Daniel R. Moore

Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men

BACKGROUNDnThe anabolic effect of resistance exercise is enhanced by the provision of dietary protein.nnnOBJECTIVESnWe aimed to determine the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. In addition, we measured the phosphorylation of candidate signaling proteins thought to regulate acute changes in MPS.nnnDESIGNnSix healthy young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, in a randomized order, drinks containing 0, 5, 10, 20, or 40 g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4 h after exercise by a primed constant infusion of [1-(13)C]leucine.nnnRESULTSnMPS displayed a dose response to dietary protein ingestion and was maximally stimulated at 20 g. The phosphorylation of ribosomal protein S6 kinase (Thr(389)), ribosomal protein S6 (Ser(240/244)), and the epsilon-subunit of eukaryotic initiation factor 2B (Ser(539)) were unaffected by protein ingestion. APS increased in a dose-dependent manner and also reached a plateau at 20 g ingested protein. Leucine oxidation was significantly increased after 20 and 40 g protein were ingested.nnnCONCLUSIONSnIngestion of 20 g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. Phosphorylation of candidate signaling proteins was not enhanced with any dose of protein ingested, which suggested that the stimulation of MPS after resistance exercise may be related to amino acid availability. Finally, dietary protein consumed after exercise in excess of the rate at which it can be incorporated into tissue protein stimulates irreversible oxidation.

Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men.

Background We aimed to determine the effect of resistance exercise intensity (% 1 repetition maximum—1RM) and volume on muscle protein synthesis, anabolic signaling, and myogenic gene expression. Methodology/Principal Findings Fifteen men (21±1 years; BMIu200a=u200a24.1±0.8 kg/m2) performed 4 sets of unilateral leg extension exercise at different exercise loads and/or volumes: 90% of repetition maximum (1RM) until volitional failure (90FAIL), 30% 1RM work-matched to 90%FAIL (30WM), or 30% 1RM performed until volitional failure (30FAIL). Infusion of [ring-13C6] phenylalanine with biopsies was used to measure rates of mixed (MIX), myofibrillar (MYO), and sarcoplasmic (SARC) protein synthesis at rest, and 4 h and 24 h after exercise. Exercise at 30WM induced a significant increase above rest in MIX (121%) and MYO (87%) protein synthesis at 4 h post-exercise and but at 24 h in the MIX only. The increase in the rate of protein synthesis in MIX and MYO at 4 h post-exercise with 90FAIL and 30FAIL was greater than 30WM, with no difference between these conditions; however, MYO remained elevated (199%) above rest at 24 h only in 30FAIL. There was a significant increase in AktSer473 at 24h in all conditions (Pu200a=u200a0.023) and mTORSer2448 phosphorylation at 4 h post-exercise (Pu200a=u200a0.025). Phosporylation of Erk1/2Tyr202/204, p70S6KThr389, and 4E-BP1Thr37/46 increased significantly (P<0.05) only in the 30FAIL condition at 4 h post-exercise, whereas, 4E-BP1Thr37/46 phosphorylation was greater 24 h after exercise than at rest in both 90FAIL (237%) and 30FAIL (312%) conditions. Pax7 mRNA expression increased at 24 h post-exercise (Pu200a=u200a0.02) regardless of condition. The mRNA expression of MyoD and myogenin were consistently elevated in the 30FAIL condition. Conclusions/Significance These results suggest that low-load high volume resistance exercise is more effective in inducing acute muscle anabolism than high-load low volume or work matched resistance exercise modes.

Exercise training and protein metabolism: influences of contraction, protein intake, and sex-based differences

Muscle contraction during exercise, whether resistive or endurance in nature, has profound affects on muscle protein turnover that can persist for up to 72 h. It is well established that feeding during the postexercise period is required to bring about a positive net protein balance (muscle protein synthesis - muscle protein breakdown). There is mounting evidence that the timing of ingestion and the protein source during recovery independently regulate the protein synthetic response and influence the extent of muscle hypertrophy. Minor differences in muscle protein turnover appear to exist in young men and women; however, with aging there may be more substantial sex-based differences in response to both feeding and resistance exercise. The recognition of anabolic signaling pathways and molecules are also enhancing our understanding of the regulation of protein turnover following exercise perturbations. In this review we summarize the current understanding of muscle protein turnover in response to exercise and feeding and highlight potential sex-based dimorphisms. Furthermore, we examine the underlying anabolic signaling pathways and molecules that regulate these processes.

Elevations in ostensibly anabolic hormones with resistance exercise enhance neither training-induced muscle hypertrophy nor strength of the elbow flexors

The aim of our study was to determine whether resistance exercise-induced elevations in endogenous hormones enhance muscle strength and hypertrophy with training. Twelve healthy young men (21.8 +/- 1.2 yr, body mass index = 23.1 +/- 0.6 kg/m(2)) trained their elbow flexors independently for 15 wk on separate days and under different hormonal milieu. In one training condition, participants performed isolated arm curl exercise designed to maintain basal hormone concentrations (low hormone, LH); in the other training condition, participants performed identical arm exercise to the LH condition followed immediately by a high volume of leg resistance exercise to elicit a large increase in endogenous hormones (high hormone, HH). There was no elevation in serum growth hormone (GH), insulin-like growth factor (IGF-1), or testosterone after the LH protocol but significant (P < 0.001) elevations in these hormones immediately and 15 and 30 min after the HH protocol. The hormone responses elicited by each respective exercise protocol late in the training period were similar to the response elicited early in the training period, indicating that a divergent postexercise hormone response was maintained over the training period. Muscle cross-sectional area (CSA) increased by 12% in LH and 10% in HH (P < 0.001) with no difference between conditions (condition x training interaction, P = 0.25). Similarly, type I (P < 0.01) and type II (P < 0.001) muscle fiber CSA increased with training with no effect of hormone elevation in the HH condition. Strength increased in both arms, but the increase was not different between the LH and HH conditions. We conclude that exposure of loaded muscle to acute exercise-induced elevations in endogenous anabolic hormones enhances neither muscle hypertrophy nor strength with resistance training in young men.

Enhanced Amino Acid Sensitivity of Myofibrillar Protein Synthesis Persists for up to 24 h after Resistance Exercise in Young Men

We aimed to determine whether an exercise-mediated enhancement of muscle protein synthesis to feeding persisted 24 h after resistance exercise. We also determined the impact of different exercise intensities (90% or 30% maximal strength) or contraction volume (work-matched or to failure) on the response at 24 h of recovery. Fifteen men (21 ± 1 y, BMI = 24.1 ± 0.8 kg · m(-2)) received a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine to measure muscle protein synthesis after protein feeding at rest (FED; 15 g whey protein) and 24 h after resistance exercise (EX-FED). Participants performed unilateral leg exercises: 1) 4 sets at 90% of maximal strength to failure (90FAIL); 2) 30% work-matched to 90FAIL (30WM); or 3) 30% to failure (30FAIL). Regardless of condition, rates of mixed muscle protein and sarcoplasmic protein synthesis were similarly stimulated at FED and EX-FED. In contrast, protein ingestion stimulated rates of myofibrillar protein synthesis above fasting rates by 0.016 ± 0.002%/h and the response was enhanced 24 h after resistance exercise, but only in the 90FAIL and 30FAIL conditions, by 0.038 ± 0.012 and 0.041 ± 0.010, respectively. Phosphorylation of protein kinase B on Ser473 was greater than FED at EX-FED only in 90FAIL, whereas phosphorylation of mammalian target of rapamycin on Ser2448 was significantly increased at EX-FED above FED only in the 30FAIL condition. Our results suggest that resistance exercise performed until failure confers a sensitizing effect on human skeletal muscle for at least 24 h that is specific to the myofibrillar protein fraction.

The Role of Milk- and Soy-Based Protein in Support of Muscle Protein Synthesis and Muscle Protein Accretion in Young and Elderly Persons

The balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB) is dependent on protein consumption and the accompanying hyperaminoacidemia, which stimulates a marked rise in MPS and mild suppression of MPB. In the fasting state, however, MPS declines sharply and MPB is increased slightly. Ultimately, the balance between MPS and MPB determines the net rate of muscle growth. Accretion of new muscle mass beyond that of normal growth can occur following periods of intense resistance exercise. Such muscle accretion is an often sought-after goal of athletes. There needs to be, however, an increased appreciation of the role that preservation of muscle can play in offsetting morbidities associated with the sarcopenia of aging, such as type 2 diabetes and declines in metabolic rate that can lead to fat mass accumulation followed by the onset or progression of obesity. Emerging evidence shows that consumption of different types of proteins can have different stimulatory effects on the amplitude and possibly duration that MPS is elevated after feeding; this may be particularly significant after resistance exercise. This effect may be due to differences in the fundamental amino acid composition of the protein (i.e., its amino acid score) and its rate of digestion. Milk proteins, specifically casein and whey, are the highest quality proteins and are quite different in terms of their rates of digestion and absorption. New data suggest that whey protein is better able to support MPS than is soy protein, a finding that may explain the greater ability of whey protein to support greater net muscle mass gains with resistance exercise. This review focuses on evidence showing the differences in responses of MPS, and ultimately muscle protein accretion, to consumption of milk- and soy-based supplemental protein sources in humans.

Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men.

We aimed to determine the effect of consuming pure isolated micellar casein or pure whey protein isolate on rates of myofibrillar protein synthesis (MPS) at rest and after resistance exercise in elderly men. Healthy elderly men (72 (sem 1) years; BMI 26·4 (sem 0·7) kg/m²) were divided into two groups (n 7 each) who received a primed, constant infusion of l-[ring-¹³C₆]phenylalanine to measure MPS at rest and during 4 h of exercise recovery. Participants performed unilateral leg resistance exercise followed by the consumption of isonitrogenous quantities (20 g) of casein or whey. Blood essential amino acids and leucine concentration peaked 60 min post-drink and were greater in amplitude after whey protein ingestion (both, P < 0·05). MPS in the rested leg was 65 % higher (P = 0·002) after ingestion of whey (0·040 (sem 0·003) %/h) when compared with micellar casein (0·024 (sem 0·002) %/h). Similarly, resistance exercise-stimulated rates of MPS were greater (P < 0·001) after whey ingestion (0·059 (sem 0·005) %/h) v. micellar casein (0·035 (sem 0·002) %/h). We conclude that ingestion of isolated whey protein supports greater rates of MPS than micellar casein both at rest and after resistance exercise in healthy elderly men. This result is probably related to a greater hyperaminoacidaemia or leucinaemia with whey ingestion.

Two Weeks of Reduced Activity Decreases Leg Lean Mass and Induces “Anabolic Resistance” of Myofibrillar Protein Synthesis in Healthy Elderly

BACKGROUNDnAlterations in muscle protein metabolism underlie age-related muscle atrophy. During periods of muscle disuse, muscle protein synthesis is blunted, and muscle atrophy occurs in young and old. The impact of a short reduction in physical activity on muscle protein metabolism in older adults is unknown.nnnPURPOSEnThe aim of this study was to investigate the impact of 14 days of reduced daily steps on fasted and fed-state rates of myofibrillar protein synthesis (MPS) to provide insight into the mechanisms for changes in muscle mass and markers of metabolic health.nnnMETHODSnBefore and after 14 days of reduced daily step-count, 10 healthy older adults (age, 72 ± 1 y) underwent measures of insulin sensitivity, muscle strength, physical function, and body composition. Using a primed constant infusion of L-[ring-(13)C6]phenylalanine with serial muscle biopsies, basal, postabsorptive, and postprandial rates of MPS were determined before and after the 14-day intervention.nnnRESULTSnDaily step-count was reduced by approximately 76% to 1413 ± 110 steps per day. Leg fat-free mass was reduced by approximately 3.9% (P < .001). Postabsorptive insulin resistance was increased by approximately 12%, and postprandial insulin sensitivity was reduced by approximately 43% after step reduction (P < .005). Concentrations of TNF-α and C-reactive protein were increased by approximately 12 and 25%, respectively, after step reduction (P < .05). Postprandial rates of MPS were reduced by approximately 26% after the intervention (P = .028), with no difference in postabsorptive rates.nnnCONCLUSIONnThe present study demonstrates that 14 days of reduced steps in older adults induces small but measurable reductions in muscle mass that appear to be underpinned by reductions in postprandial MPS and are accompanied by impairments in insulin sensitivity and systemic inflammatory markers and postprandial MPS.

Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial

BACKGROUNDnLeucine is a key amino acid involved in the regulation of skeletal muscle protein synthesis.nnnOBJECTIVEnWe assessed the effect of the supplementation of a lower-protein mixed macronutrient beverage with varying doses of leucine or a mixture of branched chain amino acids (BCAAs) on myofibrillar protein synthesis (MPS) at rest and after exercise.nnnDESIGNnIn a parallel group design, 40 men (21 ± 1 y) completed unilateral knee-extensor resistance exercise before the ingestion of 25 g whey protein (W25) (3.0 g leucine), 6.25 g whey protein (W6) (0.75g leucine), 6.25 g whey protein supplemented with leucine to 3.0 g total leucine (W6+Low-Leu), 6.25 g whey protein supplemented with leucine to 5.0 g total leucine (W6+High-Leu), or 6.25 g whey protein supplemented with leucine, isoleucine, and valine to 5.0 g total leucine. A primed continuous infusion of l-[ring-(13)C6] phenylalanine with serial muscle biopsies was used to measure MPS under baseline fasted and postprandial conditions in both a rested (response to feeding) and exercised (response to combined feeding and resistance exercise) leg.nnnRESULTSnThe area under the blood leucine curve was greatest for the W6+High-Leu group compared with the W6 and W6+Low-Leu groups (P < 0.001). In the postprandial period, rates of MPS were increased above baseline over 0-1.5 h in all treatments. Over 1.5-4.5 h, MPS remained increased above baseline after all treatments but was greatest after W25 (∼267%) and W6+High-Leu (∼220%) treatments (P = 0.002).nnnCONCLUSIONSnA low-protein (6.25 g) mixed macronutrient beverage can be as effective as a high-protein dose (25 g) at stimulating increased MPS rates when supplemented with a high (5.0 g total leucine) amount of leucine. These results have important implications for formulations of protein beverages designed to enhance muscle anabolism. This trial was registered at clinicaltrials.gov as NCT 1530646.

Neuromuscular adaptations in human muscle following low intensity resistance training with vascular occlusion.

Low-intensity (~50% of a single repetition maximum—1xa0RM) resistance training combined with vascular occlusion results in increases in muscle strength and cross-sectional area [Takarada et al. (2002) Eur J Appl Physiol 86:308–331]. The mechanisms responsible for this hypertrophy and strength gain remain elusive and no study has assessed the contribution of neuromuscular adaptations to these strength gains. We examined the effect of low-intensity training (8xa0weeks of unilateral elbow flexion at 50% 1xa0RM) both with (OCC) and without vascular occlusion (CON) on neuromuscular changes in the elbow flexors of eight previously untrained men [19.5 (0.4)xa0years]. Following training, maximal voluntary dynamic strength increased (P<0.05) in OCC (22%) and CON (23%); however, isometric maximal voluntary contraction (MVC) strength increased in OCC only (8.3%, P<0.05). Motor unit activation, assessed by interpolated twitch, was high (~98%) in OCC and CON both pre- and post-training. Evoked resting twitch torque decreased 21% in OCC (P<0.05) but was not altered in CON. Training resulted in a reduction in the twitch:MVC ratio in OCC only (29%, P<0.01). Post-activation potentiation (PAP) significantly increased by 51% in OCC (P<0.05) and was not changed in CON. We conclude that low-intensity resistance training in combination with vascular occlusion produces an adequate stimulus for increasing muscle strength and causes changes in indices of neuromuscular function, such as depressed resting twitch torque and enhanced PAP.