Exercise Protein Metabolism And Muscle Growth Pdf


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Exercise, protein metabolism, and muscle growth.

Metrics details. Provision of dietary amino acids increases skeletal muscle protein synthesis MPS , an effect that is enhanced by prior resistance exercise. As a fundamentally necessary process in the enhancement of muscle mass, strategies to enhance rates of MPS would be beneficial in the development of interventions aimed at increasing skeletal muscle mass particularly when combined with chronic resistance exercise.

The purpose of this review article is to provide an update on current findings regarding the nutritional regulation of MPS and highlight nutrition based strategies that may serve to maximize skeletal muscle protein anabolism with resistance exercise. Such factors include timing of protein intake, dietary protein type, the role of leucine as a key anabolic amino acid, and the impact of other macronutrients i.

We contend that nutritional strategies that serve to maximally stimulate MPS may be useful in the development of nutrition and exercise based interventions aimed at enhancing skeletal muscle mass which may be of interest to elderly populations and to athletes. The synergistic effects of amino acid provision and resistance exercise on skeletal muscle protein synthesis rates MPS are now well described for reviews see: [ 1 , 2 ].

Consuming dietary amino acids after resistance exercise stimulates an increase in MPS and is necessary to shift net protein balance defined as MPS minus muscle protein breakdown MPB from negative net protein loss to positive net protein gain [ 3 ]. As such, it would follow that for chronic elevations in net muscle protein balance to result in gains in muscle mass, changes in MPS are highly relevant.

We do not contend that MPB is a trivial biological process; MPB assists in maintenance of intracellular amino acid levels, and likely plays a role in maintaining muscle protein quality by removing damaged proteins and allowing their constituent amino acids to be used for the synthesis of new functional muscle proteins.

Consequently, we propose that nutritional interventions that enhance MPS may be of great scientific and clinical interest as a strategy to promote positive muscle protein balance and eventual muscle protein accrual. Further, these interventions may be of interest to athletes concerned with enhancing the adaptive response of skeletal muscle to chronic exercise training.

Other research has focused on the ability to enhance MPS by providing increased amounts of leucine [ 12 — 14 ] or arginine [ 15 ] within an amino acid containing solution. Lastly, the influence of consuming mixed macronutrients on muscle protein metabolism [ 16 — 20 ] has also received some attention.

The purpose of this review is to discuss the nutritional regulation of human MPS and provide an update on nutritional strategies that may serve to maximize MPS with feeding and resistance exercise. It is now unequivocal that immediate post-exercise amino acid provision is an effective nutrition based strategy to enhance MPS above rates observed with exercise alone [ 3 , 5 , 25 ]. Specifically, resistance exercise was performed at a relatively high load 90FAIL or low load 30FAIL , but both regimens were performed to volitional fatigue.

Thus, irrespective of exercise load, the ultimate result was eventual similar increases in muscle fibre recruitment [ 28 ]. Adptated from Burd and colleagues [ 27 ]. Previous research has shown that overnight MPS rates are quite low [ 29 ], however both intragastric protein provision during sleep [ 30 ], and oral protein ingestion after resistance exercise immediately before bed [ 31 ] are followed by normal protein digestion and absorption kinetics and an overnight stimulation of MPS.

Dietary amino acids and insulin are major nutrient-regulated effectors of MPS and MPB and recent work has shed light on the molecular pathways involved in regulating the amino acid and contraction-induced increase in MPS.

A comprehensive review of the molecular regulation of MPS in response to nutrition and exercise is beyond the scope of this article but can be found elsewhere [ 32 ].

The protein kinase mTORC1 serves as a critical point of integration from a wide range of signals that promote MPS, including dietary amino acids [ 33 ] and muscle contraction [ 34 ]. To date, several studies have demonstrated that amino acid provision after resistance exercise and the subsequent increase in MPS are associated with enhanced phosphorylation of components of the mTOR signaling cascade above levels that are observed following exercise without nutrients [ 26 , 35 — 37 ].

However, dissociation between direct measures of rates of MPS and the extent of muscle anabolic signaling molecule phosphorylation has been reported previously [ 13 , 38 ].

These transporters may play an important role in the regulation of human muscle protein metabolism based on their ability to transport amino acids across the cell membrane, and relay signals to downstream targets thought to regulate MPS [ 45 ].

An increase in the protein levels of some of these amino acid transporters has also been observed following EAA ingestion [ 43 ] and resistance exercise [ 44 ], however it is currently unclear whether increases in mRNA and protein expression of these transporters are associated with enhanced amino acid transport capacity. Clearly, further research is needed to define the functional and physiological significance of these transporters in the nutrition and exercise mediated regulation of MPS.

The ingestion of dietary proteins including whey [ 5 — 8 , 21 , 27 , 46 , 47 ], egg albumin [ 5 ], soy [ 7 , 8 ], casein [ 6 , 8 ], and beef [ 48 , 49 ] are all able to stimulate MPS. However, dietary proteins from different sources differ in their capacity to stimulate MPS both at rest [ 6 — 8 ] and following resistance exercise [ 7 , 8 ]. For example, work from our lab has shown that whey protein [ 8 ] and bovine milk [ 7 ] promote greater increases in MPS after acute resistance exercise than does consumption of an equivalent amount of plant-based soy protein despite the fact that these protein sources have protein digestibility-corrected amino acid scores PDCAAS above 1.

Whey protein is acid soluble and is associated with a very rapid, large, but transient increase in postprandial amino acid availability [ 6 , 51 ], while casein coagulates and precipitates when exposed to stomach acid and the resultant dairy curd is slowly released from the stomach resulting in a much more moderate but sustained rise in plasma amino acids [ 6 , 51 ].

Our lab has recently compared the effects of whey protein isolate to micellar casein on rates of MPS in elderly men [ 52 ]. This data corroborates our previous work showing that a rapid rate of amino acid appearance in the blood after feeding enhances MPS and anabolic cell-signaling after resistance exercise more than a slow rate of amino acid appearance [ 53 ], supporting the notion that protein digestion and absorption rate represents an important factor in the nutritional regulation of MPS in humans [ 8 , 47 , 51 , 52 , 54 , 55 ].

Interestingly, recent research suggests that the form of food i. For example, Conley and colleagues [ 59 ] showed greater increases in plasma amino acids that were more sustained following beverage administration as compared to the same supplement i. Of the amino acids, the EAA are primarily responsible for stimulating MPS [ 63 , 64 ], whereas non-essential amino acids appear ineffective in this regard [ 65 ].

For example, leucine, but not isoleucine or valine can stimulate an increase in MPS through activation of the mTOR-p70S6k pathway in animals [ 66 , 68 ]. Tipton and colleagues [ 12 ] examined the effect of free leucine 3. Future research is needed to define the amount of leucine required to stimulate MPS in both young and elderly adults and to clearly establish the role of other EAA in the regulation of MPS with feeding and resistance exercise.

Defining nutritional interventions that maximally stimulate rates of MPS are of interest in the development of therapeutic strategies designed combat age-related muscle loss sarcopenia. However, since free-living individuals typically eat after resistance exercise, it can only be speculated whether the same blunted MPS response between young and old would have been observed in the fed-state.

Despite the diminished response to amino acid provision and exercise in the elderly, it appears that the additive effects of feeding and resistance exercise on rates of MPS are preserved in this population, with several studies showing that combined feeding and exercise results in greater increases in MPS than feeding alone [ 48 , 52 , 76 ]. Our lab has recently examined the dose—response relationship between whey protein ingestion and myofibrillar protein synthesis under both rested and post-resistance exercise conditions in the elderly [ 76 ].

In support of the elderly responding to greater amounts of leucine, Katsanos and colleagues reported that a 6. These findings suggest that amino acid composition, and not simply total EAA is of key importance in determining the postprandial response of MPS in elderly muscle. However, the efficacy of free leucine supplementation with meal feeding as a strategy to augment muscle mass in the elderly is not currently supported.

Verhoeven and colleagues examined the efficacy of long-term leucine supplementation on skeletal muscle mass in elderly subjects and reported that supplemental leucine 7. Further, the leucine supplementation was associated with declines in circulating valine and isoleucine which could have become limiting for the stimulation of MPS [ 77 ].

Overall, additional dietary leucine, which may be obtained from high quality proteins and not necessarily in crystalline form, may be of some benefit to the elderly from the perspective of increasing MPS [ 70 , 71 ]. More research is needed to examine the effect of leucine-enriched amino acid provision in the early time period after resistance exercise on MPS and gains in lean mass following more long-term training.

Although the mechanisms are currently unknown, these results suggest that omega 3 polyunsaturated fatty acids possess anabolic properties via their ability to enhance the sensitivity of skeletal muscle to amino acids and insulin, even in young healthy individuals [ 80 , 81 ].

Future research should examine the role of supplemental omega 3 polyunsaturated fatty acids on lean muscle mass accrual following a period of chronic resistance exercise training in both the young and elderly. Consumption of a typical mixed meal is generally associated with the ingestion of not only dietary proteins and amino acids, but also carbohydrates and lipids. While almost nothing is known about the impact of lipid-protein co-ingestion on direct measures of MPS with feeding and resistance exercise, Elliot and colleagues [ 83 ] reported that threonine and phenylalanine uptake indicative of an anabolic response was greater after ingestion of whole milk 8.

The reason for the greater anabolism after whole milk ingestion is not entirely clear; however, it may relate to the greater muscle perfusion, at least in that study. Previous studies have investigated the role of carbohydrate CHO in the regulation of human muscle protein metabolism [ 16 — 19 , 84 ]. Intake of CHO is associated with increased levels of circulating insulin, which has a strong inhibitory effect on MPB [ 38 , 85 , 86 ], and thus is able to improve net protein balance [ 16 — 19 , 84 ].

However, in the absence of amino acid intake, CHO intake does not result in a positive net protein balance [ 19 , 84 ]. Our lab has recently examined the effect of carbohydrate-protein co-ingestion as compared to protein intake alone on rates of MPS and MPB after acute resistance exercise in young men [ 17 ].

It is important to note that although CHO may not be fundamentally important in altering net protein balance after resistance exercise when adequate protein is provided, muscle glycogen is reduced following resistance exercise [ 87 , 88 ] and CHO has an important role in muscle glycogen resynthesis and is therefore useful to enhance recovery from training [ 89 ].

Nutritional interventions designed to maximally stimulate MPS may be useful for those individuals concerned with enhancing skeletal muscle protein accretion, particularly when they are combined with a program of chronic resistance exercise. Ideal candidates to fulfill such criteria appear to be whey [ 6 , 8 ] or bovine milk [ 7 ].

Although amino acids appear to be the primary nutrient effectors of MPS and can independently enhance muscle protein accrual, their effect on MPS, and ultimately muscle growth will be enhanced by chronic resistance exercise. J Appl Physiol. Am J Physiol. Am J Clin Nutr. Am J Physiol Endocrinol Metab. J Nutr. Br J Nutr.

Medicine and science in sports and exercise. J Physiol. PLoS One. Google Scholar. Kimball SR, Jefferson LS: Control of translation initiation through integration of signals generated by hormones, nutrients, and exercise. J Biol Chem. Acta Physiol Oxf. Biochem J. Hundal HS, Taylor PM: Amino acid transceptors: gate keepers of nutrient exchange and regulators of nutrient signaling. J Nutr Health Aging. J Am Diet Assoc.

Phillips SM, Tang JE, Moore DR: The role of milk- and soy-based protein in support of muscle protein synthesis and muscle protein accretion in young and elderly persons. J Am Coll Nutr. J Nutr Biochem. Amino Acids. Doherty TJ: Invited review: Aging and sarcopenia. Volpi E, Mittendorfer B, Rasmussen BB, Wolfe RR: The response of muscle protein anabolism to combined hyperaminoacidemia and glucose-induced hyperinsulinemia is impaired in the elderly. J Clin Endocrinol Metab.

Clin Sci Lond. Gelfand RA, Barrett EJ: Effect of physiologic hyperinsulinemia on skeletal muscle protein synthesis and breakdown in man. J Clin Invest. Roy BD, Tarnopolsky MA: Influence of differing macronutrient intakes on muscle glycogen resynthesis after resistance exercise.

Download references. We thank Daniel West and Cameron Mitchell for helpful discussions and feedback on the manuscript. Correspondence to Stuart M Phillips. All authors read and approved the final manuscript. Reprints and Permissions. Churchward-Venne, T. Nutritional regulation of muscle protein synthesis with resistance exercise: strategies to enhance anabolism.

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Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Tipton and R. Tipton , R. Wolfe Published Biology, Medicine International journal of sport nutrition and exercise metabolism. Exercise has a profound effect on muscle growth, which can occur only if muscle protein synthesis exceeds muscle protein breakdown; there must be a positive muscle protein balance.


Exercise has a profound effect on muscle growth, which can occur only if muscle protein synthesis exceeds muscle protein breakdown; there must be a positive.


Muscular Hypertrophy and Your Workout

Chronic obstructive pulmonary disease COPD is the fourth leading cause of death worldwide and is projected to be the third most common cause of death by 1. Cigarette smoke constitutes the major preventable risk factor, resulting in a progressive proteolytic, inflammatory and vasoactive response that leads to emphysema, small airway obstruction and pulmonary hypertension. The oxidative stress imposed by cigarette smoking together with systemic inflammation and hypoxia are important contributors to pathogenesis of skeletal muscle wasting and dysfunction and have been previously extensively reviewed 2 - 4.

Maximizing Post-exercise Anabolism: The Case for Relative Protein Intakes

Protein metabolism and physical training: any need for amino acid supplementation?

Muscle mass is the major deposit of protein molecules with dynamic turnover between net protein synthesis and degradation. In human subjects, invasive and non-invasive techniques have been applied to determine their skeletal muscle catabolism of amino acids at rest, during and after different forms of physical exercise and training. The aim of this review is to analyse the turnover flux and the relative oxidation rate of different types of muscle proteins after one bout of exercise as well as after resistance and endurance condition of training. Protein feeding in athletes appears to be a crucial nutrition necessity to promote the maintenance of muscle mass and its adaptation to the need imposed by the imposed technical requirements. In resting human individuals, the recommended protein daily allowance is about 0.

Exercise has a profound effect on muscle growth, which can occur only if muscle protein synthesis exceeds muscle protein breakdown; there must be a positive muscle protein balance. Resistance exercise improves muscle protein balance, but, in the absence of food intake, the balance remains negative i. The response of muscle protein metabolism to a resistance exercise bout lasts for hours; thus, the interaction between protein metabolism and any meals consumed in this period will determine the impact of the diet on muscle hypertrophy. Amino acid availability is an important regulator of muscle protein metabolism. The interaction of postexercise metabolic processes and increased amino acid availability maximizes the stimulation of muscle protein synthesis and results in even greater muscle anabolism than when dietary amino acids are not present.

Chris E. Cooper, Ralph Beneke, Kevin D. Tipton, Arny A. Ferrando; Improving muscle mass: response of muscle metabolism to exercise, nutrition and anabolic agents. Essays Biochem 1 February ; 44 85—

Introduction

Hypertrophy is an increase and growth of muscle cells. Hypertrophy refers to an increase in muscular size achieved through exercise. When you work out, if you want to tone or improve muscle definition, lifting weights is the most common way to increase hypertrophy. Which type to focus on depends on your fitness goals. Myofibrillar training will help with strength and speed.

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. A whiff of vitalism, the 19th century philosophical doctrine that there is some spiritual essence associated with biological processes, is still discernible in relation to the question of how contractile activity affects protein and amino acid metabolism. The working machine of muscles is, after all, made up of proteins so the idea comes naturally that where machinery works there must be wear and tear, presumably with a greater requirement for maintenance. It is also known that during starvation, i.

Maximizing the post-exercise increase in muscle protein synthesis, especially of the contractile myofibrillar protein fraction, is essential to facilitate effective muscle remodeling, and enhance hypertrophic gains with resistance training. MPS is the primary regulated variable influencing muscle net balance with dietary amino acid ingestion representing the single most important nutritional variable enhancing post-exercise rates of muscle protein synthesis. Dose-response studies in average i. This muscle-specific bolus intake is lower than that reported to maximize whole body anabolism i. Review of the available literature suggests that potential confounders such as the co-ingestion of carbohydrate, sex, and amount of active muscle mass do not represent significant barriers to the translation of this objectively determined relative protein intake. Additional research is warranted to elucidate the effective dose for proteins with suboptimal amino acid compositions e.

Exercise has a profound effect on muscle growth, which can occur only if muscle protein synthesis exceeds muscle protein breakdown; there must be a positive muscle protein balance. Resistance exercise improves muscle protein balance, but, in the absence of food intake, the balance remains negative i. The response of muscle protein metabolism to a resistance exercise bout lasts for hours; thus, the interaction between protein metabolism and any meals consumed in this period will determine the impact of the diet on muscle hypertrophy.

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