Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states

[Effects of intermittent fasting and sports performance: a narrative review]

Recently, fasted exercise has generated interest for its potential to stimulate metabolic and performance adaptations. The present study aims to analyze the effects of fasting and fasted training on performance and metabolism, acutely and chronically. The databases Medline (PubMed), Physiotherapy Evidence Database (PEDro), Cochrane, and Google Scholar were searched. In total, 767 studies were identified. Of those, 51 studies were finally included. Acutely, exercise on fasting promotes fat oxidation at low and moderate intensities, while protein catabolism is not increased. Performance is not affected in efforts lower than 1 hour. Chronically, fasting generates greater efficiency in fat metabolism and the ability to regulate blood glucose in the long term, although it has not been possible to determine whether these findings improve sports performance. More research is needed in elite athletes, with high training loads and with a periodized approach to fasting.

Exercise-specific adaptations in human skeletal muscle: Molecular mechanisms of making muscles fit and mighty

The mechanisms leading to a predominantly hypertrophied phenotype versus a predominantly oxidative phenotype, the hallmarks of resistance training (RT) or aerobic training (AT), respectively, are being unraveled. In humans, exposure of naïve persons to either AT or RT results in their skeletal muscle exhibiting generic 'exercise stress-related' signaling, transcription, and translation responses. However, with increasing engagement in AT or RT, the responses become refined, and the phenotype typically associated with each form of exercise emerges. Here, we review some of the mechanisms underpinning the adaptations of how muscles become, through AT, 'fit' and RT, 'mighty.' Much of our understanding of molecular exercise physiology has arisen from targeted analysis of post-translational modifications and measures of protein synthesis. Phosphorylation of specific residue sites has been a dominant focus, with canonical signaling pathways (AMPK and mTOR) studied extensively in the context of AT and RT, respectively. These alone, along with protein synthesis, have only begun to elucidate key differences in AT and RT signaling. Still, key yet uncharacterized differences exist in signaling and regulation of protein synthesis that drive unique adaptation to AT and RT. Omic studies are required to better understand the divergent relationship between exercise and phenotypic outcomes of training.

Ferroptosis and aerobic training in ageing

 Ferroptosis is a form of programmed cell death that plays a significant role in causing several diseases such as heart attack and heart failure, through alterations in fat, amino acid, and iron metabolism. Comprehending the regulatory mechanisms of ferroptosis signaling is critical because it has a considerable effect on the elderly's mortality. Conversely, age-related changes in substrate metabolism and metabolite levels are recognized to give rise to obesity. Furthermore, research has proposed that aging and obesity-related changes in substrate metabolism may aggravate ferroptosis. The suppression of ferroptosis holds potential as a successful therapeutic approach for managing different diseases, including sarcopenia, cardiovascular diseases, and central nervous system diseases. However, the pathologic and biological mechanisms behind the function of ferroptosis are not fully comprehended yet. Physical activity could affect lipid, amino acid, and iron metabolism to modulate ferroptosis. The aim of this study is to showcase the current understanding of the molecular mechanisms leading to ferroptosis and discuss the role of aging and physical activity in this phenomenon.

Postabsorptive muscle protein synthesis is higher in outpatients as compared to inpatients

Several factors affect muscle protein synthesis (MPS) in the postabsorptive state. Extreme physical inactivity (e.g., bedrest) may reduce basal MPS, whereas walking may augment basal MPS. We hypothesized that outpatients would have a higher postabsorptive MPS than inpatients. To test this hypothesis, we conducted a retrospective analysis. We compared 152 outpatient participants who arrived at the research site the morning of the MPS assessment with 350 Inpatient participants who had an overnight stay in the hospital unit before the MPS assessment the following morning. We used stable isotopic methods and collected vastus lateralis biopsies ∼2 to 3 h apart to assess mixed MPS. MPS was ∼12% higher (P < 0.05) for outpatients than inpatients. Within a subset of participants, we discovered that after instruction to limit activity, outpatients (n = 13) took 800 to 900 steps in the morning to arrive at the unit, seven times more steps than inpatients (n = 12). We concluded that an overnight stay in the hospital as an inpatient is characterized by reduced morning activity and causes a slight but significant reduction in MPS compared with participants studied as outpatients. Researchers should be aware of physical activity status when designing and interpreting MPS results.NEW & NOTEWORTHY The postabsorptive muscle protein synthesis rate is lower in the morning after an overnight inpatient hospital stay compared with an outpatient visit. Although only a minimal amount of steps was conducted by outpatients (∼900), this was enough to increase postabsorptive muscle protein synthesis rate.

Acute heat stress amplifies exercise-induced metabolomic perturbations and reveals variation in circulating amino acids in endurance-trained males

NEW FINDINGS

What is the central question of this study? Whole-body substrate utilisation is altered during exercise in hot environments, characterised by increased glycolytic metabolism: does heat stress alter the serum metabolome in response to high intensity exercise? What are the main finding and its importance? Alongside increases in glycolytic metabolite abundance, circulating amino acid concentrations are reduced following exercise under heat stress. Prior research has overlooked the impact of heat stress on protein metabolism during exercise, raising important practical implications for protein intake recommendations in the heat.

ABSTRACT

Using untargeted metabolomics, we aimed to characterise the systemic impact of environmental heat stress during exercise. Twenty-three trained male triathletes (V ̇ O 2 peak ${\dot V_{{{\rm{O}}_2}{\rm{peak}}}}$  = 64.8 ± 9.2 ml kg min-1 ) completed a 30-min exercise test in hot (35°C) and temperate (21°C) conditions. Venous blood samples were collected immediately pre- and post-exercise, and the serum fraction was assessed via untargeted 1 H-NMR metabolomics. Data were analysed via uni- and multivariate analyses to identify differences between conditions. Mean power output was higher in temperate (231 ± 36 W) versus hot (223 ± 31 W) conditions (P < 0.001). Mean heart rate (temperate, 162 ± 10 beats min-1 , hot, 167 ± 9 beats min-1 , P < 0.001), peak core temperature (Trec ), core temperature change (ΔTrec ) (P < 0.001) and peak rating of perceived exertion (P = 0.005) were higher in hot versus temperate conditions. Change in metabolite abundance following exercise revealed distinct clustering following multivariate analysis. Six metabolites increased (2-hydroxyvaleric acid, acetate, alanine, glucarate, glucose, lactate) in hot relative to temperate (P < 0.05) conditions. Leucine and lysine decreased in both conditions but to a greater extent in temperate conditions (P < 0.05). Citrate (P = 0.04) was greater in temperate conditions whilst creatinine decreased in hot conditions only (P > 0.05). Environmental heat stress increased glycolytic metabolite abundance and led to distinct alterations in the circulating amino acid availability, including increased alanine, glutamine, leucine and isoleucine. The data highlight the need for additional exercise nutrition and metabolism research, specifically focusing on protein requirements for exercise under heat stress.

Acute responsiveness to single leg cycling in adults with obesity

Obesity is associated with several skeletal muscle impairments which can be improved through an aerobic exercise prescription. The possibility that exercise responsiveness is diminished in people with obesity has been suggested but not well-studied. The purpose of this study was to investigate how obesity influences acute exercise responsiveness in skeletal muscle and circulating amino metabolites. Non-obese (NO; n = 19; 10F/9M; BMI = 25.1 ± 2.8 kg/m2 ) and Obese (O; n = 21; 14F/7M; BMI = 37.3 ± 4.6 kg/m2 ) adults performed 30 min of single-leg cycling at 70% of VO2 peak. 13 C6 -Phenylalanine was administered intravenously for muscle protein synthesis measurements. Serial muscle biopsies (vastus lateralis) were collected before exercise and 3.5- and 6.5-h post-exercise to measure protein synthesis and gene expression. Targeted plasma metabolomics was used to quantitate amino metabolites before and 30 and 90 min after exercise. The exercise-induced fold change in mixed muscle protein synthesis trended (p = 0.058) higher in NO (1.28 ± 0.54-fold) compared to O (0.95 ± 0.42-fold) and was inversely related to BMI (R2  = 0.140, p = 0.027). RNA sequencing revealed 331 and 280 genes that were differentially expressed after exercise in NO and O, respectively. Gene set enrichment analysis showed O had six blunted pathways related to metabolism, cell to cell communication, and protein turnover after exercise. The circulating amine response further highlighted dysregulations related to protein synthesis and metabolism in adults with obesity at the basal state and in response to the exercise bout. Collectively, these data highlight several unique pathways in individuals with obesity that resulted in a modestly blunted exercise response.

Nutritional Regulation of Muscle Stem Cells in Exercise and Disease: The Role of Protein and Amino Acid Dietary Supplementation

Human skeletal muscle is a remarkedly plastic tissue that has a high capacity to adapt in response to various stimuli. These adaptations are due in part to the function of muscle-resident stem/progenitor cells. Skeletal muscle regeneration and adaptation is facilitated by the activation and expansion of muscle stem cells (MuSCs). MuSC fate is regulated by signals released from cells in their niche, such as fibro-adipogenic progenitors (FAPs), as well as a variety of non-cellular niche components. Sufficient dietary protein consumption is critical for maximizing skeletal muscle adaptation to exercise and maintaining skeletal muscle in disease; however, the role of dietary protein in altering MuSC and FAP responses to exercise in healthy populations and skeletal muscle disease states requires more research. The present review provides an overview of this emerging field and suggestions for future directions. The current literature suggests that in response to resistance exercise, protein supplementation has been shown to increase MuSC content and the MuSC response to acute exercise. Similarly, protein supplementation augments the increase in MuSC content following resistance training. Endurance exercise, conversely, is an area of research that is sparse with respect to the interaction of protein supplementation and exercise on muscle stem/progenitor cell fate. Initial evidence suggests that protein supplementation augments the early myogenic response to acute endurance exercise but does not enhance the MuSC response to endurance training. Resistance training increases the number of proliferating FAPs with no additional effect of protein supplementation. Future research should continue to focus on the nutritional regulation of skeletal muscle stem/progenitor cell fate paired with studies examining the effects of exercise on a variety of human populations.

(Dys)regulation of Protein Metabolism in Skeletal Muscle of Humans With Obesity

Studies investigating the proteome of skeletal muscle present clear evidence that protein metabolism is altered in muscle of humans with obesity. Moreover, muscle quality (i.e., strength per unit of muscle mass) appears lower in humans with obesity. However, relevant evidence to date describing the protein turnover, a process that determines content and quality of protein, in muscle of humans with obesity is quite inconsistent. This is due, at least in part, to heterogeneity in protein turnover in skeletal muscle of humans with obesity. Although not always evident at the mixed-muscle protein level, the rate of synthesis is generally lower in myofibrillar and mitochondrial proteins in muscle of humans with obesity. Moreover, alterations in the synthesis of protein in muscle of humans with obesity are manifested more readily under conditions that stimulate protein synthesis in muscle, including the fed state, increased plasma amino acid availability to muscle, and exercise. Current evidence supports various biological mechanisms explaining impairments in protein synthesis in muscle of humans with obesity, but this evidence is rather limited and needs to be reproduced under more defined experimental conditions. Expanding our current knowledge with direct measurements of protein breakdown in muscle, and more importantly of protein turnover on a protein by protein basis, will enhance our understanding of how obesity modifies the proteome (content and quality) in muscle of humans with obesity.

Evaluating the Effects of Increased Protein Intake on Muscle Strength, Hypertrophy and Power Adaptations with Concurrent Training: A Narrative Review

Concurrent training incorporates dual exercise modalities, typically resistance and aerobic-based exercise, either in a single session or as part of a periodized training program, that can promote muscle strength, mass, power/force and aerobic capacity adaptations for the purposes of sports performance or general health/wellbeing. Despite multiple health and exercise performance-related benefits, diminished muscle hypertrophy, strength and power have been reported with concurrent training compared to resistance training in isolation. Dietary protein is well-established to facilitate skeletal muscle growth, repair and regeneration during recovery from exercise. The degree to which increased protein intake can amplify adaptation responses with resistance exercise, and to a lesser extent aerobic exercise, has been highly studied. In contrast, much less focus has been directed toward the capacity for protein to enhance anabolic and metabolic responses with divergent contractile stimuli inherent to concurrent training and potentially negate interference in muscle strength, power and hypertrophy. This review consolidates available literature investigating increased protein intake on rates of muscle protein synthesis, hypertrophy, strength and force/power adaptations following acute and chronic concurrent training. Acute concurrent exercise studies provide evidence for the significant stimulation of myofibrillar protein synthesis with protein compared to placebo ingestion. High protein intake can also augment increases in lean mass with chronic concurrent training, although these increases do not appear to translate into further improvements in strength adaptations. Similarly, the available evidence indicates protein intake twice the recommended intake and beyond does not rescue decrements in selective aspects of muscle force and power production with concurrent training.

Muscle Protein Synthesis Responses Following Aerobic-Based Exercise or High-Intensity Interval Training with or Without Protein Ingestion: A Systematic Review

BACKGROUND

Systematic investigation of muscle protein synthesis (MPS) responses with or without protein ingestion has been largely limited to resistance training.

OBJECTIVE

This systematic review determined the capacity for aerobic-based exercise or high-intensity interval training (HIIT) to stimulate post-exercise rates of MPS and whether protein ingestion further significantly increases MPS compared with placebo.

METHODS

Three separate models analysed rates of either mixed, myofibrillar, sarcoplasmic, or mitochondrial protein synthesis (PS) following aerobic-based exercise or HIIT: Model 1 (n = 9 studies), no protein ingestion; Model 2 (n = 7 studies), peri-exercise protein ingestion with no placebo comparison; Model 3 (n = 14 studies), peri-exercise protein ingestion with placebo comparison.

RESULTS

Eight of nine studies and all seven studies in Models 1 and 2, respectively, demonstrated significant post-exercise increases in either mixed or a specific muscle protein pool. Model 3 observed significantly greater MPS responses with protein compared with placebo in either mixed or a specific muscle fraction in 7 of 14 studies. Seven studies showed no difference in MPS between protein and placebo, while three studies reported no significant increases in mitochondrial PS with protein compared with placebo.

CONCLUSION

Most studies reporting significant increases in MPS were confined to mixed and myofibrillar PS that may facilitate power generating capacity of working skeletal muscle with aerobic-based exercise and HIIT. Only three of eight studies demonstrated significant increases in mitochondrial PS post-exercise, with no further benefits of protein ingestion. This lack of change may be explained by the acute analysis window in most studies and apparent latency in exercise-induced stimulation of mitochondrial PS.

Lack of Increase in Muscle Mitochondrial Protein Synthesis During the Course of Aerobic Exercise and Its Recovery in the Fasting State Irrespective of Obesity

Acute aerobic exercise induces skeletal muscle mitochondrial gene expression, which in turn can increase muscle mitochondrial protein synthesis. In this regard, the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), is a master regulator of mitochondrial biogenesis, and thus mitochondrial protein synthesis. However, PGC-1α expression is impaired in muscle of humans with obesity in response to acute aerobic exercise. Therefore, we sought to determine whether muscle mitochondrial protein synthesis is also impaired under the same conditions in humans with obesity. To this end, we measured mitochondrial and mixed-muscle protein synthesis in skeletal muscle of untrained subjects with (body fat: 34.7 ± 2.3%) and without (body fat: 25.3 ± 3.3%) obesity in a basal period and during a continuous period that included a 45 min cycling exercise (performed at an intensity corresponding to 65% of heart rate reserve) and a 3-h post-exercise recovery. Exercise increased PGC-1α mRNA expression in muscle of subjects without obesity, but not in subjects with obesity. However, muscle mitochondrial protein synthesis did not increase in either subject group. Similarly, mixed-muscle protein synthesis did not increase in either group. Concentrations of plasma amino acids decreased post-exercise in the subjects without obesity, but not in the subjects with obesity. We conclude that neither mitochondrial nor mixed-muscle protein synthesis increase in muscle of humans during the course of a session of aerobic exercise and its recovery period in the fasting state irrespective of obesity. Trial Registration: The study has been registered within ClinicalTrials.gov (NCT01824173).

Effect of the lysosomotropic agent chloroquine on mTORC1 activation and protein synthesis in human skeletal muscle

Background

Previous work in HEK-293 cells demonstrated the importance of amino acid-induced mTORC1 translocation to the lysosomal surface for stimulating mTORC1 kinase activity and protein synthesis. This study tested the conservation of this amino acid sensing mechanism in human skeletal muscle by treating subjects with chloroquine—a lysosomotropic agent that induces in vitro and in vivo lysosome dysfunction.

Methods

mTORC1 signaling and muscle protein synthesis (MPS) were determined in vivo in a randomized controlled trial of 14 subjects (10 M, 4 F; 26 ± 4 year) that ingested 10 g of essential amino acids (EAA) after receiving 750 mg of chloroquine (CHQ, n = 7) or serving as controls (CON, n = 7; no chloroquine). Additionally, differentiated C2C12 cells were used to assess mTORC1 signaling and myotube protein synthesis (MyPS) in the presence and absence of leucine and the lysosomotropic agent chloroquine.

Results

mTORC1, S6K1, 4E-BP1 and rpS6 phosphorylation increased in both CON and CHQ 1 h post EAA ingestion (P < 0.05). MPS increased similarly in both groups (CON, P = 0.06; CHQ, P < 0.05). In contrast, in C2C12 cells, 1 mM leucine increased mTORC1 and S6K1 phosphorylation (P < 0.05), which was inhibited by 2 mg/ml chloroquine. Chloroquine (2 mg/ml) was sufficient to disrupt mTORC1 signaling, and MyPS.

Conclusions

Chloroquine did not inhibit amino acid-induced activation of mTORC1 signaling and skeletal MPS in humans as it does in C2C12 muscle cells. Therefore, different in vivo experimental approaches are required for confirming the precise role of the lysosome and amino acid sensing in human skeletal muscle.

Trial registration NCT00891696. Registered 29 April 2009.

Can High-Intensity Interval Training Promote Skeletal Muscle Anabolism?

Exercise training in combination with optimal nutritional support is an effective strategy to maintain or increase skeletal muscle mass. A single bout of resistance exercise undertaken with adequate protein availability increases rates of muscle protein synthesis and, when repeated over weeks and months, leads to increased muscle fiber size. While resistance-based training is considered the 'gold standard' for promoting muscle hypertrophy, other modes of exercise may be able to promote gains in muscle mass. High-intensity interval training (HIIT) comprises short bouts of exercise at or above the power output/speed that elicits individual maximal aerobic capacity, placing high tensile stress on skeletal muscle, and somewhat resembling the demands of resistance exercise. While HIIT induces rapid increases in skeletal muscle oxidative capacity, the anabolic potential of HIIT for promoting concurrent gains in muscle mass and cardiorespiratory fitness has received less scientific inquiry. In this review, we discuss studies that have determined muscle growth responses after HIIT, with a focus on molecular responses, that provide a rationale for HIIT to be implemented among populations who are susceptible to muscle loss (e.g. middle-aged or older adults) and/or in clinical settings (e.g. pre- or post-surgery).

Expression of titin-linked putative mechanosensing proteins in skeletal muscle after power resistance exercise in resistance-trained men

Little is known about the molecular responses to power resistance exercise that lead to skeletal muscle remodeling and enhanced athletic performance. We assessed the expression of titin-linked putative mechanosensing proteins implicated in muscle remodeling: muscle ankyrin repeat proteins (Ankrd 1, Ankrd 2, and Ankrd 23), muscle-LIM proteins (MLPs), muscle RING-finger protein-1 (MuRF-1), and associated myogenic proteins (MyoD1, myogenin, and myostatin) in skeletal muscle in response to power resistance exercise with or without a postexercise meal, in fed, resistance-trained men. A muscle sample was obtained from the vastus lateralis of seven healthy men on separate days, 3 h after 90 min of rest (Rest) or power resistance exercise with (Ex + Meal) or without (Ex) a postexercise meal to quantify mRNA and protein levels. The levels of phosphorylated HSP27 (pHSP27-Ser15) and cytoskeletal proteins in muscle and creatine kinase activity in serum were also assessed. The exercise increased (P ≤ 0.05) pHSP27-Ser15 (∼6-fold) and creatine kinase (∼50%), whereas cytoskeletal protein levels were unchanged (P > 0.05). Ankrd 1 (∼15-fold) and MLP (∼2-fold) mRNA increased, whereas Ankrd 2, Ankrd 23, MuRF-1, MyoD1, and myostatin mRNA were unchanged. Ankrd 1 (∼3-fold, Ex) and MLPb (∼20-fold, Ex + Meal) protein increased, but MLPa, Ankrd 2, Ankrd 23, and the myogenic proteins were unchanged. The postexercise meal did not affect the responses observed. Power resistance exercise, as performed in practice, induced subtle early responses in the expression of MLP and Ankrd 1 yet had little effect on the other proteins investigated. These findings suggest possible roles for MLP and Ankrd 1 in the remodeling of skeletal muscle in individuals who regularly perform this type of exercise.NEW & NOTEWORTHY This is the first study to assess the early changes in the expression of titin-linked putative mechanosensing proteins and associated myogenic regulatory factors in skeletal muscle after power resistance exercise in fed, resistance-trained men. We report that power resistance exercise induces subtle early responses in the expression of Ankrd 1 and MLP, suggesting these proteins play a role in the remodeling of skeletal muscle in individuals who regularly perform this type of exercise.

Low-dose aspirin and COX inhibition in human skeletal muscle

Skeletal muscle health has been shown to benefit from regular consumption of cyclooxygenase (COX)-inhibiting drugs. Aspirin, especially at low doses, is one of the most commonly consumed COX inhibitors, yet investigations of low-dose aspirin effects on skeletal muscle are nonexistent. The goal of this study was to examine the efficacy of low-dose aspirin on skeletal muscle COX production of the inflammatory regulator prostaglandin (PG)E₂ at rest and after exercise. Skeletal muscle biopsies (vastus lateralis) were taken from eight individuals [4 men, 4 women; 25 ± 1 yr; 81.4 ± 3.4 kg; maximal oxygen consumption (V̇o_2max): 3.33 ± 0.21 L/min] before and 3.5 h after 40 min of cycling at 70% of V̇o_2max for the measurement of ex vivo PGE₂ production. Muscle strips were incubated in Krebs-Henseleit buffer (control) or supplemented with one of two aspirin concentrations that reflected blood levels after a low (10 µM; typical oral dose: 75-325 mg) or standard (100 µM; typical oral dose: 975-1,000 mg) dose. Low (-22 ± 5%)- and standard (-28 ± 5%)-dose aspirin concentrations both reduced skeletal muscle PGE₂ production, independent of exercise (P < 0.05). There was no difference in PGE₂ suppression between the two doses (P > 0.05). In summary, low-dose aspirin levels are sufficient to inhibit the COX enzyme in skeletal muscle and significantly reduce production of PGE₂, a known regulator of skeletal muscle health. Aerobic exercise does not appear to alter the inhibitory efficacy of aspirin. These findings may have implications for the tens of millions of individuals who chronically consume low-dose aspirin.NEW & NOTEWORTHY This study demonstrated that even low-dose aspirin concentrations can significantly reduce the prostaglandin (PG)E₂/cyclooxygenase (COX) pathway activity in human skeletal muscle and this effect is not altered during the recovery period following aerobic exercise. These findings are noteworthy since aspirin is one of the most commonly consumed drugs in the world and nonaspirin COX-inhibiting drugs have been shown to regulate skeletal muscle health in sedentary and exercise-training individuals.

Effect of carbohydrate-protein supplementation on endurance training adaptations

Purpose

To examine the influence of post-exercise protein feeding upon the adaptive response to endurance exercise training.

Methods

In a randomised parallel group design, 25 healthy men and women completed 6 weeks of endurance exercise training by running on a treadmill for 30–60 min at 70–75% maximal oxygen uptake (VO_2max) 4 times/week. Participants ingested 1.6 g per kilogram of body mass (g kg BM⁻¹) of carbohydrate (CHO) or an isocaloric carbohydrate–protein solution (CHO-P; 0.8 g carbohydrate kg BM⁻¹ + 0.8 g protein kg BM⁻¹) immediately and 1 h post-exercise. Expired gas, blood and muscle biopsy samples were taken at baseline and follow-up.

Results

Exercise training improved VO_2max in both groups (p ≤ 0.001), but this increment was not different between groups either in absolute terms or relative to body mass (0.2 ± 0.2 L min⁻¹ and 3.0 ± 2 mL kg⁻¹ min⁻¹, respectively). No change occurred in plasma albumin concentration from baseline to follow-up with CHO-P (4.18 ± 0.18 to 4.23 ± 0.17 g dL⁻¹) or CHO (4.17 ± 0.17 to 4.12 ± 0.22 g dL⁻¹; interaction: p > 0.05). Mechanistic target of rapamycin (mTOR) gene expression was up-regulated in CHO-P (+ 46%; p = 0.025) relative to CHO (+ 4%) following exercise training.

Conclusion

Post-exercise protein supplementation up-regulated the expression of mTOR in skeletal muscle over 6 weeks of endurance exercise training. However, the magnitude of improvement in VO_2max was similar between groups.

Coingestion of protein and carbohydrate in the early recovery phase, compared with carbohydrate only, improves endurance performance despite similar glycogen degradation and AMPK phosphorylation

Endurance athletes competing consecutive days need optimal dietary intake during the recovery period. We report that coingestion of protein and carbohydrate soon after exhaustive exercise, compared with carbohydrate only, resulted in better performance the following day. The better performance after coingestion of protein and carbohydrate was not associated with a higher rate of glycogen synthesis or activation of anabolic signaling compared with carbohydrate only. Importantly, nitrogen balance was positive after coingestion of protein and carbohydrate, which was not the case after intake of carbohydrate only, suggesting that protein synthesis contributes to the better performance the following day.

Dose-response effects of dietary protein on muscle protein synthesis during recovery from endurance exercise in young men: a double-blind randomized trial

BACKGROUND

Protein ingestion increases skeletal muscle protein synthesis rates during recovery from endurance exercise.

OBJECTIVES

We aimed to determine the effect of graded doses of dietary protein co-ingested with carbohydrate on whole-body protein metabolism, and skeletal muscle myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis rates during recovery from endurance exercise.

METHODS

In a randomized, double-blind, parallel-group design, 48 healthy, young, endurance-trained men (mean ± SEM age: 27 ± 1 y) received a primed continuous infusion of l-[ring-2H5]-phenylalanine, l-[ring-3,5-2H2]-tyrosine, and l-[1-13C]-leucine and ingested 45 g carbohydrate with either 0 (0 g PRO), 15 (15 g PRO), 30 (30 g PRO), or 45 (45 g PRO) g intrinsically l-[1-13C]-phenylalanine and l-[1-13C]-leucine labeled milk protein after endurance exercise. Blood and muscle biopsy samples were collected over 360 min of postexercise recovery to assess whole-body protein metabolism and both MyoPS and MitoPS rates.

RESULTS

Protein intake resulted in ∼70%-74% of the ingested protein-derived phenylalanine appearing in the circulation. Whole-body net protein balance increased dose-dependently after ingestion of 0, 15, 30, or 45 g protein (mean ± SEM: -0.31± 0.16, 5.08 ± 0.21, 10.04 ± 0.30, and 13.49 ± 0.55 μmol phenylalanine · kg-1 · h-1, respectively; P < 0.001). 30 g PRO stimulated a ∼46% increase in MyoPS rates (%/h) compared with 0 g PRO and was sufficient to maximize MyoPS rates after endurance exercise. MitoPS rates were not increased after protein ingestion; however, incorporation of dietary protein-derived l-[1-13C]-phenylalanine into de novo mitochondrial protein increased dose-dependently after ingestion of 15, 30, and 45 g protein at 360 min postexercise (0.018 ± 0.002, 0.034 ± 0.002, and 0.046 ± 0.003 mole percentage excess, respectively; P < 0.001).

CONCLUSIONS

Protein ingested after endurance exercise is efficiently digested and absorbed into the circulation. Whole-body net protein balance and dietary protein-derived amino acid incorporation into mitochondrial protein respond to increasing protein intake in a dose-dependent manner. Ingestion of 30 g protein is sufficient to maximize MyoPS rates during recovery from a single bout of endurance exercise.This trial was registered at trialregister.nl as NTR5111.

Subpopulation-specific differences in skeletal muscle mitochondria in humans with obesity: insights from studies employing acute nutritional and exercise stimuli

Mitochondria from skeletal muscle of humans with obesity often display alterations with respect to their morphology, proteome, biogenesis, and function. These changes in muscle mitochondria are considered to contribute to metabolic abnormalities observed in humans with obesity. Most of the evidence describing alterations in muscle mitochondria in humans with obesity, however, lacks reference to a specific subcellular location. This is despite data over the years showing differences in the morphology and function of subsarcolemmal (found near the plasma membrane) and intermyofibrillar (nested between the myofibrils) mitochondria in skeletal muscle. Recent studies reveal that impairments in mitochondrial function in obesity with respect to the subcellular location of the mitochondria in muscle are more readily evident following exposure of the skeletal muscle to physiological stimuli. In this review, we highlight the need to understand skeletal muscle mitochondria metabolism in obesity in a subpopulation-specific manner and in the presence of physiological stimuli that modify mitochondrial function in vivo. Experimental approaches employed under these conditions will allow for more precise characterization of impairments in skeletal muscle mitochondria and their implications in inducing metabolic dysfunction in human obesity.

Aerobic exercise increases post-exercise exogenous protein oxidation in healthy young males

The capacity to utilize ingested protein for optimal support of protein synthesis and lean body mass is described within the paradigm of anabolic competence. Protein synthesis can be stimulated by physical exercise, however, it is not known if physical exercise affects post-exercise protein oxidation. Characterization of the driving forces behind protein oxidation, such as exercise, can contribute to improved understanding of whole body protein metabolism. The purpose of this study is to determine the effect of two levels of aerobic exercise intensity on immediate post-exercise exogenous protein oxidation. Sixteen healthy males with a mean (SD) age of 24 (4) years participated. The subjects' VO2-max was estimated with the Åstrand cycling test. Habitual dietary intake was assessed with a three-day food diary. Exogenous protein oxidation was measured by isotope ratio mass spectrometry. These measurements were initiated after the ingestion of a 30 g 13C-milk protein test drink that was followed by 330 minutes breath sample collection. On three different days with at least one week in between, exogenous protein oxidation was measured: 1) during rest, 2) after 15 minutes of aerobic exercise at 30% of VO2-max (moderate intensity), and 3) after 15 minutes of aerobic exercise at 60% of VO2-max (vigorous intensity). After vigorous intensity aerobic exercise, 31.8%±8.0 of the 30 g 13C-milk protein was oxidized compared to 26.2%±7.1 during resting condition (p = 0.012), and 25.4%±7.6 after moderate intensity aerobic exercise compared to resting (p = 0.711). In conclusion, exogenous protein oxidation is increased after vigorous intensity aerobic exercise which could be the result of an increased protein turnover rate.

Defective fatty acid oxidation in mice with muscle-specific acyl-CoA synthetase 1 deficiency increases amino acid use and impairs muscle function

Loss of long-chain acyl-CoA synthetase isoform-1 (ACSL1) in mouse skeletal muscle (Acsl1^{M -/-}) severely reduces acyl-CoA synthetase activity and fatty acid oxidation. However, the effects of decreased fatty acid oxidation on skeletal muscle function, histology, use of alternative fuels, and mitochondrial function and morphology are unclear. We observed that Acsl1^{M -/-} mice have impaired voluntary running capacity and muscle grip strength and that their gastrocnemius muscle contains myocytes with central nuclei, indicating muscle regeneration. We also found that plasma creatine kinase and aspartate aminotransferase levels in Acsl1^{M -/-} mice are 3.4- and 1.5-fold greater, respectively, than in control mice (Acsl1^flox/flox ), indicating muscle damage, even without exercise, in the Acsl1^{M -/-} mice. Moreover, caspase-3 protein expression exclusively in Acsl1^{M -/-} skeletal muscle and the presence of cleaved caspase-3 suggested myocyte apoptosis. Mitochondria in Acsl1^{M -/-} skeletal muscle were swollen with abnormal cristae, and mitochondrial biogenesis was increased. Glucose uptake did not increase in Acsl1^{M -/-} skeletal muscle, and pyruvate oxidation was similar in gastrocnemius homogenates from Acsl1^{M -/-} and control mice. The rate of protein synthesis in Acsl1^{M -/-} glycolytic muscle was 2.1-fold greater 30 min after exercise than in the controls, suggesting resynthesis of proteins catabolized for fuel during the exercise. At this time, mTOR complex 1 was activated, and autophagy was blocked. These results suggest that fatty acid oxidation is critical for normal skeletal muscle homeostasis during both rest and exercise. We conclude that ACSL1 deficiency produces an overall defect in muscle fuel metabolism that increases protein catabolism, resulting in exercise intolerance, muscle weakness, and myocyte apoptosis.

Acute treadmill exercise discriminately improves the skeletal muscle insulin-stimulated growth signaling responses in mice lacking REDD1

A loss of the regulated in development and DNA damage 1 (REDD1) hyperactivates mechanistic Target of Rapamycin Complex 1 (mTORC1) reducing insulin-stimulated insulin signaling, which could provide insight into mechanisms of insulin resistance. Although aerobic exercise acutely inhibits mTORC1 signaling, improvements in insulin-stimulated signaling are exhibited. The goal of this study was to determine if a single bout of treadmill exercise was sufficient to improve insulin signaling in mice lacking REDD1. REDD1 wildtype (WT) and REDD1 knockout (KO) mice were acutely exercised on a treadmill (30 min, 20 m/min, 5% grade). A within animal noninsulin-to-insulin-stimulated percent change in skeletal muscle insulin-stimulated kinases (IRS-1, ERK1/2, Akt), growth signaling activation (4E-BP1, S6K1), and markers of growth repression (REDD1, AMPK, FOXO1/3A) was examined, following no exercise control or an acute bout of exercise. Unlike REDD1 KO mice, REDD1 WT mice exhibited an increase (P < 0.05) in REDD1 following treadmill exercise. However, both REDD1 WT and KO mice exhibited an increase (P < 0.05) AMPK phosphorylation, and a subsequent reduction (P < 0.05) in mTORC1 signaling after the exercise bout versus nonexercising WT or KO mice. Exercise increased (P < 0.05) the noninsulin-to-insulin-stimulated percent change phosphorylation of mTORC1, ERK1/2, IRS-1, and Akt on S473 in REDD1 KO mice when compared to nonexercised KO mice. However, there was no change in the noninsulin-to-insulin-stimulated percent change activation of Akt on T308 and FOXO1/3A in the KO when compared to WT or KO mouse muscle after exercise. Our data show that a bout of treadmill exercise discriminately improves insulin-stimulated signaling in the absence of REDD1.

Effect of Prior Chronic Aerobic Exercise on Overload-Induced Skeletal Muscle Hypertrophy in Mice

This study aimed to examine how regular aerobic training can affect the muscle hypertrophy induced by overloading. Male C57BL/6J mice were randomly divided into three groups: rest group, low-intensity aerobic exercise group, and high-intensity aerobic exercise group. Mice in the exercise groups were assigned to run at a speed of 10 m/min (low-intensity) or 25 m/min (high-intensity) for 30 min/day, five days/week, for four weeks. Then, the right hind leg gastrocnemius muscles were surgically removed to overload the plantaris and soleus muscles, while the left hind leg was subjected to a sham-operation. Both the plantaris and soleus muscles grew larger in the overloaded legs than those in the sham-operated legs. Muscle growth increased in the plantaris muscles in the low-intensity exercise group compared to that in the rest or high-intensity exercise groups at one and two weeks after overloading. This enhancement was not observed in the soleus muscles. Consistently, we observed changes in the expression of proteins involved in anabolic intracellular signaling, including Akt, mechanistic target of rapamycin (mTOR), and p70S6K, in the plantaris muscles. Our data showed for the first time that chronic low-intensity aerobic exercise precipitates overload-induced muscle growth.

Adaptations to Endurance and Strength Training

The capacity for human exercise performance can be enhanced with prolonged exercise training, whether it is endurance- or strength-based. The ability to adapt through exercise training allows individuals to perform at the height of their sporting event and/or maintain peak physical condition throughout the life span. Our continued drive to understand how to prescribe exercise to maximize health and/or performance outcomes means that our knowledge of the adaptations that occur as a result of exercise continues to evolve. This review will focus on current and new insights into endurance and strength-training adaptations and will highlight important questions that remain as far as how we adapt to training.

Protein and the Adaptive Response With Endurance Training: Wishful Thinking or a Competitive Edge?

The significance of carbohydrates for endurance training has been well established, whereas the role of protein and the adaptive response with endurance training is unclear. Therefore, the aim of this perspective is to discuss the current evidence on the role of dietary protein and the adaptive response with endurance training. On a metabolic level, a single bout of endurance training stimulates the oxidation of several amino acids. Although the amount of amino acids as part of total energy expenditure during exercise is relatively low compared to other substrates (e.g., carbohydrates and fat), it may depress the rates of skeletal muscle protein synthesis, and thereby have a negative effect on training adaptation. A low supply of amino acids relative to that of carbohydrates may also have negative effects on the synthesis of capillaries, synthesis and turn-over of mitochondrial proteins and proteins involved in oxygen transport including hamoglobin and myoglobin. Thus far, the scientific evidence demonstrating the significance of dietary protein is mainly derived from research with resistance exercise training regimes. This is not surprising since the general paradigm states that endurance training has insignificant effects on skeletal muscle growth. This could have resulted in an underappreciation of the role of dietary protein for the endurance athlete. To conclude, evidence of the role of protein on endurance training adaptations and performance remains scarce and is mainly derived from acute exercise studies. Therefore, future human intervention studies must unravel whether dietary protein is truly capable of augmenting endurance training adaptations and ultimately performance.

Relationship between intermuscular adipose tissue infiltration and myostatin before and after aerobic exercise training

Intermuscular adipose tissue (IMAT) is associated with impaired skeletal muscle contractile and metabolic function. Myostatin and downstream signaling proteins such as cyclin-dependent kinase 2 (CDK2) contribute to the regulation of adipose and skeletal muscle mass in cell culture and animals models, but this relationship remains incompletely understood in humans. The purpose of this study was to determine if the infiltration of IMAT was associated with skeletal muscle myostatin and downstream proteins before and after 12 wk of aerobic exercise training (AET) in healthy older women (OW; 69 ± 2 yr), older men (OM; 74 ± 3 yr), and young men (YM; 20 ± 1 yr). We found that the infiltration of IMAT was correlated with myostatin and phosphorylated CDK2 at tyrosine 15 [P-CDK2(Tyr15)]. IMAT infiltration was greater in the older subjects and was associated with lower skeletal muscle function and exercise capacity. After 12 wk of AET, there was no change in body weight. Myostatin and P-CDK2(Tyr15) were both decreased after AET, and the reduction in myostatin was associated with decreased IMAT infiltration. The decrease in myostatin and IMAT occurred concomitantly with increased exercise capacity, skeletal muscle size, and function after AET. These findings demonstrate that the reduction in IMAT infiltration after AET in weight stable individuals was accompanied by improvements in skeletal muscle function and exercise capacity. Moreover, the association between myostatin and IMAT was present in the untrained state and in response to exercise training, strengthening the potential regulatory role of myostatin on IMAT.

Endurance Exercise Attenuates Postprandial Whole-Body Leucine Balance in Trained Men

PURPOSE

Endurance exercise increases indices of small intestinal damage and leucine oxidation, which may attenuate dietary amino acid appearance and postprandial leucine balance during postexercise recovery. Therefore, the purpose of this study was to examine the effect of an acute bout of endurance exercise on postprandial leucine kinetics and net leucine balance.

METHODS

In a crossover design, seven trained young men (age = 25.6 ± 2.3 yr; V˙O2peak = 61.4 ± 2.9 mL·kg·min; mean ± SEM) received a primed constant infusion of L-[1-C]leucine before and after ingesting a mixed macronutrient meal containing 18 g whole egg protein intrinsically labeled with L-[5,5,5-H3]leucine, 17 g fat, and 60 g carbohydrate at rest and after 60 min of treadmill running at 70% V˙O2peak.

RESULTS

Plasma intestinal fatty acid binding protein concentrations and leucine oxidation both increased (P < 0.01) to peaks that were ~2.5-fold above baseline values during exercise with a concomitant decrease (P < 0.01) in nonoxidative leucine disposal. Meal ingestion attenuated (P < 0.01) endogenous leucine rates of appearance at rest and after exercise. There were no differences (both, P > 0.05) in dietary leucine appearance rates or in the amount of dietary protein-derived leucine that appeared into circulation over the 5-h postprandial period at rest and after exercise (62% ± 2% and 63% ± 2%, respectively). Leucine balance over the 5-h postprandial period was positive (P < 0.01) in both conditions but was negative (P < 0.01) during the exercise trial after accounting for exercise-induced leucine oxidation.

CONCLUSIONS

We demonstrate that endurance exercise does not modulate dietary leucine availability from a mixed meal but attenuates postprandial whole-body leucine balance in trained young men.

Achieving Optimal Post-Exercise Muscle Protein Remodeling in Physically Active Adults through Whole Food Consumption

Dietary protein ingestion is critical to maintaining the quality and quantity of skeletal muscle mass throughout adult life. The performance of acute exercise enhances muscle protein remodeling by stimulating protein synthesis rates for several hours after each bout, which can be optimized by consuming protein during the post-exercise recovery period. To date, the majority of the evidence regarding protein intake to optimize post-exercise muscle protein synthesis rates is limited to isolated protein sources. However, it is more common to ingest whole food sources of protein within a normal eating pattern. Emerging evidence demonstrates a promising role for the ingestion of whole foods as an effective nutritional strategy to support muscle protein remodeling and recovery after exercise. This review aims to evaluate the efficacy of the ingestion of nutrient-rich and protein-dense whole foods to support post-exercise muscle protein remodeling and recovery with pertinence towards physically active people.

Skeletal muscle mitochondrial protein synthesis and respiration in response to the energetic stress of an ultra-endurance race

The 2016 Colorado Trail Race (CTR) was an ultra-endurance mountain bike race in which competitors cycled for up to 24 h/day between altitudes of 1,675 and 4,025 m to complete 800 km and 21,000 m of elevation gain. In one athlete, we had the unique opportunity to characterize skeletal muscle protein synthesis and mitochondrial respiration in response to a normal activity control period (CON) and the CTR. We hypothesized that mitochondrial protein synthesis would be elevated and mitochondrial respiration would be maintained during the extreme stresses of the CTR. Titrated and bolus doses of ADP were provided to determine substrate-specific oxidative phosphorylation (OXPHOS) and electron transport system (ETS) capacities in permeabilized muscle fibers via high-resolution respirometry. Protein synthetic rates were determined by daily oral consumption of deuterium oxide (²H₂O). The endurance athlete had OXPHOS (226 pmol·s^-1·mg tissue^-1) and ETS (231 pmol·s^-1·mg tissue^-1) capacities that rank among the highest published to date in humans. Mitochondrial (3.2-fold), cytoplasmic (2.3-fold), and myofibrillar (1.5-fold) protein synthesis rates were greater during CTR compared with CON. With titrated ADP doses, the apparent K_m of ADP, OXPHOS, and ETS increased after the CTR. With provision of ADP boluses after the CTR, the addition of fatty acids (-12 and -14%) mitigated the decline in OXPHOS and ETS capacity during carbohydrate-supported respiration (-26 and -31%). In the face of extreme stresses during the CTR, elevated rates of mitochondrial protein synthesis may contribute to rapid adaptations in mitochondrial bioenergetics. NEW & NOTEWORTHY The mechanisms that maintain skeletal muscle function during extreme stresses remain incompletely understood. In the current study, greater rates of mitochondrial protein synthesis during the energetic demands of ultra-endurance exercise may contribute to rapid adaptations in mitochondrial bioenergetics. The endurance athlete herein achieved mitochondrial respiratory capacities among the highest published for humans. Greater mitochondrial protein synthesis during ultra-endurance exercise may contribute to improved mitochondrial respiration and serve as a mechanism to resist cellular energetic stresses.

A2 Milk Enhances Dynamic Muscle Function Following Repeated Sprint Exercise, a Possible Ergogenic Aid for A1-Protein Intolerant Athletes?

Hyperaminoacidemia following ingestion of cows-milk may stimulate muscle anabolism and attenuate exercise-induced muscle damage (EIMD). However, as dairy-intolerant athletes do not obtain the reported benefits from milk-based products, A2 milk may offer a suitable alternative as it lacks the A1-protein. This study aimed to determine the effect of A2 milk on recovery from a sports-specific muscle damage model. Twenty-one male team sport players were allocated to three independent groups: A2 milk (n = 7), regular milk (n = 7), and placebo (PLA) (n = 7). Immediately following muscle-damaging exercise, participants consumed either A2 milk, regular milk or PLA (500 mL each). Visual analogue scale (muscle soreness), maximal voluntary isometric contraction (MVIC), countermovement jump (CMJ) and 20-m sprint were measured prior to and 24, 48, and 72 h post EIMD. At 48 h post-EIMD, CMJ and 20-m sprint recovered quicker in A2 (33.4 ± 6.6 and 3.3 ± 0.1, respectively) and regular milk (33.1 ± 7.1 and 3.3 ± 0.3, respectively) vs. PLA (29.2 ± 3.6 and 3.6 ± 0.3, respectively) (p < 0.05). Relative to baseline, decrements in 48 h CMJ and 20-m sprint were minimised in A2 (by 7.2 and 5.1%, respectively) and regular milk (by 6.3 and 5.2%, respectively) vs. PLA. There was a trend for milk treatments to attenuate decrements in MVIC, however statistical significance was not reached (p = 0.069). Milk treatments had no apparent effect on muscle soreness (p = 0.152). Following muscle-damaging exercise, ingestion of 500 mL of A2 or regular milk can limit decrements in dynamic muscle function in male athletes, thus hastening recovery and improving subsequent performance. The findings propose A2 milk as an ergogenic aid following EIMD, and may offer an alternative to athletes intolerant to the A1 protein.

Short-term intense exercise training reduces stress markers and alters the transcriptional response to exercise in skeletal muscle

The purpose of this investigation was to examine the influence of short-term intense endurance training on cycling performance, along with the acute and chronic signaling responses of skeletal muscle stress and stability markers. Ten recreationally active subjects (25 ± 2 yr, 79 ± 3 kg, 47 ± 2 ml·kg^-1·min^-1) were studied before and after a 12-day cycling protocol to examine the effects of short-term intense (70-100% V̇o_2max) exercise training on resting and exercise-induced regulation of molecular factors related to skeletal muscle cellular stress and protein stability. Skeletal muscle biopsies were taken at rest and 3 h following a 20-km cycle time trial on days 1 and 12 to measure mRNA expression and protein content. Training improved (P < 0.05) cycling performance by 5 ± 1%. Protein oxidation was unaltered on day 12, while resting SAPK/JNK phosphorylation was reduced (P < 0.05), suggesting a reduction in cellular stress. The maintenance in the myocellular environment may be due to synthesis of cytoprotective markers, along with enhanced degradation of damage proteins, as training tended (P < 0.10) to increase resting protein content of manganese superoxide dismutase and heat shock protein 70 (HSP70), while mRNA expression of MuRF-1 was elevated (P < 0.05). Following training (day 12), the acute exercise-induced transcriptional response of TNF-α, NF-κB, MuRF-1, and PGC1α was attenuated (P < 0.05) compared with day 1 Collectively, these data suggest that short-term intense training enhances protein stability, creating a cellular environment capable of resistance to exercise-induced stress, which may be favorable for adaptation.

Nutritional implications for ultra-endurance walking and running events

This paper examines the various nutritional challenges which athletes encounter in preparing for and participating in ultra-endurance walking and running events. Special attention is paid to energy level, performance, and recovery within the context of athletes' intake of carbohydrate, protein, fat, and various vitamins and minerals. It outlines, by way of a review of literature, those factors which promote optimal performance for the ultra-endurance athlete and provides recommendations from multiple researchers concerned with the nutrition and performance of ultra-endurance athletes. Despite the availability of some research about the subject, there is a paucity of longitudinal material which examines athletes by nature and type of ultra-endurance event, gender, age, race, and unique physiological characteristics. Optimal nutrition results in a decreased risk of energy depletion, better performance, and quicker full-recovery.

Fiber Type-Specific Satellite Cell Content in Cyclists Following Heavy Training with Carbohydrate and Carbohydrate-Protein Supplementation

The central purpose of this study was to evaluate the fiber type-specific satellite cell and myonuclear responses of endurance-trained cyclists to a block of intensified training, when supplementing with carbohydrate (CHO) vs. carbohydrate-protein (PRO). In a crossover design, endurance-trained cyclists (n = 8) performed two consecutive training periods, once supplementing with CHO (de facto “control” condition) and the other with PRO. Each training period consisted of 10 days of intensified cycle training (ICT–120% increase in average training duration) followed by 10 days of recovery (RVT–reduced volume training; 33% volume reduction vs. normal training). Skeletal muscle biopsies were obtained from the vastus lateralis before and after ICT and again following RVT. Immunofluorescent microscopy was used to quantify SCs (Pax7+), myonuclei (DAPI+), and myosin heavy chain I (MyHC I). Data are expressed as percent change ± 90% confidence limits. The 10-day block of ICT_CHO increased MyHC I SC content (35 ± 28%) and myonuclear density (16 ± 6%), which remained elevated following RVT_CHO (SC = 69 ± 50% vs. PRE; Nuclei = 17 ± 15% vs. PRE). MyHC II SC and myonuclei were not different following ICT_CHO, but were higher following RVT_CHO (SC = +33 ± 31% vs. PRE; Nuclei = 15 ± 14% vs. PRE), indicating a delayed response compared to MyHC I fibers. The MyHC I SC pool increased following ICT_PRO (37 ± 37%), but without a concomitant increase in myonuclei. There were no changes in MyHC II SC or myonuclei following ICT_PRO. Collectively, these trained endurance cyclists possessed a relatively large pool of SCs that facilitated rapid (MyHC I) and delayed (MyHC II) satellite cell proliferation and myonuclear accretion under carbohydrate conditions. The current findings strengthen the growing body of evidence demonstrating alterations in satellite cell number in the absence of hypertrophy. Satellite cell pool expansion is typically viewed as an advantageous response to exercise. However, when coupled with our previous report that PRO possibly enhanced whole muscle recovery and increased MyHC I and II fiber size, the limited satellite cell/myonuclear response observed with carbohydrate-protein seem to indicate that protein supplementation may have minimized the necessity for satellite cell involvement, thereby suggesting that protein may benefit skeletal muscle during periods of heavy training.

Exercise Intervention for Anti-Sarcopenia in Community-Dwelling Older People

Sarcopenia is an age-related health problem in general communities. Effective exercise programs against sarcopenia remain necessary for community-dwelling older people. In order to summarize the available knowledge on this subject, we collected English articles from a MEDLINE/Pubmed database examining the effects of exercise interventions on sarcopenia-related outcome measures in community-dwelling older people. When nine articles, including eight randomized controlled trials, were reviewed, most studies demonstrated significant improvements in some outcome measures. Indeed, a significant improvement in the muscle mass in one study, muscle strength in two studies and physical performance in two studies was reported among five studies using exercise (E) alone. A significant improvement in the muscle mass in two studies, muscle strength in one study and physical performance in two studies was also reported among four studies using exercise plus nutritional supplementation (EN). Notably, the EN studies appeared to have less extensive exercise interventions than the E studies. One EN study further exhibited significant improvements in all outcome measures. Collectively, exercise could be used as anti-sarcopenic strategies and nutritional interventions when combined with exercise might play a compensated or perhaps a comprehensive role among community-dwelling older people. Limited studies exist and more studies are required for the optimum programs in the community settings.

Effects of blood-flow restriction on biomarkers of myogenesis in response to resistance exercise

We investigated the acute myogenic response to resistance exercise with and without blood-flow restriction (BFR). Six men and women (age, 22 ± 1 years) performed unilateral knee extensions at 40% of 1-repetition maximum with or without (CNTRL) BFR applied via pressure cuff inflated to 220 mm Hg. Muscle biopsies were collected at 4 h and 24 h postexercise. Addition of BFR increased myoD and c-Met messenger RNA expression relative to CNTRL. Expression of hepatocyte growth factor protein was significantly higher following CNTRL.

Effects of skeletal muscle energy availability on protein turnover responses to exercise

Skeletal muscle adaptation to exercise training is a consequence of repeated contraction-induced increases in gene expression that lead to the accumulation of functional proteins whose role is to blunt the homeostatic perturbations generated by escalations in energetic demand and substrate turnover. The development of a specific 'exercise phenotype' is the result of new, augmented steady-state mRNA and protein levels that stem from the training stimulus (i.e. endurance or resistance based). Maintaining appropriate skeletal muscle integrity to meet the demands of training (i.e. increases in myofibrillar and/or mitochondrial protein) is regulated by cyclic phases of synthesis and breakdown, the rate and turnover largely determined by the protein's half-life. Cross-talk among several intracellular systems regulating protein synthesis, breakdown and folding is required to ensure protein equilibrium is maintained. These pathways include both proteasomal and lysosomal degradation systems (ubiquitin-mediated and autophagy, respectively) and the protein translational and folding machinery. The activities of these cellular pathways are bioenergetically expensive and are modified by intracellular energy availability (i.e. macronutrient intake) and the 'training impulse' (i.e. summation of the volume, intensity and frequency). As such, exercise-nutrient interactions can modulate signal transduction cascades that converge on these protein regulatory systems, especially in the early post-exercise recovery period. This review focuses on the regulation of muscle protein synthetic response-adaptation processes to divergent exercise stimuli and how intracellular energy availability interacts with contractile activity to impact on muscle remodelling.

Protein Requirements Are Elevated in Endurance Athletes after Exercise as Determined by the Indicator Amino Acid Oxidation Method

A higher protein intake has been recommended for endurance athletes compared with healthy non-exercising individuals based primarily on nitrogen balance methodology. The aim of this study was to determine the estimated average protein requirement and recommended protein intake in endurance athletes during an acute 3-d controlled training period using the indicator amino acid oxidation method. After 2-d of controlled diet (1.4 g protein/kg/d) and training (10 and 5km/d, respectively), six male endurance-trained adults (28±4 y of age; Body weight, 64.5±10.0 kg; VO₂peak, 60.3±6.7 ml·kg^-1·min^-1; means±SD) performed an acute bout of endurance exercise (20 km treadmill run) prior to consuming test diets providing variable amounts of protein (0.2–2.8 g·kg^-1·d^-1) and sufficient energy. Protein was provided as a crystalline amino acid mixture based on the composition of egg protein with [1-¹³C]phenylalanine provided to determine whole body phenylalanine flux, ¹³CO₂ excretion, and phenylalanine oxidation. The estimated average protein requirement was determined as the breakpoint after biphasic linear regression analysis with a recommended protein intake defined as the upper 95% confidence interval. Phenylalanine flux (68.8±8.5 μmol·kg^-1·h^-1) was not affected by protein intake. ¹³CO₂ excretion displayed a robust bi-phase linear relationship (R² = 0.86) that resulted in an estimated average requirement and a recommended protein intake of 1.65 and 1.83 g protein·kg^-1·d^-1, respectively, which was similar to values based on phenylalanine oxidation (1.53 and 1.70 g·kg^-1·d^-1, respectively). We report a recommended protein intake that is greater than the RDA (0.8 g·kg^-1·d^-1) and current recommendations for endurance athletes (1.2–1.4 g·kg^-1·d^-1). Our results suggest that the metabolic demand for protein in endurance-trained adults on a higher volume training day is greater than their sedentary peers and current recommendations for athletes based primarily on nitrogen balance methodology.

Trial Registration: ClinicalTrial.gov NCT02478801

Rapamycin does not prevent increases in myofibrillar or mitochondrial protein synthesis following endurance exercise

The present study aimed to investigate the role of the mechanistic target of rapamycin complex 1 (mTORC1) in the regulation of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis following endurance exercise. Forty-two female C57BL/6 mice performed 1 h of treadmill running (18 m min(-1) ; 5° grade), 1 h after i.p. administration of rapamycin (1.5 mg · kg(-1) ) or vehicle. To quantify skeletal muscle protein fractional synthesis rates, a flooding dose (50 mg · kg(-1) ) of l-[ring-(13) C6 ]phenylalanine was administered via i.p. injection. Blood and gastrocnemius muscle were collected in non-exercised control mice, as well as at 0.5, 3 and 6 h after completing exercise (n = 4 per time point). Skeletal muscle MyoPS and MitoPS were determined by measuring isotope incorporation in their respective protein pools. Activation of the mTORC1-signalling cascade was measured via direct kinase activity assay and immunoblotting, whereas genes related to mitochondrial biogenesis were measured via a quantitative RT-PCR. MyoPS increased rapidly in the vehicle group post-exercise and remained elevated for 6 h, whereas this response was transiently blunted (30 min post-exercise) by rapamycin. By contrast, MitoPS was unaffected by rapamycin, and was increased over the entire post-exercise recovery period in both groups (P < 0.05). Despite rapid increases in both MyoPS and MitoPS, mTORC1 activation was suppressed in both groups post-exercise for the entire 6 h recovery period. Peroxisome proliferator activated receptor-γ coactivator-1α, pyruvate dehydrogenase kinase 4 and mitochondrial transcription factor A mRNA increased post-exercise (P < 0.05) and this response was augmented by rapamycin (P < 0.05). Collectively, these data suggest that endurance exercise stimulates MyoPS and MitoPS in skeletal muscle independently of mTORC1 activation.

Role of Ingested Amino Acids and Protein in the Promotion of Resistance Exercise-Induced Muscle Protein Anabolism

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.

Muscle growth across a variety of exercise modalities and intensities: Contributions of mechanical and metabolic stimuli

This paper reviews the existing evidence for the potential contribution of metabolic and mechanical stimuli to muscle growth in response to a variety of exercise modalities and intensities. Recent research has demonstrated that low-load resistance training can elicit comparable hypertrophy to that of high-load resistance training when each set is performed until failure. The degree of metabolic fatigue would be greater for resistance training with lower loads compared to higher loads at the point of muscle failure, which may compensate for the lower mechanical stress. This may also explain why muscle hypertrophy occurs to varying magnitudes when activities such as cycling and walking are performed. Furthermore, the application of blood flow restriction to the working muscles during these activities induces greater hypertrophy albeit at the same level of mechanical stress, which would suggest a possible contribution from metabolic stress. Thus, it is plausible that both mechanical and metabolic stimuli are primary mechanisms for muscle hypertrophy and the degree of contributions of both stimuli determines the exercise-induced muscle hypertrophy.

Skeletal muscle homeostasis and plasticity in youth and ageing: impact of nutrition and exercise

Skeletal muscles comprise a substantial portion of whole body mass and are integral for locomotion and metabolic health. Increasing age is associated with declines in both muscle mass and function (e.g. strength‐related performance, power) with declines in muscle function quantitatively outweighing those in muscle volume. The mechanisms behind these declines are multi‐faceted involving both intrinsic age‐related metabolic dysregulation and environmental influences such as nutritional and physical activity. Ageing is associated with a degree of ‘anabolic resistance’ to these key environmental inputs, which likely accelerates the intrinsic processes driving ageing. On this basis, strategies to sensitize and/or promote anabolic responses to nutrition and physical activity are likely to be imperative in alleviating the progression and trajectory of sarcopenia. Both resistance‐ and aerobic‐type exercises are likely to confer functional and health benefits in older age, and a clutch of research suggests that enhancement of anabolic responsiveness to exercise and/or nutrition may be achieved by optimizing modifications of muscle‐loading paradigms (workload, volume, blood flow restriction) or nutritional support (e.g. essential amino acid/leucine) patterns. Nonetheless, more work is needed in which a more holistic view in ageing studies is taken into account. This should include improved characterization of older study recruits, that is physical activity/nutritional behaviours, to limit confounding variables influencing whether findings are attributable to age, or other environmental influences. Nonetheless, on balance, ageing is associated with declines in muscle mass and function and a partially related decline in aerobic capacity. There is also good evidence that metabolic flexibility is impaired in older age.

Acute molecular responses to concurrent resistance and high-intensity interval exercise in untrained skeletal muscle

Concurrent training involving resistance and endurance exercise may augment the benefits of single-mode training for the purpose of improving health. However, muscle adaptations, associated with resistance exercise, may be blunted by a subsequent bout of endurance exercise, via molecular interference. High-intensity interval training (HIIT), generating similar adaptations to endurance exercise, may offer an alternative exercise mode to traditional endurance exercise. This study examined the influence of an acute HIIT session on the molecular responses following resistance exercise in untrained skeletal muscle. Ten male participants performed resistance exercise (4 × 8 leg extensions, 70% 1RM, (RE)) or RE followed by HIIT (10 × 1 min at 90% HRmax, (RE+HIIT)). Muscle biopsies were collected from the vastus lateralis before, 2 and 6 h post-RE to determine intramuscular protein phosphorylation and mRNA responses. Phosphorylation of Akt (Ser(473)) decreased at 6 h in both trials (P < 0.05). Phosphorylation of mTOR (Ser(2448)) was higher in RE+HIIT (P < 0.05). All PGC-1α mRNA variants increased at 2 h in RE+HIIT with PGC-1α and PGC-1α-ex1b remaining elevated at 6 h, whereas RE-induced increases at 2 and 6 h for PGC-1α-ex1b only (P < 0.05). Myostatin expression decreased at 2 and 6 h in both trials (P < 0.05). MuRF-1 was elevated in RE+HIIT versus RE at 2 and 6 h (P < 0.05). Atrogin-1 was lower at 2 h, with FOXO3A downregulated at 6 h (P < 0.05). These data do not support the existence of an acute interference effect on protein signaling and mRNA expression, and suggest that HIIT may be an alternative to endurance exercise when performed after resistance exercise in the same training session to optimize adaptations.

High responders and low responders: factors associated with individual variation in response to standardized training

The response to an exercise intervention is often described in general terms, with the assumption that the group average represents a typical response for most individuals. In reality, however, it is more common for individuals to show a wide range of responses to an intervention rather than a similar response. This phenomenon of 'high responders' and 'low responders' following a standardized training intervention may provide helpful insights into mechanisms of training adaptation and methods of training prescription. Therefore, the aim of this review was to discuss factors associated with inter-individual variation in response to standardized, endurance-type training. It is well-known that genetic influences make an important contribution to individual variation in certain training responses. The association between genotype and training response has often been supported using heritability estimates; however, recent studies have been able to link variation in some training responses to specific single nucleotide polymorphisms. It would appear that hereditary influences are often expressed through hereditary influences on the pre-training phenotype, with some parameters showing a hereditary influence in the pre-training phenotype but not in the subsequent training response. In most cases, the pre-training phenotype appears to predict only a small amount of variation in the subsequent training response of that phenotype. However, the relationship between pre-training autonomic activity and subsequent maximal oxygen uptake response appears to show relatively stronger predictive potential. Individual variation in response to standardized training that cannot be explained by genetic influences may be related to the characteristics of the training program or lifestyle factors. Although standardized programs usually involve training prescribed by relative intensity and duration, some methods of relative exercise intensity prescription may be more successful in creating an equivalent homeostatic stress between individuals than other methods. Individual variation in the homeostatic stress associated with each training session would result in individuals experiencing a different exercise 'stimulus' and contribute to individual variation in the adaptive responses incurred over the course of the training program. Furthermore, recovery between the sessions of a standardized training program may vary amongst individuals due to factors such as training status, sleep, psychological stress, and habitual physical activity. If there is an imbalance between overall stress and recovery, some individuals may develop fatigue and even maladaptation, contributing to variation in pre-post training responses. There is some evidence that training response can be modulated by the timing and composition of dietary intake, and hence nutritional factors could also potentially contribute to individual variation in training responses. Finally, a certain amount of individual variation in responses may also be attributed to measurement error, a factor that should be accounted for wherever possible in future studies. In conclusion, there are several factors that could contribute to individual variation in response to standardized training. However, more studies are required to help clarify and quantify the role of these factors. Future studies addressing such topics may aid in the early prediction of high or low training responses and provide further insight into the mechanisms of training adaptation.

Co-ingestion of carbohydrate with branched-chain amino acids or L-leucine does not preferentially increase serum IGF-1 and expression of myogenic-related genes in response to a single bout of resistance exercise

The purpose of this study was to determine if the co-ingestion of carbohydrate (CHO) with branched-chain amino acids (BCAA) or L-leucine (LEU) preferentially affected serum IGF-1 and the expression of myogenic-related genes in response to resistance exercise (RE). Forty-one college-age males were randomly assigned to 1 of 4 groups: CHO, CHO-BCAA, CHO-LEU, or placebo (PLC). Resistance exercise consisted of 4 sets of 10 repetitions of leg press and leg extension at 80 % 1RM. Supplements were ingested peri-exercise, and venous blood and muscle biopsies were obtained pre-exercise (PRE), and at 30, 120, and 360 min post-exercise. Serum IGF-1 was determined with ELISA, and skeletal muscle mRNA expression of myostatin, ACTRIIB, p21kip, p27kip, CDK2, cyclin B1, cyclin D1, Myo-D, myogenin, MRF-4, and myf5 was determined using real-time PCR. Results were analyzed by two-way ANOVA for serum IGF-1 and two-way MANOVA for mRNA expression. Serum IGF-1 in CHO + BCAA was greater than PLC (p < 0.05) but was not affected by RE (p > 0.05). A significant group × time interaction was located for cylin D1 (p < 0.05), but not for any other genes. However, significant time effects were noted for cyclin B1 and p21cip (p < 0.05). At 30, 120 and 360 min post-exercise, p21cip was significantly less than PRE. Cyclin D1 was greater than PRE and 30 min post-exercise at 120 and 360 min post-exercise, whereas cyclin B1 was significantly greater than PRE at 120 min post-exercise (p < 0.05). Unlike the co-ingestion of CHO with either BCAA or L-leucine in conjunction with RE, the expression of various myogenically related genes were up-regulated with RE.

Carbohydrate restricted recovery from long term endurance exercise does not affect gene responses involved in mitochondrial biogenesis in highly trained athletes

The aim was to determine if the metabolic adaptations, particularly PGC-1α and downstream metabolic genes were affected by restricting CHO following an endurance exercise bout in trained endurance athletes. A second aim was to compare baseline expression level of these genes to untrained. Elite endurance athletes (VO2max 66 ± 2 mL·kg(-1)·min(-1), n = 15) completed 4 h cycling at ~56% VO2max. During the first 4 h recovery subjects were provided with either CHO or only H2O and thereafter both groups received CHO. Muscle biopsies were collected before, after, and 4 and 24 h after exercise. Also, resting biopsies were collected from untrained subjects (n = 8). Exercise decreased glycogen by 67.7 ± 4.0% (from 699 ± 26.1 to 239 ± 29.5 mmol·kg(-1)·dw(-1)) with no difference between groups. Whereas 4 h of recovery with CHO partly replenished glycogen, the H2O group remained at post exercise level; nevertheless, the gene expression was not different between groups. Glycogen and most gene expression levels returned to baseline by 24 h in both CHO and H2O. Baseline mRNA expression of NRF-1, COX-IV, GLUT4 and PPAR-α gene targets were higher in trained compared to untrained. Additionally, the proportion of type I muscle fibers positively correlated with baseline mRNA for PGC-1α, TFAM, NRF-1, COX-IV, PPAR-α, and GLUT4 for both trained and untrained. CHO restriction during recovery from glycogen depleting exercise does not improve the mRNA response of markers of mitochondrial biogenesis. Further, baseline gene expression of key metabolic pathways is higher in trained than untrained.