Muscle Glycogen Degradation Research Articles

Differences in exercise capacity and muscle glycogen metabolism in C57BL/6J and BALB/cA mice.

This study compared differences in exercise capacity as well as muscle glycogen content and degradation, and mitochondrial enzyme activity between C57BL/6J and BALB/cA mice. In exercise tests, grip strength was higher in BALB/cA mice. In Rotarod and Inverted screen test, C57BL/6J mice had significantly longer exercise durations and showed differences in motor function and muscle endurance time. Glycogen in the liver and muscle of C57BL/6J mice was significantly decreased after 20 min of swimming. Muscle glycogen content in BALB/cA mice was higher than in C57BL/6J, but swimming induced no decrease in glycogen content. Glycogen phosphorylase in muscle was inactive in the absence of AMP, and its activity increased in a concentration-dependent manner with the addition of AMP in C57BL/6J mice. In BALB/cA mice, phosphorylase activity was increased by AMP, but not further increased by higher concentrations of AMP. The citrate synthase activity in muscle did not differ between C57BL/6J and BALB/cA mice. The results of this study suggested that the reactivity of muscle glycogen phosphorylase to AMP differs among strains of mice and affects glycogen availability during exercise.

The physiology of ice hockey performance: An update.

Ice hockey is an intense team sport characterized by repeated bursts of fast-paced skating, rapid changes in speed and direction and frequent physical encounters. These are performed in on-ice shifts of ~30-80 s interspersed with longer sequences of passive recovery, resulting in about 15-25 min on-ice time per player. Nearly 50% of the distance is covered at high-intensity skating speeds and with an accentuated intense activity pattern in forwards compared to defensemen. During ice hockey match-play, both aerobic and anaerobic energy systems are significantly challenged, with the heart rate increasing toward maximum levels during each shift, and with great reliance on both glycolytic and phosphagen ATP provision. The high-intensity activity pattern favors muscle glycogen as fuel, leading to pronounced reductions despite the relatively brief playing time, including severe depletion of a substantial proportion of individual fast- and slow-twitch fibers. Player-tracking suggests that the ability to perform high-intensity skating is compromised in the final stages of a game, which is supported by post-game reductions in repeated-sprint ability. Muscle glycogen degradation, in particular in individual fibers, as well as potential dehydration and hyperthermia, may be prime candidates implicated in exacerbated fatigue during the final stages of a game, whereas multiple factors likely interact to impair exercise tolerance during each shift. This includes pronounced PCr degradation, with potential inadequate resynthesis in a proportion of fast-twitch fibers in situations of repeated intense actions. Finally, the recovery pattern is inadequately described, but seems less long-lasting than in other team sports.

Muscle Metabolism and Fatigue during Simulated Ice Hockey Match-Play in Elite Players.

The present study investigated muscle metabolism and fatigue during simulated elite male ice hockey match-play. Thirty U20 male national team players completed an experimental game comprising three periods of 8 × 1-min shifts separated by 2-min recovery intervals. Two vastus lateralis biopsies were obtained either during the game (n = 7) or pregame and postgame (n = 6). Venous blood samples were drawn pregame and at the end of the first and last periods (n = 14). Activity pattern and physiological responses were continuously monitored using local positioning system and heart rate recordings. Further, repeated-sprint ability was tested pregame and after each period. Total distance covered was 5980 ± 199 m with almost half the distance covered at high skating speeds (>17 km·h). Average and peak on-ice heart rate was 84% ± 2% and 97% ± 2% of maximum heart rate, respectively. Muscle lactate increased (P ≤ 0.05) more than fivefold and threefold, whereas muscle pH decreased (P ≤ 0.05) from 7.31 ± 0.04 pregame to 6.99 ± 0.07 and 7.13 ± 0.11 during the first and last periods, respectively. Muscle glycogen decreased by 53% postgame (P ≤ 0.05) with ~65% of fast- and slow-twitch fibers depleted of glycogen. Blood lactate increased sixfold (P ≤ 0.05), whereas plasma free fatty acid levels increased 1.5-fold and threefold (P ≤ 0.05) after the first and last periods. Repeated-sprint ability was impaired (~3%; P ≤ 0.05) postgame concomitant with a ~10% decrease in the number of accelerations and decelerations during the second and last periods (P ≤ 0.05). Our findings demonstrate that a simulated ice hockey match-play scenario encompasses a high on-ice heart rate response and glycolytic loading resulting in a marked degradation of muscle glycogen, particularly in specific sub-groups of fibers. This may be of importance both for fatigue in the final stages of a game and for subsequent recovery.

2-deoxy-2-[18]fluoro-D-glucose PET/CT (18FDG PET/CT) may not be a viable biomarker in Pompe disease

BackgroundPompe disease (PD) is an autosomal recessive, lysosomal storage disease due to a mutation of the acid α-glucosidase (GAA) gene. In adult patients, PD is characterized by slowly progressive limb-girdle and trunk myopathy and restrictive respiratory insufficiency. Enzyme replacement therapy (ERT) is available, improving or stabilizing muscle-function in some and slowing deterioration in other patients. Unfortunately, there is no biomarker available to indicate therapeutic efficacy and/or disease activity. Whole body MRI depicts all skeletal muscles demonstrating foci of atrophic muscles, i.e., late and irreversible pathological changes. Any method indicating the localizations of increased muscle glycogen storage, muscle inflammation and/or degradation could possibly help identifying newly afflicted tissue and may be of prognostic value. We therefore investigated 2-deoxy-2-[18]fluoro-D-glucose (FDG) PET, a biomarker for glucose-metabolism, as a tool to evaluate disease activity and prognosis in PD.MethodsIn a pilot study, we investigated four patients by FDG dynamic PET/CT while on ERT. One patient had FDG-PET/CT twice, before and after 12 months on ERT. Dynamic FDG-PET/CT quantifies the metabolic rate of glucose utilisation in mg/ml/min. MRI was performed in parallel with pelvic and thigh muscles semi-quantitatively scored for atrophy and disease-activity.ResultsNone of the muscles analysed showed a focally increased FDG-uptake. Thus, quantification of muscle glucose metabolism could not be calculated. However, increased FDG-uptake, i.e., increased glucose utilisation, was observed in the respiratory muscles of one patient with severe, restrictive respiratory failure. In contrast, specific MRI sequences showed oedematous as well as atrophic muscle areas in PD.ConclusionsOur pilot study demonstrates that FDG-uptake does not correlate with glycogen storage in vivo. In contrast, MRI is an excellent tool to demonstrate the extent of muscle involvement. Specific MRI sequences may even demonstrate early changes possibly allowing prognostic predictions or localization of early stages of PD.

Influence of Post-Exercise Carbohydrate-Protein Ingestion on Muscle Glycogen Metabolism in Recovery and Subsequent Running Exercise.

We examined whether carbohydrate-protein ingestion influences muscle glycogen metabolism during short-term recovery from exhaustive treadmill running and subsequent exercise. Six endurance-trained individuals underwent two trials in a randomized double-blind design, each involving an initial run-to-exhaustion at 70% VO2max (Run-1) followed by 4-h recovery (REC) and subsequent run-to-exhaustion at 70% VO2max (Run-2). Carbohydrate-protein (CHO-P; 0.8 g carbohydrate·kg body mass [BM-1]·h-1 plus 0.4 g protein·kg BM-1·h-1) or isocaloric carbohydrate (CHO; 1.2 g carbohydrate·kg BM-1·h-1) beverages were ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run-1, postrecovery and fatigue in Run-2. Time-to-exhaustion in Run-1 was similar with CHO and CHO-P (81 ± 17 and 84 ± 19 min, respectively). Muscle glycogen concentrations were similar between treatments after Run-1 (99 ± 3 mmol·kg dry mass [dm-1]). During REC, muscle glycogen concentrations increased to 252 ± 45 mmol·kg dm-1 in CHO and 266 ± 30 mmol·kg dm-1 in CHO-P (p = .44). Muscle glycogen degradation during Run-2 was similar between trials (3.3 ± 1.4 versus 3.5 ± 1.9 mmol·kg dm-1·min-1 in CHO and CHO-P, respectively) and no differences were observed at the respective points of exhaustion (93 ± 21 versus 100 ± 11 mmol·kg dm-1; CHO and CHO-P, respectively). Similarly, time-to-exhaustion was not different between treatments in Run-2 (51 ± 13 and 49 ± 15 min in CHO and CHO-P, respectively). Carbohydrate-protein ingestion equally accelerates muscle glycogen resynthesis during short-term recovery from exhaustive running as when 1.2 g carbohydrate·kg BM-1·h-1 are ingested. The addition of protein did not alter muscle glycogen utilization or time to fatigue during repeated exhaustive running.

Impact of Muscle Glycogen Availability on the Capacity for Repeated Exercise in Man.

This study aims to examine whether muscle glycogen availability is associated with fatigue in a repeated exercise bout following short-term recovery. Ten endurance-trained individuals underwent two trials in a repeated-measures experimental design, each involving an initial run to exhaustion at 70% of VO2max (Run 1) followed by a 4-h recovery and a subsequent run to exhaustion at 70% of VO2max (Run 2). A low-carbohydrate (L-CHO; 0.3 g · kg body mass(-1) · h(-1)) or high-carbohydrate (H-CHO; 1.2 g · kg body mass(-1) · h(-1)) beverage was ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run 1, after recovery, and at exhaustion during Run 2 in L-CHO (F2). In H-CHO, muscle biopsies were obtained after recovery, at the time point coincident with fatigue in L-CHO (F2), and at the point of fatigue during the subsequent exercise bout (F3). Run 2 was more prolonged for participants on H-CHO (80 ± 16 min) than for participants on L-CHO (48 ± 11 min; P < 0.001). Muscle glycogen concentrations were higher at the end of recovery for participants on H-CHO (269 ± 84 mmol · kg dry mass(-1)) than for participants on L-CHO (157 ± 37 mmol · kg dry mass(-1); P = 0.001). The rate of muscle glycogen degradation during Run 2 was higher with H-CHO (3.1 ± 1.5 mmol · kg dry mass(-1) · min(-1)) than with L-CHO (1.6 ± 1.3 mmol · kg dry mass(-1) · min(-1); P = 0.05). The concentration of muscle glycogen was higher with H-CHO than with L-CHO at F2 (123 ± 28 mmol · kg dry mass(-1); P < 0.01), but no differences were observed between treatments at the respective points of exhaustion (78 ± 22 mmol · kg dry mass(-1) · min(-1 )for H-CHO vs 72 ± 21 mmol · kg dry mass(-1) · min(-1) for L-CHO). Increasing carbohydrate intake during short-term recovery accelerates glycogen repletion in previously exercised muscles and thus improves the capacity for repeated exercise. The availability of skeletal muscle glycogen is therefore an important factor in the restoration of endurance capacity because fatigue during repeated exercise is associated with a critically low absolute muscle glycogen concentration.

Rat skeletal muscle glycogen degradation pathways reveal differential association of glycogen-related proteins with glycogen granules.

Glycogenin, glycogen-debranching enzyme (GDE) and glycogen phosphorylase (GP) are important enzymes that contribute to glycogen particle metabolism. In Long-Evans Hooded rat whole muscle homogenates prepared from extensor digitorum longus (EDL, fast-twitch) and soleus (SOL, oxidative, predominantly slow twitch), it was necessary to include α-amylase, which releases glucosyl units from glycogen, to detect glycogenin but not GDE or GP. Up to ∼12 % of intramuscular glycogen pool was broken down using either in vitro electrical stimulation or leaving muscle at room temperature >3 h (delayed, post-mortem). Electrical stimulation did not reveal glycogenin unless α-amylase was added, although in post-mortem muscle ∼50 and ∼30 % of glycogenin in EDL and SOL muscles, respectively, was detected compared to the amount detected with α-amylase treatment. Single muscle fibres were dissected from fresh or post-mortem EDL muscles, mechanically skinned to remove surface membrane and the presence of glycogenin, GDE and GP as freely diffusible proteins (i.e. cytoplasmic localization) compared by Western blotting. Diffusibility of glycogenin (∼20 %) and GP (∼60 %) was not different between muscles, although GDE increased from ∼15 % diffusible in fresh muscle to ∼60 % in post-mortem muscle. Under physiologically relevant circumstances, in rat muscle and within detection limits: (1) The total cellular pool of glycogenin is always associated with glycogen granules, (2) GDE is associated with glycogen granules with over half the total pool associated with the outer tiers of glycogen, (3) GP is only ever weakly associated with glycogen granules and (4) addition of α-amylase is necessary in order to detect glycogenin, but not GDE or GP.

Distinct effects of leucine or a mixture of the branched-chain amino acids (leucine, isoleucine, and valine) supplementation on resistance to fatigue, and muscle and liver-glycogen degradation, in trained rats

ObjectiveThe aim of this study was to evaluate the effects of the mixture of branched-chain amino acids (BCAAs) supplementation compared with leucine administered orally on muscle biochemical parameters of trained rats submitted to an exercise-induced protocol of glycogen depletion. MethodsAfter 6 wk of swimming exercise, 8 wk-old (250 g, adult) male Wistar rats were randomly divided into three experimental groups (n = 8 per group): the mixture of BCAAs (BCAAs), leucine (LEU), and placebo (PLA). All groups were submitted to swimming exercise for 6 wk and supplemented with either the mixture of BCAAs, leucine, or placebo during the last week of training. At week 7 of the protocol, the rats were submitted to an intermittent, progressive swimming test until exhaustion and sacrificed. Muscle gastrocnemius and liver were depicted to determine total glycogen, tricarboxylic acid cycle (TCA) intermediates, and enzymatic activities. Statistical evaluation was performed by one-way analysis of variance with Tukey post hoc test. ResultsBoth muscle and liver glycogen degradation ratio were significantly higher in the mixture of BCAAs group compared to the PLA group (P < 0.05) and the LEU group presented decreased liver glycogen degradation ratio compared with the mixture of BCAAs group (P < 0.05). Both muscle and liver glycogen content were significantly spared in the mixture of BCAAs and LEU groups compared to the PLA group (P < 0.01). A performance test demonstrated that LEU supplementation enhanced resistance to exhaustion compared to the mixture of BCAAs (P < 0.001), however, no difference was found when LEU supplementation was compared to PLA (P > 0.05) Muscle citrate content was significantly higher in the mixture of BCAAs group compared with the PLA group (P < 0.001). Muscle malate content was significantly elevated in the mixture of BCAAs group compared with both the PLA (P < 0.001) and LEU groups (P < 0.001). BCAT activity was significantly reduced in the mixture of BCAAs supplementation group compared with the LEU group (P < 0.001). ConclusionLeucine supplementation improved performance compared with the mixture of BCAAs supplementation, sparing muscle glycogen stores despite the augmentation of some TCA intermediate concentrations on the left side of the TCA cycle.

Contribution of creatine to protein homeostasis in athletes after endurance and sprint running

Few studies have focused on the metabolic changes induced by creatine supplementation. This study investigated the effects of creatine supplementation on plasma and urinary metabolite changes of athletes after endurance and sprint running. Twelve male athletes (20.3 ± 1.4 y) performed two identical (65-70 % maximum heart rate reserved) 60 min running exercises (endurance trial) before and after creatine supplementation (12 g creatine monohydrate/day for 15 days), followed by a 5-day washout period. Subsequently, they performed two identical 100 m sprint running exercises (power trial) before and after 15 days of creatine supplementation in accordance with the supplementary protocol of the endurance trial. Body composition measurements were performed during the entire study. Plasma samples were examined for the concentrations of glucose, lactate, branched-chain amino acids (BCAAs), free-tryptophan (f-TRP), glutamine, alanine, hypoxanthine, and uric acid. Urinary samples were examined for the concentrations of hydroxyproline, 3-methylhistidine, urea nitrogen, and creatinine. Creatine supplementation significantly increased body weights of the athletes of endurance trial. Plasma lactate concentration and ratio of f-TRP/BCAAs after recovery from endurance running were significantly decreased with creatine supplementation. Plasma purine metabolites (the sum of hypoxanthine and uric acid), glutamine, urinary 3-methylhistidine, and urea nitrogen concentrations tended to decrease before running in trials with creatine supplements. After running, urinary hydroxyproline concentration significantly increased in the power trial with creatine supplements. The findings suggest that creatine supplementation tended to decrease muscle glycogen and protein degradation, especially after endurance exercise. However, creatine supplementation might induce collagen proteolysis in athletes after sprint running.

Single fiber analyses of glycogen-related proteins reveal their differential association with glycogen in rat skeletal muscle

To understand how glycogen affects skeletal muscle physiology, we examined enzymes essential for muscle glycogen synthesis and degradation using single fibers from quiescent and stimulated rat skeletal muscle. Presenting a shift in paradigm, we show these proteins are differentially associated with glycogen granules. Protein diffusibility and/or abundance of glycogenin, glycogen branching enzyme (GBE), debranching enzyme (GDE), phosphorylase (GP), and synthase (GS) were examined in fibers isolated from rat fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscle. GDE and GP proteins were more abundant (~10- to 100-fold) in fibers from EDL compared with SOL muscle. GS and glycogenin proteins were similar between muscles while GBE had an approximately fourfold greater abundance in SOL muscle. Mechanically skinned fibers exposed to physiological buffer for 10 min showed ~70% total pools of GBE and GP were diffusible (nonbound), whereas GDE and GS were considerably less diffusible. Intense in vitro stimulation, sufficient to elicit a ~50% decrease in intracellular glycogen, increased diffusibility of GDE, GP, and GS (~15-60%) and decreased GBE diffusibility (~20%). Amylase treatment, which breaks α-1,4 linkages of glycogen, indicated differential diffusibilities and hence glycogen associations of GDE and GS. Membrane solubilization (1% Triton-X-100) allowed a small additional amount of GDE and GS to diffuse from fibers, suggesting the majority of nonglycogen-associated GDE/GS is associated with myofibrillar/contractile network of muscle rather than membranes. Given differences in enzymes required for glycogen metabolism, the current findings suggest glycogen particles have fiber-type-dependent structures. The greater catabolic potential of glycogen breakdown in fast-twitch fibers may account for different contraction induced rates of glycogen utilization.

GLUT4 is not essential for exercise-induced exaggerated muscle glycogen degradation in AMPKα2 knockout mice

The purpose of this study was to explore the effects of AMPKα2 knockout on expression of GLUT4 after exercise with different intensities. This was investigated in the quadriceps femoris muscle from control, lower intensity (12m/minute) and higher intensity (20m/minute) running groups of wild-type (WT) and AMPKα2 knockout (KO) mice. The skeletal muscle glycogen content was also measured to investigate the role of AMPK in regulation of glycogen metabolism. GLUT4 mRNA was increased immediately at the end of 60minutes of running, but there were no differences between WT and KO mice, and between lower intensity and higher intensity groups. Pre-exercise muscle glycogen levels were not different between WT and KO; however, the lack of the α2-isoform was associated with a generally lower level of muscle glycogen after 60minutes of running either with lower intensity or higher intensity. The finding that KO of the AMPKα2 isoform had no effect on expressions of GLUT4 mRNA and protein expression in mouse skeletal muscle and that muscle glycogen degradation was greater in AMPKα2 KO mice than that in WT mice after different intensity exercises, provides further evidence that AMPK is dispensable in exercise-induced expression of GLUT4, and suggests alternative pathways other than GLUT4 being involved in the regulation of muscle glycogen degradation by AMPK. Also, the present investigation demonstrated that higher intensity (20m/minute) treadmill running, lasting 1h, increased GLUT4 mRNA in mice skeletal muscle to a level similar to that attained after 1h of lower intensity (12m/minute) treadmill running.

Phosphoglucomutase (PGM 1) Deficiency: A Novel Defect of Muscle Glycogen Degradation and Synthesis (P07.200)

Objective: Evaluate the cause of exertional muscle fatigue, contractures and rhabdomyolysis in a young woman. Background An 18 year old woman reported lifelong fatigue with modest exercise and episodes of muscle contractures, pain and swelling with marked elevations in serum creatine kinase levels after more vigorous exercise. Design/Methods: Forearm and cycle exercise, muscle glycogen determinations, and relevant enzymatic and genetic evaluation were performed. Results: Ischemic forearm exercise resulted in no increase in lactate, an exaggerated increase in ammonia, rapid contractile fatigue and a finger flexor muscle contracture. Cycle exercise revealed low oxidative capacity and a spontaneous second wind, associated with a 40 beat per minute (bpm) drop in exercise heart rate, from 159 (between minute 5-6) to 119 bpm at minute 14 of sustained exercise with a corresponding fall in perceived exertion, thus mirroring the response heretofore considered diagnostic of McArdle disease. However enzymatic activity of muscle phosphorylase and other known defects of muscle glycogenolysis were within normal limits and muscle glycogen levels were low normal as assessed biochemically (controls = 1.1±0.2%; patient = 0.7%) and with 13-C MRS in contrast to McArdle disease (2.5±0.4 %). Evaluation of other glycolytic enzymes revealed a complete absence of muscle phosphoglucomutase (PGM1) activity, the enzyme that catalyzes the conversion of phosphorylase-derived glucose-1-phosphate to glucose-6-phosphate for metabolism via glycolysis and the reverse reaction for glycogen synthesis from glucose. Genetic analysis revealed that the patient was a compound heterozygote for a nonsense mutation (Q530X in exon 10) and a missense mutation (R422W) in exon 8 of PGM1. Conclusions: This patient has a novel defect in phosphoglucomutase (PGM1) that mimics the clinical and physiological features of impaired muscle glycogenolysis due to muscle phosphorylase deficiency (McArdle disease). The finding of blocked muscle glycogenolysis in combination with low muscle glycogen implies that this enzymatic defect impairs both glycogen degradation and synthesis. Supported by: The Muscular Dystrophy Association and The Giant Tiger Foundation. Disclosure: Dr. Haller has nothing to disclose. Dr. Heinicke has nothing to disclose. Dr. Newby has nothing to disclose. Dr. Wyrick has nothing to disclose. Dr. Dimitrov has nothing to disclose. Dr. Mancias has nothing to disclose. Dr. Cohen has nothing to disclose.

Effects of Acute Bouts of Swimming Exercise on AMPKα2 Expression in Mouse Skeletal Muscle

The 5′-AMP-activated protein kinase (AMPK) is a multisubstrate serine/threonine protein kinase that is ubiquitously expressed and functions as an intracellular fuel sensor activated by depletion of high energy phosphate compounds. The a2 isoform is by far the most abundant in skeletal muscle, representing at least 66% of total AMPK activity. The purpose of this study was to determine the effects of the different exercise (swimming) durations on AMPKα2 gene and protein expression, and the relationships between the expression of AMPK and blood glucose and muscle glycogen. C57 mice were divided into three groups: a sedentary control group, a 90-minute swimming exercise group, and an exhaustive swimming exercise group. AMPKα2 gene and protein expression in the quadriceps muscle were measured separately by real-time quantitative PCR and Western immunoblot after the swimming exercise. Blood glucose and muscle glycogen were also measured at the same time. The results showed that 90-minute and exhaustive swimming exercise induced significant increases in skeletal muscle AMPKα2 gene and protein expression compared to in the control group, and AMPKα2 expression was higher after exhaustive swimming than after 90-minute swimming exercise. There was a significant negative correlation between AMPKα2 expression and blood glucose level. The high AMPKα2 gene and protein expression induced by exercise might be one of the reasons for blood glucose reduction, but not the key factor which regulates the degradation of muscle glycogen during swimming exercise.

Increased Carbohydrate Oxidation after Ingesting Carbohydrate with Added Protein

To examine the metabolic impact of including protein in a postexercise carbohydrate supplement when ingested between two bouts of prolonged running performed within the same day. Six healthy men participated in two trials separated by 14 d, each involving a 90-min treadmill run at 70% VO2max followed by 4 h of recovery and a subsequent 60-min run at the same intensity. At 30-min intervals during recovery, participants ingested either a solution containing 0.8 g.kg(-1)h(-1) of carbohydrate (CHO) or the same solution plus an additional 0.3 g.kg(-1)h(-1) of whey protein isolate (CHO-PRO). Muscle biopsies were obtained from the vastus lateralis at the beginning and end of the recovery period, with a third muscle biopsy taken following the second treadmill run. Despite higher insulinemic responses to the CHO-PRO solution than to the CHO solution (P < 0.05), rates of muscle glycogen resynthesis during recovery were not different between treatments (CHO = 12.3 +/- 2.2 and CHO-PRO = 12.1 +/- 2.7 mmol glucosyl units per kilogram of dry mass per hour). Furthermore, there were no differences between treatments in muscle glycogen degradation during subsequent exercise (CHO = 2.2 +/- 0.3 and CHO-PRO = 2.0 +/- 0.1 mmol glucosyl units per kilogram of dry mass per minute). In contrast, whole-body carbohydrate oxidation during the second run was significantly greater with the CHO-PRO treatment than with the CHO treatment (48.4 +/- 2.2 and 41.7 +/- 2.6 mg.kg(-1)min(-1), respectively; P < 0.01). These data show that the inclusion of protein in a carbohydrate-recovery supplement can increase the oxidation of extramuscular carbohydrate sources during subsequent exercise without altering the rate of muscle glycogen degradation.

Ein 12-Stunden-Schwimmen führt zu keinem nachweisbaren Verlust an subkutanem Fett – eine Fallstudie

In a 12-hour swimming event, an athlete with constant body weight lost 1.1 kg of muscle mass and 21 of total body fluids whereas fat mass remained stable. Based both on the urine's specific gravity and haematological parameters, the athlete did not suffer from dehydration. We assume that loss of skeletal muscle mass occurred due to degradation of intramyocellular lipids and muscle glycogen. In order to confirm these results obtained in a case study regarding the decrease of skeletal muscle mass with stable fat mass during prolonged swimming exercise, a larger number of athletes would have to be analyzed.

The Effect of Carbohydrate-Protein Mixtures on Muscle Glycogen Resynthesis following Prolonged Treadmill Running

The ingestion of both carbohydrate and protein during recovery from prolonged exercise has previously been demonstrated to result in a more rapid restoration of treadmill running capacity than ingestion of carbohydrate alone. Evidence based on prolonged cycling suggests that this ergogenic effect might be related to an increased rate of muscle glycogen resynthesis during recovery. PURPOSE: To determine whether the addition of protein to a carbohydrate solution accelerates the rate of muscle glycogen resynthesis during recovery from prolonged treadmill running. METHODS: Six recreationally active male volunteers (age 22 ± 1.3 y, body mass 73.8 ± 6.7 kg, VO2max 60.5 ± 6.3 ml·kg−1mm−1; mean ± SD) participated in 2 trials separated by 14 days. Each main trial involved a glycogen lowering run (R1; 90 min at 70% VO max) followed by a 4 hour recovery. At 30 min intervals during recovery, participants ingested either a solution containing 0.8 g CHO· kg−1· h−1 (CHO trial) or the same solution plus an additional 0.3 g· kg−1· h−1 of protein (CHO-PRO trial). Muscle biopsies were obtained from the vastus lateralis at the beginning and end of recovery to asses the rate of muscle glycogen resynthesis over the intervening period. Furthermore, a third muscle biopsy was taken following a repeated treadmill run subsequent to recovery (R2; 60 min at 70% VO2max). RESULTS: Despite a higher insulinemic response to the CHO-PRO solution than to the CHO solution (P <0.05), rates of muscle glycogen resynthesis during recovery were not different between treatments (CHO: 12.3 ± 2.2 and CHO-PRO: 12.0 ± 2.7 mmol glucosyl units-kg dm·h−1; mean ± SEM). Similarly, the additional protein did not influence the rate of muscle glycogen degradation during subsequent exercise (CHO: 2.2 ±0.3 and CHO: 2.0 ±0.1 mmol glucosyl units·kg dm−1h−1; mean± SEM). CONCLUSIONS: Combined ingestion of carbohydrate and protein did not increase muscle glycogen storage during recovery from prolonged treadmill running nor spare this carbohydrate store during a repeated exercise session. It is possible that, in contrast to prolonged cycling, the proposed benefit of ingesting carbohydrate-protein following running might involve mechanisms other than improved muscle glycogen status.

Muscle glycogen degradation during simulation of a fatiguing soccer match in elite soccer players examined noninvasively by 13C-MRS.

The purpose of this research project was to noninvasively determine individual muscle glycogen [Gly] degradation during a test intended to predict individual fatigue in intense soccer matches. The [Gly] of the calf muscles of 17 elite soccer players [age = 17.4 +/- 0.8 (SD)] were measured with 13C-MRS before and after an alternating velocity test to exhaustion. Blood samples were taken before and 3 min after the test for determination of blood metabolites. Average muscle [Gly] was 135 +/- 53 mmol x (kg wet weight)(-1) before and 87 +/- 27 mmol x (kg wet weight)(-1) (P < 0.001) after exhaustion (42 +/- 25 min). There was a high correlation (r = 0.87, P < 0.0001) between muscle [Gly] at rest and net muscle [Gly] utilized. There was also a more moderate correlation (r = 0.62, P < 0.01) between net muscle [Gly] used and time to exhaustion during the soccer-specific test. There was some evidence of correlation (r = 0.42, P = 0.09) between resting [Gly] and time to exhaustion. Plasma lactate increased (P < 0.001) from 0.8 +/- 0.4 before the test to 2.5 +/- 1.0 mmol x L(-1) at exhaustion, whereas ammonia was raised (P < 0.0001) from 44.1 +/- 10.3 to 89.7 +/- 14.9 micromol x L(-1). Similarly, plasma free fatty acids were elevated (P < 0.0001) from 148 +/- 106 to 797 +/- 401 micromol x L(-1), and glycerol was increased (P < 0.0001) from 48.3 +/- 17.7 to 182.2 +/- 61.8 micromol x L(-1). Insulin levels (11.9 +/- 3.7 vs 11.7 +/- 4.8 microU x mL(-1)) remained the same. Creatine kinase levels increased (P < 0.0001) from 486 +/- 501 to 640 +/- 548 micromol x L(-1) after the test. We conclude that exhaustion during soccer-specific performance is related to the capacity to utilize muscle [Gly]. The results underline the importance of dietary counseling (glycogen loading and resynthesis strategies) and proper training to enhance the glycogen levels and glycogenolytic capacity of the players.

Leucine supplementation and intensive training.

Leucine, isoleucine and valine, the branched-chain amino acids (BCAA), make up about one-third of muscle protein. Of these, leucine has been the most thoroughly investigated because its oxidation rate is higher than that of isoleucine or valine. Leucine also stimulates protein synthesis in muscle and is closely associated with the release of gluconeogenic precursors, such as alanine, from muscle. Significant decreases in plasma or serum levels of leucine occur following aerobic (11 to 33%), anaerobic lactic (5 to 8%) and strength exercise (30%) sessions. In skeletal muscle, there is a decrease in leucine level and a reduction in glycogen stores during exhaustive aerobic exercise. Basal fasting serum leucine levels decrease by 20% during 5 weeks of speed and strength training in power-trained athletes on a daily protein intake of 1.26 g/kg bodyweight. The leucine content of protein is assumed to vary between 5 and 10%. There are suggestions that the current recommended dietary intake of leucine be increased from 14 mg/kg bodyweight/day to a minimum of 45 mg/kg bodyweight/day for sedentary individuals, and more for those participating in intensive training in order to optimise rates of whole body protein synthesis. Consumption of BCAA (30 to 35% leucine) before or during endurance exercise may prevent or decrease the net rate of protein degradation, may improve both mental and physical performance and may have a sparing effect on muscle glycogen degradation and depletion of muscle glycogen stores. However, leucine supplementation (200 mg/kg bodyweight) 50 minutes before anaerobic running exercise had no effect on performance. During 5 weeks of strength and speed training, leucine supplementation of 50 mg/kg bodyweight/day, supplementary to a daily protein intake of 1.26 g/kg bodyweight/day, appeared to prevent the decrease in the serum leucine levels in power-trained athletes. According to 1 study, dietary supplementation of the leucine metabolite beta-hydroxy-beta-methylbutyrate (HMB) 3 g/day to humans undertaking intensive resistance training exercise resulted in an increased deposition of fat-free mass and an accompanying increase in strength. Muscle proteolysis was also decreased with HMB, accompanied by lower plasma levels of enzymes indicating muscle damage and an average 50% decrease in plasma essential amino acid levels. Furthermore, BCAA supplementation (76% leucine) in combination with moderate energy restriction has been shown to induce significant and preferential losses of visceral adipose tissue and to allow maintenance of a high level of performance. Caution must be paid when interpreting the limited number of studies in this area since, in many studies, leucine has been supplemented as part of a mixture of BCAA. Consequently, further research into the effects of leucine supplementation alone is needed.

Training decreases muscle glycogen turnover during exercise.

The present study was undertaken to determine the effects of endurance training on glycogen kinetics during exercise. A new model describing glycogen kinetics was applied to quantitate the rates of synthesis and degradation of glycogen. Trained and untrained rats were infused with a 25% glucose solution with 6-3H-glucose and U-14C-lactate at 1.5 and 0.5 microCi x min(-1) (where 1 Ci=3.7 x 10(10) Bq), respectively, during rest (30 min) and exercise (60 min). Blood samples were taken at 10-min intervals starting just prior to isotopic infusion, until the cessation of exercise. Tissues harvested after the cessation of exercise were muscle (soleus, deep, and superficial vastus lateralis, gastrocnemius), liver, and heart. Tissue glycogen was quantitated and analyzed for incorporation of 3H and 14C via liquid scintillation counting. There were no net decreases in muscle glycogen concentration from trained rats, whereas muscle glycogen concentration decreased to as much as 64% (P < 0.05) in soleus in muscles from untrained rats after exercise. Liver glycogen decreased in both trained (30%) and untrained (40%) rats. Glycogen specific activity increased in all tissues after exercise indicating isotope incorporation and, thus, glycogen synthesis during exercise. There were no differences in muscle glycogen synthesis rates between trained and untrained rats after exercise. However, training decreased muscle glycogen degradation rates in total muscle (i.e., the sum of the degradation rates of all of the muscles sampled) tenfold (P < 0.05). We have applied a model to describe glycogen kinetics in relation to glucose and lactate metabolism during exercise in trained and untrained rats. Training significantly decreases muscle glycogen degradation rates during exercise.

Effects of increased fat availability on fat-carbohydrate interaction during prolonged exercise in men.

The study examined the existence and regulation of fat-carbohydrate interaction during low- and moderate-intensity exercise. Eight males cycled for 10 min at 40% and 60 min at 65% maximal O2 uptake (VO2max) while infused with either Intralipid and heparin (Int) or saline (Con). Before exercise, plasma arterial free fatty acid (FFA) was 0.69 +/- 0.04 mM (Int) vs. 0.25 +/- 0.04 mM (Con). Muscle biopsies were taken at rest and at 10, 20, and 70 min of exercise. Arterial and femoral venous blood samples and expired gases were collected simultaneously throughout exercise, and blood flow was estimated from pulmonary O2 uptake and the leg arterial-venous O2 difference. Respiratory exchange ratio was higher in Con (0.94 +/- 0.01) compared with Int (0.91 +/- 0.01). Mean net leg FFA uptake was higher in Int (0.16 +/- 0.03 vs. 0.04 +/- 0.01 mmol/min), and net lactate efflux was reduced (Int, 1.55 +/- 0.36 vs. Con, 3.07 +/- 0.47 mmol/min). Leg net glucose uptake was unaffected by Int. Muscle glycogen degradation was 23% lower in Int [230 +/- 29 vs. 297 +/- 36 mmol glucosyl units/kg dry muscle (dm)]. Pyruvate dehydrogenase activity in the a form (PDHa) was lower during Int (1.61 +/- 0.17 vs. 2.22 +/- 0.24 mmol.min-1.kg wet muscle-1), and muscle citrate was higher (0.59 +/- 0.04 vs. 0.48 +/- 0.04 mmol/kg dm). Muscle lactate, phosphocreatine, ATP, acetyl-CoA, acetyl-carnitine, and P(i) were unaffected by Int. Calculated free AMP was significantly lower in Int compared with Con at 70 min of exercise (3.3 +/- 0.8 vs. 1.5 +/- 0.3 mumol/kg dm). The high FFA-induced reduction in glycogenolysis and carbohydrate oxidation at 65% VO2max appears to be due to regulation at several sites. The reduced flux through phosphorylase and phosphofructokinase during Int may have been due to reduced free AMP accumulation and increased cytoplasmic citrate. The mechanism for reduced PDH transformation to the a form is unknown but suggests reduced flux through PDH.