Effect of fructose ingestion on muscle glycogen usage during exercise

Eight healthy males were studied to compare the effects of preexercise fructose and glucose ingestion on muscle glycogen usage during exercise. Subjects performed three randomly assigned trials, each involving 30 min of cycling exercise at 75% VO2max. Forty-five min prior to commencing each trial, subjects ingested either 50 g of glucose (G), 50 g of fructose (F), or sweet placebo (C). No differences in VO2 or respiratory exchange ratio were observed between the trials. Blood glucose was elevated (P less than 0.05) as a result of the glucose feeding. With the onset of exercise, blood glucose declined rapidly during G, reaching a nadir of 3.18 +/- 0.15 (SE) mmol X 1(-1) at 20 min of exercise. This value was lower (P less than 0.05) than the corresponding values in F (3.79 +/- 0.20) and C (3.99 +/- 0.18). No differences in exercise blood glucose levels were observed between F and C. Muscle glycogen utilization was greater (P less than 0.05) during G (55.4 +/- 3.3 mmol X kg-1 w.w.) than C (42.8 +/- 4.2). No difference was observed between F (45.6 +/- 4.3) and C. There was a trend (P = 0.07) for muscle glycogen usage to be lower during F than G. These results suggest that the adverse effects of preexercise glucose ingestion are, in general, not observed with either fructose or sweet placebo.     

Exercise and newer insulins: how much glucose supplement to avoid hypoglycemia?

PURPOSE: To determine the glucose supplement required to prevent hypoglycemia during moderate-intensity exercise in Type 1 diabetic patients using newer analog insulins. METHODS: Nine subjects performed 60 min of ergocycle exercise (50% VO2max), 3 h after a standard breakfast in three different conditions. Subjects were randomly assigned to preexercise liquid glucose supplement of 0 g of glucose (0G), 15 g of glucose (15G), and 30 g of glucose (30G). Blood glucose (BG) was measured before, during, and following the exercise. All subjects used Humulin N (N) and analog insulin Humalog (Lispro). A dextrose infusion was initiated when BG fell below 5 mmol x L(-1). RESULTS: There was no significant difference in the magnitude of the decrease in BG exercise-induced when comparing the three experimental conditions. However, the quantity of dextrose infused was significantly higher in the 0G (10.5 +/- 3.2 g) than in the 15G (3.5 +/- 1.8 g) or the 30G conditions (1.6 +/- 1.0 g). The addition of a glucose supplement (15G or 30G) significantly prolonged the delay before the need for dextrose infusion (31.7 +/- 7.5, 51.3 +/- 4.2, and 55.6 +/- 2.6 min; 0G, 15G, and 30G, respectively). The quantity of dextrose infusion was plotted against the three preexercise glucose supplements and a regression equation obtained. Solving this equation, a glucose supplement of 40 g was estimated in order to maintain BG levels within the normal range during and after exercise. CONCLUSION: For 60 min of late postprandial exercise followed by 60 min of recovery, an estimated 40 g of a liquid glucose supplement, ingested 15 min prior exercise, would seem likely to help maintain safe BG levels in subjects using N-Lispro.     

Oxidation of exogenous carbohydrate during prolonged exercise in fed and fasted conditions

The oxidation of glucose and fructose ingested during moderate exercise performed on a cycle ergometer (120 min, 52% VO2max) was compared in ten young males fasted (n = 5) or fed (n = 5) before exercise. The subjects ingested randomly 1.33 g/kg body weight (approximately 96 +/- 9 g) of either enriched 13C-glucose (G), 13C-fructose (F), or water only (W); the solutions were evenly distributed over the exercise period. The fasted subjects began the three exercises with a lower blood glucose (P less than or equal to 0.05 for F only) and insulin (P less than or equal to 0.05) levels and a higher free fatty acid (FFA) concentration (P less than or equal to 0.05) than the fed ones. Throughout the exercise period, blood glucose level was maintained in fasted as well as in fed group for G and F ingestions, while it decreased (P less than or equal to 0.05 at the 100th min in fasted subjects) with water ingestion. Insulin level was similar in both fed and fasted conditions with F and W ingestions and lower than G trials for the fed subjects. For the three ingestions, FFA was lower (P less than or equal to 0.05) in the fasted than in the fed group over the exercise period. Over the 2-h period of exercise, a greater (P less than or equal to 0.05) amount of exogenous F was oxidized in the fasted (49 +/- 6 g) than in the fed (36 +/- 5 g) group, which represent 31% and 20% of the total carbohydrate energy supply, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of pre-exercise fructose ingestion on endurance performance in fed men

Twelve trained males, in a fed state, were studied to examine the effect of pre-exercise fructose ingestion on endurance capacity during prolonged cycling exercise. Sixty minutes prior to exercise, subjects ingested either 60 or 85 g fructose or a sweet placebo. Mean exercise intensity initially required 62% of the maximal aerobic power and thereafter increased to elicit 72 and 81% of maximal aerobic power at 90 and 120 min of exercise, respectively. Exercise time (mean +/- SE) to exhaustion was significantly increased after fructose ingestion, as compared to placebo ingestion (145 +/- 4 vs 132 +/- 3 min, P less than 0.01). During the exercise, no differences were observed between both trials for oxygen uptake, heart rate, or perceived exertion. Serum glucose and insulin levels between both trials were not significantly different throughout the experiment. There were also no significant differences in serum-free fatty acids and glycerol levels as well as respiratory exchange ratio between fructose and placebo trials during the exercise. The results suggest that fructose ingestion is of benefit before prolonged exercise, because it provides a carbohydrate source to contracting muscles without transient hypoglycemia and a depression of fat utilization, and thereby delays the fatigue.     

Comparaison de l'oxydation de glucose, d'un mélange de glucose et de fructose, et de saccharose ingérés en bolus ou en doses fractionnées au cours de l'exercice

The purpose of this study was to compare the oxidation rates ofisocaloric amounts of glucose (G), of a mixture of glucose and fructose (G+F), and of sucrose (S) ingested during prolonged exercise (120 min, 58 % V0₂max). The mode of ingestion, that is in a bolus at the onset of exercise or in fractionated doses during the exercise, was also investigated. Six young male subjects ingested a placebo (P), 100 g of G, 50 g of G + 50 g of F, or 95 g of S (13 % concentration) in fractionated doses during exercise, and 100 g of G and 50 g of G + 50 g of F in a bolus at the beginning of exercise. Blood samples were taken before and during the last minute of exercise period. Ingestion of carbohydrates (CHO) does not influence the blood glucose and insulin levels, but decreases by 50% the response of plasma free fatty acid concentration. During the 120-min exercise period, the amounts of ingested carbohydrates which were oxidized were similar for G (53 ± 5 g), G+F (57 ± 6 g) and S (50 ± 7 g). Exogenous CHO oxidation contributed to increasing the total CHO utilization (from 181 to 200 g/120 min) and to reducing fat oxidation (from 86 to 72 g/120 min). Ingestion of CHO as a bolus at the beginning of exercise does not influence G oxidation (58 ± 6 g) but significantly increased the oxidation of the mixture G+F (67 ± 6), probably by favoring fructose utilization which requires a delay. From a practical viewpoint, these results show that the oxidation of S, which is the most widely available oligosaccharide, is similar to that of G or a mixture of G+F. Moreover, in order to maximize exogenous CHO oxidation during exercise, CHO should be ingested early in the exercise period, and not in fractionated doses throughout the exercise period.     

High oxidation rates from combined carbohydrates ingested during exercise

Studies that have investigated oxidation of a single carbohydrate (CHO) during exercise have reported oxidation rates of up to 1 g x min(-1). Recent studies from our laboratory have shown that a mixture of glucose and sucrose or glucose and fructose ingested at a high rate (1.8 g x min(-1)) leads to peak oxidation rates of approximately 1.3 g x min(-1) and results in approximately 20 to 55% higher exogenous CHO oxidation rates compared with the ingestion of an isocaloric amount of glucose. PURPOSE: The purpose of the present study was to examine whether a mixture of glucose, sucrose and fructose ingested at a high rate would result in even higher exogenous CHO oxidation rates (>1.3 g x min(-1)). METHODS: Eight trained male cyclists (VO2max: 64 +/- 1 mL x kg(-1) BM x min(-1)) cycled on three different occasions for 150 min at 62 +/- 1% VO2max and consumed either water (WAT) or a CHO solution providing 2.4 g x min(-1) of glucose (GLU) or 1.2 g x min(-1) of glucose + 0.6 g x min(-1) of fructose + 0.6 g x min(-1) of sucrose (MIX). RESULTS: High peak exogenous CHO oxidation rates were found in the MIX trial (1.70 +/- 0.07 g x min(-1)), which were approximately 44% higher (P < 0.01) compared with the GLU trial (1.18 +/- 0.04 g x min(-1)). Endogenous CHO oxidation was lower (P < 0.05) in MIX compared with GLU (0.76 +/- 0.12 and 1.05 +/- 0.06 g x min(-1), respectively). CONCLUSION: When glucose, fructose and sucrose are ingested simultaneously at high rates (2.4 g x min(-1)) during cycling exercise, exogenous CHO oxidation rates can reach peak values of approximately 1.7 g x min(-1) and estimated endogenous CHO oxidation is reduced compared with the ingestion of an isocaloric amount of glucose.     

Superior endurance performance with ingestion of multiple transportable carbohydrates

INTRODUCTION: The aim of the present study was to investigate the effect of ingesting a glucose plus fructose drink compared with a glucose-only drink (both delivering carbohydrate at a rate of 1.8 g.min(-1)) and a water placebo on endurance performance. METHODS: Eight male trained cyclists were recruited (age 32 +/- 7 yr, weight 84.4 +/- 6.9 kg, .VO(2max) 64.7 +/- 3.9 mL.kg(-1).min(-1), Wmax 364 +/- 31 W). Subjects ingested either a water placebo (P), a glucose (G)-only beverage (1.8 g.min(-1)), or a glucose and fructose (GF) beverage in a 2:1 ratio (1.8 g.min(-1)) during 120 min of cycling exercise at 55% Wmax followed by a time trial in which subjects had to complete a set amount of work as quickly as possible (approximately 1 h). Every 15 min, expired gases were analyzed and blood samples were collected. RESULTS: Ingestion of GF resulted in an 8% quicker time to completion during the time trial (4022 s) compared with G (3641 s) and a 19% improvement compared with W (3367 s). Total carbohydrate (CHO) oxidation was not different between GF (2.54 +/- 0.25 g.min(-1)) and G (2.50 g.min(-1)), suggesting that GF led to a sparing of endogenous CHO stores, because GF has been shown to have a greater exogenous CHO oxidation than G. CONCLUSION: Ingestion of GF led to an 8% improvement in cycling time-trial performance compared with ingestion of G.     

Effect of carbohydrate feeding frequencies and dosage on muscle glycogen use during exercise

Nine men were studied during three 4-h cycling bouts to determine the effect of frequency and dosage of solid carbohydrate (CHO) feedings (86 g) on muscle glycogen utilization and exercise performance. In the frequency trial (F), the subjects ingested 10.75 g of CHO along with 200 ml of water at 30-min intervals; in the dosage trial (D), the subjects ingested 21.5 g of CHO with 400 ml of water at 60-min intervals. During the control trial (C), the subjects ingested 400 ml of an artificially sweetened placebo at 60-min intervals. Respiratory exchange ratios were significantly elevated in both trials D and F (P less than 0.05). Blood glucose was significantly elevated in trial D 20 min post-feeding but had returned to control levels by 50 min. In trial F, blood glucose was maintained at a constant level throughout the entire 4 h. In trial C, blood glucose declined steadily during the entire 4 h. Despite the differences in blood glucose levels between the three trials, there were no significant differences in the rate of muscle glycogen utilization in any of the trials (D = 82.9 +/- 6.6 [SE] mmol X kg-1 vs C = 80.9 +/- 6.9 mmol X kg-1 vs F = 74.4 +/- 12.2 mmol X kg-1). In a sprint ride (100% VO2max) to exhaustion at the end of each trial, the subjects performed significantly longer in trial F compared to C (120.97 +/- 9.6 vs 81.0 +/- 7.1 s).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis

The effect of repeated ingestions of fructose, sucrose, and various amounts of glucose on muscle glycogen synthesis during the first 6 h after exhaustive bicycle exercise was studied. Muscle biopsies for glycogen determination were taken before and after exercise, and every second hour during recovery. Blood samples for plasma glucose and insulin determination were taken before and after exercise, and every hour during recovery. When 0.35 (low glucose: N = 5), 0.70 (medium glucose: N = 5), or 1.40 (high glucose: N = 5) g.kg-1 body weight of glucose were given orally at 0, 2, and 4 h after exercise, the rates of glycogen synthesis were (mean +/- SE) 2.1 +/- 0.5, 5.8 +/- 1.0, and 5.7 +/- 0.9 mmol.kg-1.h-1, respectively. When 0.70 g.kg-1 body weight of sucrose (medium sucrose: N = 5), or fructose (medium fructose: N = 7) was ingested accordingly, the rates were 6.2 +/- 0.5 and 3.2 +/- 0.7 mmol.kg-1.h-1. Average plasma glucose level during recovery were similar in low glucose, medium glucose, and high glucose groups (5.76 +/- 0.24, 6.31 +/- 0.64, and 6.52 +/- 0.24 mM), while average plasma insulin levels were higher with higher glucose intake (16 +/- 1, 21 +/- 3, and 38 +/- 4 microU.ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of pre-exercise carbohydrate feedings on endurance cycling performance

Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 +/- 5.2 min, FRU = 90.6 +/- 12.4, and GLU = 92.8 +/- 11.3, mean +/- SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 +/- 0.34 mmol X l-1 at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 +/- 8.2 mmol X kg-1 wet weight, FRU = 56.3 +/- 3.0 mmol X kg-1 wet weight, GLU = 50.0 +/- 4.9 mmol X kg-1 wet weight) and total glycogen use (CON = 93.4 +/- 11.1, FRU = 118.8 +/- 10.9, and GLU = 99.5 +/- 4.3) were similar in the three trials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxidation of corn starch, glucose, and fructose ingested before exercise

The purpose of this study was to compare the metabolic and endocrine responses, and the amounts of exogenous carbohydrate oxidized, during prolonged moderate cycle ergometer exercise (120 min, 60% VO2max), preceded by ingestion of 13C enriched glucose (G), fructose (F), or pure corn starch (S) (1,592 kJ ingested with 400 ml of water, 60 min before the beginning of exercise) in six healthy young male subjects. Plasma glucose and insulin concentrations significantly increased in response to G and S feeding. The high plasma insulin values resulted in a significant transient reduction in plasma glucose concentration in the first hour of exercise and blunted the response of plasma free fatty acid and glycerol concentrations, when compared to the values observed with F ingestion, which did not modify plasma glucose or insulin concentrations. Over the 2 h exercise period, the percentages of exogenous G (67 +/- 9%) and S (73 +/- 8%) oxidized were not significantly different but were significantly higher than the percentage of exogenous F oxidized (54 +/- 6%). These results confirm that 1) exogenous F is less readily available for oxidation than G or S and 2) pure corn starch does not offer any advantage over glucose as a pre-exercise meal.     

Pre-exercise glucose ingestion at different time periods and blood glucose concentration during exercise

The purpose of this study was to investigate the effects of glucose ingestion (GI) at different time periods prior to exercise on blood glucose (BG) levels during prolonged treadmill running. Eight subjects (X+/-SD), age 20+/-0.5yr, bodymass 70.7+/-4.1 kg, height 177+/-4 cm, VO2max 52.8+/-7.8 ml x kg(-1) x min(-1) who underwent different experimental conditions ingested a glucose solution (1 g/kg at 350 ml) 30 min (gl-30), 60 min (gl-60), 90 min (gl-90), and a placebo one 60 min (pl-60) prior to exercise in a counterbalanced design. Afterwards they ran at 65% of VO2max for 1 hour and then at 75 % of VO2max till exhaustion. Fingertip blood samples (10 microl) were drawn every 15 min before and during exercise for the determination of BG levels. Oxygen uptake (VO2), heart rate (HR), and blood lactate (La) were also measured every 15 min during exercise. Peak BG values were reached within 30 min after GI but were different (p < 0.01) at the onset of exercise (gl-30: 147+/-22, gl-60: 118+/-25, gl-90: 109+/-22, pl-60: 79+/-5mg/dl). The two-way ANOVA repeated measures and the Tukey post-hoc test revealed a higher BG concentration (p < 0.05) for the gl-30 and the pl-60 as compared to the gl-60 and gl-90 during running (e.g. 15min run: 82+/-11, 68+/-5, 64+/-3, 78+/-7, and 60min run: 98+/-12, 85+/-12, 83+/-11, 94+/-11 mg/dl for gl-30, gl-60, gl-90, and pl-60, respectively). However, this did not significantly affect the duration of treadmill running. The La levels were higher (p < 0.05) after GI as compared to placebo throughout exercise (values at exhaustion: 4.6+/-0.2, 5.0+/-1.5, 4.8+/- 1.7 mmol/l for gl-30, gl-60, gl-90, and 3.5+/-0.8 mmol/l for placebo). The gl-30 and the placebo fluctuated closer to normoglycaemic levels. The glucose ingestion (60 to 90 min) prior to exercise lowered the blood glucose levels without affecting the duration of running performance at 75% VO2max. Thus, in order to maintain normoglycaemic levels, pre-exercise glucose supplementation should be given 30 min before the onset of exercise.     

Effect of carbohydrate feeding during recovery from prolonged running on muscle glycogen metabolism during subsequent exercise

This study examined the effect of carbohydrate (CHO) intake during a 4 h recovery from prolonged running on muscle glycogen metabolism during subsequent exercise. On 2 occasions, 7 male subjects ran for 90 min at 70 % maximum oxygen uptake VO(2 max) on a motorized treadmill (R1) followed by a 4 h rest period (REC) and a 15 min run (R2) consisting of 5 min at 60 % and 10 min at 70 % VO(2 max) During REC, each subject ingested a total of 2.7 l of an isotonic solution containing either 50 g of CHO (LOW) or 175 g of CHO (HIGH). Biopsy samples were obtained from the vastus lateralis immediately after R1, REC and R2. During REC, a higher muscle glycogen resynthesis was observed in HIGH when compared with LOW trial (75 +/- 20 vs. 31 +/- 11 mmol x kg dry matter (dm) -1, respectively; p < 0.01). Muscle glycogen utilization during R2 was similar between the HIGH and LOW trials (39 +/- 10 vs. 46 +/- 11 mmol x kg dm -1, respectively). These results suggest that ingestion of a large amount of CHO at frequent intervals during recovery from exercise does not affect the rate of muscle glycogen utilization during subsequent exercise.     

Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes.

The aim of this study was to determine whether or not variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age: 33+/-5 years, mass: 74+/-4 kg, VO2max: 62+/-5 mL kg(-1) min(-1), maximal aerobic power: 392+/-17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating +/-15%, +/-5%, and +/-10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal voluntary activation level and excitation-contraction coupling process of knee extensor muscles were evaluated before and immediately after the exercise using the technique of electrically evoked contractions (single and paired stimulations). Oxygen uptake, ventilation and heart rate were also measured at regular intervals during the exercise. Averaged metabolic variables were not significantly different between the two conditions. Similarly, reductions in MVC torque (approximately -11%, P<0.05) after cycling were not different (P>0.05) between CP and VP trials. The magnitude of central and peripheral fatigue was also similar at the end of the two cycling exercises. It is concluded that, following 30 min of endurance cycling, semi-elite triathletes experienced no additional neuromuscular fatigue by varying power (from +/-5% to 15%) compared with a protocol that involved a constant power.     

Oxidation of combined ingestion of maltodextrins and fructose during exercise

PURPOSE: To determine whether combined ingestion of maltodextrin and fructose during 150 min of cycling exercise would lead to exogenous carbohydrate oxidation rates higher than 1.1 g.min. METHODS: Eight trained cyclists VO2max: 64.1 +/- 3.1 mL.kg.min) performed three exercise trials in a random order. Each trial consisted of 150 min cycling at 55% maximum power output (64.2+/-3.5% VO2max) while subjects received a solution providing either 1.8 g.min of maltodextrin (MD), 1.2 g.min of maltodextrin + 0.6 g.min of fructose (MD+F), or plain water. To quantify exogenous carbohydrate oxidation, corn-derived MD and F were used, which have a high natural abundance of C. RESULTS: Peak exogenous carbohydrate oxidation (last 30 min of exercise) rates were approximately 40% higher with combined MD+F ingestion compared with MD only ingestion (1.50+/-0.07 and 1.06+/-0.08 g.min, respectively, P<0.05). Furthermore, the average exogenous carbohydrate oxidation rate during the last 90 min of exercise was higher with combined MD+F ingestion compared with MD alone (1.38+/-0.06 and 0.96+/-0.07 g.min, respectively, P<0.05). CONCLUSIONS: The present study demonstrates that with ingestion of large amounts of maltodextrin and fructose during cycling exercise, exogenous carbohydrate oxidation can reach peak values of approximately 1.5 g.min, and this is markedly higher than oxidation rates from ingesting maltodextrin alone.     

Carbohydrate-electrolyte ingestion during intermittent high-intensity running.

PURPOSE: The purpose of this study was to examine the effects of ingesting a carbohydrate-electrolyte beverage or a noncarbohydrate placebo on muscle glycogen utilization during 90 min of intermittent high-intensity running. METHODS: Six trained games players (age 24.6 +/- 2.2 yr; height 179.6 +/- 1.9 cm; body mass 74.5 +/- 2.0 kg; VO2max 56.3 +/- 1.3 mL x kg(-1) x min(-1); mean +/- SEM) performed two exercise trials, 7 d apart. The subjects were university soccer, hockey, or rugby players. On each occasion, they completed six 15-min periods of intermittent running, consisting of maximal sprinting, interspersed with less intense periods of running and walking. During each trial, subjects consumed either a 6.9% carbohydrate-electrolyte solution (CHO-E: the CHO trial) or a noncarbohydrate placebo (the CON trial) immediately before exercise (5 mL x kg(-1) BM) and after every 15 min of exercise thereafter (2 mL x kg(-1) BM). Drinks were administered in a double-blind, counter-balanced order, and the total volume of fluid consumed during each trial was 1114 +/- 30 mL. Needle biopsy samples were obtained from the vastus lateralis muscle before and after 90 min of exercise. Venous blood samples were collected from an antecubital vein at rest and every 30 min during exercise. RESULTS: Muscle glycogen utilization in mixed muscle samples was lower (P < 0.05) during CHO [192.5 +/- 26.3 mmol glucosyl units (kg x DM(-1))] than CON [245.3 +/- 22.9 mmol glucosyl units (kg x DM(-1))]. Single fiber analysis on the biopsy samples of the subjects during the CON trial showed a greater glycogen utilization in the Type II fibers compared with Type I fibers during this type of exercise [Type I: 182.2 +/- 34.5 vs Type II: 287.4 +/- 41.2 mmol glucosyl units (kg x DM(-1)); P < 0.05). After 30 min of exercise, blood lactate was significantly greater (P < 0.05) and serum insulin concentration lower (P < 0.05) in CON. CONCLUSIONS: In summary, when trained games players ingested a carbohydrate-electrolyte beverage, muscle glycogen utilization was reduced by 22% when compared with a control condition.     

Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement

PURPOSE: This study assessed whether liquid carbohydrate-protein (C+P) supplements, ingested early during recovery, enhance muscle glycogen resynthesis versus isoenergetic liquid carbohydrate (CHO) supplements, given early or an isoenergetic solid meal given later during recovery (PLB). METHODS: Two hours after breakfast (7.0 kcal.kg; 0.3 g.kg P, 1.2 g.kg C, 0.1 g.kg F), six male cyclists performed a 60-min time trial (AMex). Pre- and postexercise, vastus lateralis glycogen concentrations were determined using nMRS. Immediately, 1 h, and 2 h postexercise, participants ingested C+P (4.8 kcal.kg; 0.8 g.kg C, 0.4 g.kg P), CHO (4.8 kcal.kg; 1.2 g.kg C), or PLB (no energy). Four hours postexercise, a solid meal was ingested. At that time, C+P and CHO received a meal identical to breakfast, whereas PLB received 21 kcal.kg (1 g.kg P, 3.6 g.kg C, 0.3 g.kg F); energy intake during 6 h of recovery was identical among treatments. After 6 h of recovery, measurement and cycling protocols (PMex) were repeated. RESULTS: Absolute muscle glycogen utilization was 18% greater (P 相似文献   

The effect of food matrix on carbohydrate utilization during moderate exercise.

The effect of food matrix on carbohydrate utilization during moderate exercise. Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 320-326, 1992. To determine the effect of food type and form on the rate of assimilation and utilization of a meal given before exercise, five physically active adult males walked for 4 h on a 10% uphill graded treadmill at 40% VO2max. After a 12-h fast, and 30 min before exercise, subjects ingested 70 g of liquid glucose (G), a refined "hot cereal" (R), a refined "hot cereal" with water-soluble fiber (R/F), an oat bar (O), or placebo (P). Meals R/F, R, and O had significantly lower (P less than 0.05) peak plasma glucose responses than meal G (0.8, 0.9, 1.0, and 2.4 mmol.l-1, respectively). Meals R, O, and R/F had significantly lower (P less than 0.01) peak insulin responses than meal G (135, 150, 190, and 340 pmol.l-1, respectively). All meals except P contained an extrinsic tracer of 200 mg UL-13C-glucose. Mean (+/- SD) total recovery of the administered dose of 13C for all meals was 81 +/- 2%. Both O (34 +/- 4% dose.h-1) and R/F (30 +/- 3% dose.h-1) had significantly lower peak recoveries than did meal G (41 +/- 5% dose.h-1). Meal R/F had a significantly lower (P less than 0.05) rate of exogenous glucose oxidation than meal G during the first hour of exercise. These data suggest that meal R/F slows the rate of assimilation and utilization of exogenous glucose, but does not alter the cumulative 4-h utilization.     

Influence of a carbohydrate-electrolyte solution ingested during running on muscle glycogen utilisation in fed humans

This study investigated whether the ingestion of a carbohydrate-electrolyte solution during running would influence muscle glycogen utilisation in subjects who had consumed a carbohydrate meal 3 hours before exercise. Eight men completed two 60-min treadmill runs at 70% VO(2)max. Before each run they consumed a carbohydrate meal (183 +/- 7 g) 3 hours before exercise and either 1) a carbohydrate-electrolyte solution during the run (46 +/- 1 g) (M+C), or 2) water during the run (M + W). Biopsy samples were obtained from the vastus lateralis muscle at rest and after 60 min of running. Serum insulin concentrations were higher (p < 0.01) in both trials at the start of exercise compared with fasting values, whereas blood glucose concentrations were higher (p < 0.01) after 60 min of running in the M+C trial. Pre-exercise muscle glycogen concentrations were similar in both trials (M+C: 321.9 +/- 27.2 vs M+W: 338.8 +/- 32.8 mmol x kg x dry weight (-1) [dw]; NS). There was no difference in the amount of glycogen used during exercise (M+C: 96.1 +/- 22.1 vs M+W: 77.9 +/- 11.7 mmol x kg x dw (-1); NS). In conclusion, a carbohydrate-electrolyte solution ingested during treadmill running at 70 % VO(2)max does not influence muscle glycogen use during the first hour of exercise when a carbohydrate meal is consumed 3 hours before exercise.     

Effects of a moderate glycemic meal on exercise duration and substrate utilization

PURPOSE: To determine whether eating a breakfast cereal with a moderate glycemic index could alter substrate utilization and improve exercise duration. METHODS: Six active women (age, 24 +/- 2 yr; weight, 62.2 +/- 2.6 kg; VO(2peak), 46.6 +/- 3.8 mL x kg(-1) x min(-1)) ate 75 g of available carbohydrate in the form of regular whole grain rolled oats (RO) mixed with 300 mL of water or water alone (CON). The trials were performed in random order and the meal or water was ingested 45 min before performing cycling exercise to exhaustion (60% of VO(2peak)). Blood samples were drawn for glucose, glucose kinetics, free fatty acids (FFA), glycerol, insulin, epinephrine (EPI), and norepinephrine (NE) determination. A muscle biopsy was obtained from the vastus lateralis muscle before the trial and immediately after exercise for glycogen determination. Glucose kinetics (Ra) were determined using a [6,6-(2)H] glucose tracer. RESULTS: Compared with CON, plasma FFA and glycerol levels were suppressed (P < 0.05) during the first 120 min of exercise for the RO trial. Respiratory exchange ratios (RER) were also higher (P < 0.05) for the first 120 min of exercise for the RO trial. At exhaustion, glucose, insulin, FFA, glycerol, EPI, NE, RER, and muscle glycogen were not different between trials. Glucose Ra was greater (P < 0.05) during the RO trial compared with CON (2.36 +/- 0.22 and 1.92 +/- 0.27 mg x kg(-1) x min(-1), respectively). Exercise duration was 5% longer during RO, but the mean times were not significantly different (253.6 +/- 6 and 242.0 +/- 15 min, respectively). CONCLUSIONS: Increased hepatic glucose output before fatigue provides some evidence of glucose sparing after the breakfast cereal trial. However, exercise duration was not significantly altered, possibly because of the sustained suppression of lipid metabolism and increased carbohydrate utilization throughout much of the exercise period.