Replenishment Of Muscle Glycogen Research Articles

Effect of multiday exercise on serum hormones and metabolic substrate concentrations in racing sled dogs

Prolonged submaximal exercise relies on the steady delivery of oxidizable substrates to the working muscle, with the sources of those substrates either stored reserves or food absorbed from the gastrointestinal tract during exercise. Fat oxidation could be advantageous for this type of exercise because of potentially greater reserves, but recent studies suggest that athletic dogs remain highly dependent on carbohydrate to fuel exercise despite ingesting a high fat diet. The purpose of this study was to characterise the pattern of exercise-induced hormone and substrate concentrations as they relate to carbohydrate and fat metabolism during prolonged submaximal exercise in dogs. Two studies (a 10-dog pilot study and a subsequent primary study using 54 Alaskan sled dogs) were conducted with the dogs running 160 km/day for 4 or 5 days. Blood samples were obtained within 60 min of cessation of daily exercise and in the second study within 30 min of the start of the next day of exercise. Samples were analysed for key hormones and substrates. Results demonstrated the development of a strong hormonal stimulus for glycogenolysis/gluconeogenesis that coincided with sparing and replenishment of muscle glycogen. The stimulus for glycogenolysis/gluconeogenesis tended to diminish during rest periods in the early stages of the exercise challenge, but remained increased during later rest periods and for several days after the conclusion of exercise. These data support the hypothesis that in the face of a high-fat diet, ultra-endurance racing sled dogs rely on large amounts of hepatic glucose output to support prolonged submaximal exercise.

Metabolic demands and replenishment of muscle glycogen after a rugby league match simulation protocol.

The metabolic requirements of a rugby league match simulation protocol and the timing of carbohydrate provision on glycogen re-synthesis in damaged muscle were examined. Fifteen (mean±SD: age 20.9±2.9 year, body-mass 87.3±14.1kg, height 177.4±6.0cm) rugby league (RL) players consumed a 6gkgday-1 CHO diet for 7-days, completed a time to exhaustion test (TTE) and a glycogen depletion protocol on day-3, a RL simulated-match protocol (RLMSP) on day-5 and a TTE on day-7. Players were prescribed an immediate or delayed (2-h-post) re-feed post-simulation. Muscle biopsies and blood samples were obtained post-depletion, before and after simulated match-play, and 48-h after match-play with PlayerLoad and heart-rate collected throughout the simulation. Data were analysed using effects sizes±90% CI and magnitude-based inferences. PlayerLoad (8.0±0.7 AUmin-1) and %HRpeak (83±4.9%) during the simulation were similar to values reported for RL match-play. Muscle glycogen very likely increased from immediately after to 48-h post-simulation (272±97 cf. 416±162mmolkg-1d.w.; ES±90%CI) after immediate re-feed, but changes were unclear (283±68 cf. 361±144mmolkg-1d.w.; ES±90%CI) after delayed re-feed. CK almost certainly increased by 77.9±25.4% (0.75±0.19) post-simulation for all players. The RLMSP presents a replication of the internal loads associated with professional RL match-play, although difficulties in replicating the collision reduced the metabolic demands and glycogen utilisation. Further, it is possible to replete muscle glycogen in damaged muscle employing an immediate re-feed strategy.

The effect of an amino acid beverage on glucose response and glycogen replenishment after strenuous exercise.

We previously reported that an amino acid mixture (AA) was able to lower the glucose response to an oral glucose challenge in both rats and humans. Increased glucose uptake and glycogen storage in muscle might be associated with the faster blood glucose clearance. We therefore tested the effect of two different doses of AA provided with a carbohydrate supplement on blood glucose homeostasis and muscle glycogen replenishment in human subjects after strenuous aerobic exercise. Ten subjects received a carbohydrate (1.2g/kg body weight, CHO), CHO/HAA (CHO+13g AA), or CHO/LAA (CHO+6.5g AA) supplement immediately and 2h after an intense cycling bout. Muscle biopsies were performed immediately and 4h after exercise. The glucose responses for CHO/HAA and CHO/LAA during recovery were significantly lower than CHO, as was the glucose area under the curve (CHO/HAA 1259.9±27.7, CHO/LAA 1251.5±47.7, CHO 1376.8±52.9mmol/L 4h, p<0.05). Glycogen storage rate was significantly lower in CHO/HAA compared with CHO, while it did not differ significantly between CHO/LAA or CHO (CHO/HAA 15.4±2.0, CHO/LAA 18.1±2.0, CHO 21.5±1.4µmol/g wet muscle 4h). CHO/HAA caused a significantly higher insulin response and a greater effect on mTOR and Akt/PKB phosphorylation compared with CHO. Phosphorylation of AS160 and glycogen synthase did not differ across treatments. Likewise, there were no differences in blood lactate across treatments. The AA lowered the glucose response to a carbohydrate supplement after strenuous exercise. However, it was not effective in facilitating subsequent muscle glycogen storage.

The effects of intermittent training and age on blood lactate (La) Level and lactate dehydrogenase enzyme (LDH) activity in male wistar rats.

Introduction: Physical activity and age are among the factors affecting lactate levels and lactate dehydrogenase activity. Physical activity appears to be able to counterbalance the morphological and metabolic changes associated with aging that decrease physical ability and performance. Objectives: The purpose of the present study was to assess the effects of interval training on blood lactate levels and lactate dehydrogenase activity in young and old rats. Materials and Methods: A total of 40 male rats were selected and then divided into two age groups -the old group (20 rats aged 27 months and weighing 389±31 g) and the young group (20 rats aged 3 months and weighing 224±13 g). Each group was itself randomly divided into an experimental group (n=10) and a control group (n=10). The training protocol involved 4 minutes of running on the treadmill with intervals of 2 minutes active resting in 10 training bouts of 60 minutes, for 6 sessions per week and for 8 weeks and gradually increasing in intensity. Twenty-four hours after the last training session, the rats were anesthetized with a mixture of ketamine and xylazine in order for their blood sample to be collected from their cardiac puncture. Their lactate levels and LDH activity were then measured by an enzymatic method. Data were analyzed using the one-way ANOVA and Tukey's post-hoc test. Results: The results showed no significant differences in blood lactate levels between the four groups; however, LDH activity was significantly higher in the young experimental group than in the young control group (p<0/05). Conclusion: The results indicate that lactate is increasingly cleared by interval training. It also appears that the effect of training on lactate clearance is similar in both young age and old age. Monitoring blood lactate levels benefits muscle glycogen replenishment and intracellular pH (pHi) regulation.

Metabolic responses to exhaustive exercise change markedly during the protracted non-trophic spawning migration of the lamprey Geotria australis

Adults of the Southern hemisphere lamprey Geotria australis were subjected to an exercise/recovery regime at the commencement and end of their 12-15 month non-trophic, upstream spawning migration. In early (immature) migrants and pre-spawning females, muscle glycogen was markedly depleted during exercise, but became rapidly replenished. As muscle lactate rose during exercise and peaked 1-1.5 h into the recovery period, and therefore after muscle glycogen had become replenished, it cannot be the direct source for that replenishment. However, both plasma lactate and glycerol (but not muscle glycerol and glucose) rose sharply during exercise and then declined markedly during the first 0.5 h of recovery and thus exhibited the opposite trend to that of muscle glycogen, implying that these limited pools of glycogenic precursors contribute to glycogen replenishment. Although plasma glucose rose following exercise, and consequently could also be a precursor for muscle glycogen replenishment, it remained elevated even after muscle glycogen had become replenished. While resting pre-spawning females and mature males retained high muscle glycogen concentrations, this energy store became permanently depleted in females during spawning. In mature males, muscle glycogen remained high and lactate low during the exercise/recovery regime, whereas muscle glycerol declined precipitously during exercise and then rose rapidly. In summary, vigorous activity by G. australis is fuelled extensively by anaerobic metabolism of glycogen early in the spawning run and by pre-spawning females, but by aerobic metabolism of its energy reserves in mature males.

Food-dependent, exercise-induced gastrointestinal distress

Among athletes strenuous exercise, dehydration and gastric emptying (GE) delay are the main causes of gastrointestinal (GI) complaints, whereas gut ischemia is the main cause of their nausea, vomiting, abdominal pain and (blood) diarrhea. Additionally any factor that limits sweat evaporation, such as a hot and humid environment and/or body dehydration, has profound effects on muscle glycogen depletion and risk for heat illness. A serious underperfusion of the gut often leads to mucosal damage and enhanced permeability so as to hide blood loss, microbiota invasion (or endotoxemia) and food-born allergen absorption (with anaphylaxis). The goal of exercise rehydration is to intake more fluid orally than what is being lost in sweat. Sports drinks provide the addition of sodium and carbohydrates to assist with intestinal absorption of water and muscle-glycogen replenishment, respectively. However GE is proportionally slowed by carbohydrate-rich (hyperosmolar) solutions. On the other hand, in order to prevent hyponatremia, avoiding overhydration is recommended. Caregiver's responsibility would be to inform athletes about potential dangers of drinking too much water and also advise them to refrain from using hypertonic fluid replacements.

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrolyte solution (electrolyte) via nasogastric tube, followed by a typical hay/grain meal, or a hay/grain meal alone (control). The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 +/- 0.3 liters and 22.6%, respectively, in the control treatment, and 8.2 +/- 0.4 liters and 21.9% in the electrolyte treatment. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma protein concentration, maintenance of plasma osmolality, and greater muscle intracellular fluid volume) during the recovery period compared with control. There were no differences in muscle Na, K, Cl, or Mg contents between the two treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate-intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared with control. It is speculated that postexercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses.

Effects of dietary glycaemic response after exercise on blood concentrations of substrates used indirectly for muscle glycogenesis

Exercise depletes muscle glycogen stores, which could subsequently impair performance. Muscle glycogen replenishment is determined by substrate availability. To study the effects of feeding meals of varying glycaemic responses on blood concentrations of substrates used for glycogenesis in horses with exercise-induced glycogen depletion. In a 3-way crossover study, 7 horses received each of 3 isocaloric diets for 72 h after undergoing glycogen-depleting exercise: 1) a high soluble-carbohydrate diet, which induced a high-glycaemic (HGI) response; 2 and 3) a low soluble-carbohydrate or a mixed soluble-carbohydrate diet (control group), which both induced a similar low-to-moderate glycaemic (LGI) response. Muscle biopsies and venous samples were collected before and up to 72 h after exercise. Feeding HGI diet resulted in a higher (P<0.001) rate of muscle glycogenesis over 72 h compared to LGI diets. Plasma glycerol, triglyceride, lactate, serum NEFA and total protein concentrations, and haematocrit were significantly (P<0.001) higher after compared to before exercise. Whereas no significant overall dietary effect was observed on these metabolites over 72 h, there was a tendency for glycerol, NEFA and triglyceride concentrations to be lower for LGI compared to HGI diets over 6 h after exercise (P<0.05; 1, 6 and 4-6 h after exercise, respectively). These data suggest that horses fed LGI meals after exercise had limited lipid utilisation without any significant shift of substrate utilisation toward gluconeogenesis, which could have contributed to the slower rate of muscle glycogenesis compared to horses fed HGI diets.

Ingestion of starch-rich meals after exercise increases glucose kinetics but fails to enhance muscle glycogen replenishment in horses

Fatiguing exercise substantially decreases muscle glycogen concentration in horses, impairing athletic performance in subsequent exercise bouts. Our objective was to determine the effect of ingestion of starch-rich meals after exercise on whole body glucose kinetics and muscle glycogen replenishment. In a randomized, cross-over study seven horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed half of the daily energy requirements (∼15 Mcal DE) as hay, or fed an isocaloric amount of corn 15 min and 4 h after exercise. Starch-rich meals fed after exercise, when compared to feed withholding, resulted in mild to moderate hyperglycemia (5.7 ± 0.3 vs. 4.7 ± 0.3 mM, P < 0.01) and hyperinsulinemia (79.9 ± 9.3 vs. 39.0 ± 1.9 pM, P < 0.001), 3-fold greater whole body glucose kinetics (15.5 ± 1.4 vs. 5.3 ± 0.4 μmol kg −1 min −1, P < 0.05), but these only minimally enhanced muscle glycogen replenishment (171 ± 19 vs. 170 ± 56 and 260 ± 45 vs. 294 ± 29 mmol/kg dry weight immediately and 24 h after exercise, P > 0.05). It is concluded that after substantial exercise-induced muscle glycogen depletion, feeding status only minimally affects net muscle glycogen concentrations after exercise, despite marked differences in soluble carbohydrate ingestion and availability of glucose to skeletal muscle.

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.

Effects of Recovery Beverages on Glycogen Restoration and Endurance Exercise Performance

The restorative capacities of a high carbohydrate-protein (CHO-PRO) beverage containing electrolytes and a traditional 6% carbohydrate-electrolyte sports beverage (SB) were assessed after glycogen-depleting exercise. Postexercise ingestion of the CHO-PRO beverage, in comparison with the SB, resulted in a 55% greater time to exhaustion during a subsequent exercise bout at 85% maximum oxygen consumption (Vo2max). The greater recovery after the intake of the CHO-PRO beverage could be because of a greater rate of muscle glycogen storage. Therefore, a second study was designed to investigate the effects of after exercise CHO-PRO and SB supplements on muscle glycogen restoration. Eight endurance-trained cyclists (Vo2max = 62.1 ± 2.2 ml·kg-1 body wt·min-1) performed 2 trials consisting of a 2-hour glycogen-depletion ride at 65–75% Vo2max. Carbohydrate-protein (355 ml; ∼0.8 g carbohydrate (CHO)·kg-1 body wt and ∼0.2 g protein·kg-1 body wt) or SB (355 ml; ∼0.3 g CHO·kg-1 body wt) was provided immediately and 2 hours after exercise. Trials were randomized and separated by 7–15 days. Ingestion of the CHO-PRO beverage resulted in a 17% greater plasma glucose response, a 92% greater insulin response, and a 128% greater storage of muscle glycogen (159 ± 18 and 69 ± 32 fxmol·g-1 dry weight for CHO-PRO and SB, respectively) compared with the SB (p < 0.05). These findings indicate that the rate of recovery is coupled with the rate of muscle glycogen replenishment and suggest that recovery supplements should be consumed to optimize muscle glycogen synthesis as well as fluid replacement.

Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement.

In the present study, we tested the hypothesis that a carbohydrate-protein (CHO-Pro) supplement would be more effective in the replenishment of muscle glycogen after exercise compared with a carbohydrate supplement of equal carbohydrate content (LCHO) or caloric equivalency (HCHO). After 2.5 +/- 0.1 h of intense cycling to deplete the muscle glycogen stores, subjects (n = 7) received, using a rank-ordered design, a CHO-Pro (80 g CHO, 28 g Pro, 6 g fat), LCHO (80 g CHO, 6 g fat), or HCHO (108 g CHO, 6 g fat) supplement immediately after exercise (10 min) and 2 h postexercise. Before exercise and during 4 h of recovery, muscle glycogen of the vastus lateralis was determined periodically by nuclear magnetic resonance spectroscopy. Exercise significantly reduced the muscle glycogen stores (final concentrations: 40.9 +/- 5.9 mmol/l CHO-Pro, 41.9 +/- 5.7 mmol/l HCHO, 40.7 +/- 5.0 mmol/l LCHO). After 240 min of recovery, muscle glycogen was significantly greater for the CHO-Pro treatment (88.8 +/- 4.4 mmol/l) when compared with the LCHO (70.0 +/- 4.0 mmol/l; P = 0.004) and HCHO (75.5 +/- 2.8 mmol/l; P = 0.013) treatments. Glycogen storage did not differ significantly between the LCHO and HCHO treatments. There were no significant differences in the plasma insulin responses among treatments, although plasma glucose was significantly lower during the CHO-Pro treatment. These results suggest that a CHO-Pro supplement is more effective for the rapid replenishment of muscle glycogen after exercise than a CHO supplement of equal CHO or caloric content.

Muscle glycogen depletion and subsequent replenishment affect anaerobic capacity of horses

The purpose of this study was to determine the effect of muscle glycogen depletion and subsequent replenishment on anaerobic capacity of horses. In a blinded crossover study, seven fit horses performed glycogen-depleting exercise on two occasions. Horses were infused after glycogen-depleting exercise with either 6 g/kg body wt of glucose as a 13.5% solution in 0.9% NaCl (Glu) or with 0.9% NaCl (Sal) of equivalent volume. Subsequently, horses performed a high-speed exercise test (120% of maximal rate of oxygen consumption) to estimate maximum accumulated oxygen deficit. Replenishment of muscle glycogen was greater (P < 0.05) in Glu [from 24.7 +/- 7.2 (SE) to 116.5 +/- 7 mmol/kg wet wt before and after infusion, respectively] than in Sal (from 23.4 +/- 7.2 to 47.8 +/- 5.7 mmol/kg wet wt before and after infusion, respectively). Run time to fatigue during the high-speed exercise test (97.3 +/- 8.2 and 70.8 +/- 8.3 s, P < 0.05), maximal accumulated oxygen deficit (105.7 +/- 9.3 and 82.4 +/- 10.3 ml O(2) equivalent/kg, P < 0.05), and blood lactate concentration at the end of the high-speed exercise test (11.1 +/- 1.4 and 9.2 +/- 3.7 mmol/l, P < 0.05) were greater for Glu than for Sal, respectively. We concluded that decreased availability of skeletal muscle glycogen stores diminishes anaerobic power generation and capacity for high-intensity exercise in horses.

Dietary Strategies to Promote Glycogen Synthesis After Exercise

Muscle glycogen is an essential fuel for prolonged intense exercise, and therefore it is important that the glycogen stores be copious for competition and strenuous training regimens. While early research focused on means of increasing the muscle glycogen stores in preparation for competition and its day-to-day replenishment, recent research has focused on the most effective means of promoting its replenishment during the early hours of recovery. It has been observed that muscle glycogen synthesis is twice as rapid if carbohydrate is consumed immediately after exercise as opposed to waiting several hours, and that a rapid rate of synthesis can be maintained if carbohydrate is consumed on a regular basis. For example, supplementing at 30-min intervals at a rate of 1.2 to 1.5 g CHO x kg(-1) body wt x h(-1) appears to maximize synthesis for a period of 4- to 5-h post exercise. If a lighter carbohydrate supplement is desired, however, glycogen synthesis can be enhanced with the addition of protein and certain amino acids. Furthermore, the combination of carbohydrate and protein has the added benefit of stimulating amino acid transport, protein synthesis and muscle tissue repair. Research suggests that aerobic performance following recovery is related to the degree of muscle glycogen replenishment.

Influence of Fluid Replacement on Short-Term Recovery and Subsequent Exercise Performance

LANGUAGE NOTE | Document text in English; abstract also in Chinese.Rapid fluid replacement and replenishment of muscle glycogen after prolonged exercise are vital for optimal substrate provision, cardiovascular function, and thermoregulation during subsequent bouts of vigorous exercise on the same day. This paper reviews recent work relating to the effects of rehydration with carbohydrate-electrolyte solutions during a short-term recovery period on hydration status, physiological responses, and subsequent endurance capacity. Issues investigated and discussed were drinking patterns, amount of carbohydrate (CHO) consumed, and the volume of fluid ingested. The data are presented as a series of summaries of experiments, followed by a discussion of the implications. The main findings of the studies reported suggest that in order to achieve euhydration during short-term recovery, a volume of fluid substantially larger than that lost must be ingested. The provision of additional CHO would be expected to restore the body's CHO stores to a greater extent than a smaller amount of CHO during the recovery and, thereby, improve the subsequent endurance capacity. However, this was not the case. It appears that the ingestion of large amounts of CHO, during a short recovery period, resulted in disturbances in fat and CHO metabolism which prevented an improvement in endurance capacity during subsequent exercise, after consumption of the additional CHO.運動後迅速補充水份及恢復肌肉內的糖元對同日要進行的激烈運動十分重要，因爲能量代謝、心肺功能及體溫調節也以此爲基礎。本文主要綜述最近有關此課題之研究，旨在探討在含有碳水化合物及電解質之飮品影響下，體內水份所作出之調節、各項生理變化及恢復後之運動能力。研究結果顯示，若要在短時間之恢復期內重新達至水份平衡，人體有需要攝取比在運動時所失去之水份爲多之液體。在此短暫恢復期間，若攝取大量的碳水化合物將會引致能量代謝出現不正常的反應，並會影響隨後的運動能力。

Postexercise recovery of skeletal muscle malonyl-CoA, acetyl-CoA carboxylase, and AMP-activated protein kinase.

Previous studies have demonstrated that oxygen consumption and fat oxidation remain elevated in the postexercise period. The purpose of this study was to determine whether malonyl-CoA, an inhibitor of fatty acid oxidation, remains depressed in muscle after exercise. Rats were sprinted for 5 min (40 m/min, 5% grade) or run for 30 min (21 m/min, 15% grade). Red quadriceps malonyl-CoA returned to resting values by 90 min postexercise in the sprinting rats and remained significantly lower at least 90 min postexercise in the 30-min exercise group. AMP-activated protein kinase activity remained significantly elevated (P < 0.05) for 10 min after exercise in both groups. The most rapid rate of glycogen repletion was in the first 30 min postexercise. The respiratory exchange ratio decreased from a nonexercise value of 0.87 +/- 0.01 to an average 0.82 +/- 0.01 during the 90-min period after 30 min of exercise. Thus muscle malonyl-CoA remains depressed and fat oxidation is elevated for relatively prolonged periods after a single bout of exercise. This may allow fat oxidation to contribute more to muscle energy requirements, thus leaving more glucose for replenishment of muscle glycogen.

Glycogen Resynthesis After Exercise: Effect of Carbohydrate Intake

To maximize glycogen resynthesis after exercise, a carbohydrate supplement in excess of 1.0 g x kg(-1) body wt should be consumed immediately after competition or a training bout. Continuation of supplementation every two hours will maintain a rapid rate of storage up to six hours post exercise. Supplements composed of glucose or glucose polymers are the most effective for replenishment of muscle glycogen, whereas fructose is most beneficial for the replenishment of liver glycogen. The addition of protein to a carbohydrate supplement may also increase the rate of glycogen storage due to the ability of protein and carbohydrate to act synergistically on insulin secretion.

Replenishment of muscle glycogen after high-intensity exercise: a role for intramuscular lactate glyconeogenesis?

Replenishment of muscle glycogen after high-intensity exercise: a role for intramuscular lactate glyconeogenesis?

Systemic effects of ingesting varying amounts of a commercial carbohydrate beverage postexercise.

Although the role of postexercise carbohydrate intake in the replenishment of muscle glycogen is well established, large amounts of carbohydrate may affect other systems which are recovering from exercise as well. We varied the timing and amount of a commercial glucose polymer/fructose (CHO) beverage ingested postexercise in 2 groups of 8 normotensive men following 1 hour of cycling exercise. In Study A the subjects ingested 1 L of a 200 g CHO solution or 1 L of water (W) immediately postexercise. The participants in Study B consumed 1 L of a 1.5 g/kg CHO solution, or W, immediately and 2 hours postexercise. Recovery systolic blood pressure was elevated after 200 g CHO as compared to water, but not after 1.5 g/kg CHO. Diastolic blood pressure was decreased, while heart rate, insulin and glucose increased following both doses of CHO. Despite the potassium (K) content of the beverages, serum K decreased in Study A and B, while a trend was noted following CHO for decreased urinary K excretion at 2 hours and for increased sodium excretion at 4 hours in Study B. Post CHO aldosterone declined more rapidly than after W, and urine volumes were decreased compared to W in both studies 2 hours after CHO. We speculate that hyperinsulinemia contributed to the rapid decline in K and aldosterone by creating a flux of K to the intracellular space. It appears that CHO ingestion postexercise results in systemic effects that are related to the amount and timing of CHO consumed.

Lactate Metabolism In Rainbow Trout

ABSTRACT We have investigated the metabolic fate of blood lactate in resting rainbow trout and in fish recovering from a bout of exhaustive exercise. At rest and during recovery from exercise, the majority of blood lactate was oxidized, the proportion increasing with increasing oxygen consumption. It is estimated that, during recovery from exhaustive exercise, lactate released from the muscle has the potential to fuel a significant portion of oxidative metabolism. The bulk of the remaining blood lactate reappeared in the muscle lactate pool, probably via direct uptake by the muscle. There was a significant incorporation of blood lactate into the muscle glycogen pool, providing strong evidence for in situ glycogenesis as the mode for muscle glycogen replenishment. To investigate the role of the liver in blood lactate clearance, trout were functionally hepatectomized by ligation of the hepatic portal circulation. The exercise performance of hepatectomized fish was equal to that of sham-operated fish and controls, indicating that muscle relies primarily on endogenous fuel stores. Furthermore, blood lactate levels immediately after exercise were greater and muscle metabolic recovery was faster in hepatectomized fish than in sham-operated fish and controls. These observations suggest that glycogen resynthesis in trout muscle may be retarded because of a non-recoverable loss of substrate (i.e. lactate) from the muscle, because the lactate released is utilized by the liver. These results are discussed in view of what is known about these processes in other ectothermic vertebrates.