Rise In Muscle Protein Synthesis Research Articles

Understanding the effects of nutrition and post-exercise nutrition on skeletal muscle protein turnover: Insights from stable isotope studies

Understanding the effects of nutrition and post-exercise nutrition on skeletal muscle protein turnover: Insights from stable isotope studies

Effects of Protein Supplementation on Performance and Recovery in Resistance and Endurance Training.

There is robust evidence which shows that consuming protein pre- and/or post-workout induces a significant rise in muscle protein synthesis. It should be noted, however, that total daily caloric and protein intake over the long term play the most crucial dietary roles in facilitating adaptations to exercise. However, once these factors are accounted for, it appears that peri-exercise protein intake, particularly in the post-training period, plays a potentially useful role in terms of optimizing physical performance and positively influencing the subsequent recovery processes for both resistance training and endurance exercise. Factors that affect the utility of pre- or post-workout feeding include but are not necessarily limited to: training status (e.g., novice vs. advanced, or recreational vs. competitive athlete), duration of exercise, the number of training sessions per day, the number of competitive events per day, etc. From a purely pragmatic standpoint, consuming protein post-workout represents an opportunity to feed; this in turn contributes to one's total daily energy and protein intake. Furthermore, despite recent suggestions that one does not “need” to consume protein during the immediate (1 h or less) post-training time frame, it should be emphasized that consuming nothing offers no advantage and perhaps even a disadvantage. Thus, based on performance and recovery effects, it appears that the prudent approach would be to have athletes consume protein post-training and post-competition.

Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training.

Skeletal muscle supports locomotion and serves as the largest site of postprandial glucose disposal; thus it is a critical organ for physical and metabolic health. Skeletal muscle mass is regulated by the processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB), both of which are sensitive to external loading and aminoacidemia. Hyperaminoacidemia results in a robust but transient increase in rates of MPS and a mild suppression of MPB. Resistance exercise potentiates the aminoacidemia-induced rise in MPS that, when repeated over time, results in gradual radial growth of skeletal muscle (i.e., hypertrophy). Factors that affect MPS include both quantity and composition of the amino acid source. Specifically, MPS is stimulated in a dose-responsive manner and the primary amino acid agonist of this process is leucine. MPB also appears to be regulated in part by protein intake, which can exert a suppressive effect on MPB. At high protein doses the suppression of MPB may interfere with skeletal muscle adaptation following resistance exercise. In this review, we examine recent advancements in our understanding of how protein ingestion impacts skeletal muscle growth following resistance exercise in young adults during energy balance and energy restriction. We also provide practical recommendations for exercisers who wish to maximize the hypertrophic response of skeletal muscle during resistance exercise training.

CrossTalk proposal: The dominant mechanism causing disuse muscle atrophy is decreased protein synthesis.

CrossTalk proposal: The dominant mechanism causing disuse muscle atrophy is decreased protein synthesis.

Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein

Regardless of age or gender, resistance training or provision of adequate amounts of dietary protein (PRO) or essential amino acids (EAA) can increase muscle protein synthesis (MPS) in healthy adults. Combined PRO or EAA ingestion proximal to resistance training, however, can augment the post-exercise MPS response and has been shown to elicit a greater anabolic effect than exercise plus carbohydrate. Unfortunately, chronic/adaptive response data comparing the effects of different protein sources is limited. A growing body of evidence does, however, suggest that dairy PRO, and whey in particular may: 1) stimulate the greatest rise in MPS, 2) result in greater muscle cross-sectional area when combined with chronic resistance training, and 3) at least in younger individuals, enhance exercise recovery. Therefore, this review will focus on whey protein supplementation and its effects on skeletal muscle mass when combined with heavy resistance training.

Physiologic and molecular bases of muscle hypertrophy and atrophy: impact of resistance exercise on human skeletal muscle (protein and exercise dose effects)This paper is one of a selection of papers published in this Special Issue, entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and has undergone the Journal’s usual peer review process.

Normally, skeletal muscle mass is unchanged, beyond periods of growth, but it begins to decline in the fourth or fifth decade of life. The mass of skeletal muscle is maintained by ingestion of protein-containing meals. With feeding, muscle protein synthesis (MPS) is stimulated and a small suppression of muscle protein breakdown (MPB) occurs, such that protein balance becomes positive (MPS>MPB). As the postprandial period subsides and a transition toward fasting occurs, the balance of muscle protein turnover becomes negative again (MPB>MPS). Thus, during maintenance of skeletal muscle mass, the long-term net result is that MPS is balanced by MPB. Acutely, however, it is of interest to determine what regulates feeding-induced increases in MPS, since it appears that, in a number of scenarios (for example aging, disuse, and wasting diseases), a suppression of MPS in response to feeding is a common finding. In fact, recent findings point to the fact that loss of skeletal muscle mass with disuse and aging is due not chronic changes in MPS or MPB, but to a blunted feeding-induced rise in MPS. Resistance exercise is a potent stimulator of MPS and appears to synergistically enhance the gains stimulated by feeding. As such, resistance exercise is an important countermeasure to disuse atrophy and to age-related declines in skeletal muscle mass. What is less well understood is how the intensity and volume of the resistance exercise stimulus is sufficient to result in rises in MPS. Recent advances in this area are discussed here, with a focus on human in vivo data.

Sirolimus and mTORC1: centre stage in the story of what makes muscles bigger?

Sirolimus, or rapamycin as it commonly known, is a potent immunosuppressant and possesses both antifungal and antineoplastic properties. As such it has clinically important uses in oncology, cardiology and transplantation medicine. In this issue of The Journal of Physiology, Drummond and co-workers used rapamycin to elucidate in greater detail the signalling pathways that are activated by high force contractions in human skeletal muscle (Drummond et al. 2009). We have known for some time that resistance exercise employing high force contractions stimulates muscle protein synthesis (Chesley et al. 1992; Welle et al. 1993). The critical experiments in humans, following some very elegant work in rodents (Bodine et al. 2001; Kubica et al. 2005), showed that phosphorylation of a critical activation site on the mammalian target of rapamycin complex 1 (mTORC1), namely Ser2448 (Nave et al. 1999), was increased following resistance exercise (Dreyer et al. 2006). With excitement, many exercise physiologists no doubt rushed to see whether mTORC1 activation was as critical in humans as it appeared to be in rats. Sadly, however, many other studies have not reported phosphorylation of mTORC1 following resistance exercise (Eliasson et al. 2006; Glover et al. 2008). Issues of the timing of muscle sampling along with differences in nutritional status have no doubt contributed to the confusion. Nonetheless, the intriguing results of Drummond et al. (2009) show us that somewhere along the way mTORC1 is involved in turning on the process of protein synthesis following resistance exercise. Complicating the picture, however, are the findings that proteins downstream of mTORC1 such as ribosomal S6 kinase 1 (S6K1) and ribosomal protein S6 (rpS6) as well mTORC1 do get phosphorylated, but not until some 2 h after exercise. Why then did protein synthesis not rise at that time? Several other recent papers have shown that other proteins such as mammalian vacuole protein sorting 34 (mVsp34) are also probably playing a role in activating high force contraction-induced muscle protein synthesis (MacKenzie et al. 2009). Thus, what is perhaps now much clearer than before is that there is tremendous redundancy in how signalling processes affect muscle protein synthesis. Indeed, recent data even show that changes in signalling protein phosphorylation can be almost completely divorced from protein synthesis with a stimulus such as insulin (Greenhaff et al. 2008). It appears that we are inching closer to an understanding of how high force contractions, a potent anabolic and anti-catabolic stimulus, may be triggering a rise in muscle protein synthesis. The work from Drummond and colleagues (Drummond et al. 2009) sheds new light on the importance of mTOR in the post-exercise phenotype and these workers are to be congratulated for their efforts. At the same time, the results of this study raise important questions. For example, what is the true role of the extracellular regulated kinase (ERK) pathway? This pathway too appears to be affected by rapamycin. We know that protein synthesis is elevated for some time (at least 24–48 h) after resistance exercise; hence, what mechanisms are active at the later times beyond the initial 1–2 h? No doubt mTORC1 will be playing a role at some point.

Maximizing muscle protein anabolism: the role of protein quality

Muscle protein synthesis (MPS) and muscle protein breakdown are simultaneous ongoing processes. Here, we examine evidence for how protein quality can affect exercise-induced muscle protein anabolism or protein balance (MPS minus muscle protein breakdown). Evidence is highlighted showing differences in the responses of MPS, and muscle protein accretion, with ingestion of milk-based and soy-based proteins in young and elderly persons. Protein consumption, and the accompanying hyperaminoacidemia, stimulates an increase in MPS and a small suppression of muscle protein breakdown. Beyond the feeding-induced rise in MPS, small incremental addition of new muscle protein mass occurs following intense resistance exercise which over time (i.e. resistance training) leads to muscle hypertrophy. Athletes make use of the paradigm of resistance training and eating to maximize the gains in their skeletal muscle mass. Importantly, however, metabolically active skeletal muscle can offset the morbidities associated with the sarcopenia of aging such as type II diabetes, decline in aerobic fitness and the reduction in metabolic rate that can lead to fat mass accumulation. Recent evidence suggests that consumption of different proteins can affect the amplitude and possibly duration of MPS increases after feeding and this effect interacts and is possibly accentuated with resistance exercise.

Minimal whey protein with carbohydrate stimulates muscle protein synthesis following resistance exercise in trained young men

Whey protein is a supplemental protein source often used by athletes, particularly those aiming to gain muscle mass; however, direct evidence for its efficacy in stimulating muscle protein synthesis (MPS) is lacking. We aimed to determine the impact of consuming whey protein on skeletal muscle protein turnover in the post-exercise period. Eight healthy resistance-trained young men (age=21+/-1 .0 years; BMI=26.8+/-0.9 kg/m2 (means+/-SE)) participated in a double-blind randomized crossover trial in which they performed a unilateral leg resistance exercise workout (EX: 4 sets of knee extensions and 4 sets of leg press; 8-10 repetitions/set; 80% of maximal), such that one leg was not exercised and acted as a rested (RE) comparator. After exercise, subjects consumed either an isoenergetic whey protein plus carbohydrate beverage (WHEY: 10 g protein and 21 g fructose) or a carbohydrate-only beverage (CHO: 21 g fructose and 10 g maltodextran). Subjects received pulse-tracer injections of L-[ring-2H5]phenylalanine and L-[15N]phenylalanine to measure MPS. Exercise stimulated a rise in MPS in the WHEY-EX and CHO-EX legs, which were greater than MPS in the WHEY-RE leg and the CHO-RE leg (all p<0.05), respectively. The rate of MPS in the WHEY-EX leg was greater than in the CHO-EX leg (p<0.001). We conclude that a small dose (10 g) of whey protein with carbohydrate (21 g) can stimulate a rise in MPS after resistance exercise in trained young men that would be supportive of a positive net protein balance, which, over time, would lead to hypertrophy.

Minimal whey protein with carbohydrate stimulates muscle protein synthesis following resistance exercise in young men.

Whey protein is a supplemental protein source used by athletes, particularly those aiming to gain muscle mass; however, direct evidence for its efficacy in stimulating muscle protein synthesis (MPS) is lacking. We aimed to determine the impact of consuming whey protein on skeletal muscle protein turnover in the post-exercise period. Eight healthy young men (BMI = 26.8±0.9; age = 21±1) participated in a double-blind randomized cross-over trial in which they performed a unilateral leg resistance exercise workout – EX – (4 sets of knee extensions and 4 sets of leg press – 8–10 reps per set), such that the other leg was not exercised and acted as a rested (RE) comparator. After exercise subjects consumed either an isocaloric whey protein plus carbohydrate beverage (10g whey and 21g fructose) – WHEY – or a carbohydrate beverage containing fructose and maltodextrin (21g and 10g, respectively) – CHO. Subjects received pulse-tracer injections of L[ring-2H5]phenylalanine and L-[15N]phenylalanine to measure MPS. Exercise stimulated a rise in MPS only in the WHEY-EX leg, which was greater than MPS in the WHEY-RE leg and also the CHO-EX leg (all P<0.01). We conclude that a small dose (10g) of whey protein with carbohydrate (21g) can stimulate a rise in MPS after resistance exercise which, overtime, would be supportive of a net muscle protein accrual and hypertrophy. Supported by the US National Dairy Council.

Amino acid infusion increases the sensitivity of muscle protein synthesis in vivo to insulin. Effect of branched-chain amino acids.

Rates of muscle protein synthesis were measured in vivo in tissues of post-absorptive young rats that were given intravenous infusions of various combinations of insulin and amino acids. In the absence of amino acid infusion, there was a steady rise in muscle protein synthesis with plasma insulin concentration up to 158 mu units/ml, but when a complete amino acids mixtures was included maximal rates were obtained at 20 mu units/ml. The effect of the complete mixture could be reproduced by a mixture of essential amino acids or of branched-chain amino acids, but not by a non-essential mixture, alanine, methionine or glutamine. It is concluded that amino acids, particularly the branched-chain ones, increase the sensitivity of muscle protein synthesis to insulin.