Replenishment Of Muscle Glycogen Research Articles

Effects of eccentric and concentric exercise on muscle glycogen replenishment

Eccentric contractions appear to reduce muscle glycogen replenishment during the 1- to 10-day period after exercise. The main purpose of this study was to determine whether consuming a large amount of carbohydrate (1.6 g.kg-1.h-1) during the 4 h after glycogen-reducing exercise would produce different patterns of glycogen replenishment in human muscle that had undergone either eccentric or concentric contractions approximately 2 or 48 h earlier. Subjects cycled for 75 min and undertook interval exercise to deplete glycogen on days 1 and 3. After cycling exercise on day 1 only, subjects performed 10 sets of 10 repetitions of either concentric or eccentric contractions in opposite legs. During the 4 h after exercise, subjects consumed 0.4 g carbohydrate/kg body wt every 15 min. Biopsies were obtained immediately before the feedings and 4 h later, and blood was sampled every 15 min. For days 1 and 3 combined, total integrated areas for the glucose and insulin response curves averaged 1,683 mumol.ml-1.240 min-1 and 21,450 microU.ml-1.240 min-1, respectively. For days 1 and 3 combined, muscle glycogen replenishment after concentric exercise averaged 10 mmol.kg-1.h-1. On day 1 glycogen replenishment was similar for subjects performing either concentric or eccentric contractions. On day 3, however, glycogen replenishment was 25% lower (P < 0.05) in muscle that had undertaken eccentric contractions 48 h earlier than in concentrically exercised muscle. In conclusion, glycogen replenishment can be stimulated to a high rate when a large amount of carbohydrate is consumed after glycogen-depleting concentric exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery from endurance exercise

1) During training for and competition in endurance exercise athletes often significantly reduce both liver and muscle glycogen reserves. 2) Replenishment of muscle glycogen probably occurs preferentially over the replenishment of liver glycogen after exercise. 3) Muscle and liver glycogen can be replenished within 24 h after exercise provided adequate carbohydrate is consumed. 4) To replenish muscle glycogen within 24 h, 8-10 g carbohydrate.kg-1 body weight should be consumed. 5) To optimize muscle glycogen synthesis during the 4-6 h after exercise, carbohydrate must be consumed immediately after exercise and at frequent intervals thereafter. 6) While normal muscle and/or liver glycogen levels can be normalized 24 h after exercise, muscle function may or may not be fully recovered.

Patterns of Metabolic Recovery from Exercise in Amphibians and Reptiles

ABSTRACT The physiological responses of amphibians and reptiles undergoing vigorous exercise are qualitatively similar to those of other vertebrates. Oxygen consumption increases rapidly to rates that are three-to 10-fold the rates at rest. The aerobic response to graded exercise in locomoting reptiles and amphibians is for the most part linear. Oxygen transport by the cardiovascular system during exercise is accomplished by factorial increases in heart rate and oxygen extraction from arterial blood in a fashion similar to that in mammals. Increments in stroke volume during exercise are small or in some cases negative. The influence of temperature or of intracardiac shunting on the cardiovascular function of active amphibians and reptiles is poorly understood. These aerobic responses to exercise are accompanied by robust anaerobic contributions to energy metabolism, resulting in significant lactate accumulation and glycogen depletion. The rate of lactate accumulation during exercise is generally greater in reptiles than in amphibians, but in all cases is so rapid that the only significant substrate source to support anaerobic energy production is muscle glycogen. Vigorous behavior in these animals is therefore limited to some degree by the maintenance and replenishment of muscle glycogen stores. Whereas data from rats and dogs suggest that most lactate is oxidized to CO2 following exercise, amphibians and reptiles appear to use lactate as a substrate for immediate muscle glycogen replenishment. Data from a variety of amphibians and lizards demonstrate that lactate removal following activity and glycogen replenishment are stoichiometrically and temporally related. Studies employing isotopically labelled compounds in intact frogs and lizards indicate that most lactate is resynthesized to glycogen during recovery. In vivo studies suggest skeletal muscle as the site for glycogenesis from lactate, and in vitro studies from many laboratories demonstrate a gluconeogenic capacity in skeletal muscle of lizards, frogs and salamanders. The liver appears to play no significant role in recovery metabolism in any of these classes. Data from lizard muscle suggest that oxidative fiber types have the most significant gluconeogenic capacity, and that the process may be stimulated by the hormonal milieu that exists following exercise. Whereas the recovery metabolism of many mammals seems to facilitate the rapid return of acid-base balance via lactate oxidation, the strategy of lactate removal employed by amphibians and reptiles provides for a mechanism of immediate muscle glycogen replenishment and consequently a reestablished capacity for subsequent activity.

Lactate and Glycogen Metabolism in the Lizard Dipsosaurus Dorsalis following Exhaustive Exercise

ABSTRACT We evaluated the metabolic mechanisms by which the iguanid lizard Dipsosaurus dorsalis deals with the lactate which accumulates during vigorous exercise. Fasted, cannulated lizards were run for 5 min on a treadmill at 40°C, which elevated whole-body lactate to 24 mmol l-1 and depleted hindlimb glycogen to 70% of resting levels. Oxygen consumption increased fivefold and respiratory exchange ratios approached 2·0. Exhausted animals were then injected intravenously with either [U-14C]lactate or [U-14C]glucose, and allowed to recover quietly on the treadmill at 40°C. After 2h, 79% of the accumulated lactate had been removed and hindlimb muscle glycogen stores had returned to pre-exercise levels. Although blood glucose remained unchanged at 8·6 ± 0·27 mmol l-1 throughout the recovery period, whole-body glucose increased significantly from 1·6 ±0·23 to 5·5 ± 0·38mmoll-1 (P&amp;lt;0·05). Based on isotope distribution, 50% of the lactate removed was used to synthesize glucose and glycogen, but only 16 % of the lactate was oxidized. Lactate oxidation accounted for about 40% of the post-exercise oxygen consumption. Lactate rather than glucose appeared to be the prevalent substrate for muscle glycogen synthesis under these conditions. These animals appear to employ a strategy of lactate removal which is different from that in mammals; favoring lactate-supported gluco-and glyconeogenesis and rapid muscle glycogen replenishment instead of rapid lactate removal via oxidative pathways.

Effects of gluconeogenic precursor flux alterations on glycogen resynthesis after prolonged exercise.

The importance of gluconeogenic substrates (i.e., lactate, glycerol, and alanine) in the glycogen resynthesis observed in fasting rats after exhausting submaximal exercise [R.D. Fell et al. Am. J. Physiol. 238 (Regulatory Integrative Comp. Physiol. 7): R328-R332, 1980] was examined in muscles and liver in response to pharmacological alterations of gluconeogenic precursor flux. The minor role of lactate for glycogen resynthesis after prolonged submaximal exercise was confirmed by the insignificant accumulation of lactate neither in muscles nor in plasma. When the rate of lipolysis is reduced either by beta-blockade or by nicotinic acid injection, the replenishment of muscle glycogen persisted, suggesting that glycerol released by triglycerides hydrolysis did not play an important role in glycogen resynthesis. On the other hand, when pyruvate oxidation is enhanced by dichloroacetate (DCA), thus reducing plasma levels of lactate and alanine, glycogen resynthesis was completely blocked in liver and partly in some but not all muscles. This failure in total inhibition of glycogen resynthesis associated with the significant reduction of the plasma alanine level could be attributed to the possible stimulation of gluconeogenesis from alanine by DCA (R.A. Harris and D.W. Crabb. Arch. Biochem. Biophys. 189: 364-371, 1978). The results could point out alanine as the major gluconeogenic substrate during recovery from exhaustive exercise in fasting conditions.

Glycogen replenishment following exercise: effects of denervation and tenotomy.

To examine the role of the nervous system in the rapid replenishment of muscle glycogen that occurs after exhaustive exercise, glycogen stores and glycogen synthetase activity of normal gastrocnemius muscles of untrained and trained guinea pigs were compared to glycogen and synthetase activity of trained gastrocnemius muscles that were denervated or tenotomized immediately after exhaustive exercise and then allowed to recover for 48 h. The trained tenotomized muscles, but not the denervated muscles, had significantly (P smaller than 0.05) less glycogen than the trained normal muscles. These results suggest that neither nerve impulse conduction nor tropic substances contained in neural tissue proximal to the site of denervation mediate glycogen replenishment after exercise. The active, glucose 6-phosphate independent (I) form of glycogen synthetase activity was reduced by both denervation and tenotomy at 48 h after exercise with no significant (P greater than 0.05) differences detected for the total of I and D (glucose 6-phosphate dependent) synthetase activity. Synthetase I relative to total synthetase activity was similar in trained and untrained normal muscles, both of which had significantly (P smaller than 0.05) greater relative I activities than denervated or tenotomized muscles. These synthetase data show that elevated glycogen stores following recovery from exercise may be observed in the absence of increased levels of glycogen synthetase activity.

Postexercise glycogen replenishment in untrained animals

To test the hypothesis that an intact nerve supply is essential to normal replenishment of muscle glycogen after exhaustive exercise, glycogen concentration in normal gastrocnemius muscles from guinea pigs exhausted 48 hr previously was compared to glycogen in contralateral muscles that had been denervated at the muscle or high in the thigh immediately after exercise. Each animal of another group underwent tenotomy of one Achilles tendon after exercise so that any effect of disuse could be distinguished from effects of denervation. All muscles were able to replenish glycogen to normal control values 48 hr after exercise and surgery; there were no significant (greater than .05) effects of any of the surgical interventions. Therefore, it appears that glycogen concentration in skeletal muscle 48 hr after exhaustive exercise is independent of both neural phenomena and muscle tension.