Dietary effects on liver and muscle glycogen repletion in exhaustively exercised rats: energy composition and type of complex carbohydrates

Previous reports have indicated that administration of a glucose-citrate (G-C) drink after a bout of exhaustive exercise results in more effective glycogen repletion in liver and skeletal muscle in rats as compared with administration of glucose alone. The present studies report the effects of the energy pattern and the type of carbohydrates, dextrin or starch from rice, in diet given following the G-C drink after exercise, on further glycogen repletion in the tissues of rats. Rats were adapted to meal-feeding 3 times a day and trained with light swimming for 7 to 10 days. On the final day of experiments, rats received the G-C drink after 2 h of exhaustive swimming and were then fed on diets with different energy patterns or carbohydrate types. Results showed that a high-carbohydrate diet is more effective than a high-fat diet for further glycogen repletion in liver and skeletal muscle. In addition, dextrin was revealed to be superior to starch as a carbohydrate source in tissue glycogen repletion. As compared with the high-fat diet, the high-carbohydrate diet, however, resulted in a lower serum free fatty acid concentration 4 h after ingestion of food possibly by decreasing adipose tissue lipolysis.     

Oral hydroxycitrate supplementation enhances glycogen synthesis in exercised human skeletal muscle

Glycogen stored in skeletal muscle is the main fuel for endurance exercise. The present study examined the effects of oral hydroxycitrate (HCA) supplementation on post-meal glycogen synthesis in exercised human skeletal muscle. Eight healthy male volunteers (aged 22·0 (se 0·3) years) completed a 60-min cycling exercise at 70-75 % VO?max and received HCA or placebo in a crossover design repeated after a 7 d washout period. They consumed 500 mg HCA or placebo with a high-carbohydrate meal (2 g carbohydrate/kg body weight, 80 % carbohydrate, 8 % fat, 12 % protein) for a 3-h post-exercise recovery. Muscle biopsy samples were obtained from vastus lateralis immediately and 3 h after the exercise. We found that HCA supplementation significantly lowered post-meal insulin response with similar glucose level compared to placebo. The rate of glycogen synthesis with the HCA meal was approximately onefold higher than that with the placebo meal. In contrast, GLUT4 protein level after HCA supplementation was significantly decreased below the placebo level, whereas expression of fatty acid translocase (FAT)/CD36 mRNA was significantly increased above the placebo level. Furthermore, HCA supplementation significantly increased energy reliance on fat oxidation, estimated by the gaseous exchange method. However, no differences were found in circulating NEFA and glycerol levels with the HCA meal compared with the placebo meal. The present study reports the first evidence that HCA supplementation enhanced glycogen synthesis rate in exercised human skeletal muscle and improved post-meal insulin sensitivity.     

Carbohydrate-loading during the follicular phase of the menstrual cycle: effects on muscle glycogen and exercise performance

The effects of employing a high-carbohydrate diet (carbohydrate-loading) to increase glycogen storage in skeletal muscle are not well established in female athletes. On 4 occasions--2 familiarization trials and 2 experimental trials--6 well-trained female subjects completed 6 x 15-min continuous intervals of cycling (12 min at 72% VO2max, 1 min at maximal effort, and 2 min at 50% VO2max), followed by a time trial 15 min later. The women consumed their habitual diets (HD; 6-7 g carbohydrate/kg lean body mass) for 3 days after the second familiarization trial and before the first experimental trial. During the 3 days following the first experimental trial, the subjects consumed a high-carbohydrate diet (CD; 9-10 g carbohydrate/kg lean body mass) prior to the second experimental trial. Mean (+/-SEM) pre-exercise muscle glycogen concentrations were greater after CD versus HD (171.9+/-8.7 vs. 131.4+/-10.3 mmol/kg wet weight, P < 0.003). Although 4 of the 6 subjects improved their time-trial performance after CD, mean performance for the time trial was not significantly different between diets (HD: 763.9+/-35.6 s; CD: 752.9+/-30.1 s). Thus, female cyclists can increase their muscle glycogen stores after a carbohydrate-loading diet during the follicular phase of the menstrual cycle, but we found no compelling evidence of a dietary effect on performance of a cycling time trial performed after 90 min of moderate-intensity exercise.     

Rapid rehydration and moderate plasma glucose elevation by fluid containing enzymatically synthesized glycogen

Enzymatically synthesized glycogen (ESG) has high solubility and its solution has low osmotic pressure. Therefore ESG solution could be rapidly absorbed and could be adequate for water rehydration and carbohydrate supplementation during exercise. The object of this study was to evaluate the gastric emptying time and plasma glucose elevation after an administration of ESG solution in comparison with another carbohydrate solution by using a laboratory animal. Male BALB/c mice were administered 10% w/v solution of glucose, maltodextrin, starch, naturally synthesized glycogen (NSG) and ESG at a dose of 20 μL/g body weight for the measurement of gastric emptying rate (Experiment 1) and 10 μL/g body weight for the measurement of plasma glucose elevation (Experiment 2). The osmolarity of gastric content was lower in the ESG and maltodextrin group than the other carbohydrate group. Weight of gastric fluid was significantly lower in the ESG and water group than the glucose group (p<0.01). Plasma glucose level was significantly lower in the ESG group than the glucose group from 0 to 60 min after administration (p<0.01), whereas plasma glucose level was same from 60 to 120 min for the ESG and glucose group (p=0.948). In Experiment 3, BALB/c mice ran on a treadmill for 2 h and were administered 8% of ESG or glucose solution (1.75, 3.5 or 7.0 μL/g body weight) every 20 min during running. There was no difference in post-exercise muscle glycogen level. These data suggest that 1) ESG beverage does not disturb water absorption because of its short gastric emptying time and 2) ESG slowly elevates plasma glucose level and maintains it for a prolonged time compared to the glucose solution.     

Leucine supplementation enhances skeletal muscle recovery in rats following exercise.

This study was designed to determine the ability of leucine to enhance muscle recovery after exercise. Male rats (200 g) were divided into five groups: sedentary, food-deprived (SF); exercised, food-deprived (EF); exercised, fed a carbohydrate meal (EC); exercised, fed a leucine meal (EL); and exercised, fed a combination of carbohydrate and leucine (ECL). All meals were administered by oral gavage immediately following exercise. EC and ECL meals were isocaloric and provided 15% of daily energy intake. EL and ECL meals each provided 270 mg leucine. Rats ran on a motor-driven treadmill for 2 h at 36 m/min and were killed 1 h postexercise. Plasma glucose and insulin were measured, and the gastrocnemius and plantaris muscles were excised as a unit to determine glycogen levels and the fractional rate of skeletal muscle protein synthesis (Ks). Exercise did not alter plasma glucose or insulin. In contrast, prolonged exercise reduced muscle glycogen (-51%) and Ks (-18%). Refeeding a combination of carbohydrate and leucine increased plasma insulin relative to the EF and SF groups and produced complete recovery of muscle Ks and glycogen to values not different from those in SF rats. Feeding leucine alone restored Ks to that in the SF group without affecting plasma glucose or insulin concentrations. Feeding carbohydrate alone enhanced the rate of glycogen repletion compared to the EF group, concomitant with increases in plasma glucose and insulin. The degree of glycogen recovery correlated with plasma insulin concentrations (r = 0.58, P < 0.05). These data suggest that leucine stimulates muscle protein synthesis following exercise, independent of increased plasma insulin. This is the first demonstration that orally administered leucine stimulates recovery of skeletal muscle protein synthesis after exercise.     

A reduced carbohydrate, increased protein diet stabilizes glycemic control and minimizes adipose tissue glucose disposal in rats

The dietary reference intakes (DRIs) established an acceptable macronutrient distribution range (AMDR); however, few studies have evaluated differences in metabolic regulations across the DRI range. This study examined differences in glycemic regulations associated with specific ratios of carbohydrate and protein. Male rats ( approximately 200 g) were fed either a high-carbohydrate diet (CHO group: 60% of energy as carbohydrates, 12% protein, 28% fat) or a reduced-carbohydrate diet [PRO (protein) group: 42% carbohydrates, 30% protein, 28% fat]. Rats consumed 3 meals/d with energy distributed as 16, 42, and 42%. On d 25, blood and tissues were obtained after 12 h of food deprivation and at 30 and 90 min after the first meal. Before the meal, the CHO group had lower plasma glucose and insulin, reduced liver glycogen, lower expression of hepatic phosphoenolpyruvate carboxylase (PEPCK), and increased fatty acid synthase (FAS) in adipose tissue. After the meal, the CHO group had greater increases in plasma glucose and insulin, producing increased skeletal muscle phosphatidylinositol 3-kinase (PI3-kinase) activity, glucose uptake, and glycogen content, and increased adipose PI3-kinase activity, glucose uptake, and FAS. In contrast, the PRO group had limited postprandial changes in plasma glucose and insulin with reduced muscle PI3-kinase activity and glucose uptake, and no postprandial changes in adipose PI3-kinase activity or FAS. This study demonstrates that changes in carbohydrate and protein intakes within the AMDR produce fundamental shifts in glycemic regulation from high-CHO diets that require insulin-mediated peripheral glucose disposal to high-PRO diets that increase hepatic regulation of glucose appearance into the blood.     

Effects of a Short-Term “Fat Adaptation with Carbohydrate Restoration” Diet on Metabolic Responses and Exercise Performance in Well-Trained Runners

Periodized carbohydrate availability can enhance exercise capacity, but the effects of short-term fat adaptation carbohydrate restoration (FACR) diets on metabolic responses and exercise performance in endurance athletes have not been conclusively determined. This study aimed to investigate the effect of a FACR diet on measures of resting metabolism, exercise metabolism, and exercise performance. Well-trained male runners (n = 8) completed a FACR dietary intervention (five days’ carbohydrate < 20% and fat > 60% energy, plus one-day carbohydrate ≥ 70% energy), and a control high-carbohydrate (HCHO) diet for six days (carbohydrate > 60% energy; fat < 20% energy) in a randomized crossover design. Pre- and post-intervention metabolic measures included resting metabolic rate (RMR), respiratory quotient (RQ), maximum fat oxidation rate during exercise (MFO), and maximum fat oxidation intensity (FATmax). Measures of exercise performance included maximal oxygen uptake (VO₂max), running economy (RE), and 5 km running time trial (5 km-TT). In FACR compared with HCHO, there were significant improvements in FATmax (p = 0.006) and RE (p = 0.048). There were no significant differences (p > 0.05) between FACR and HCHO in RMR, RQ, VO₂max, or 5 km-TT. Findings suggest that a short-term (six days) FACR diet may facilitate increased fat oxidation and submaximal exercise economy but does not improve 5 km-TT performance.     

Nutrition and exercise determinants of postexercise glycogen synthesis.

During the initial hours of recovery from prolonged exhaustive lower body exercise, muscle glycogen synthesis occurs at rates approximating 1-2 mmol.kg-1 wet wt.hr-1 if no carbohydrate is consumed. When carbohydrate is consumed during the recovery, the maximal rate of glycogen synthesis approximates 7-10 mmol.kg-1 wet wt.hr-1. The rate of post-exercise glycogen synthesis is lower if the magnitude of glycogen degradation is small, if less than 0.7 gm glucose.kg-1 body wt.hr-1 is ingested, when the recovery is active, and when the carbohydrate feeding is delayed. The rate of postexercise glycogen synthesis is not reduced during the initial hours (< 4) after eccentric exercise. For studies evaluating muscle glycogen synthesis in excess of 12 hours of recovery, average rates of glycogen synthesis are below 4 mmol.kg-1 wet wt.hr-1. Glycogen synthesis is known to be impaired for time periods in excess of 24 hours following exercise causing eccentric muscle damage. Following intense exercise resulting in high concentrations of muscle lactate, muscle glycogen synthesis occurs at between 15-25 mmol.kg-1 wet wt.hr-1. These synthesis rates occur without ingested carbohydrate during the recovery period and are maintained when a low intensity active recovery is performed.     

Postprandial glycogen and lipid synthesis in prednisolone-treated rats maintained on high-protein diets with varied carbohydrate levels

OBJECTIVE: The present experiment was designed to study the effect of a high-protein, high-carbohydrate diet versus a high-protein, low-carbohydrate diet on in vivo postprandial glycogen and lipid synthesis of rats treated with prednisolone. METHODS: Thirty-two 6-wk-old male Sprague-Dawley rats were randomly assigned to one of four equal groups: high-protein, high-carbohydrate; high-protein, high-carbohydrate with prednisolone; high-protein, low-carbohydrate; and high-protein, low-carbohydrate with prednisolone. Rats were sham operated or subcutaneously implanted with prednisolone pellets while being maintained on their respective diets (39% of energy from protein) for 6 wk. Food intake and body weight were monitored throughout the experiment. At the end of the feeding period, overnight-fasted rats were fed a test meal and injected with 3H2O to measure in vivo rates of glycogen and lipid synthesis. Final plasma glucose, insulin, and triacylglycerol concentrations and hepatic glycogen content were also measured. RESULTS: Results showed that hepatic glycogen content (milligrams per gram of liver) was similar across all four experimental groups. Total hepatic glycogen synthesis and its percentage synthesis via pyruvate (indirect pathway) were higher in rats maintained on the high-protein, high-carbohydrate diet compared with those on the high-protein, low-carbohydrate diet and this was not substantially affected by prednisolone administration. Hepatic and epididymal fat pad lipid syntheses were not altered by diet or prednisolone treatments. CONCLUSION: Under long-term high-protein conditions, prednisolone administration does not seem to affect hepatic glycogen synthesis, which was increased with the increased carbohydrate content of the diet.     

Effect of isoenergetic low- and high-carbohydrate diets on substrate kinetics and oxidation in healthy men

The effect of diet composition on post-absorptive (15 h fast) fatty acid and glucose metabolism was investigated in five healthy men after 2 weeks on a low-carbohydrate (Low-CHO) diet (30 % energy intake from carbohydrates, 55 % from fat, 15 % from protein) and after 2 weeks on a high-carbohydrate (High-CHO) diet (energy intake 75, 10 and 15 % from carbohydrates, fat and protein respectively). The diets were isoenergetic and comprised real foods. Stable-isotope tracer methodology and indirect calorimetry were employed to measure glucose and fatty acid kinetics and oxidation. The relative contribution of carbohydrate to the total energy expenditure was significantly higher after the High-CHO diet. After the High-CHO diet, total and plasma fatty oxidation (2.4 (SE 0.7) and 2.1 (SE 0.4) micromol/kg per min respectively) were significantly lower than after the Low-CHO diet (4.8 (SE 0.5) and 4.6 (SE 0.8) micromol/kg per min for total and plasma fatty oxidation respectively). The rate of appearance (Ra) of non-esterified fatty acids (NEFA) in plasma and the arterial NEFA concentration were both significantly lower following the High-CHO than the Low-CHO diet. However, even after the High-CHO diet, NEFA Ra was threefold higher than plasma fatty acid oxidation. Thus, the decrease in fatty acid oxidation after consumption of a high-carbohydrate diet for 2 weeks in healthy men is unlikely to result from decreased fatty acid delivery to the tissues. Glucose Ra and arterial plasma glucose concentration were similar after the two diets. After the High-CHO diet, arterial lactate concentration was higher and total carbohydrate oxidation rate well exceeded glucose Ra in plasma. Therefore, alterations in intracellular mechanisms may limit fatty acid oxidation after high-carbohydrate diets.     

Human metabolic response to exercise

The energy necessary to support prolonged submaximal exercise is provided by the aerobic metabolism of carbohydrate and fatty acids. Carbohydrate is stored as glycogen, a polymer of glucose, in the liver and in the skeletal muscles, whereas the fatty acids used by working muscles are mainly derived from triglycerides stored in white adipose tissue cells. The relative contributions of carbohydrate and fatty acids to muscle metabolism depend on the relative exercise intensity. The relative exercise intensity is defined as the oxygen cost of the exercise (V0₂) expressed as a percentage of the individual's maximum oxygen uptake (% V0₂ max). At exercise intensities which represent a large % V0₂ max for an individual, muscle glycogen is the main contributor to muscle metabolism. Fatigue is associated with the depletion of the limited intramuscular glycogen stores. When a carbohydrate-rich diet is consumed during recovery after exercise, the muscle glycogen stores are increased above theirpre-exercise concentrations. Thus an exercise and diet regime has been developed to exploit the glycogen supercompensa-tion phenomenon and so increase endurance capacity.     

Coffee Increases Post-Exercise Muscle Glycogen Recovery in Endurance Athletes: A Randomized Clinical Trial

Coffee is one of the most widely consumed beverages worldwide and caffeine is known to improve performance in physical exercise. Some substances in coffee have a positive effect on glucose metabolism and are promising for post-exercise muscle glycogen recovery. We investigated the effect of a coffee beverage after exhaustive exercise on muscle glycogen resynthesis, glycogen synthase activity and glycemic and insulinemic response in a double-blind, crossover, randomized clinical trial. Fourteen endurance-trained men performed an exhaustive cycle ergometer exercise to deplete muscle glycogen. The following morning, participants completed a second cycling protocol followed by a 4-h recovery, during which they received either test beverage (coffee + milk) or control (milk) and a breakfast meal, with a simple randomization. Blood samples and muscle biopsies were collected at the beginning and by the end of recovery. Eleven participants were included in data analysis (age: 39.0 ± 6.0 years; BMI: 24.0 ± 2.3 kg/m²; VO_2max: 59.9 ± 8.3 mL·kg⁻¹·min⁻¹; PPO: 346 ± 39 W). The consumption of coffee + milk resulted in greater muscle glycogen recovery (102.56 ± 18.75 vs. 40.54 ± 18.74 mmol·kg dw⁻¹; p = 0.01; d = 0.94) and greater glucose (p = 0.02; d = 0.83) and insulin (p = 0.03; d = 0.76) total area under the curve compared with control. The addition of coffee to a beverage with adequate amounts of carbohydrates increased muscle glycogen resynthesis and the glycemic and insulinemic response during the 4-h recovery after exhaustive cycling exercise.     

Low Aerobic Capacity Accelerates Lipid Accumulation and Metabolic Abnormalities Caused by High-Fat Diet-Induced Obesity in Postpartum Mice

Women during pregnancy and postpartum show high rates of obesity and metabolic diseases, especially women with excessive caloric intake. In the past, it was proved that individuals with high intrinsic aerobic exercise capacities showed higher lipid metabolism and lower fat production than those with low intrinsic aerobic exercise capacities. The purpose of this study was to determine whether mice with the low-fitness phenotype (LAEC) were more likely to develop metabolic abnormalities and obesity under dietary induction after delivery, and if mice with a high-fitness phenotype (HAEC) had a protective mechanism. After parturition and weaning, postpartum Institute of Cancer Research (ICR) mice received dietary induction for 12 weeks and were divided into four groups (n = 8 per group): high-exercise capacity postpartum mice with a normal chow diet (HAEC-ND); high-exercise capacity postpartum mice with a high-fat diet (HAEC-HFD); low-exercise capacity postpartum mice with a normal chow diet (LAEC-ND); and low-exercise capacity postpartum mice with a high-fat diet (LAEC-HFD). Obesity caused by a high-fat diet led to decreased exercise performance (p < 0.05). Although there were significant differences in body posture under congenital conditions, the LAEC mice gained more weight and body fat after high-fat-diet intake (p < 0.05). Compared with HAEC-HFD, LAEC-HFD significantly increased blood lipids, such as total cholesterol (TC), triacylglycerol (TG), low-density lipoprotein (LDL) and other parameters (p < 0.05), and the content of TG in the liver, as well as inducing poor glucose tolerance (p < 0.05). In addition, after HFD intake, excessive energy significantly increased glycogen storage (p < 0.05), but the LAEC mice showed significantly lower muscle glycogen storage (p < 0.05). In conclusion, although we observed significant differences in intrinsic exercise capacity, and body posture and metabolic ability were also different, high-fat-diet intake caused weight gain and a risk of metabolic disorders, especially in postpartum low-fitness mice. However, HAEC mice still showed better lipid metabolism and protection mechanisms. Conversely, LAEC mice might accumulate more fat and develop metabolic diseases compared with their normal rodent chow diet (ND) control counterparts.     

Recovery from cycling exercise: effects of carbohydrate and protein beverages

The effects of different carbohydrate-protein (CHO + Pro) beverages were compared during recovery from cycling exercise. Twelve male cyclists (VO(2peak): 65 ± 7 mL/kg/min) completed ~1 h of high-intensity intervals (EX1). Immediately and 120 min following EX1, subjects consumed one of three calorically-similar beverages (285-300 kcal) in a cross-over design: carbohydrate-only (CHO; 75 g per beverage), high-carbohydrate/low-protein (HCLP; 45 g CHO, 25 g Pro, 0.5 g fat), or low-carbohydrate/high-protein (LCHP; 8 g CHO, 55 g Pro, 4 g fat). After 4 h of recovery, subjects performed subsequent exercise (EX2; 20 min at 70% VO(2peak) + 20 km time-trial). Beverages were also consumed following EX2. Blood glucose levels (30 min after beverage ingestion) differed across all treatments (CHO > HCLP > LCHP; p < 0.05), and serum insulin was higher following CHO and HCLP ingestion versus LCHP. Peak quadriceps force, serum creatine kinase, muscle soreness, and fatigue/energy ratings measured pre- and post-exercise were not different between treatments. EX2 performance was not significantly different between CHO (48.5 ± 1.5 min), HCLP (48.8 ± 2.1 min) and LCHP (50.3 ± 2.7 min). Beverages containing similar caloric content but different proportions of carbohydrate/protein provided similar effects on muscle recovery and subsequent exercise performance in well-trained cyclists.     

Effect of Different Carbohydrate Intakes within 24 Hours after Glycogen Depletion on Muscle Glycogen Recovery in Japanese Endurance Athletes

Daily muscle glycogen recovery after training is important for athletes. Few studies have reported a continuous change in muscle glycogen for 24 h. We aimed to investigate the changes in carbohydrate intake amount on muscle glycogen recovery for 24 h after exercise using ¹³C-magnetic resonance spectroscopy (¹³C-MRS). In this randomized crossover study, eight male participants underwent prolonged high-intensity exercise, and then consumed one of the three carbohydrate meals (5 g/kg body mass (BM)/d, 7 g/kg BM/d, or 10 g/kg BM/d). Glycogen content of thigh muscle was measured using ¹³C-MRS before, immediately after, and 4 h, 12 h and 24 h after exercise. Muscle glycogen concentration decreased to 29.9 ± 15.9% by exercise. Muscle glycogen recovery 4–12 h after exercise for the 5 g/kg group was significantly lower compared to those for 7 g/kg and 10 g/kg groups (p < 0.05). Muscle glycogen concentration after 24 h recovered to the pre-exercise levels for 7 g/kg and 10 g/kg groups; however, there was a significant difference for the 5 g/kg group (p < 0.05). These results suggest that carbohydrate intake of 5 g/kg BM/d is insufficient for Japanese athletes to recover muscle glycogen stores 24 h after completing a long-term high-intensity exercise.     

罗格列酮及饮食干预对胰岛素抵抗大鼠骨骼肌GLUT4转位的影响

目的　探讨罗格列酮对胰岛素抵抗大鼠骨骼肌细胞葡萄糖转运蛋白 4(GLUT4)转位的影响。方法　利用高脂饲料喂养 ,使Sprague -Dawley(SD)大鼠产生胰岛素抵抗 ,用罗格列酮及饮食干预治疗 4周后 ,取骨骼肌组织 ,应用Western -bloting印迹法分析骨骼细胞膜GLUT4表达量。结果　在胰岛素刺激下 ,胰岛素抵抗大鼠骨骼肌细胞膜GLUT4表达较正常大鼠下降 5 2 72 %(P <0 0 0 1) ,罗格列酮及饮食干预组 ,细胞膜GLUT4表达较未干预胰岛素抵抗大鼠分别增加 49 5 3 %、5 0 3 4%(P <0 0 0 1)。结论　罗格列酮可促进胰岛素刺激的GLUT4转位 ,从而改善高脂喂养所引起的骨骼肌组织胰岛素抵抗     

Preexercise ingestion of carbohydrate plus whey protein hydrolysates attenuates skeletal muscle glycogen depletion during exercise in rats

ObjectiveDepletion of glycogen stores is associated with fatigue during both sprint and endurance exercises and therefore it is considered important to maintain adequate tissue stores of glycogen during exercise. The aims of the present study in rats were therefore to investigate the effects of preexercise supplementation with carbohydrate and whey protein hydrolysates (WPH) on glycogen content, and phosphorylated signaling molecules of key enzymes that regulate glucose uptake and glycogen synthesis during exercise.MethodsMale SD rats were used in the study (n = 7/group). Prior to exercise, one group of rats was sacrificed, whereas the other groups were given either water, glucose, or glucose plus WPH solutions. After ingestion of the test solutions, glycogen-depleting exercise was carried out for 60 min. The rats were then sacrificed and the triceps muscles excised quickly.ResultsCompared to water or glucose only, preexercise ingestion of glucose plus WPH caused a significant attenuation of muscle glycogen depletion during the postexercise period. Coingestion of glucose and WPH also significantly lowered phosphorylated glycogen synthase levels compared to ingestion of water only. In the glucose plus WPH group, the levels of phosphorylated Akt were increased significantly compared to the group ingesting water only, while the levels of phosphorylated PKC were significantly higher than in the groups ingesting only water or glucose.ConclusionTaken together, these results indicate that, compared to ingestion of glucose or water only, preexercise ingestion of carbohydrate plus WPH activates skeletal muscle proteins of key enzymes that regulate glucose uptake and glycogen synthesis during exercise, thereby attenuating exercise-induced glycogen depletion.     

Effect of the classic 1-week glycogen-loading regimen on fat-loading in rats and humans

The purpose of this study was to elucidate the fat-loading effect of the classic 1-wk glycogen-loading regimen histologically in rats and physiologically in humans. In the rat and human studies, an exhaustive swimming exercise and cycle ergometer exercise were loaded on day 1 of a 6-d feeding period, respectively. Thereafter, both the rats and humans were divided into a glycogen-loading regimen consisting of a 3-d high-fat diet and a 3-d high-carbohydrate diet or a 6-d high-carbohydrate diet. After the feeding period in the human study, the human subjects performed a test exercise on day 7 using a cycle ergometer. In the rat study, the intramuscular triglyceride (IMTG) content was 69% greater (p<0.05) after the glycogen-loading regimen than after the high-carbohydrate diet feeding on day 7. In the human study, the respiratory exchange ratios (RER) after the glycogen-loading regimen were 4.9-6% lower than those after the high-carbohydrate diet during the test exercise on day 7 (p<0.05). Our findings suggest that the classical 1-wk glycogen-loading regimen maintained the storage and enhanced the utilization of energy sources during exercise in the skeletal muscle, and that it provides a fat-loading effect, in addition to the glycogen-loading effect, to the skeletal muscle.