Muscle Glycogen Resynthesis Research Articles

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

0157 A single bout of endurance exercise stimulates lipolysis and enhances fat oxidation in humans. An increased rate of fat oxidation is beneficial during exercise as it spares muscle glycogen. Consuming high glycaemic index (HGI) carbohydrates (CHO) after exercise is the recommended method of increasing the rate of muscle glycogen resynthesis. However, the increase in the insulin response following the consumption of HGI CHO suppresses fatty acid metabolism. PURPOSE: To examine whether low glycaemic index (LGI) CHO meals during 24h recovery from prolonged exercise result in a greater rate of fat oxidation and a better endurance capacity during exercise the following day than the consumption of HGI meals. METHODS: Nine recreationally active males (age 22.4 ± 0.6 years; body mass (BM) 79.4 ± 4.1kg; VO2 max 61.0 ± 2.2 ml•kg−1•min−1) took part in this study. Each subject participated in two trials separated by 7 days in a randomised cross-over design. The experimental protocol was completed over two days. On day 1, subjects completed a 90min treadmill run at 70% VO2max (R1). Thereafter, they were supplied with a recovery diet which consisted of either HGI or LGI CHO and provided 8g CHO• kgBM-1. On day 2, after an overnight fast, subjects ran to exhaustion at 70% VO2max (R2). RESULTS: Only eight subjects completed both performance runs (R2). Run time to exhaustion during R2 was longer in the LGI trial (108.9 ± 7.4min) than in the HGI trial (96.9 ± 4.8min) (p<0.05). Average RER values were higher in the HGI trial compared to the LGI trial (p<0.05). Fat oxidation rates and Free fatty acid concentrations were higher in the LGI trial than the HGI trial (p<0.05). CONCLUSION: The results of the study suggest that the increased endurance capacity during R2 was largely a consequence of the greater fat oxidation, and possibly glycogen sparing, following the consumption of the LGI meals.

Carbohydrate metabolism in exercising horses

AbstractCarbohydrate and fat are the predominant sources of energy during exercise in mammals. Carbohydrates, such as muscle glycogen and plasma glucose, and fats from adipose tissue and intramuscular triglycerides are oxidized during exercise in amounts and proportions that vary depending on the exercise intensity, level of fitness and nutritional status. In horses, muscle glycogen, and to a lesser extent plasma glucose, are oxidized in substantial amounts during low-, moderate- and high-intensity exercise. Carbohydrate availability to skeletal muscle affects exercise performance in humans, however this relationship is not well outlined in horses. Glucose supplementation by intravenous administration during exercise in horses increases duration of moderate-intensity exercise. However, the effect of glucose supplementation by ingestion of a soluble carbohydrate-rich meal prior to exercise on athletic performance has not been established in horses. Low muscle glycogen concentrations prior to exercise in horses are associated with decreased time to exhaustion at moderate- and high-intensity exercise. Nutritional interventions intended to enhance muscle glycogen resynthesis have proved less successful in horses than in other species. Replenishment of muscle glycogen after strenuous exercise in horses is not complete until 48–72 h after exercise, whereas in humans and laboratory animals it is complete by 24 h. The slower rate of muscle glycogen replenishment after exercise in horses may be related to an inherent lower ability to digest starch and other sources of glucose, a lower ability to synthesize muscle glycogen, or both. The aim of this review is to describe the present understanding of carbohydrate metabolism in the exercising horse, its implications on nutrition and athletic performance, and to contrast it with that in other species.

Further glycogen decrease during early recovery after eccentric exercise despite a high carbohydrate intake

Delayed onset muscle soreness (DOMS) is a well-known phenomenon of athletes. It has been reported from muscle biopsies that the rate of muscle glycogen resynthesis is reduced after eccentric compared to concentric exercise. Try to compensate by a carbohydrate (CHO)-rich diet the decelerated glycogen resynthesis after eccentric exercise, measured by magnetic resonance spectroscopy. Glycogen, phosphocreatine, ATP, and Pi were measured in the human calf muscle. Twenty athletes divided into two groups (DOMS and CONTROL), reduced glycogen in M. gastrocnemius during two different running protocols. Additionally, 12 DOMS subjects performed an eccentric exercise while the CONTROL group rested. Subsequently, subjects consumed a CHO-rich diet (> 10 g/kg body mass/24 h). In both groups, glycogen has been reduced by about 50%. The first 2 h after exercise, glycogen dropped further (-15.6 +/- 15.7 mmol/ kg ww) in the DOMS but rose by +18.4 +/- 20.8 mmol/kg ww in the CONTROL group (P < 0.001). CONTROL subjects reached resting glycogen within 24 h (137 +/- 47 mmol/kg ww), while DOMS subjects needed more than one day (91 +/- 23 mmol/kg ww; P < 0.001). Pi and Pi/PCr, indicators of muscle injury, rose significantly in the DOMS but not in the CONTROL group. The diet rich in CHO's was not able to refill glycogen stores after eccentric exercise. Glycogen decreased even further during the beginning of recovery. This loss, which to our knowledge has not been measured before is probably the consequence of muscle cell damage and their reparation.

Macronutrient considerations for the sport of bodybuilding.

Participants in the sport of bodybuilding are judged by appearance rather than performance. In this respect, increased muscle size and definition are critical elements of success. The purpose of this review is to evaluate the literature and provide recommendations regarding macronutrient intake during both 'off-season' and 'pre-contest' phases. Body builders attempt to increase muscle mass during the off-season (no competitive events), which may be the great majority of the year. During the off-season, it is advantageous for the bodybuilder to be in positive energy balance so that extra energy is available for muscle anabolism. Additionally, during the off-season, adequate protein must be available to provide amino acids for protein synthesis. For 6-12 weeks prior to competition, body builders attempt to retain muscle mass and reduce body fat to very low levels. During the pre-contest phase, the bodybuilder should be in negative energy balance so that body fat can be oxidised. Furthermore, during the pre-contest phase, protein intake must be adequate to maintain muscle mass. There is evidence that a relatively high protein intake (approximately 30% of energy intake) will reduce lean mass loss relative to a lower protein intake (approximately 15% of energy intake) during energy restriction. The higher protein intake will also provide a relatively large thermic effect that may aid in reducing body fat. In both the off-season and pre-contest phases, adequate dietary carbohydrate should be ingested (55-60% of total energy intake) so that training intensity can be maintained. Excess dietary saturated fat can exacerbate coronary artery disease; however, low-fat diets result in a reduction in circulating testosterone. Thus, we suggest dietary fats comprise 15-20% of the body builders' off-season and pre-contest diets. Consumption of protein/amino acids and carbohydrate immediately before and after training sessions may augment protein synthesis, muscle glycogen resynthesis and reduce protein degradation. The optimal rate of carbohydrate ingested immediately after a training session should be 1.2 g/kg/hour at 30-minute intervals for 4 hours and the carbohydrate should be of high glycaemic index. In summary, the composition of diets for body builders should be 55-60% carbohydrate, 25-30% protein and 15-20% of fat, for both the off-season and pre-contest phases. During the off-season the diet should be slightly hyperenergetic (approximately 15% increase in energy intake) and during the pre-contest phase the diet should be hypoenergetic (approximately 15% decrease in energy intake).

Carbohydrate Supplementation and Resistance Training

There is a growing body of evidence suggesting that the performance of resistance-training exercises can elicit a significant glycogenolytic effect that potentially could result in performance decrements. These decrements may result in less than optimal physiological adaptations to training. Currently some scientific evidence suggests that carbohydrate supplementation prior to and during high-volume resistance training results in the maintenance of muscle glycogen concentration, which potentially could result in the maintenance or increase of performance during a training bout. Some researchers suggest that ingesting carbohydrate supplements prior to and during resistance training may improve resistance-training performance. Additionally the ingestion of carbohydrates following resistance exercise enhances the re-synthesis of muscle glycogen, which may result in a faster time of recovery from resistance training, thus possibly allowing for a greater training volume. On the basis of the current scientific literature, it may be advisable for athletes who are performing high-volume resistance training to ingest carbohydrate supplements before, during, and immediately after resistance training.

Carbohydrate supplementation and resistance training.

There is a growing body of evidence suggesting that the performance of resistance-training exercises can elicit a significant glycogenolytic effect that potentially could result in performance decrements. These decrements may result in less than optimal physiological adaptations to training. Currently some scientific evidence suggests that carbohydrate supplementation prior to and during high-volume resistance training results in the maintenance of muscle glycogen concentration, which potentially could result in the maintenance or increase of performance during a training bout. Some researchers suggest that ingesting carbohydrate supplements prior to and during resistance training may improve resistance-training performance. Additionally, the ingestion of carbohydrates following resistance exercise enhances the resynthesis of muscle glycogen, which may result in a faster time of recovery from resistance training, thus possibly allowing for a greater training volume. On the basis of the current scientific literature, it may be advisable for athletes who are performing high-volume resistance training to ingest carbohydrate supplements before, during, and immediately after resistance training.

Postexercise muscle glycogen resynthesis in obese insulin-resistant Zucker rats.

We determined the effect of an acute bout of swimming (8 x 30 min) followed by either carbohydrate administration (0.5 mg/g glucose ip and ad libitum access to chow; CHO) or fasting (Fast) on postexercise glycogen resynthesis in soleus muscle and liver from female lean (ZL) and obese insulin-resistant (ZO) Zucker rats. Resting soleus muscle glycogen concentration ([glycogen]) was similar between genotypes and was reduced by 73 (ZL) and 63% (ZO) after exercise (P < 0.05). Liver [glycogen] at rest was greater in ZO than ZL (334 +/- 31 vs. 247 +/- 16 micromol/g wet wt; P < 0.01) and fell by 44 and 94% after exercise (P < 0.05). The fractional activity of glycogen synthase (active/total) increased immediately after exercise (from 0.22 +/- 0.05 and 0.32 +/- 0.04 to 0.63 +/- 0.08 vs. 0.57 +/- 0.05; P < 0.01 for ZL and ZO rats, respectively) and remained elevated above resting values after 30 min of recovery. During this time, muscle [glycogen] in ZO increased 68% with CHO (P < 0.05) but did not change in Fast. Muscle [glycogen] was unchanged in ZL from postexercise values after both treatments. After 6 h recovery, GLUT-4 protein concentration was increased above resting levels by a similar extent for both genotypes in both fasted (approximately 45%) and CHO-supplemented (approximately 115%) rats. Accordingly, during this time CHO refeeding resulted in supercompensation in both genotypes (68% vs. 44% for ZL and ZO). With CHO, liver [glycogen] was restored to resting levels in ZL but remained at postexercise values for ZO after both treatments. We conclude that the increased glucose availability with carbohydrate refeeding after glycogen-depleting exercise resulted in glycogen supercompensation, even in the face of muscle insulin-resistance.

Resynthesis of muscle glycogen after soccer specific performance examined by 13C-magnetic resonance spectroscopy in elite players.

The purpose of this study was to examine using 13C-magnetic resonance spectroscopy whether muscle glycogen (Gly) utilized during a simulation of a fatiguing soccer match followed by repeated sprints would be resynthesized during the next 24 h while players consumed their habitual diet. A group of 12 elite young players [mean age 17.5 (SD 0.8) years, mean body mass 68.9 (SD 6.6) kg, mean height 177.0 (SD 5.4) cm] participated in the study. Average muscle Gly content before the simulation was 134 (SD 16) mmol.(kg wet mass)-1 and decreased during the test (P < 0.001) to 80 (SD 29) mmol.(kg wet mass)-1. The value had increased (P < 0.01) to 122 (SD 33) mmol.(kg wet mass)-1 24 h later but it was not significantly different from the value obtained before the soccer test. Dietary analysis of the food intake during the 24 h after the running test revealed that players consumed an average of 2,681 (SD 970) kcal.day-1. Mean daily protein, fat, and carbohydrate (CHO) intakes were 85 (SD 29), 99 (SD 44), and 327 (SD 116) g, respectively. The mean amounts of CHO intake normalised to body mass were 4.8 (SD 1.8) g.(kg body mass)-1. In conclusion, the results of this study showed that despite a CHO intake of less than 5 g.(kg body mass)-1 the habitual diet of soccer players might be sufficient to replenish in 24 h the muscle Gly utilized during soccer specific performance. However, cumulative deficits of about 10% in Gly replenishment as found in the present study might provoke decrements in performance. Thus, players should pay attention to their habitual diets and add more carbohydrates to replenish their daily deficits and perhaps increase their basal levels of intake.

EFFECT OF CARBOHYDRATE SUPPLEMENTATION ON THE TIME-COURSE OF POST-EXERCISE GLYCOGEN RESYNTHESIS IN INSULIN-RESISTANT ZUCKER RATS

Glucose transport is the rate-limiting step for glucose uptake and storage in skeletal muscle. We determined the effect of an acute bout of swimming (8 × 30 min) followed by either carboydrate administration (i.p. 0.5 mg/g weight of glucose and free access to chow; CHO) or fasting (FAST) on the time-course (0, 30 min, 6 h post-exercise) of glycogen resynthesis in skeletal muscle (soleus) and liver from lean (L) and insulin resistant (IR) obese Zucker rats. Muscle [glycogen] at rest was similar between L and IR (29 ± 2 vs. 38 ± 4 μmol/g wet weight; mean ± SEM) and was reduced by ∼65% after exercise (p < 0.05). Liver [glycogen] was greater in IR than L (334 ± 31 vs. 247 ± 16 μmol/g; p < 0.05) and fell by 44% and 94% after exercise (P < 0.05). Muscle and liver [glycogen] remained unchanged after 30 min in L for both FAST and CHO. Liver and muscle [glycogen] was also unaltered by FAST in IR after 30 min, but muscle [glycogen] increased 68% from 14 ± 1 to 24 ± 3 μmol/g (P < 0.05) with CHO. After 6 h FAST, muscle [glycogen] of IR was restored to pre-exercise levels, but liver [glycogen] did not change with FAST or CHO. Muscle [glycogen] for L remained 56% below rest after 6 h, while liver [glycogen] had not increased above post-exercise values. After 6 h CHO, liver [glycogen] in L had been restored to resting levels while muscle [glycogen] was supercompensated by 68% (50 ± 4 μmol/g; p < 0.05). At this time, muscle [glycogen] in IR was 44% higher than rest (55 ± 3 μmol/g; p < 0.05). We conclude that with carbohydrate administration, 1) the rapid (≤ 30 min post-exercise) phase of muscle glycogen resynthesis was greater in insulin-resistant than lean animals, 2) most of the muscle glycogen resynthesis in lean animals occurred in the slow (> 30 min) phase, 3) there was an additive effect on muscle glycogen resynthesis in insulin-resistant animals, and 4) muscle, but not liver, glycogen was supercompensated 6 h following an intense bout of exercise in both lean and insulin-resistant obese Zucker rats.

THE REGULATION OF MUSCLE GLYCOGEN RESYNTHESIS IN FED RATS DURING RECOVERY FROM HIGH-INTENSITY EXERCISE

The aim of this study was to determine the role of phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulation of muscle glycogen repletion in fed rats recovering from high-intensity exercise. Groups of rats in the absorptive state were swum to exhaustion and allowed to recover for up to 60 minutes without access to food. Swimming to exhaustion resulted in substantial glycogen breakdown and lactate accumulation in the tibialis anterior, red, white and mixed gastrocnemius muscles, whereas the glycogen content in the soleus muscle remained stable. During 30 minutes of recovery, significant and rapid repletion of glycogen occurred in all muscles examined except the soleus muscle. Lactate returned to basal rapidly within 15 minutes after exercise in all muscles examined. A significant decrease in liver glycogen concentration was observed following exercise but returned to basal within 15 minutes of recovery. Exercise resulted in significant elevation of plasma glucose level. However, plasma glucose returned to pre-exercise level within 15 minutes of recovery. These findings indicate that liver glycogen and plasma glucose, other than lactate, are likely to be major carbon precursors for the repletion of muscle glycogen in fed rats following high-intensity exercise. At the onset of recovery, the fractional velocities of glycogen synthase in the red, white and mixed gastrocnemius muscles were higher than basal and remained elevated for 15 minutes before returning to pre-exercise levels within 30 minutes after exercise. In contrast, the activity ratios of glycogen phosphorylase in the same muscles were lower than basal and remained low for 15 minutes before increasing to pre-exercise levels within 30 minutes of recovery. This pattern of changes in glycogen synthase and phosphorylase activities, never observed before, following high-intensity exercise suggests that the integrated regulation of the phosphorylation state of both glycogen synthase and phosphorylase in the control of glycogen resynthesis in the skeletal muscle is sensitive to the nutritional status of the animal.

Muscle glycogen resynthesis during recovery from cycle exercise: no effect of additional protein ingestion.

In the present study, we have investigated the effect of carbohydrate and protein hydrolysate ingestion on muscle glycogen resynthesis during 4 h of recovery from intense cycle exercise. Five volunteers were studied during recovery while they ingested, immediately after exercise, a 600-ml bolus and then every 15 min a 150-ml bolus containing 1) 1.67 g. kg body wt(-1). l(-1) of sucrose and 0.5 g. kg body wt(-1). l(-1) of a whey protein hydrolysate (CHO/protein), 2) 1.67 g. kg body wt(-1). l(-1) of sucrose (CHO), and 3) water. CHO/protein and CHO ingestion caused an increased arterial glucose concentration compared with water ingestion during 4 h of recovery. With CHO ingestion, glucose concentration was 1-1.5 mmol/l higher during the first hour of recovery compared with CHO/protein ingestion. Leg glucose uptake was initially 0.7 mmol/min with water ingestion and decreased gradually with no measurable glucose uptake observed at 3 h of recovery. Leg glucose uptake was rather constant at 0.9 mmol/min with CHO/protein and CHO ingestion, and insulin levels were stable at 70, 45, and 5 mU/l for CHO/protein, CHO, and water ingestion, respectively. Glycogen resynthesis rates were 52 +/- 7, 48 +/- 5, and 18 +/- 6 for the first 1.5 h of recovery and decreased to 30 +/- 6, 36 +/- 3, and 8 +/- 6 mmol. kg dry muscle(-1). h(-1) between 1.5 and 4 h for CHO/protein, CHO, and water ingestion, respectively. No differences could be observed between CHO/protein and CHO ingestion ingestion. It is concluded that coingestion of carbohydrate and protein, compared with ingestion of carbohydrate alone, did not increase leg glucose uptake or glycogen resynthesis rate further when carbohydrate was ingested in sufficient amounts every 15 min to induce an optimal rate of glycogen resynthesis.

Intramuscular glycogen and intramyocellular lipid utilization during prolonged exercise and recovery in man: a 13C and 1H nuclear magnetic resonance spectroscopy study.

Depletion of muscle glycogen is considered a limiting performance factor during prolonged exercise, whereas the role of the intramyocellular lipid (IMCL) pool is not yet fully understood. We examined 1) intramyocellular glycogen and lipid utilization during prolonged exercise, 2) resynthesis of muscle glycogen and lipids during recovery, and 3) changes in glycogen content between nonexercising and exercising muscles during recovery. Subjects ran on a treadmill at submaximal intensity until exhaustion. Glycogen concentrations were assessed in thigh, calf, and nonexercising forearm muscle, and IMCL content was measured in soleus muscle using magnetic resonance spectroscopy techniques. At the time of exhaustion, glycogen depletion was 2-fold greater in calf than in thigh muscles, but a significant amount of glycogen was left in both leg muscles. The glycogen concentration in nonexercising forearm muscle decreased during the initial 5 h of recovery to 73% of the baseline value. Duringthe exercise, the IMCL content decreased to 67% and subsequently during recovery increased to 83% of the baseline value. In summary, we found during prolonged running 1) significantly greater muscle glycogen utilization in the calf muscle group than in the thigh muscle group, 2) significant utilization of IMCL in the soleus muscle, and 3) a decrease in glycogen content in nonexercising muscle and an increase in glycogen content in recovering muscles during the postexercise phase. These latter data are consistent with the hypothesis that there is transfer of glycogen by the glucose-lactate and the glucose-->alanine cycle from the resting muscle (forearm) to recovering muscles (thigh and calf) after running exercise.

Muscle glycogen resynthesis rate in humans after supplementation of drinks containing carbohydrates with low and high molecular masses.

The rate of muscle glycogen synthesis during 2 and 4 h of recovery after depletion by exercise was studied using two energy equivalent carbohydrate drinks, one containing a polyglucoside with a mean molecular mass of 500 000-700 000 (C drink), and one containing monomers and oligomers of glucose with a mean molecular mass of approximately 500 (G drink). The osmolality was 84 and 350 mosmol. l(-1), respectively. A group of 13 healthy well-trained men ingested the drinks after glycogen depleting exercise, one drink at each test occasion. The total amount of carbohydrates consumed was 300 g (4.2 g. kg(-1)) body mass given as 75 g in 500 ml water immediately after exercise and again 30, 60 ad 90-min post exercise. Blood glucose and insulin concentrations were recorded at rest and every 30 min throughout the 4-h recovery period. Muscle biopsies were obtained at the end of exercise and after 2 and 4 h of recovery. Mean muscle glycogen contents after exercise were 52.9 (SD 27.4) mmol glycosyl units. kg(-1) (dry mass) in the C group and 58.3 (SD 35.4) mmol glycosyl units. kg(-1) (dry mass) in the G group. Mean glycogen synthesis rate was significantly higher during the initial 2 h for the C drink compared to the G drink: 50.2 (SD 13.7) mmol. kg(-1) (dry mass). h(-1) in the C group and 29.9 (SD 12.5) mmol. kg(-1) (dry mass). h(-1) in the G group. During the last 2 h the mean synthesis rate was 18.8 (SD 33.3) and 23.3 (SD 22.4) mmol. kg(-1) (dry mass). h(-1) in the C and G group, respectively (n.s.). Mean blood glucose and insulin concentrations did not differ between the two drinks. Our data indicted that the osmolality of the carbohydrate drink may influence the rate of resynthesis of glycogen in muscle after its depletion by exercise.

Postexercise glucose uptake and glycogen synthesis in skeletal muscle from GLUT4-deficient mice.

To determine the role of GLUT4 on postexercise glucose transport and glycogen resynthesis in skeletal muscle, GLUT4-deficient and wild-type mice were studied after a 3 h swim exercise. In wild-type mice, insulin and swimming each increased 2-deoxyglucose uptake by twofold in extensor digitorum longus muscle. In contrast, insulin did not increase 2-deoxyglucose glucose uptake in muscle from GLUT4-null mice. Swimming increased glucose transport twofold in muscle from fed GLUT4-null mice, with no effect noted in fasted GLUT4-null mice. This exercise-associated 2-deoxyglucose glucose uptake was not accompanied by increased cell surface GLUT1 content. Glucose transport in GLUT4-null muscle was increased 1.6-fold over basal levels after electrical stimulation. Contraction-induced glucose transport activity was fourfold greater in wild-type vs. GLUT4-null muscle. Glycogen content in gastrocnemius muscle was similar between wild-type and GLUT4-null mice and was reduced approximately 50% after exercise. After 5 h carbohydrate refeeding, muscle glycogen content was fully restored in wild-type, with no change in GLUT4-null mice. After 24 h carbohydrate refeeding, muscle glycogen in GLUT4-null mice was restored to fed levels. In conclusion, GLUT4 is the major transporter responsible for exercise-induced glucose transport. Also, postexercise glycogen resynthesis in muscle was greatly delayed; unlike wild-type mice, glycogen supercompensation was not found. GLUT4 it is not essential for glycogen repletion since muscle glycogen levels in previously exercised GLUT4-null mice were totally restored after 24 h carbohydrate refeeding.-Ryder, J. W., Kawano, Y., Galuska, D., Fahlman, R., Wallberg-Henriksson, H., Charron, M. J., Zierath, J. R. Postexercise glucose uptake and glycogen synthesis in skeletal muscle from GLUT4-deficient mice.

NMR of glycogen in exercise.

Natural-abundance 13C NMR spectroscopy is a non-invasive technique that enables in vivo assessments of muscle and/or liver glycogen concentrations. Over the last several years, 13C NMR has been developed and used to obtain information about human glycogen metabolism with diet and exercise. Since NMR is non-invasive, more data points are available over a specified time course, dramatically improving the time resolution. This improved time resolution has enabled the documentation of subtleties of muscle glycogen re-synthesis following severe glycogen depletion that were not previously observed. Muscle and liver glycogen concentrations have been tracked in several different human populations under conditions that include: (1) muscle glycogen recovery from intense localized exercise with normal insulin and with insulin suppressed; (2) muscle glycogen recovery in an insulin-resistant population; (3) muscle glycogen depletion during prolonged low-intensity exercise; (4) effect of a mixed meal on postprandial muscle and liver glycogen synthesis. The present review focuses on basic 13C NMR and gives results from selected studies.

INFLUENCE OF CARBOHYDRATE-PROTEIN SUPPLEMENTATION AFTER 30KM RUNNING ON BLOOD ENERGY SUBSTRATE AND HORMONE KINETICS

881 It was reported that post-exercise carbohydrate(CHO)-protein(PRO) supplementation which induced higher insulin secretion and lower plasma glucose level can potentiate muscle glycogen resynthesis after prolonged cycling compared with CHO supplementation (Zawadzki et al. 1995). We investigated the influence of CHO-PRO supplementation on blood energy substrate and several hormone kinetics in the first 2 h after 30km outdoor running. Eight male runners (age; 20.3±0.5yr, Weight; 62.0±1.9kg, %fat; 10.9±1.0%, Vo2max; 4.5±0.2L, mean±SE) completed 30km running on two separate occasions. Immediately after each running, they ingested a solution containing 1) CHO (1.5g/kg) or 2) CHO (1.5g/kg) + PRO (0.5g/kg). Blood samples were collected before and immediately after running and at 1 and 2 h in recovery period to determine the concentrations of blood energy substrates (serum glucose, FFA and total protein), blood lactate and hormones (plasma insulin, cortisol, adrenaline, noradrenaline and free testosterone). Although at 1h after running plasma insulin level of CHO-PRO treatment (28.0±4.0μU) was significantly higher than that of CHO treatment (16.9±2.4μU), there were no differences in all blood substrates, blood lactate and the other hormones between the two treatments. Therefore, it was likely that glucose uptake and muscle glycogen resynthesis were not different between the two treatments, which was explained by 1) the impairment of glucose uptake induced by muscle damage due to eccentric contraction during outdoor running and/or 2) lower insulin secretion in CHO-PRO treatment than that of previous study by Zawadzki et al. These results indicate that CHO-PRO treatment after running can increase insulin secretion compared with CHO treatment, but not always potentiate glucose uptake.

POST-EXERCISE GLYCOGEN RESYNTHESIS IN RAT SKELETAL MUSCLE IS NOT MEDIATED BY BRADYKININ

85 Increasing evidence indicates that insulin action on skeletal muscle glucose metabolism can be modulated by the nonapeptide bradykinin, likely through the interaction of bradykinin with its BK2 receptor on skeletal muscle. The purpose of the present investigation was to determine if the marked resynthesis of glycogen that takes place in rat skeletal muscle immediately following an exhaustive bout of exercise is mediated by bradykinin interaction with BK2 receptors. Young, female Wistar rats swam for a total of 2 hr in order to deplete epitrochlearis muscle glycogen. Thereafter, half of the animals received intraperitoneal injections (100μg/kg body weight, in 0.9% saline) of the specific BK2-antagonist HOE 140 every 30 min, while the other half of the animals received saline only. All animals had free access to chow and a 10% sucrose solution during the recovery period. The exercise bout induced a significant glycogen depletion in the epitrochlearis muscle (21.4 ± 1.4 nmol/mg muscle in sedentary animals vs. 7.7 ± 0.4 nmol/mg in animals immediately after exercise, P<0.05). At 2 hr of recovery, the glycogen concentration in muscle from the saline-treated animals had increased to 31.4 ± 2.0 nmol/mg (P<0.05), while this value in the HOE 140-treated group was slightly, but not significantly, less (27.9 ± 2.5 nmol/mg). The results of this study indicate that the rapid glycogen resynthesis in skeletal muscle that takes place during the first 2 hr following a glycogen-depleting bout of swim exercise is likely not mediated by the nonapeptide bradykinin.

13C nuclear magnetic resonance study of glycogen resynthesis in muscle after glycogen-depleting exercise in healthy men receiving an infusion of lipid emulsion.

In healthy individuals, glycogen recovery after a strong depletion is known to be rapid and insulin independent during the initial phase, and subsequently, slow and insulin dependent. Free fatty acids (FFAs) as a putative source of insulin resistance (IR) could thus impair glycogen recovery during the second period. Using in vivo 13C nuclear magnetic resonance (NMR), we studied the effect of long-chain triglyceride emulsion on gastrocnemius glycogen resynthesis during a 3-h recovery period after 90 min of moderate exercise consisting of plantar flexion on overnight-fasted healthy men (n = 8). In separate experiments, each subject was infused with 10% Ivelip (0.015 ml x kg(-1) x min(-1)) or 10% glycerol (0.13 mg x kg(-1) x min(-1)). NMR spectra were acquired before and at the end of the exercise and during the recovery period. Whole-body glucose and lipid oxidation rates (indirect calorimetry), plasma insulin, C-peptide, glucose, lactate, beta-hydroxybutyrate, triglycerides, and FFAs were determined. Glycogen consumption was 47.6 +/- 4.5% (glycerol) and 49.7 +/- 4.8% (Ivelip) of the initial glycogen. An acquired IR in the Ivelip group was significant at the onset of the recovery period by homeostasis model assessment (P = 0.002). Glycogen resynthesis in the glycerol group appeared faster during the 1st h than during the subsequent 2nd h of the postexercise period. The glycogen resynthesis level was significantly lower in the Ivelip group than in the glycerol group during the recovery period (P = 0.04 during the 1st h and P = 0.001 during the next 2 h). During the recovery, plasma lactate and whole-body oxidation rates were similar in the two groups, whereas glycemia was significantly higher in the Ivelip group. A decreased cellular uptake of glucose as a substrate for glycogenosynthesis, rather than a competition between oxidation of carbohydrate and FFA, is discussed.

Utilization of skeletal muscle triacylglycerol during postexercise recovery in humans.

The utilization of muscle triacylglycerols was studied during and after prolonged bicycle ergometer exercise to exhaustion in eight healthy young men. Two days before exercise and in the postexercise recovery period, subjects were fed a carbohydrate-rich diet (65-70% of energy from carbohydrates). Exercise decreased muscle glycogen concentrations from 533 +/- 18 to 108 +/- 10 mmol/kg dry wt, whereas muscle triacylglycerol concentrations were unaffected (49 +/- 5 before vs. 49 +/- 8 mmol/kg dry wt after exercise). During the first 18 h after exercise, muscle glycogen concentrations were restored to 409 +/- 20 mmol/kg dry wt. In contrast, muscle triacylglycerol concentrations decreased (P < 0.05) to a nadir of 38 +/- 5 mmol/kg dry wt, and muscle lipoprotein lipase activity increased by 72% compared with values before exercise. Pulmonary respiratory exchange ratio values of 0.80-0.82 indicated a relatively high fractional lipid combustion despite the high carbohydrate intake. From 18 to 42 h of recovery, muscle glycogen synthesis was slow and muscle triacylglycerol concentrations and lipoprotein lipase activity were restored to the preexercise values. It is concluded that muscle triacylglycerol concentrations are not diminished during exhaustive glycogen-depleting exercise. However, in the postexercise recovery period, muscle glycogen resynthesis has high metabolic priority, resulting in postexercise lipid combustion despite a high carbohydrate intake. It is suggested that muscle triacylglycerols, and probably very low density lipoprotein triacylglycerols, are important in providing fuel for muscle metabolism in the postexercise recovery period.

Effect of fatty acid infusion on muscle glycogen resynthesis after exercise in healthy subjects: 13C NMR study

Effect of fatty acid infusion on muscle glycogen resynthesis after exercise in healthy subjects: ¹³C NMR study