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Waldauf P, Urban T, Krajčová A, Jiroutková K, Blahutová B, Bakalář B, Řasová K, Grünerová-Lippertová M, Gojda J, Duška F. Can functional electrical stimulation-assisted cycle ergometry replace insulin infusion in patients? A nested substudy in a randomized controlled trial with 6 months' follow-up. JPEN J Parenter Enteral Nutr 2021; 46:249-253. [PMID: 34165818 DOI: 10.1002/jpen.2213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Accepted: 06/21/2021] [Indexed: 11/07/2022]
Abstract
BACKGROUND Functional electrical stimulation-assisted cycle ergometry (FESCE) can deliver active exercise to critically ill patients, including those who are sedated. Aerobic exercise is known to stimulate skeletal muscle glucose uptake. We asked whether FESCE can reduce intravenous insulin requirements and improve insulin sensitivity in intensive care unit (ICU) patients. METHOD We performed an a priori-planned secondary analysis of data from an outcome-based randomized controlled trial (NCT02864745) of FESCE-based early-mobility program vs standard of care in mechanically ventilated patients. We analyzed glucose profile, glucose intake, and insulin requirements during ICU stay in all enrolled patients. In a nested subgroup, we performed hyperinsulinemic (120 mIU/min/m2 ) euglycemic clamps at days 0, 7, and 180 (n = 30, 23, and 11, respectively). RESULTS We randomized 150 patients 1:1 to receive intervention or standard of care. Seventeen (23%) patients in each study arm had a history of diabetes. During ICU stay, patients received 137 ± 65 and 137 ± 88 g/day carbohydrate (P = .97), and 31 vs 35 (P = .62) of them required insulin infusion to maintain blood glucose 8.61 ± 2.82 vs 8.73 ± 2.67 mM (P = .75, n = 11,254). In those treated with insulin, median daily dose was 53 IU (interquartile range [IQR], 25-95) vs 62 IU (IQR, 26-96) in the intervention and control arm, respectively (P = .44). In the subgroup of patients undergoing hyperglycemic clamps, insulin sensitivities improved similarly and significantly from acute and protracted critical illness to 6 months after discharge. CONCLUSION The FESCE-based early-mobility program does not significantly reduce insulin requirements in critically ill patients on mechanical ventilation.
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Affiliation(s)
- Petr Waldauf
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Tomáš Urban
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Adéla Krajčová
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Kateřina Jiroutková
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Barbora Blahutová
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Bob Bakalář
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Kamila Řasová
- Department of Rehabilitation, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Marcela Grünerová-Lippertová
- Department of Rehabilitation, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - Jan Gojda
- Department of Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
| | - František Duška
- Department of Anaesthesia and Intensive Care Medicine, Charles University, The Third Faculty of Medicine and FNKV University Hospital, Prague, Czech Republic
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Suginohara T, Wakabayashi K, Ato S, Ogasawara R. Effect of 2-deoxyglucose-mediated inhibition of glycolysis on the regulation of mTOR signaling and protein synthesis before and after high-intensity muscle contraction. Metabolism 2021; 114:154419. [PMID: 33161019 DOI: 10.1016/j.metabol.2020.154419] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 10/29/2020] [Accepted: 11/02/2020] [Indexed: 02/07/2023]
Abstract
BACKGROUND Glycolysis controls mTORC1 signaling and protein synthesis. In skeletal muscle, glucose metabolism increases with both exercise/contraction intensity and volume, and therefore, high-intensity muscle contraction (HiMC) such as resistance exercise facilitates glycolysis including glucose uptake and glycogen breakdown. However, it is unknown whether glycolysis regulates HiMC-induced mTORC1 activation and increase in protein synthesis. METHODS To determine whether glycolysis regulates basal and HiMC-induced mTORC1 signaling and protein synthesis, we employed 2-deoxyglucose (2-DG) to inhibit glycolysis and isometrically contracted the gastrocnemius muscle of Sprague Dawley rats using percutaneous electrical stimulation. RESULTS Inhibition of glycolysis by 2-DG inhibited basal phosphorylation of p70S6K and 4E-BP1 (downstream targets of mTORC1) and protein synthesis (all P < 0.05) independent of AMPK phosphorylation. AMPK phosphorylation was comparably increased after HiMC at 0 h post HiMC and returned to basal levels 6 h post HiMC in both vehicle- and 2-DG-treated groups. Glycolysis inhibition attenuated muscle contraction-induced phosphorylation of 4E-BP1 at 6 h post HiMC (P < 0.05) but not p70S6K phosphorylation and protein synthesis. CONCLUSION Although glycolysis is involved in basal but not HiMC-induced muscle protein synthesis, it regulates both basal and HiMC-induced mTORC1 signaling, and may play key roles in skeletal muscle adaptation to HiMC.
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Affiliation(s)
- Takeshi Suginohara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Koki Wakabayashi
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Satoru Ato
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Riki Ogasawara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan.
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Horiuchi M, Thijssen DHJ. Ischemic preconditioning prevents impact of prolonged sitting on glucose tolerance and markers of cardiovascular health but not cerebrovascular responses. Am J Physiol Endocrinol Metab 2020; 319:E821-E826. [PMID: 32865010 DOI: 10.1152/ajpendo.00302.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Prolonged, uninterrupted sitting is demonstrated to acutely impair glucose homeostasis, but it also leads to detrimental cardiovascular health effects. We examined whether ischemic preconditioning (IPC) prevents the impact of prolonged sitting-induced glucose intolerance and measured related influencing factors such as (para)sympathetic nerve activity [assessed by heart rate variability (HRV)] and blood pressure during 2 h of prolonged sitting. In this randomized, controlled crossover study, 15 healthy participants (80% men) with a mean age of 21 ± 1 yr (means ± SD) and body mass index of 25.0 ± 2.4 kg/m2 performed IPC (IPC, 4 × 5-min 220-mmHg unilateral occlusion at the thigh muscle) or a sham intervention (sham, 4 × 5 min 20-mmHg), followed by 2 h of sitting. After IPC or sham intervention, fingertip blood glucose was measured before and after 30, 60, 90, and 120 min of 75 g of glucose ingestions. Blood glucose responses during an oral glucose tolerance test were significantly attenuated, resulting in a lower area under the curve when sitting was preceded by a bout of IPC than sham (P < 0.05). IPC increased high-frequency oscillations and decreased the ratio of low-frequency-to-high-frequency oscillations at 120 min in HRV (P < 0.05). Moreover, a lower blood pressure was observed with IPC compared with sham (P < 0.05). Prolonged sitting or IPC did not affect cerebrovascular responses (P > 0.05). Collectively, these results indicate that the application of IPC before prolonged, uninterrupted sitting bout was associated with a better glucose tolerance and prevented impairment in (para)sympathetic nerve activity and blood pressure in healthy young men and women.
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Affiliation(s)
- Masahiro Horiuchi
- Division of Human Environmental Science, Mount Fuji Research Institute, Kamiyoshida, Fujiyoshida, Yamanashi, Japan
| | - Dick H J Thijssen
- Research Institute of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- Department of Physiology, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
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Poortmans JR, Carpentier A. Protein metabolism and physical training: any need for amino acid supplementation? ACTA ACUST UNITED AC 2016. [DOI: 10.1186/s41110-016-0022-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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5
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Witard OC, Wardle SL, Macnaughton LS, Hodgson AB, Tipton KD. Protein Considerations for Optimising Skeletal Muscle Mass in Healthy Young and Older Adults. Nutrients 2016; 8:181. [PMID: 27023595 PMCID: PMC4848650 DOI: 10.3390/nu8040181] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 03/16/2016] [Accepted: 03/18/2016] [Indexed: 12/12/2022] Open
Abstract
Skeletal muscle is critical for human health. Protein feeding, alongside resistance exercise, is a potent stimulus for muscle protein synthesis (MPS) and is a key factor that regulates skeletal muscle mass (SMM). The main purpose of this narrative review was to evaluate the latest evidence for optimising the amino acid or protein source, dose, timing, pattern and macronutrient coingestion for increasing or preserving SMM in healthy young and healthy older adults. We used a systematic search strategy of PubMed and Web of Science to retrieve all articles related to this review objective. In summary, our findings support the notion that protein guidelines for increasing or preserving SMM are more complex than simply recommending a total daily amount of protein. Instead, multifactorial interactions between protein source, dose, timing, pattern and macronutrient coingestion, alongside exercise, influence the stimulation of MPS, and thus should be considered in the context of protein recommendations for regulating SMM. To conclude, on the basis of currently available scientific literature, protein recommendations for optimising SMM should be tailored to the population or context of interest, with consideration given to age and resting/post resistance exercise conditions.
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Affiliation(s)
- Oliver C Witard
- Health & Exercise Sciences Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling FK9 4LA, UK.
| | - Sophie L Wardle
- Health & Exercise Sciences Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling FK9 4LA, UK.
| | - Lindsay S Macnaughton
- Health & Exercise Sciences Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling FK9 4LA, UK.
| | - Adrian B Hodgson
- Lucozade Ribena Suntory Limited, 2 Longwalk Road, Stockley Park, Uxbridge UB11 1BA, UK.
| | - Kevin D Tipton
- Health & Exercise Sciences Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling FK9 4LA, UK.
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Reidy PT, Rasmussen BB. Role of Ingested Amino Acids and Protein in the Promotion of Resistance Exercise-Induced Muscle Protein Anabolism. J Nutr 2016; 146:155-83. [PMID: 26764320 PMCID: PMC4725426 DOI: 10.3945/jn.114.203208] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Revised: 06/03/2015] [Accepted: 11/25/2015] [Indexed: 12/16/2022] Open
Abstract
The goal of this critical review is to comprehensively assess the evidence for the molecular, physiologic, and phenotypic skeletal muscle responses to resistance exercise (RE) combined with the nutritional intervention of protein and/or amino acid (AA) ingestion in young adults. We gathered the literature regarding the translational response in human skeletal muscle to acute exposure to RE and protein/AA supplements and the literature describing the phenotypic skeletal muscle adaptation to RE and nutritional interventions. Supplementation of protein/AAs with RE exhibited clear protein dose-dependent effects on translational regulation (protein synthesis) through mammalian target of rapamycin complex 1 (mTORC1) signaling, which was most apparent through increases in p70 ribosomal protein S6 kinase 1 (S6K1) phosphorylation, compared with postexercise recovery in the fasted or carbohydrate-fed state. These acute findings were critically tested via long-term exposure to RE training (RET) and protein/AA supplementation, and it was determined that a diminishing protein/AA supplement effect occurs over a prolonged exposure stimulus after exercise training. Furthermore, we found that protein/AA supplements, combined with RET, produced a positive, albeit minor, effect on the promotion of lean mass growth (when assessed in >20 participants/treatment); a negligible effect on muscle mass; and a negligible to no additional effect on strength. A potential concern we discovered was that the majority of the exercise training studies were underpowered in their ability to discern effects of protein/AA supplementation. Regardless, even when using optimal methodology and large sample sizes, it is clear that the effect size for protein/AA supplementation is low and likely limited to a subset of individuals because the individual variability is high. With regard to nutritional intakes, total protein intake per day, rather than protein timing or quality, appears to be more of a factor on this effect during long-term exercise interventions. There were no differences in strength or mass/muscle mass on RET outcomes between protein types when a leucine threshold (>2 g/dose) was reached. Future research with larger sample sizes and more homogeneity in design is necessary to understand the underlying adaptations and to better evaluate the individual variability in the muscle-adaptive response to protein/AA supplementation during RET.
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Affiliation(s)
- Paul T Reidy
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX
| | - Blake B Rasmussen
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX
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Abstract
Protein quality control (proteostasis) depends on constant protein degradation and resynthesis, and is essential for proper homeostasis in systems from single cells to whole organisms. Cells possess several mechanisms and processes to maintain proteostasis. At one end of the spectrum, the heat shock proteins modulate protein folding and repair. At the other end, the proteasome and autophagy as well as other lysosome-dependent systems, function in the degradation of dysfunctional proteins. In this review, we examine how these systems interact to maintain proteostasis. Both the direct cellular data on heat shock control over autophagy and the time course of exercise-associated changes in humans support the model that heat shock response and autophagy are tightly linked. Studying the links between exercise stress and molecular control of proteostasis provides evidence that the heat shock response and autophagy coordinate and undergo sequential activation and downregulation, and that this is essential for proper proteostasis in eukaryotic systems.
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Key Words
- AKT, v-akt murine thymoma viral oncogene homolog 1
- AMPK, adenosine monophosphate-activated protein kinase
- ATG, autophagy-related
- BECN1, Beclin 1, autophagy related
- EIF4EBP1, eukaryotic translation initiation factor 4E binding protein 1
- ER, endoplasmic reticulum
- FOXO, forkhead box O
- HSF1, heat shock transcription factor 1
- HSP, heat shock protein
- HSP70
- HSPA8/HSC70, heat shock 70kDa protein 8
- IL, interleukin
- LC3, MAP1LC3, microtubule-associated protein 1 light chain 3
- MTMR14/hJumpy, myotubularin related protein 14
- MTOR, mechanistic target of rapamycin
- NR1D1/Rev-Erb-α, nuclear receptor subfamily 1, group D, member 1
- PBMC, peripheral blood mononuclear cell
- PPARGC1A/PGC-1α, peroxisome proliferator-activated receptor, gamma, coactivator 1 α
- RHEB, Ras homolog enriched in brain
- SOD, superoxide dismutase
- SQSTM1/p62, sequestosome 1
- TPR, translocated promoter region, nuclear basket protein
- TSC, tuberous sclerosis complex
- ULK1, unc-51 like autophagy activating kinase 1
- autophagy
- exercise
- heat shock response
- humans
- protein breakdown
- protein synthesis
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Affiliation(s)
- Karol Dokladny
- a Department of Internal Medicine; Health Sciences Center; Health, Exercise & Sports Science of University of New Mexico ; Albuquerque , NM USA
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Elsisia HF, Aneisb YM, Mounirc KM. Impact of high-intensity interval training on HbA1c in patients with type 2 diabetes mellitus. BULLETIN OF FACULTY OF PHYSICAL THERAPY 2015. [DOI: 10.4103/1110-6611.174710] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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9
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Makhro A, Hänggi P, Goede JS, Wang J, Brüggemann A, Gassmann M, Schmugge M, Kaestner L, Speer O, Bogdanova A. N-methyl-D-aspartate receptors in human erythroid precursor cells and in circulating red blood cells contribute to the intracellular calcium regulation. Am J Physiol Cell Physiol 2013; 305:C1123-38. [PMID: 24048732 DOI: 10.1152/ajpcell.00031.2013] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The presence of N-methyl-d-aspartate receptor (NMDAR) was previously shown in rat red blood cells (RBCs) and in a UT-7/Epo human myeloid cell line differentiating into erythroid lineage. Here we have characterized the subunit composition of the NMDAR and monitored its function during human erythropoiesis and in circulating RBCs. Expression of the NMDARs subunits was assessed in erythroid progenitors during ex vivo erythropoiesis and in circulating human RBCs using quantitative PCR and flow cytometry. Receptor activity was monitored using a radiolabeled antagonist binding assay, live imaging of Ca(2+) uptake, patch clamp, and monitoring of cell volume changes. The receptor tetramers in erythroid precursor cells are composed of the NR1, NR2A, 2C, 2D, NR3A, and 3B subunits of which the glycine-binding NR3A and 3B and glutamate-binding NR2C and 2D subunits prevailed. Functional receptor is required for survival of erythroid precursors. Circulating RBCs retain a low number of the receptor copies that is higher in young cells compared with mature and senescent RBC populations. In circulating RBCs the receptor activity is controlled by plasma glutamate and glycine. Modulation of the NMDAR activity in RBCs by agonists or antagonists is associated with the alterations in whole cell ion currents. Activation of the receptor results in the transient Ca(2+) accumulation, cell shrinkage, and alteration in the intracellular pH, which is associated with the change in hemoglobin oxygen affinity. Thus functional NMDARs are present in erythroid precursor cells and in circulating RBCs. These receptors contribute to intracellular Ca(2+) homeostasis and modulate oxygen delivery to peripheral tissues.
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Affiliation(s)
- Asya Makhro
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
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BURKE LOUISEM, HAWLEY JOHNA, ROSS MEGANL, MOORE DANIELR, PHILLIPS STUARTM, SLATER GARYR, STELLINGWERFF TRENT, TIPTON KEVIND, GARNHAM ANDREWP, COFFEY VERNONG. Preexercise Aminoacidemia and Muscle Protein Synthesis after Resistance Exercise. Med Sci Sports Exerc 2012; 44:1968-77. [DOI: 10.1249/mss.0b013e31825d28fa] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Poortmans JR, Carpentier A, Pereira-Lancha LO, Lancha A. Protein turnover, amino acid requirements and recommendations for athletes and active populations. Braz J Med Biol Res 2012; 45:875-90. [PMID: 22666780 PMCID: PMC3854183 DOI: 10.1590/s0100-879x2012007500096] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 05/25/2012] [Indexed: 12/13/2022] Open
Abstract
Skeletal muscle is the major deposit of protein molecules. As for any cell or tissue, total muscle protein reflects a dynamic turnover between net protein synthesis and degradation. Noninvasive and invasive techniques have been applied to determine amino acid catabolism and muscle protein building at rest, during exercise and during the recovery period after a single experiment or training sessions. Stable isotopic tracers (13C-lysine, 15N-glycine, 2H5-phenylalanine) and arteriovenous differences have been used in studies of skeletal muscle and collagen tissues under resting and exercise conditions. There are different fractional synthesis rates in skeletal muscle and tendon tissues, but there is no major difference between collagen and myofibrillar protein synthesis. Strenuous exercise provokes increased proteolysis and decreased protein synthesis, the opposite occurring during the recovery period. Individuals who exercise respond differently when resistance and endurance types of contractions are compared. Endurance exercise induces a greater oxidative capacity (enzymes) compared to resistance exercise, which induces fiber hypertrophy (myofibrils). Nitrogen balance (difference between protein intake and protein degradation) for athletes is usually balanced when the intake of protein reaches 1.2 g·kg−1·day−1 compared to 0.8 g·kg−1·day−1 in resting individuals. Muscular activities promote a cascade of signals leading to the stimulation of eukaryotic initiation of myofibrillar protein synthesis. As suggested in several publications, a bolus of 15-20 g protein (from skimmed milk or whey proteins) and carbohydrate (± 30 g maltodextrine) drinks is needed immediately after stopping exercise to stimulate muscle protein and tendon collagen turnover within 1 h.
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Affiliation(s)
- J R Poortmans
- Laboratory for Biometry and Sport Nutrition, Faculty of Motor Sciences, Free University of Brussels, Brussels, Belgium
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12
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Beelen M, Zorenc A, Pennings B, Senden JM, Kuipers H, van Loon LJC. Impact of protein coingestion on muscle protein synthesis during continuous endurance type exercise. Am J Physiol Endocrinol Metab 2011; 300:E945-54. [PMID: 21364122 DOI: 10.1152/ajpendo.00446.2010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
This study investigates the impact of protein coingestion with carbohydrate on muscle protein synthesis during endurance type exercise. Twelve healthy male cyclists were studied during 2 h of fasted rest followed by 2 h of continuous cycling at 55% W(max). During exercise, subjects received either 1.0 g·kg(-1)·h(-1) carbohydrate (CHO) or 0.8 g·kg(-1)·h(-1) carbohydrate with 0.2 g·kg(-1)·h(-1) protein hydrolysate (CHO+PRO). Continuous intravenous infusions with l-[ring-(13)C(6)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied, and blood and muscle biopsies were collected to assess whole body protein turnover and muscle protein synthesis rates at rest and during exercise conditions. Protein coingestion stimulated whole body protein synthesis and oxidation rates during exercise by 22 ± 3 and 70 ± 17%, respectively (P < 0.01). Whole body protein breakdown rates did not differ between experiments. As a consequence, whole body net protein balance was slightly negative in CHO and positive in the CHO+PRO treatment (-4.9 ± 0.3 vs. 8.0 ± 0.3 μmol Phe·kg(-1)·h(-1), respectively, P < 0.01). Mixed muscle protein fractional synthetic rates (FSR) were higher during exercise compared with resting conditions (0.058 ± 0.006 vs. 0.035 ± 0.006%/h in CHO and 0.070 ± 0.011 vs. 0.038 ± 0.005%/h in the CHO+PRO treatment, respectively, P < 0.05). FSR during exercise did not differ between experiments (P = 0.46). We conclude that muscle protein synthesis is stimulated during continuous endurance type exercise activities when carbohydrate with or without protein is ingested. Protein coingestion does not further increase muscle protein synthesis rates during continuous endurance type exercise.
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Affiliation(s)
- Milou Beelen
- Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, Maastricht, the Netherlands
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Schmitz JPJ, van Riel NAW, Nicolay K, Hilbers PAJ, Jeneson JAL. Silencing of glycolysis in muscle: experimental observation and numerical analysis. Exp Physiol 2009; 95:380-97. [PMID: 19801387 DOI: 10.1113/expphysiol.2009.049841] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The longstanding problem of rapid inactivation of the glycolytic pathway in skeletal muscle after contraction was investigated using (31)P NMR spectroscopy and computational modelling. Accumulation of phosphorylated glycolytic intermediates (hexose monophosphates) during cyclic contraction and subsequent turnover during metabolic recovery was measured in vivo in human quadriceps muscle using dynamic (31)P NMR spectroscopy. The concentration of hexose monophosphates in muscle peaked 40 s into metabolic recovery from maximal contractile work at 6.9 +/- 1.3 mm (mean +/- s.d.; n = 8) and subsequently declined at a rate of 0.009 +/- 0.001 mm s(1). It was next tested whether the current knowledge of the kinetic controls in the glycolytic pathway in muscle integrated in the Lambeth and Kushmerick computational model of skeletal muscle glycolysis explained the experimental data. It was found that the model underestimated the magnitude of deactivation of the glycolytic pathway in resting muscle, resulting in depletion of glycolytic intermediates and substrate for oxidative ATP synthesis. Numerical analysis of the model identified phosphofructokinase and pyruvate kinase as the kinetic control sites involved in deactivation of the glycolytic pathway. Ancillary 100-fold inhibition of both phosphofructokinase and pyruvate kinase was found necessary to predict glycolytic intermediate and ADP concentrations correctly in resting human muscle. Incorporation of this information into the model resulted in highly improved agreement between predicted and measured in vivo dynamics of hexose monophosphates in muscle following contraction. We concluded that silencing of the glycolytic pathway in muscle following contraction is most likely to be mediated by phosphofructokinase and pyruvate kinase inactivation on a time scale of seconds and minutes, respectively, and is necessary to prevent depletion of vital cellular substrates.
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Affiliation(s)
- Joep P J Schmitz
- BioModeling and BioInformatics Group, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
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Kumar V, Atherton P, Smith K, Rennie MJ. Human muscle protein synthesis and breakdown during and after exercise. J Appl Physiol (1985) 2009; 106:2026-39. [DOI: 10.1152/japplphysiol.91481.2008] [Citation(s) in RCA: 171] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Skeletal muscle demonstrates extraordinary mutability in its responses to exercise of different modes, intensity, and duration, which must involve alterations of muscle protein turnover, both acutely and chronically. Here, we bring together information on the alterations in the rates of synthesis and degradation of human muscle protein by different types of exercise and the influences of nutrition, age, and sexual dimorphism. Where possible, we summarize the likely changes in activity of signaling proteins associated with control of protein turnover. Exercise of both the resistance and nonresistance types appears to depress muscle protein synthesis (MPS), whereas muscle protein breakdown (MPB) probably remains unchanged during exercise. However, both MPS and MPB are elevated after exercise in the fasted state, when net muscle protein balance remains negative. Positive net balance is achieved only when amino acid availability is increased, thereby raising MPS markedly. However, postexercise-increased amino acid availability is less important for inhibiting MPB than insulin, the secretion of which is stimulated most by glucose availability, without itself stimulating MPS. Exercise training appears to increase basal muscle protein turnover, with differential responses of the myofibrillar and mitochondrial protein fractions to acute exercise in the trained state. Aging reduces the responses of myofibrillar protein and anabolic signaling to resistance exercise. There appear to be few, if any, differences in the response of young women and young men to acute exercise, although there are indications that, in older women, the responses may be blunted more than in older men.
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15
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Mero A, Leikas A, Knuutinen J, Hulmi JJ, Kovanen V. Effect of strength training session on plasma amino acid concentration following oral ingestion of leucine, BCAAs or glutamine in men. Eur J Appl Physiol 2008; 105:215-23. [PMID: 19015870 DOI: 10.1007/s00421-008-0892-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/29/2008] [Indexed: 10/21/2022]
Abstract
We examined the acute effects of a 1-h strength training session (STS) on plasma amino acid concentration following orally ingestion of leucine, branched-chain amino acids (BCAAs) or glutamine in nine physically active men who participated in double-blinded and randomised experiments. The subjects took placebo, leucine, BCAAs, or glutamine capsules (50 mg/kg) in either rest (REST) or STS condition. Blood samples were taken before and at 30, 60, 90, and 120 min after the beginning of the treatment and they were assayed for plasma amino acids with HPLC. Following both leucine and BCAA ingestion the peak concentration of leucine was similar at rest (524 +/- 46 and 530 +/- 29 nmol/ml, respectively) and similar after STS (398 +/- 43 and 387 +/- 46 nmol/ml, respectively) but the rest and STS concentrations differed from each other (P < 0.01-0.001). The modelled polynomial data for the leucine treatment showed that the peak concentration of leucine occurred at 67 min at rest and at 90 min in STS (difference between REST and STS: P = 0.012). For the BCAA treatment the polynomial data showed that the peak concentration of leucine occurred at 72 min at rest and at 78 min in STS (P = 0.067). The peak concentration of glutamine was similar in both rest and STS condition and occurred at 60 min at rest and at 57 min in STS. In conclusion, 1-h of STS slows the increase in the peak concentration of plasma leucine similarly after oral ingestion of leucine or BCAAs but after oral ingestion of glutamine it has no slowing effect on glutamine concentration.
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Affiliation(s)
- Antti Mero
- Department of Biology of Physical Activity, University of Jyväskylä, PO Box 35, 40014 Jyväskylä, Finland.
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Lima LCJ, Assis GV, Hiyane W, Almeida WS, Arsa G, Baldissera V, Campbell CSG, Simões HG. Hypotensive effects of exercise performed around anaerobic threshold in type 2 diabetic patients. Diabetes Res Clin Pract 2008; 81:216-22. [PMID: 18571267 DOI: 10.1016/j.diabres.2008.04.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Accepted: 04/28/2008] [Indexed: 12/17/2022]
Abstract
AIM To verify the occurrence of post-exercise hypotension (PEH) in type 2 diabetics (DM(2)) and the effects of exercise intensity on post-exercise blood pressure (BP). METHODS Eleven men and women with DM(2) (58.5+/-10.2 years; 160+/-0.1cm; 80.6+/-13.5kg; 31.2+/-3.8kg/m(2), 19+/-3.2mLkgmin(-1) of VO(2max), 155.0+/-39.2mgdL(-1) of fasting blood glucose and 126+/-10/75+/-7mmHg of resting BP) performed an incremental test (IT) for cardiovascular evaluation and anaerobic threshold (AT) determination. Then, participants randomly underwent 2 exercise sessions (90% and 110% AT) and a control session (CON). In all sessions, BP was measured at resting, during 20min of exercise/control and at each 15min through 120min of post-exercise recovery (R15-R120). RESULTS The mean results of systolic BP (SBP)/diastolic BP (DBP) over the 120min of recovery were 125+/-16/76+/-7mmHg, 122+/-13/75+/-6mmHg and 129+/-16/78+/-7mmHg, respectively for 90%, 110% and CON. Significant reductions of SBP occurred after 90% (R15-R45) and 110% (R15-R90), while only after 110% there were reductions of DBP (R15, R45) and MAP (R15, R45, R75, R90, R105). CONCLUSIONS Both exercise intensities evoked reductions in SBP while DBP and MAP were reduced only after 110%. Despite the higher intensity exercise to be more effective in promoting BP reductions, we suggest caution while prescribing exercise for DM(2).
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Beelen M, Koopman R, Gijsen AP, Vandereyt H, Kies AK, Kuipers H, Saris WHM, van Loon LJC. Protein coingestion stimulates muscle protein synthesis during resistance-type exercise. Am J Physiol Endocrinol Metab 2008; 295:E70-7. [PMID: 18430966 DOI: 10.1152/ajpendo.00774.2007] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In contrast to the effect of nutritional intervention on postexercise muscle protein synthesis, little is known about the potential to modulate protein synthesis during exercise. This study investigates the effect of protein coingestion with carbohydrate on muscle protein synthesis during resistance-type exercise. Ten healthy males were studied in the evening after they consumed a standardized diet throughout the day. Subjects participated in two experiments in which they ingested either carbohydrate or carbohydrate with protein during a 2-h resistance exercise session. Subjects received a bolus of test drink before and every 15 min during exercise, providing 0.15 g x kg(-1) x h(-1) carbohydrate with (CHO + PRO) or without (CHO) 0.15 g x kg(-1) x h(-1) protein hydrolysate. Continuous intravenous infusions with l-[ring-(13)C(6)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied, and blood and muscle biopsies were collected to assess whole body and muscle protein synthesis rates during exercise. Protein coingestion lowered whole body protein breakdown rates by 8.4 +/- 3.6% (P = 0.066), compared with the ingestion of carbohydrate only, and augmented protein oxidation and synthesis rates by 77 +/- 17 and 33 +/- 3%, respectively (P < 0.01). As a consequence, whole body net protein balance was negative in CHO, whereas a positive net balance was achieved after the CHO + PRO treatment (-4.4 +/- 0.3 vs. 16.3 +/- 0.4 micromol phenylalanine x kg(-1) x h(-1), respectively; P < 0.01). In accordance, mixed muscle protein fractional synthetic rate was 49 +/- 22% higher after protein coingestion (0.088 +/- 0.012 and 0.060 +/- 0.004%/h in CHO + PRO vs. CHO treatment, respectively; P < 0.05). We conclude that, even in a fed state, protein coingestion stimulates whole body and muscle protein synthesis rates during resistance-type exercise.
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Affiliation(s)
- Milou Beelen
- Department of Human Movement Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands.
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18
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Mero A, Leikas A, Rinkinen N, Huhta P, Hulmi JJ, Pitkänen H, Knuutinen J. Effect of strength training session on plasma amino acid concentration following oral ingestion of arginine or taurine in men. Amino Acids 2008; 35:99-106. [DOI: 10.1007/s00726-007-0619-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Accepted: 10/08/2007] [Indexed: 12/01/2022]
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20
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Tipton KD, Elliott TA, Cree MG, Aarsland AA, Sanford AP, Wolfe RR. Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise. Am J Physiol Endocrinol Metab 2007; 292:E71-6. [PMID: 16896166 DOI: 10.1152/ajpendo.00166.2006] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Timing of nutrient ingestion has been demonstrated to influence the anabolic response of muscle following exercise. Previously, we demonstrated that net amino acid uptake was greater when free essential amino acids plus carbohydrates were ingested before resistance exercise rather than following exercise. However, it is unclear if ingestion of whole proteins before exercise would stimulate a superior response compared with following exercise. This study was designed to examine the response of muscle protein balance to ingestion of whey proteins both before and following resistance exercise. Healthy volunteers were randomly assigned to one of two groups. A solution of whey proteins was consumed either immediately before exercise (PRE; n = 8) or immediately following exercise (POST; n = 9). Each subject performed 10 sets of 8 repetitions of leg extension exercise. Phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. Arterial amino acid concentrations were elevated by approximately 50%, and net amino acid balance switched from negative to positive following ingestion of proteins at either time. Amino acid uptake was not significantly different between PRE and POST when calculated from the beginning of exercise (67 +/- 22 and 27 +/- 10 for PRE and POST, respectively) or from the ingestion of each drink (60 +/- 17 and 63 +/- 15 for PRE and POST, respectively). Thus the response of net muscle protein balance to timing of intact protein ingestion does not respond as does that of the combination of free amino acids and carbohydrate.
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Affiliation(s)
- Kevin D Tipton
- The Univ. of Birmingham, School of Sport & Exercise Sciences, Edgbaston, Birmington B15 2TT, UK.
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21
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Dreyer HC, Fujita S, Cadenas JG, Chinkes DL, Volpi E, Rasmussen BB. Resistance exercise increases AMPK activity and reduces 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle. J Physiol 2006; 576:613-24. [PMID: 16873412 PMCID: PMC1890364 DOI: 10.1113/jphysiol.2006.113175] [Citation(s) in RCA: 374] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Resistance exercise is a potent stimulator of muscle protein synthesis and muscle cell growth, with the increase in protein synthesis being detected within 2-3 h post-exercise and remaining elevated for up to 48 h. However, during exercise, muscle protein synthesis is inhibited. An increase in AMP-activated protein kinase (AMPK) activity has recently been shown to decrease mammalian target of rapamycin (mTOR) signalling to key regulators of translation initiation. We hypothesized that the cellular mechanism for the inhibition of muscle protein synthesis during an acute bout of resistance exercise in humans would be associated with an activation of AMPK and an inhibition of downstream components of the mTOR pathway (4E-BP1 and S6K1). We studied 11 subjects (seven men, four women) before, during, and for 2 h following a bout of resistance exercise. Muscle biopsy specimens were collected at each time point from the vastus lateralis. We utilized immunoprecipitation and immunoblotting methods to measure muscle AMPKalpha2 activity, and mTOR-associated upstream and downstream signalling proteins, and stable isotope techniques to measure muscle fractional protein synthetic rate (FSR). AMPKalpha2 activity (pmol min(-1) (mg protein)(-1)) at baseline was 1.7 +/- 0.3, increased immediately post-exercise (3.0 +/- 0.6), and remained elevated at 1 h post-exercise (P < 0.05). Muscle FSR decreased during exercise and was significantly increased at 1 and 2 h post-exercise (P < 0.05). Phosphorylation of 4E-BP1 at Thr37/46 was significantly reduced immediately post-exercise (P < 0.05). We conclude that AMPK activation and a reduced phosphorylation of 4E-BP1 may contribute to the inhibition of muscle protein synthesis during resistance exercise. However, by 1-2 h post-exercise, muscle protein synthesis increased in association with an activation of protein kinase B, mTOR, S6K1 and eEF2.
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Affiliation(s)
- Hans C Dreyer
- University of Texas Medical Branch, Department of Physical Therapy, Division of Rehabilitation Sciences, 301 University Blvd, Galveston, TX 77555-1144, USA
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Haus JM, Miller BF, Carroll CC, Weinheimer EM, Trappe TA. The effect of strenuous aerobic exercise on skeletal muscle myofibrillar proteolysis in humans. Scand J Med Sci Sports 2006; 17:260-6. [PMID: 16787442 DOI: 10.1111/j.1600-0838.2006.00566.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Relatively little is known about the dynamics of the skeletal muscle protein pool following aerobic exercise. Myofibrillar protein synthesis has recently been shown to be substantially elevated for 3 days after a strenuous 60 min bout of one-legged aerobic exercise, and this increase was surprisingly equal to or greater than what has been shown numerous times following resistance exercise over the same time course. Because net protein accretion is the sum of protein synthesis and degradation, we sought to directly measure skeletal muscle myofibrillar proteolysis in five healthy young males in response to an identical strenuous 60 min aerobic exercise bout and at the same time points (rest, 6, and 24 h post-exercise and 48 and 72 h post-exercise in a subset of subjects). We measured skeletal muscle myofibrillar proteolysis by monitoring the release of the natural tracer 3-methylhistidine (3MH) from the vastus lateralis muscle into the interstitial space via microdialysis. Skeletal muscle interstitial 3MH concentration was no different (P>0.05) from rest (5.16+/-0.38 nmol/mL) after 6 (5.37+/-0.55 nmol/mL), 24 (5.40+/-0.26 nmol/mL), 48 (5.50+/-0.74 nmol/mL), or 72 h (4.73+/-0.28 nmol/mL). These results suggest that proteolysis of the myofibrillar fraction of skeletal muscle is relatively refractory to an intense aerobic exercise stimulus for up to 3 days, despite the large increase in synthesis of this muscle fraction following the same exercise stimulus. The apparent net myofibrillar protein accretion in the hours and days after exercise may occur in order to offset the large elevation in mixed muscle proteolysis that has been shown during similar bouts of intense one-legged aerobic exercise.
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Affiliation(s)
- J M Haus
- Human Performance Laboratory, Ball State University, Muncie, Indiana 47306, USA
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Norton LE, Layman DK. Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. J Nutr 2006; 136:533S-537S. [PMID: 16424142 DOI: 10.1093/jn/136.2.533s] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
High-performance physical activity and postexercise recovery lead to significant changes in amino acid and protein metabolism in skeletal muscle. Central to these changes is an increase in the metabolism of the BCAA leucine. During exercise, muscle protein synthesis decreases together with a net increase in protein degradation and stimulation of BCAA oxidation. The decrease in protein synthesis is associated with inhibition of translation initiation factors 4E and 4G and ribosomal protein S6 under regulatory controls of intracellular insulin signaling and leucine concentrations. BCAA oxidation increases through activation of the branched-chain alpha-keto acid dehydrogenase (BCKDH). BCKDH activity increases with exercise, reducing plasma and intracellular leucine concentrations. After exercise, recovery of muscle protein synthesis requires dietary protein or BCAA to increase tissue levels of leucine in order to release the inhibition of the initiation factor 4 complex through activation of the protein kinase mammalian target of rapamycin (mTOR). Leucine's effect on mTOR is synergistic with insulin via the phosphoinositol 3-kinase signaling pathway. Together, insulin and leucine allow skeletal muscle to coordinate protein synthesis with physiological state and dietary intake.
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Affiliation(s)
- Layne E Norton
- Division of Nutritional Sciences, Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Kerksick CM, Leutholtz B. Nutrient administration and resistance training. J Int Soc Sports Nutr 2005; 2:50-67. [PMID: 18500951 PMCID: PMC2129163 DOI: 10.1186/1550-2783-2-1-50] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2005] [Accepted: 06/11/2005] [Indexed: 11/10/2022] Open
Abstract
Skeletal muscle tissue is tightly regulated throughout our bodies by balancing its synthesis and breakdown. Many factors are known to exist that cause profound changes on the overall status of skeletal muscle, some of which include exercise, nutrition, hormonal influences and disease. Muscle hypertrophy results when protein synthesis is greater than protein breakdown. Resistance training is a popular form of exercise that has been shown to increase muscular strength and muscular hypertrophy. In general, resistance training causes a stimulation of protein synthesis as well as an increase in protein breakdown, resulting in a negative balance of protein. Providing nutrients, specifically amino acids, helps to stimulate protein synthesis and improve the overall net balance of protein. Strategies to increase the concentration and availability of amino acids after resistance exercise are of great interest and have been shown to effectively increase overall protein synthesis. 123 After exercise, providing carbohydrate has been shown to mildly stimulate protein synthesis while addition of free amino acids prior to and after exercise, specifically essential amino acids, causes a rapid pronounced increase in protein synthesis as well as protein balance.13 Evidence exists for a dose-response relationship of infused amino acids while no specific regimen exists for optimal dosing upon ingestion. Ingestion of whole or intact protein sources (e.g., protein powders, meal-replacements) has been shown to cause similar improvements in protein balance after resistance exercise when compared to free amino acid supplements. Future research should seek to determine optimal dosing of ingested intact amino acids in addition to identifying the cellular mechanistic machinery (e.g. transcriptional and translational mechanisms) for causing the increase in protein synthesis.
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Affiliation(s)
- Chad M Kerksick
- Exercise and Sport Nutrition Laboratory, Center for Exercise, Nutrition and Preventive Health Research, Department of Health, Human Performance and Recreation, Baylor University.
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Beramendi A, Peron S, Megighian A, Reggiani C, Cantera R. The inhibitorκB-ortholog Cactus is necessary for normal neuromuscular function in Drosophila melanogaster. Neuroscience 2005; 134:397-406. [PMID: 15975723 DOI: 10.1016/j.neuroscience.2005.04.046] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Revised: 04/22/2005] [Accepted: 04/23/2005] [Indexed: 10/25/2022]
Abstract
The Drosophila inhibitor-kappaB ortholog Cactus acts as an inhibitor of the Rel-transcription factors Dorsal and Dif. In blastoderm cells and immune competent cells, Cactus inhibits Dorsal and Dif by preventing their nuclear localization. Cactus, Dorsal and Dif are also expressed in somatic muscles, where Cactus and Dorsal, but not Dif, are enriched at the neuromuscular junction. Mutations in dorsal cause neuromuscular defects and mislocalization of Cactus. Here, we investigated whether mutations in cactus affect the neuromuscular system and subcellular localization of Dorsal and Dif. Using locomotion assays, as well as physiological and immunochemical methods, we found that wild type Cactus is necessary for the normal function of the larval neuromuscular system. The phenotype comprises i) altered bouton numbers and impaired neurotransmitter release in the neuromuscular junctions in the abdominal segments, ii) muscular weakness and iii) poor locomotion performance, probably reflecting a general neuromuscular impairment. Interestingly, in cactus mutants the subcellular localization of Dorsal and Dif in muscle is not affected, whereas cactus protein is not detected in the nucleus. This suggests, together with the similarities between the phenotypes induced by cactus and dorsal mutations, that in larval muscles the function of Cactus might be cooperation to the transcriptional activity of Rel proteins more than their cytoplasmic retention. The similarities with inhibitor-kappaB/nuclear factor kappaB interactions and muscle pathology in mammals point to Drosophila as a suitable experimental system to clarify the complex interactions of these proteins in muscle postembryonic development and activity.
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Affiliation(s)
- A Beramendi
- Department of Zoology, Stockholm University, S-106 91 Stockholm, Sweden
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