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.

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.

Bolus arginine supplementation affects neither muscle blood flow nor muscle protein synthesis in young men at rest or after resistance exercise.

The aim of this study was to investigate the ergogenic potential of arginine on NO synthesis, muscle blood flow, and skeletal muscle protein synthesis (MPS). Eight healthy young men (22.1 ± 2.6 y, 1.79 ± 0.06 m, 76.6 ± 6.2 kg; mean ± SD) participated in 2 trials where they performed a bout of unilateral leg resistance exercise and ingested a drink containing either 10 g essential amino acids with 10 g l-arginine (ARG) or an isonitrogenous control (CON). Femoral artery blood flow of both the nonexercised and exercised leg was measured continuously using pulsed-wave Doppler ultrasound, while rates of mixed and myofibrillar MPS were determined using a primed continuous infusion of L-[ring-(13)C(6)] or L-[ring-(2)H(5)]phenylalanine. The plasma arginine concentration increased 300% during the ARG trial but not during the CON trial (P < 0.001). Plasma nitrate, nitrite, and endothelin-1, all markers of NO synthesis, did not change during either the ARG or CON trial. Plasma growth hormone increased to a greater degree after exercise in the ARG trial than CON trial (P < 0.05). Femoral artery blood flow increased 270% above basal in the exercised leg (P < 0.001) but not in the nonexercised leg, with no differences between the ARG and CON trials. Mixed and myofibrillar MPS were both greater in the exercised leg compared with the nonexercised leg (P < 0.001), but did not differ between the ARG and CON treatments. We conclude that an oral bolus (10 g) of arginine does not increase NO synthesis or muscle blood flow. Furthermore, arginine does not enhance mixed or myofibrillar MPS either at rest or after resistance exercise beyond that achieved by feeding alone.

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.

Body composition and strength changes in women with milk and resistance exercise.

PURPOSE: We aimed to determine whether women consuming fat-free milk versus isoenergetic carbohydrate after resistance exercise would see augmented gains in lean mass and reductions in fat mass similar to what we observed in young men. METHODS: Young women were randomized to drink either fat-free milk (MILK: n = 10; age (mean +/- SD) = 23.2 +/- 2.8 yr; BMI = 26.2 +/- 4.2 kg x m(-2)) or isoenergetic carbohydrate (CON: n = 10; age = 22.4 +/- 2.4 yr; BMI = 25.2 +/- 3.8 kg x m(-2)) immediately after and 1 h after exercise (2 x 500 mL). Subjects exercised 5 d x wk(-1) for 12 wk. Body composition changes were measured by dual-energy x-ray absorptiometry, and subjects' strength and fasting blood were measured before and after training. RESULTS: CON gained weight after training (CON: +0.86 +/- 0.4 kg, P < 0.05; MILK: +0.50 +/- 0.4 kg, P = 0.29). Lean mass increased with training in both groups (P < 0.01), with a greater net gain in MILK versus CON (1.9 +/- 0.2 vs 1.1 +/- 0.2 kg, respectively, P < 0.01). Fat mass decreased with training in MILK only (-1.6 +/- 0.4 kg, P < 0.01; CON: -0.3 +/- 0.3 kg, P = 0.41). Isotonic strength increased more in MILK than CON (P < 0.05) for some exercises. Serum 25-hydroxyvitamin D increased in both groups but to a greater extent in MILK than CON (+6.5 +/- 1.1 vs +2.8 +/- 1.3 nM, respectively, P < 0.05), and parathyroid hormone decreased only in MILK (-1.2 +/- 0.2 pM, P < 0.01). CONCLUSIONS: Heavy, whole-body resistance exercise with the consumption of milk versus carbohydrate in the early postexercise period resulted in greater muscle mass accretion, strength gains, fat mass loss, and a possible reduction in bone turnover in women after 12 wk. Our results, similar to those in men, highlight that milk is an effective drink to support favorable body composition changes in women with resistance training.

Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men.

We aimed to determine whether exercise-induced elevations in systemic concentration of testosterone, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) enhanced post-exercise myofibrillar protein synthesis (MPS) and phosphorylation of signalling proteins important in regulating mRNA translation. Eight young men (20 +/- 1.1 years, BMI = 26 +/- 3.5 kg m(-2)) completed two exercise protocols designed to maintain basal hormone concentrations (low hormone, LH) or elicit increases in endogenous hormones (high hormone, HH). In the LH protocol, participants performed a bout of unilateral resistance exercise with the elbow flexors. The HH protocol consisted of the same elbow flexor exercise with the contralateral arm followed immediately by high-volume leg resistance exercise. Participants consumed 25 g of protein after arm exercise to maximize MPS. Muscle biopsies and blood samples were taken as appropriate. There were no changes in serum testosterone, GH or IGF-1 after the LH protocol, whereas there were marked elevations after HH (testosterone, P < 0.001; GH, P < 0.001; IGF-1, P < 0.05). Exercise stimulated a rise in MPS in the biceps brachii (rest = 0.040 +/- 0.007, LH = 0.071 +/- 0.008, HH = 0.064 +/- 0.014% h(-1); P < 0.05) with no effect of elevated hormones (P = 0.72). Phosphorylation of the 70 kDa S6 protein kinase (p70S6K) also increased post-exercise (P < 0.05) with no differences between conditions. We conclude that the transient increases in endogenous purportedly anabolic hormones do not enhance fed-state anabolic signalling or MPS following resistance exercise. Local mechanisms are likely to be of predominant importance for the post-exercise increase in MPS.

Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men.

This study was designed to compare the acute response of mixed muscle protein synthesis (MPS) to rapidly (i.e., whey hydrolysate and soy) and slowly (i.e., micellar casein) digested proteins both at rest and after resistance exercise. Three groups of healthy young men (n = 6 per group) performed a bout of unilateral leg resistance exercise followed by the consumption of a drink containing an equivalent content of essential amino acids (10 g) as either whey hydrolysate, micellar casein, or soy protein isolate. Mixed MPS was determined by a primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Ingestion of whey protein resulted in a larger increase in blood essential amino acid, branched-chain amino acid, and leucine concentrations than either casein or soy (P < 0.05). Mixed MPS at rest (determined in the nonexercised leg) was higher with ingestion of faster proteins (whey = 0.091 +/- 0.015, soy = 0.078 +/- 0.014, casein = 0.047 +/- 0.008%/h); MPS after consumption of whey was approximately 93% greater than casein (P < 0.01) and approximately 18% greater than soy (P = 0.067). A similar result was observed after exercise (whey > soy > casein); MPS following whey consumption was approximately 122% greater than casein (P < 0.01) and 31% greater than soy (P < 0.05). MPS was also greater with soy consumption at rest (64%) and following resistance exercise (69%) compared with casein (both P < 0.01). We conclude that the feeding-induced simulation of MPS in young men is greater after whey hydrolysate or soy protein consumption than casein both at rest and after resistance exercise; moreover, despite both being fast proteins, whey hydrolysate stimulated MPS to a greater degree than soy after resistance exercise. These differences may be related to how quickly the proteins are digested (i.e., fast vs. slow) or possibly to small differences in leucine content of each protein.

Differential stimulation of myofibrillar and sarcoplasmic protein synthesis with protein ingestion at rest and after resistance exercise.

We aimed to determine whether there is a differential stimulation of the contractile myofibrillar and the cellular sarcoplasmic proteins after ingestion of protein and how this is affected by resistance exercise. Fasted (FAST) muscle protein synthesis was measured in seven healthy young men with a primed constant infusion of L-[ring-(13)C(6)]phenylalanine. Participants then performed an intense bout of unilateral resistance exercise followed by the consumption of 25 g of whey protein to maximally stimulate protein synthesis. In the rested (FED) leg myofibrillar (MYO) protein synthesis was elevated (P < 0.01) above FAST at 3 h (approximately 163%) but not at 1 and 5 h (P > 0.05). In contrast, MYO protein synthesis in the exercised (FED-EX) leg was stimulated above FAST at 1, 3 and 5 h (approximately 100, 216, and 229%, respectively; P < 0.01) with the increase at 5 h being greater than FED (P < 0.01). Thus, the synthesis of muscle contractile proteins is stimulated by both feeding and resistance exercise early (1 h) but has a greater duration and amplitude after resistance exercise. Sarcoplasmic (SARC) protein synthesis was similarly elevated (P < 0.01) above FAST by approximately 104% at 3 h in both FED and FED-EX suggesting SARC protein synthesis is stimulated by feeding but that this response is not augmented by resistance exercise. In conclusion, myofibrillar and sarcoplasmic protein synthesis are similarly, but transiently, stimulated with protein feeding. In contrast, resistance exercise rapidly stimulates and sustains the synthesis of only the myofibrillar protein fraction after protein ingestion. These data highlight the importance of measuring the synthetic response of specific muscle protein fractions when examining the effects of exercise and nutrition.

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.

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

BACKGROUND: The anabolic effect of resistance exercise is enhanced by the provision of dietary protein. OBJECTIVES: We 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. DESIGN: Six 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. RESULTS: MPS 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. CONCLUSIONS: Ingestion 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.

Maximizing muscle protein anabolism: the role of protein quality.

PURPOSE OF REVIEW: 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. RECENT FINDINGS: 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. SUMMARY: 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.

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.

Immobilization induces anabolic resistance in human myofibrillar protein synthesis with low and high dose amino acid infusion.

We tested the hypothesis that increasing blood amino acid (AA) availability would counter the physical inactivity-induced reduction in muscle protein synthesis. We determined how 14 days of unilateral knee immobilization affected quadriceps myofibrillar protein synthesis (MPS) in young healthy subjects (10 men, 2 women, 21 +/- 1 years; 80.2 +/- 4.0 kg, mean +/- S.E.M.) in the post-absorptive state and after infusing AA (10% Primene) at low or high doses (43 and 261 mg kg(-1) h(-1)). Muscle cross-sectional area (MRI) and peak isometric torque declined in the immobilized leg (-5.0 +/- 1.2% and -25 +/- 3%, respectively, both P < 0.005), but were unchanged (all P > 0.6) in the non-immobilized leg. Immobilization induced a 27% decline in the rate of post-absorptive MPS (immobilized, 0.027 +/- 0.003: non-immobilized, 0.037 +/- 0.003% h(-1); P < 0.001). Regardless of dose, AA infusion stimulated a greater rise in MPS in the non-immobilized legs; at 4 h MPS was greater by +54 +/- 12% with low dose and +68 +/- 17% with high dose AA infusion (both P < 0.001). There was some evidence of delayed responsiveness of phosphorylation of Akt to high doses of AA and p70S6k at both doses but no marked differences in that of mTOR, GSK3beta or eEF2. Phosphorylation of focal adhesion kinase (Tyr(576/577)) was reduced (P < 0.05) with immobilization. We observed no change in polyubiquitinated protein content after immobilization. We confirm that 14 days of immobilization reduces MPS in the post-absorptive state and this diminution is reduced but not abolished by increased provision of AA, even at high rates. The immobilization-induced decline in post-absorptive MPS with the 'anabolic resistance' to amino acids can account for much of immobilization-induced muscle atrophy.

Resistance exercise decreases eIF2Bepsilon phosphorylation and potentiates the feeding-induced stimulation of p70S6K1 and rpS6 in young men.

We investigated the effect of resistance exercise and feeding on the activation of signaling proteins involved in translation initiation. Nine young men (23.7+/-0.41 yr; BMI=25.5+/-1.0 kg/m2; means+/-SE) were tested twice after they performed a strenuous bout of unilateral resistance exercise, such that their contralateral leg acted as a nonexercised comparator, in either the fasted and fed [1,000 kJ, each 90 min (3 doses): 10 g protein, 41 g carbohydrate, 4 g fat] states. Muscle biopsies were obtained 6 h postexercise from both legs, resulting in four experimental conditions: rest-fasted, rest-fed, exercise-fasted, and exercise-fed. Feeding increased PKB/Akt (Ser473) phosphorylation (P<0.05), while exercise increased the phosphorylation of Akt and the downstream 70 kDa S6 protein kinase (p70S6K1, Thr389) and ribosomal protein S6 (rpS6, Ser235/236, Ser240/244; all P<0.05). The combination of resistance exercise and feeding increased the phosphorylation of p70S6K1 (Thr389) and rpS6 (Ser240/244) above exercise alone (P<0.05). Exercise also reduced phosphorylation of the catalytic epsilon subunit of eukaryotic initiation factor 2B (eIF2Bepsilon, Ser540; P<0.05). Mammalian target of rapamycin (mTOR, Ser2448), glycogen synthase kinase-3beta (GSK-3beta, Ser9), and focal adhesion kinase (FAK, Tyr576/577) phosphorylation were unaffected by either feeding or resistance exercise (all P>0.14). In summary, feeding resulted in phosphorylation of Akt, while resistance exercise stimulated phosphorylation of Akt, p70S6K1, rpS6, and dephosphorylation eIF2Bepsilon with a synergistic effect of feeding and exercise on p70(S6K1) and its downstream target rpS6. We conclude that resistance exercise potentiates the effect of feeding on the phosphorylation and presumably activation of critical proteins involved in the regulation of muscle protein synthesis in young men.

Resistance training alters the response of fed state mixed muscle protein synthesis in young men.

Ten healthy young men (21.0 +/- 1.5 yr, 1.79 +/- 0.1 m, 82.7 +/- 14.7 kg, means +/- SD) participated in 8 wk of intense unilateral resistance training (knee extension exercise) such that one leg was trained (T) and the other acted as an untrained (UT) control. After the 8 wk of unilateral training, infusions of L-[ring-d(5)]phenylalanine, L-[ring-(13)C(6)]phenylalanine, and d(3)-alpha-ketoisocaproic acid were used to measure mixed muscle protein synthesis in the T and UT legs by the direct incorporation method [fractional synthetic rate (FSR)]. Protein synthesis was determined at rest as well as 4 h and 28 h after an acute bout of resistance exercise performed at the same intensity relative to the gain in single repetition maximum before and after training. Training increased mean muscle fiber cross-sectional area only in the T leg (type I: 16 +/- 10%; type II: 20 +/- 19%, P < 0.05). Acute resistance exercise increased muscle protein FSR in both legs at 4 h (T: 162 +/- 76%; UT: 108 +/- 62%, P < 0.01 vs. rest) with the increase in the T leg being significantly higher than in the UT leg at this time (P < 0.01). At 28 h postexercise, FSR in the T leg had returned to resting levels; however, the rate of protein synthesis in the UT leg remained elevated above resting (70 +/- 49%, P < 0.01). We conclude that resistance training attenuates the protein synthetic response to acute resistance exercise, despite higher initial increases in FSR, by shortening the duration for which protein synthesis is elevated.

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.

A critical examination of dietary protein requirements, benefits, and excesses in athletes.

There is likely no other dietary component that inspires as much debate, insofar as athletes are concerned, as protein. How much dietary protein is required, optimal, or excessive? Dietary guidelines from a variety of sources have settled on an adequate dietary protein intake for those over the age of 19 of ~0.8-0.9 g protein.kg body weight(-1).d(-1). According to U.S. and Canadian dietary reference intakes (33), the recommended allowance for protein of 0.8 g protein.kg(-1).d(-1) is "the average daily intake level that is sufficient to meet the nutrient requirement of nearly all [~98%] . . . healthy individuals" (p. 22). The panel also stated, "in view of the lack of compelling evidence to the contrary, no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise" (33, p. 661). Currently, no group or groups of scientists involved in establishing dietary guidelines see a need for any statement that athletes or people engaging in regular physical activity require more protein than their sedentary counterparts. Popular magazines, numerous Web sites, trainers, and many athletes decry protein intakes even close to those recommended. Even joint position stands from policy-setting groups state that "protein recommendations for endurance athletes are 1.2 to 1.4 g/kg body weight per day, whereas those for resistance and strength-trained athletes may be as high as 1.6 to 1.7 g/kg body weight per day" (1, p. 1544). The divide between those setting dietary protein requirements and those who might be making practical recommendations for athletes appears substantial, but ultimately, most athletes indicate that they consume protein at levels beyond even the highest recommendations. Thus, one might conclude that any debate on protein "requirements" for athletes is inconsequential; however, a critical analysis of existing and new data reveals novel ideas and concepts that may represent some common ground between these apparently conflicted groups. The goal of this review was to provide a critical and thorough analysis of current data on protein requirements in an attempt to provide some guidance to athletes, trainers, coaches, and sport dietitians on athletes' protein intake. In addition, an effort was made to clearly distinguish between "required" dietary protein, "optimal" intakes, and intakes that are likely "excessive," perhaps not from the standpoint of health, but certainly from the standpoint of potentially compromised performance.

Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters.

BACKGROUND: Acute consumption of fat-free fluid milk after resistance exercise promotes a greater positive protein balance than does soy protein. OBJECTIVE: We aimed to determine the long-term consequences of milk or soy protein or equivalent energy consumption on training-induced lean mass accretion. DESIGN: We recruited 56 healthy young men who trained 5 d/wk for 12 wk on a rotating split-body resistance exercise program in a parallel 3-group longitudinal design. Subjects were randomly assigned to consume drinks immediately and again 1 h after exercise: fat-free milk (Milk; n = 18); fat-free soy protein (Soy; n = 19) that was isoenergetic, isonitrogenous, and macronutrient ratio matched to Milk; or maltodextrin that was isoenergetic with Milk and Soy (control group; n = 19). RESULTS: Muscle fiber size, maximal strength, and body composition by dual-energy X-ray absorptiometry (DXA) were measured before and after training. No between-group differences were seen in strength. Type II muscle fiber area increased in all groups with training, but with greater increases in the Milk group than in both the Soy and control groups (P < 0.05). Type I muscle fiber area increased after training only in the Milk and Soy groups, with the increase in the Milk group being greater than that in the control group (P < 0.05). DXA-measured fat- and bone-free mass increased in all groups, with a greater increase in the Milk group than in both the Soy and control groups (P < 0.05). CONCLUSION: We conclude that chronic postexercise consumption of milk promotes greater hypertrophy during the early stages of resistance training in novice weightlifters when compared with isoenergetic soy or carbohydrate consumption.

Resistance training reduces fasted- and fed-state leucine turnover and increases dietary nitrogen retention in previously untrained young men.

We aimed to determine the impact of intense resistance training, designed to increase lean body mass (LBM), on both fasted and fed whole body protein kinetics in untrained young men. Twelve healthy males (22 +/- 2 y of age; BMI, 24.3 +/- 2.4 kg/m(2)) participated in a 12-wk (5-d/wk) resistance training program. Before and after training, a primed constant infusion of [1-(13)C]leucine was used to measure whole body leucine turnover, protein breakdown, and nonoxidative leucine disposal in the fasted and fed states. Participants were studied during 5-d controlled diet periods that provided a moderate protein intake [1.4 g/(kg body wt . d)]. We estimated protein turnover and nitrogen balance. Training increased LBM (61.6 +/- 6.9 vs. 64.8 +/- 6.7 kg, P < 0.05). After training, whole body leucine turnover was reduced (P < 0.01) in both fasted (167 +/- 18 vs. 152 +/- 17) and fed (197 +/- 23 vs. 178 +/- 21) states [all values micromol/(kg LBM . h)]. Training-induced decreases (P < 0.01) in protein breakdown occurred in the fasted (165 +/- 18 vs. 144 +/- 17) and fed (111 +/- 23 vs. 93 +/- 20) states. Following training, nonoxidative leucine disposal was similarly reduced (P < 0.01) in the fasted (144 +/- 18 vs. 126 +/- 18) and fed (151 +/- 20 vs. 133 +/- 19) states. Nitrogen balance was more positive after training (13.7 +/- 8.1 vs. 33.4 +/- 12.5 g/(kg LBM . d), P < 0.01) indicating an increased retention of dietary nitrogen. Intense resistance training alters whole body protein kinetics in novice weightlifters regardless of feeding status. The increase in nitrogen balance after training demonstrates a more efficient utilization of dietary nitrogen, suggesting that protein requirements for novice weightlifters are not elevated.

Increased muscle oxidative potential following resistance training induced fibre hypertrophy in young men.

Some evidence suggests that resistance training may lower relative muscle mitochondrial content via "dilution" of the organelle in a larger muscle fibre. Such an adaptation would reduce fatigue resistance, as well as compromise oxidative ATP synthesis and the capacity for fatty-acid oxidation. We investigated the effect of resistance training on mitochondrial enzymes of the citric acid cycle (citrate synthase; CS) and beta-oxidation (beta-hydroxyacyl CoA dehydrogenase; beta-HAD), as well as markers of the potential for glucose phosphorylation (hexokinase; HK) and glycolysis (phosphofructokinase; PFK). Twelve untrained men (21.9 +/- 0.5 y; 1.79 +/- 0.03 m; 83.2 +/- 3.2 kg) participated in a 12 week progressive resistance-training program. Muscle biopsies were taken from the vastus lateralis before (PRE) and after (POST) training. Training increased mean muscle fibre cross-sectional area (p < 0.05) and the activities of CS (PRE = 4.53 +/- 0.44 mol.kg protein(-1).h(-1); POST = 5.63 +/- 0.40 mol.kg protein(-1).h(-1); p < 0.001) and beta-HAD (PRE = 2.55 +/- 0.28 mol.kg protein(-1).h(-1); POST = 3.11 +/- 0.21 mol.kg protein(-1).h(-1); p < 0.05). The activity of HK increased 42% (p < 0.05), whereas the activity of PFK remained unchanged. We conclude that resistance training provides a stimulus for improving muscle oxidative potential, as reflected by the increased activities of CS and beta-HAD following resistance training induced hypertrophy.