in a decreased AUCGLUC (–37%, p < .05). However, insulin values and AUCINS were not different between OFI and PL. In conclusion, the current study shows that OFI extract can increase plasma insulin and thereby facilitate the clearance of an oral glucose load from the circulation at rest and after endurance exercise in healthy men.
Stavros A. Kavouras, John P. Troup and Jacqueline R. Berning
To examine the effects of a 3-day high carbohydrate (H-CHO) and low carbohydrate (L-CHO) diet on 45 min of cycling exercise, 12 endurance-trained cyclists performed a 45-min cycling exercise at 82 ± 2% VO2peak following an overnight fast, after a 6-day diet and exercise control. The 7-day protocol was repeated under 2 randomly assigned dietary trials H-CHO and L-CHO. On days 1–3, subjects consumed a mixed diet for both trials and for days 4–6 consumed isocaloric diets that contained either 600 g or 100 g of carbohydrates, for the HCHO and the L-CHO trials, respectively. Muscle biopsy samples, taken from the vastus lateralis prior to the beginning of the 45-min cycling test, indicated that muscle glycogen levels were significantly higher (p < .05) for the H-CHO trial (104.5 ± 9.4 mmol/kg wet wt) when compared to the L-CHO trial (72.2 ± 5.6 mmol/kg wet wt). Heart rate, ratings of perceived exertion, oxygen uptake, and respiratory quotient during exercise were not significantly different between the 2 trials. Serum glucose during exercise for the H-CHO trial significantly increased (p < .05) from 4.5 ± 0.1 mmol · L−1 (pre) to 6.7 ± 0.6 mmol · L−1 (post), while no changes were found for the L-CHO trial. In addition, post-exercise serum glucose was significantly greater (p < .05) for the H-CHO trial when compared to the L-CHO trial (H-CHO, 6.7 ± 0.6 mmol · L−1; L-CHO, 5.2 ± 0.2 mmol · L−1). No significant changes were observed in serum free fatty acid, triglycerides, or insulin concentration in either trial. The findings suggest that L-CHO had no major effect on 45-min cycling exercise that was not observed with H-CHO when the total energy intake was adequate.
Zandrie Hofman, Harm Kuipers, Hans A. Keizer, Erik J. Fransen and Roderique C.J. Servais
This investigation examined the plasma glucose and insulin response in 6 trained athletes after consumption of four commercially available sport feedings 2 hr before as well as immediately after 1 hr of running under common training conditions. Four feedings were compared: Feeding 1, 160 g CHO/400 ml; Feeding 2, 69 g CHO/400 ml; Feeding 3, 69 g CHO + 6 g protein/400 ml; and Feeding 4, solid 69 g CHO + 5 g protein + 4 g fat. Before the training session, there were no differences between the four sport feedings in the area under the glucose and insulin curves and the insulin/glucose ratio. However, after exercise, Feeding 2 resulted in a significantly greater area under the glucose curve compared with Feedings 1, 3, and 4 (respectively, 352 vs. 241, 251, and 182) and a significantly lower insulin/glucose ratio compared with Feeding 1 (respectively, 6.2 vs. 15.8). Therefore, it is concluded that the kind of sport feeding may influence postexercise glucose and insulin responses.
James R. Rowe, Kyle D. Biggerstaff, Vic Ben-Ezra, David L. Nichols and Nancy DiMarco
This study examined the effect of prior exercise on postprandial lipemia (PPL) concentration following a mixed meal (MM) made with either glucose or fructose. Sedentary women completed four trials in random order: 1) Rest-Fructose: RF, 2) Rest-Glucose: RG, 3) Exercise-Fructose: EF, 4) Exercise-Glucose: EG. Exercise expended 500 kcal while walking at 70%VO2max. Rest was 60 min of sitting. The morning after each trial, a fasting (12 hr) blood sample was collected followed by consumption of the MM. The MM was blended with whole milk and ice cream plus a glucose or fructose powder. Glucose and fructose powder accounted for 30% of the total kcal within the MM. Blood was collected periodically for 6 hr post-MM and analyzed for PPL. Magnitude of PPL over the 6 hr postmeal was quantified using the triglyceride incremental area under the curve (TG AUCI). Significant differences (p < .05) between trials were determined using repeated-measures ANOVA and Bonferroni post hoc test. There was no significant difference in the TG AUCI between the four trials (p > .05). A significant trial by time interaction for TG concentration was reported (p < .05). Despite lack of change in the AUCI with prior exercise, the lower TG concentration at multiple time points in the EG trial does indicate that prior exercise has some desirable effect on PPL. This study suggests that replacing fructose with glucose sugars and incorporating exercise may minimize PPL following a mixed meal but exercise will need to elicit greater energy expenditure.