Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression

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.

Effects of Whey Protein Alone or as Part of a Multi-ingredient Formulation on Strength, Fat-Free Mass, or Lean Body Mass in Resistance-Trained Individuals: A Meta-analysis

BACKGROUND

Even though the positive effects of whey protein-containing supplements for optimizing the anabolic responses and adaptations process in resistance-trained individuals have been supported by several investigations, their use continues to be controversial. Additionally, the administration of different multi-ingredient formulations where whey proteins are combined with carbohydrates, other protein sources, creatine, and amino acids or derivatives, has been extensively proposed as an effective strategy to maximize strength and muscle mass gains in athletes.

OBJECTIVE

We aimed to systematically summarize and quantify whether whey protein-containing supplements, administered alone or as a part of a multi-ingredient, could improve the effects of resistance training on fat-free mass or lean body mass, and strength in resistance-trained individuals when compared with other iso-energetic supplements containing carbohydrates or other sources of proteins.

METHODS

A structured literature search was conducted on PubMed, Science Direct, Web of Science, Cochrane Libraries, US National Institutes of Health clinicaltrials.gov, SPORTDiscus, and Google Scholar databases. Main inclusion criteria comprised randomized controlled trial study design, adults (aged 18 years and over), resistance-trained individuals, interventions (a resistance training program for a period of 6 weeks or longer, combined with whey protein supplementation administered alone or as a part of a multi-ingredient), and a calorie equivalent contrast supplement from carbohydrates or other non-whey protein sources. Continuous data on fat-free mass and lean body mass, and maximal strength were pooled using a random-effects model.

RESULTS

Data from nine randomized controlled trials were included, involving 11 treatments and 192 participants. Overall, with respect to the ingestion of contrast supplements, whey protein supplementation, administered alone or as part of a multi-ingredient, in combination with resistance training, was associated with small extra gains in fat-free mass or lean body mass, resulting in an effect size of g = 0.301, 95% confidence interval (CI) 0.032-0.571. Subgroup analyses showed less clear positive trends resulting in small to moderate effect size g = 0.217 (95% CI -0.113 to 0.547) and g = 0.468 (95% CI 0.003-0.934) in favor of whey and multi-ingredient, respectively. Additionally, a positive overall extra effect was also observed to maximize lower (g = 0.316, 95% CI 0.045-0.588) and upper body maximal strength (g = 0.458, 95% CI 0.161-0.755). Subgroup analyses showed smaller superiority to maximize strength gains with respect to the contrast groups for lower body (whey protein: g = 0.343, 95% CI -0.016 to 0.702, multi-ingredient: g = 0.281, 95% CI -0.135 to 0.697) while in the upper body, multi-ingredient (g = 0.612, 95% CI 0.157-1.068) seemed to produce more clear effects than whey protein alone (g = 0.343, 95% CI -0.048 to 0.735).

LIMITATIONS

Studies involving interventions of more than 6 weeks on resistance-training individuals are scarce and account for a small number of participants. Furthermore, no studies with an intervention longer than 12 weeks have been found. The variation regarding the supplementation protocol, namely the different doses criteria or timing of ingestion also add some concerns to the studies comparison.

CONCLUSIONS

Whey protein alone or as a part of a multi-ingredient appears to maximize lean body mass or fat-free mass gain, as well as upper and lower body strength improvement with respect to the ingestion of an iso-energetic equivalent carbohydrate or non-whey protein supplement in resistance-training individuals. This enhancement effect seems to be more evident when whey proteins are consumed within a multi-ingredient containing creatine.

Dietary Protein Intake and Lean Muscle Mass in Survivors of Childhood Acute Lymphoblastic Leukemia: Report From the St. Jude Lifetime Cohort Study

BACKGROUND

Survivors of childhood acute lymphoblastic leukemia (ALL) are at risk for low lean muscle mass and muscle weakness, which may contribute to inactivity and early development of chronic diseases typically seen in older adults. Although increasing protein intake, in combination with resistance training, improves lean muscle mass in other populations, it is not known whether muscular tissue among survivors of ALL, whose impairments are treatment-related, will respond similarly.

OBJECTIVE

The aim of this study was to evaluate associations among dietary protein intake, resistance training, and lean muscle mass in survivors of ALL and age-, sex-, and race-matched controls.

DESIGN

This was a cross-sectional study.

METHODS

Lean muscle mass was determined with dual-energy x-ray absorptiometry, dietary information with 24-hour recalls, and participation in resistance training with a questionnaire. Participants were 365 survivors of ALL (52% male; 87% white; median age=28.5 years, range=23.6-31.7) and 365 controls with no previous cancer.

RESULTS

Compared with controls, survivors of ALL had lower lean muscle mass (55.0 versus 57.2 kg, respectively) and lower percentage of lean muscle mass (68.6% versus 71.4%, respectively) than controls. Similar proportions of survivors (71.1%) and controls (69.7%) met recommended dietary protein intake (0.8 g/kg/d). Survivors (45.4%) were less likely to report resistance training than controls (53.8%). In adjusted models, 1-g higher protein intake per kilogram of body mass per day was associated with a 7.9% increase and resistance training ≥1×wk, with a 2.8% increase in lean muscle mass.

LIMITATIONS

The cross-sectional study design limits temporal evaluation of the association between protein intake and lean muscle mass.

CONCLUSIONS

The findings suggest that survivors of childhood ALL with low lean muscle mass may benefit from optimizing dietary protein intake in combination with resistance training. Research is needed to determine whether resistance training with protein supplementation improves lean muscle mass in survivors of childhood ALL.

Protein Supplementation Does Not Further Increase Latissimus Dorsi Muscle Fiber Hypertrophy after Eight Weeks of Resistance Training in Novice Subjects, but Partially Counteracts the Fast-to-Slow Muscle Fiber Transition

The response to resistance training and protein supplementation in the latissimus dorsi muscle (LDM) has never been investigated. We investigated the effects of resistance training (RT) and protein supplementation on muscle mass, strength, and fiber characteristics of the LDM. Eighteen healthy young subjects were randomly assigned to a progressive eight-week RT program with a normal protein diet (NP) or high protein diet (HP) (NP 0.85 vs. HP 1.8 g of protein·kg⁻¹·day⁻¹). One repetition maximum tests, magnetic resonance imaging for cross-sectional muscle area (CSA), body composition, and single muscle fibers mechanical and phenotype characteristics were measured. RT induced a significant gain in strength (+17%, p < 0.0001), whole muscle CSA (p = 0.024), and single muscle fibers CSA (p < 0.05) of LDM in all subjects. Fiber isometric force increased in proportion to CSA (+22%, p < 0.005) and thus no change in specific tension occurred. A significant transition from 2X to 2A myosin expression was induced by training. The protein supplementation showed no significant effects on all measured outcomes except for a smaller reduction of 2X myosin expression. Our results suggest that in LDM protein supplementation does not further enhance RT-induced muscle fiber hypertrophy nor influence mechanic muscle fiber characteristics but partially counteracts the fast-to-slow fiber shift.

Effects of combined β-hydroxy-β-methylbutyrate (HMB) and whey protein ingestion on symptoms of eccentric exercise-induced muscle damage

BACKGROUND

The purpose of this study was to examine the effects of combined β-hydroxy-β-methylbutyrate (HMB) and whey protein ingestion on muscle strength and damage following a single bout of eccentric exercise.

METHODS

Eighteen untrained male subjects were assigned to HMB and Whey protein (HMB + Whey; 3 g/day HMB and 36.6 g/day whey protein, n = 6), HMB (3 g/day, n = 6), or whey protein (36.6 g/day, n = 6) groups. Ingestion commenced 7 days before non-dominant elbow flexor eccentric exercise (30 deg/sec, 6 reps × 7 sets) and continued until 4 days post-exercise. The maximal isometric strength, muscle soreness, plasma creatine kinase (CK), lactate dehydrogenase (LDH) were assessed pre-exercise, and at 1, 2, 3, and 5 days after exercise.

RESULTS

The change scores of maximal isometric strength significantly decreased at day 1, 2, and 5 in the whey protein group compared to pre value and that in HMB + Whey protein and HMB groups decreased at day 1 and 5. The muscle soreness significantly increased in the whey and HMB + Whey protein groups at day 3 compared to pre value (p < 0.05). CK and LDH significantly increased (time effect: p < 0.05) after exercise. However, all data were not significant difference among the groups.

CONCLUSIONS

These results suggest that ingestion of combined HMB and whey protein does not have a role to inhibit muscle strength loss and soreness, and decrease in muscle damage markers after eccentric exercise in comparison with HMB and whey protein alone.

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.

Heterogeneity in resistance training-induced muscle strength and mass responses in men and women of different ages

Physical activity recommendations for public health include typically muscle-strengthening activities for a minimum of 2 days a week. The range of inter-individual variation in responses to resistance training (RT) aiming to improve health and well-being requires to be investigated. The purpose of this study was to quantify high and low responders for RT-induced changes in muscle size and strength and to examine possible effects of age and sex on these responses. Previously collected data of untrained healthy men and women (age 19 to 78 years, n = 287 with 72 controls) were pooled for the present study. Muscle size and strength changed during RT are 4.8 ± 6.1 % (range from -11 to 30 %) and 21.1 ± 11.5 % (range from -8 to 60 %) compared to pre-RT, respectively. Age and sex did not affect to the RT responses. Fourteen percent and 12 % of the subjects were defined as high responders (>1 standard deviation (SD) from the group mean) for the RT-induced changes in muscle size and strength, respectively. When taking into account the results of non-training controls (upper 95 % CI), 29 and 7 % of the subjects were defined as low responders for the RT-induced changes in muscle size and strength, respectively. The muscle size and strength responses varied extensively between the subjects regardless of subject's age and sex. Whether these changes are associated with, e.g., functional capacity and metabolic health improvements due to RT requires further studies.

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.

Body composition and power performance improved after weight reduction in male athletes without hampering hormonal balance

The aim of this study was to investigate the effects of a 4-week weight reduction period with high protein and reduced carbohydrate intake on body composition, explosive power, speed, serum hormones, and acid-base balance in male track and field jumpers and sprinters. Eight participants were assigned to a high weight reduction group (HWR; energy restriction 750 kcal·d) and 7 to a low weight reduction group (LWR; energy restriction 300 kcal·d). Energy and carbohydrate intake decreased significantly (p ≤ 0.05) only in HWR by 740 ± 330 kcal·d and 130 ± 29 g·d, respectively. Furthermore, total body mass and fat mass decreased (p ≤ 0.05) only in HWR by 2.2 ± 1.0 kg and 1.7 ± 1.6 kg, respectively. Fat-free mass (FFM), serum testosterone, cortisol, and sex hormone-binding globulin did not change significantly. Ca ion and pH decreased (p ≤ 0.05) only in HWR (3.1 ± 2.8% and 0.8 ± 0.8%, respectively), whereas (Equation is included in full-text article.)declined (p ≤ 0.05) in both groups by 19.3 ± 6.2% in HWR and by 13.1 ± 8.5% in LWR. The countermovement jump and 20-m sprint time improved consistently (p ≤ 0.05) only in HWR, by 2.6 ± 2.5 cm and 0.04 ± 0.04 seconds, respectively. Finally, athletes with a fat percentage of 10% or more at the baseline were able to preserve FFM. In conclusion, altered acid-base balance but improved weight-bearing power performance was observed without negative consequences on serum hormones and FFM after a 4-week weight reduction of 0.5 kg·wk achieved by reduced carbohydrate but maintained high protein intake.

The effects of whey protein with or without carbohydrates on resistance training adaptations

Background

Nutrition intake in the context of a resistance training (RT) bout may affect body composition and muscle strength. However, the individual and combined effects of whey protein and carbohydrates on long-term resistance training adaptations are poorly understood.

Methods

A four-week preparatory RT period was conducted in previously untrained males to standardize the training background of the subjects. Thereafter, the subjects were randomized into three groups: 30 g of whey proteins (n = 22), isocaloric carbohydrates (maltodextrin, n = 21), or protein + carbohydrates (n = 25). Within these groups, the subjects were further randomized into two whole-body 12-week RT regimens aiming either for muscle hypertrophy and maximal strength or muscle strength, hypertrophy and power. The post-exercise drink was always ingested immediately after the exercise bout, 2–3 times per week depending on the training period. Body composition (by DXA), quadriceps femoris muscle cross-sectional area (by panoramic ultrasound), maximal strength (by dynamic and isometric leg press) and serum lipids as basic markers of cardiovascular health, were analysed before and after the intervention.

Results

Twelve-week RT led to increased fat-free mass, muscle size and strength independent of post-exercise nutrient intake (P < 0.05). However, the whey protein group reduced more total and abdominal area fat when compared to the carbohydrate group independent of the type of RT (P < 0.05). Thus, a larger relative increase (per kg bodyweight) in fat-free mass was observed in the protein vs. carbohydrate group (P < 0.05) without significant differences to the combined group. No systematic effects of the interventions were found for serum lipids. The RT type did not have an effect on the adaptations in response to different supplementation paradigms.

Conclusions

Post-exercise supplementation with whey proteins when compared to carbohydrates or combination of proteins and carbohydrates did not have a major effect on muscle size or strength when ingested two to three times a week. However, whey proteins may increase abdominal fat loss and relative fat-free mass adaptations in response to resistance training when compared to fast-acting carbohydrates.

Eight weeks of pre- and postexercise whey protein supplementation increases lean body mass and improves performance in Division III collegiate female basketball players

We examined if 8 weeks of whey protein (WP) supplementation improved body composition and performance measures in NCAA Division III female basketball players. Subjects were assigned to consume 24 g WP (n = 8; age, 20 ± 2 years; height, 170 ± 6 cm; weight, 66.0 ± 3.1 kg) or 24 g of maltodextrin (MD) (n = 6; age, 21 ± 3 years; height, 169 ± 6 cm; weight, 68.2 ± 7.6 kg) immediately prior to and following training (4 days/week anaerobic and resistance training) for 8 weeks. Prior to (T1) and 8 weeks following supplementation (T2), subjects underwent dual X-ray absorptiometry body composition assessment as well as performance tests. The WP group gained lean mass from T1 to T2 (+1.4 kg, p = 0.003) whereas the MD group trended to gain lean mass (+0.4 kg, p = 0.095). The WP group also lost fat mass from T1 to T2 (-1.0 kg, p = 0.003) whereas the MD group did not (-0.5 kg, p = 0.41). The WP group presented greater gains in 1-repetition maximum (1RM) bench press (+4.9 kg) compared with the MD group (+2.3 kg) (p < 0.05). Moreover, the WP group improved agility from T1 to T2 (p = 0.001) whereas the MD group did not (p = 0.38). Both groups equally increased leg press 1RM, vertical jump, and broad jump performances. This study demonstrates that 8 weeks of WP supplementation improves body composition and select performance variables in previously trained female athletes.

Protein supplementation increases postexercise plasma myostatin concentration after 8 weeks of resistance training in young physically active subjects

Myostatin (MSTN) is a negative regulator of muscle growth even if some studies have shown a counterintuitive positive correlation between MSTN and muscle mass (MM). Our aim was to investigate the influence of 2 months of resistance training (RT) and diets with different protein contents on plasma MSTN, interleukin 1 beta (IL-1β), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and insulin-like growth factor 1 (IGF-1). Eighteen healthy volunteers were randomly divided in two groups: high protein (HP) and normal protein (NP) groups. Different protein diet contents were 1.8 and 0.85 g of protein·kg bw(-1)·day(-1) for HP and NP, respectively. Subjects underwent 8 weeks of standardized progressive RT. MSTN, IGF-1, IL-1β, IL-6, and TNF-α were analyzed before and after the first and the last training sessions. Lean body mass, MM, upper-limb muscle area, and strength were measured. Plasma MSTN showed a significant increase (P<.001) after the last training in the HP group compared with NP group and with starting value. IGF-1 plasma concentration showed a positive correlation with MSTN in HP after the last training (r(2)=0.6456; P=.0295). No significant differences were found between NP and HP for IL-1β, IL-6, TNF-α, and strength and MM or area. These findings suggest a "paradoxical" postexercise increase of plasma MSTN after 8 weeks of RT and HP diets. This MSTN elevation correlates positively with IGF-1 plasma level. This double increase of opposite (catabolic/anabolic) mediators could explain the substantial overlapping of MM increases in the two groups.

Protein supplementation does not alter intramuscular anabolic signaling or endocrine response after resistance exercise in trained men

The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway appears to be the primary regulator of muscle protein synthesis. A variety of stimuli including resistance exercise, amino acids, and hormonal signals activate mTORC1 signaling. The purpose of this study was to investigate the effect of a protein supplement on mTORC1 signaling following a resistance exercise protocol designed to promote elevations in circulating hormone concentrations. We hypothesized that the protein supplement would augment the intramuscular anabolic signaling response. Ten resistance-trained men (age, 24.7 ± 3.4 years; weight, 90.1 ± 11.3 kg; height, 176.0 ± 4.9 cm) received either a placebo or a supplement containing 20 g protein, 6 g carbohydrates, and 1 g fat after high-volume, short-rest lower-body resistance exercise. Blood samples were obtained at baseline, immediately, 30 minutes, 1 hour, 2 hours, and 5 hours after exercise. Fine-needle muscle biopsies were completed at baseline, 1 hour, and 5 hours after exercise. Myoglobin, lactate dehydrogenase, and lactate concentrations were significantly elevated after resistance exercise (P < .0001); however, no differences were observed between trials. Resistance exercise also elicited a significant insulin, growth hormone, and cortisol response (P < .01); however, no differences were observed between trials for insulin-like growth factor-1, insulin, testosterone, growth hormone, or cortisol. Intramuscular anabolic signaling analysis revealed significant elevations in RPS6 phosphorylation after resistance exercise (P = .001); however, no differences were observed between trials for signaling proteins including Akt, mTOR, p70S6k, and RPS6. The endocrine response and phosphorylation status of signaling proteins within the mTORC1 pathway did not appear to be altered by ingestion of supplement after resistance exercise in resistance-trained men.

The metabolic and temporal basis of muscle hypertrophy in response to resistance exercise

Constituting ∼40% of body mass, skeletal muscle has essential locomotory and metabolic functions. As such, an insight into the control of muscle mass is of great importance for maintaining health and quality-of-life into older age, under conditions of cachectic disease and with rehabilitation. In healthy weight-bearing individuals, muscle mass is maintained by the equilibrium between muscle protein synthesis (MPS) and muscle protein breakdown; when this balance tips in favour of MPS hypertrophy occurs. Despite considerable research into pharmacological/nutraceutical interventions, resistance exercise training (RE-T) remains the most potent stimulator of MPS and hypertrophy (in the majority of individuals). However, the mechanism(s) and time course of hypertrophic responses to RE-T remain poorly understood. We would suggest that available data are very much in favour of the notion that the majority of hypertrophy occurs in the early phases of RE-T (though still controversial to some) and that, for the most part, continued gains are hard to come by. Whilst the mechanisms of muscle hypertrophy represent the culmination of mechanical, auto/paracrine and endocrine events, the measurement of MPS remains a cornerstone for understanding the control of hypertrophy - mainly because it is the underlying driving force behind skeletal muscle hypertrophy. Development of sophisticated isotopic techniques (i.e. deuterium oxide) that lend to longer term insight into the control of hypertrophy by sustained RE-T will be paramount in providing insights into the metabolic and temporal regulation of hypertrophy. Such technologies will have broad application in muscle mass intervention for both athletes and for mitigating disease/age-related cachexia and sarcopenia, alike.

Effects of oral phosphatidic acid feeding with or without whey protein on muscle protein synthesis and anabolic signaling in rodent skeletal muscle

Background

Phosphatidic acid (PA) is a diacyl-glycerophospholipid that acts as a signaling molecule in numerous cellular processes. Recently, PA has been proposed to stimulate skeletal muscle protein accretion, but mechanistic studies are lacking. Furthermore, it is unknown whether co-ingesting PA with other leucine-containing ingredients can enhance intramuscular anabolic signaling mechanisms. Thus, the purpose of this study was to examine if oral PA feeding acutely increases anabolic signaling markers and muscle protein synthesis (MPS) in gastrocnemius with and without whey protein concentrate (WPC).

Methods

Overnight fasted male Wistar rats (~250 g) were randomly assigned to four groups: control (CON, n = 6-13), PA (29 mg; n = 8), WPC (197 mg; n = 8), or PA + WPC (n = 8). Three hours post-feeding, gastrocnemius muscle was removed for markers of Akt-mTOR signaling, gene expression patterns related to skeletal muscle mass regulation and metabolism, and MPS analysis via the SUnSET method.

Results

Compared to CON rats, PA, WPC and PA + WPC resulted in a significant elevation in the phosphorylation of mTOR (Ser2481) and rps6 (Ser235/236) (p < 0.05) in the gastrocnemius though there were no differences between the supplemented groups. MPS levels in the gastrocnemius were significantly (p < 0.05) elevated in WPC versus CON rats, and tended to be elevated in PA versus CON rats (p = 0.08), though MPS was less in PA + WPC versus WPC rats (p < 0.05) in spite of robust increases in mTOR pathway activity markers in the former group. C₂C₁₂ myoblast data agreed with the in vivo data herein showing that PA increased MPS levels 51 % (p < 0.001) phosphorylated p70s6k (Thr389) levels 67 % (p < 0.001).

Conclusions

Our results are the first in vivo evidence to demonstrate that PA tends to increases MPS 3 h post-feeding, though PA may delay WPC-mediated MPS kinetics within a 3 h post-feeding window.

Exercise and Gene Expression

Acute and transient changes in gene transcription following a single exercise bout, if reinforced by repeated exercise stimuli, result in the longer lasting effects on protein expression and function that form the basis of skeletal muscle training adaptations. Changes in skeletal muscle gene expression occur in response to multiple stimuli associated with skeletal muscle contraction, various signaling kinases that respond to these stimuli, and numerous downstream pathways and targets of these kinases. In addition, DNA methylation, histone acetylation and phosphorylation, and micro-RNAs can alter gene expression via epigenetic mechanisms. Contemporary studies rely upon "big omics data," in combination with computational and systems biology, to interrogate, and make sense of, the complex interactions underpinning exercise adaptations. The exciting potential is a greater understanding of the integrative biology of exercise.

The effects of protein supplements on muscle mass, strength, and aerobic and anaerobic power in healthy adults: a systematic review

BACKGROUND

Protein supplements are frequently consumed by athletes and recreationally active adults to achieve greater gains in muscle mass and strength and improve physical performance.

OBJECTIVE

This review provides a systematic and comprehensive analysis of the literature that tested the hypothesis that protein supplements accelerate gains in muscle mass and strength resulting in improvements in aerobic and anaerobic power. Evidence statements were created based on an accepted strength of recommendation taxonomy.

DATA SOURCES

English language articles were searched through PubMed and Google Scholar using protein and supplements together with performance, exercise, strength, and muscle, alone or in combination as keywords. Additional articles were retrieved from reference lists found in these papers.

STUDY SELECTION

Studies recruiting healthy adults between 18 and 50 years of age that evaluated the effects of protein supplements alone or in combination with carbohydrate on a performance metric (e.g., one repetition maximum or isometric or isokinetic muscle strength), metrics of body composition, or measures of aerobic or anaerobic power were included in this review. The literature search identified 32 articles which incorporated test metrics that dealt exclusively with changes in muscle mass and strength, 5 articles that implemented combined resistance and aerobic training or followed participants during their normal sport training programs, and 1 article that evaluated changes in muscle oxidative enzymes and maximal aerobic power.

STUDY APPRAISAL AND SYNTHESIS METHODS

All papers were read in detail, and examined for experimental design confounders such as dietary monitoring, history of physical training (i.e., trained and untrained), and the number of participants studied. Studies were also evaluated based on the intensity, frequency, and duration of training, the type and timing of protein supplementation, and the sensitivity of the test metrics.

RESULTS

For untrained individuals, consuming supplemental protein likely has no impact on lean mass and muscle strength during the initial weeks of resistance training. However, as the duration, frequency, and volume of resistance training increase, protein supplementation may promote muscle hypertrophy and enhance gains in muscle strength in both untrained and trained individuals. Evidence also suggests that protein supplementation may accelerate gains in both aerobic and anaerobic power.

LIMITATIONS

To demonstrate measureable gains in strength and performance with exercise training and protein supplementation, many of the studies reviewed recruited untrained participants. Since skeletal muscle responses to exercise and protein supplementation differ between trained and untrained individuals, findings are not easily generalized for all consumers who may be considering the use of protein supplements.

CONCLUSIONS

This review suggests that protein supplementation may enhance muscle mass and performance when the training stimulus is adequate (e.g., frequency, volume, duration), and dietary intake is consistent with recommendations for physically active individuals.

Effects of different doses of leucine ingestion following eight weeks of resistance exercise on protein synthesis and hypertrophy of skeletal muscle in rats

[Purpose]

This study was designed to determine the appropriate Leucine intake volume to obtain the effects of restoring damaged muscle through the synthesis of muscle proteins to increase skeletal muscle and improve exercise performance, and to achieve enhanced muscle hypertrophy.

[Methods]

To clarify the effects of leucine on skeletal muscle hypertrophy of SD rats, following eight weeks of resistance exercise (climbing ladder), the mass of the FHL (Flexor hallucis longus) was measured after extraction, after which change in the activity of muscle signaling proteins (PKB/Akt, mTOR, p70S6K, 4EBP1) was analyzed.

[Results]

The expressions of PKB/Akt, mTOR and p70S6K were increased in L5 (Leucine 50% administration group) compared with the control group (CON) and exercise group (Ex, exercise training group); EL1 (exercise + 10% leucine administration group) and EL5 (exercise + 50% Leucine administration) also exhibited increased expressions of PKB/Akt, mTOR, and p70S6K, while no difference between EL1 and EL5 were observed. No significant differences in 4EBP1 were found among any of the groups. In addition, there were no differences in FHL mass, while relative mass (FHL/body mass) was increased in the exercise group (Ex, EL1, EL5) compared with the control group. No differences were observed among the exercise groups.

[Conclusion]

The present study demonstrated that the relative body mass was increased in the EX group compared with the CON group, while no significant differences in muscle mass could be found among the groups. Even though some signaling proteins were increased, or some differences existed among groups, there were no differences in muscle mass between the leucine administration and exercise training combined with leucine administration groups in the present study.

Is there a need for protein ingestion during exercise?

Dietary protein ingestion following exercise increases muscle protein synthesis rates, stimulates net muscle protein accretion, and facilitates the skeletal muscle adaptive response to prolonged exercise training. Furthermore, recent studies show that protein ingestion before and during exercise also increases muscle protein synthesis rates during resistance- and endurance-type exercise. Therefore, protein ingestion before and during prolonged exercise may represent an effective dietary strategy to enhance the skeletal muscle adaptive response to each exercise session by extending the window of opportunity during which the muscle protein synthetic response is facilitated. Protein ingestion during exercise has also been suggested to improve performance capacity acutely. However, recent studies investigating the impact of protein ingestion during exercise on time trial performance, as opposed to time to exhaustion, do not report ergogenic benefits of protein ingestion. Therefore, it is concluded that protein ingestion with carbohydrate during exercise does not further improve exercise performance when compared with the ingestion of ample amounts of carbohydrate only.

Muscle performance, size, and safety responses after eight weeks of resistance training and protein supplementation: a randomized, double-blinded, placebo-controlled clinical trial

The purpose of this study was to examine the effects of 2 different types of protein supplementation on thigh muscle cross-sectional area (CSA), blood markers, muscular strength, endurance, and body composition after 8 weeks of low- or moderate-volume resistance training in healthy, recreationally trained, college-aged men. One hundred and six men were randomized into 5 groups: low-volume resistance training with bioenhanced whey protein (BWPLV; n = 22), moderate-volume resistance training with BWP (BWPMV; n = 20), moderate-volume resistance training with standard whey protein (SWPMV; n = 22), moderate-volume resistance training with a placebo (PLA; n = 21), or moderate-volume resistance training with no supplementation (CON; n = 21). Except for CON, all groups consumed 1 shake before and after each exercise session and one each on the nontraining day. The BWPLV, BWPMV, and SWPMV groups received approximately 20 g of whey protein per shake, whereas the BWP groups received 5 g of additional polyethylene glycosylated (PEG) leucine. Resistance training sessions were performed 3 times per week for 8 weeks. There were no interactions (p > 0.05) for muscle strength and endurance variables, body composition, muscle CSA, and safety blood markers, but the main effects for training were observed (p ≤ 0.05). However, the Albumin:Globulin ratio for SWPMV was lower (p = 0.037) than BWPLV and BWPMV. Relative protein intake (PROREL) indicated a significant interaction (p < 0.001) with no differences across groups at pre; however, BWPLV, BWPMV, and SWPMV had a greater intake than did PLA or CON at post (p < 0.001). This study indicated that 8 weeks of resistance training improved muscle performance and size similarly among groups regardless of supplementation.

Protein and Essential Amino Acids to Protect Musculoskeletal Health during Spaceflight: Evidence of a Paradox?

Long-duration spaceflight results in muscle atrophy and a loss of bone mineral density. In skeletal muscle tissue, acute exercise and protein (e.g., essential amino acids) stimulate anabolic pathways (e.g., muscle protein synthesis) both independently and synergistically to maintain neutral or positive net muscle protein balance. Protein intake in space is recommended to be 12%-15% of total energy intake (≤1.4 g∙kg-1∙day-1) and spaceflight is associated with reduced energy intake (~20%), which enhances muscle catabolism. Increasing protein intake to 1.5-2.0 g∙kg-1∙day-1 may be beneficial for skeletal muscle tissue and could be accomplished with essential amino acid supplementation. However, increased consumption of sulfur-containing amino acids is associated with increased bone resorption, which creates a dilemma for musculoskeletal countermeasures, whereby optimizing skeletal muscle parameters via essential amino acid supplementation may worsen bone outcomes. To protect both muscle and bone health, future unloading studies should evaluate increased protein intake via non-sulfur containing essential amino acids or leucine in combination with exercise countermeasures and the concomitant influence of reduced energy intake.

Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation

The popularity of natural bodybuilding is increasing; however, evidence-based recommendations for it are lacking. This paper reviewed the scientific literature relevant to competition preparation on nutrition and supplementation, resulting in the following recommendations. Caloric intake should be set at a level that results in bodyweight losses of approximately 0.5 to 1%/wk to maximize muscle retention. Within this caloric intake, most but not all bodybuilders will respond best to consuming 2.3-3.1 g/kg of lean body mass per day of protein, 15-30% of calories from fat, and the reminder of calories from carbohydrate. Eating three to six meals per day with a meal containing 0.4-0.5 g/kg bodyweight of protein prior and subsequent to resistance training likely maximizes any theoretical benefits of nutrient timing and frequency. However, alterations in nutrient timing and frequency appear to have little effect on fat loss or lean mass retention. Among popular supplements, creatine monohydrate, caffeine and beta-alanine appear to have beneficial effects relevant to contest preparation, however others do not or warrant further study. The practice of dehydration and electrolyte manipulation in the final days and hours prior to competition can be dangerous, and may not improve appearance. Increasing carbohydrate intake at the end of preparation has a theoretical rationale to improve appearance, however it is understudied. Thus, if carbohydrate loading is pursued it should be practiced prior to competition and its benefit assessed individually. Finally, competitors should be aware of the increased risk of developing eating and body image disorders in aesthetic sport and therefore should have access to the appropriate mental health professionals.

Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle

Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.

Acute dietary protein intake restriction is associated with changes in myostatin expression after a single bout of resistance exercise in healthy young men

Skeletal muscle satellite cells (SCs) play an important role in the myogenic adaptive response to exercise. It remains to be established whether nutrition plays a role in SC activation in response to exercise. In the present study, we assessed whether dietary protein alters the SC response to a single bout of resistance exercise. Twenty healthy young (aged 21 ± 2 y) males were randomly assigned to consume a 4-d controlled diet that provided either 1.2 g protein ⋅ kg body weight(-1) ⋅ d(-1) [normal protein diet (NPD)] or 0.1 g protein ⋅ kg body weight(-1) ⋅ d(-1) [low protein diet (LPD)]. On the second day of the controlled diet, participants performed a single bout of resistance exercise. Muscle biopsies from the vastus lateralis were collected before and after 12, 24, 48, and 72 h of post-exercise recovery. SC content and activation status were determined using immunohistochemistry. Protein and mRNA expression were determined using Western blotting and reverse transcription polymerase chain reaction. The number of myostatin + SCs decreased significantly at 12, 24, and 48 h (range, -14 to -49%; P < 0.05) after exercise cessation, with no differences between groups. Although the number of myostatin + SCs returned to baseline in the type II fibers on the NPD after 72 h of recovery, the number remained low on the LPD. At the 48 and 72 h time points, myostatin protein expression was elevated (86 ± 26% and 88 ± 29%, respectively) on the NPD (P < 0.05), whereas it was reduced at 72 h (-36 ± 12% compared with baseline) in the LPD group (P < 0.05). This study demonstrates that dietary protein intake does not modulate the post-exercise increase in SC content but modifies myostatin expression in skeletal muscle tissue. This trial was registered at clinicaltrials.gov as NCT01220037.

Ageing has no effect on the regulation of the ubiquitin proteasome-related genes and proteins following resistance exercise

Skeletal muscle atrophy is a critical component of the ageing process. Age-related muscle wasting is due to disrupted muscle protein turnover, a process mediated in part by the ubiquitin proteasome pathway (UPP). Additionally, older subjects have been observed to have an attenuated anabolic response, at both the molecular and physiological levels, following a single-bout of resistance exercise (RE). We investigated the expression levels of the UPP-related genes and proteins involved in muscle protein degradation in 10 older (60–75 years) vs. 10 younger (18–30 years) healthy male subjects at basal as well as 2 h after a single-bout of RE. MURF1, atrogin-1 and FBXO40, their substrate targets PKM2, myogenin, MYOD, MHC and EIF3F as well as MURF1 and atrogin-1 transcriptional regulators FOXO1 and FOXO3 gene and/or protein expression levels were measured via real time PCR and western blotting, respectively. At basal, no age-related difference was observed in the gene/protein levels of atrogin-1, MURF1, myogenin, MYOD and FOXO1/3. However, a decrease in FBXO40 mRNA and protein levels was observed in older subjects, while PKM2 protein was increased. In response to RE, MURF1, atrogin-1 and FBXO40 mRNA were upregulated in both the younger and older subjects, with changes observed in protein levels. In conclusion, UPP-related gene/protein expression is comparably regulated in healthy young and old male subjects at basal and following RE. These findings suggest that UPP signaling plays a limited role in the process of age-related muscle wasting. Future studies are required to investigate additional proteolytic mechanisms in conjunction with skeletal muscle protein breakdown (MPB) measurements following RE in older vs. younger subjects.

Periodized resistance training with and without supplementation improve body composition and performance in older men

PURPOSE

To examine the effects of 12 weeks of periodized resistance training (RT) with and without combined creatine and whey protein supplementation on changes in body composition, muscular strength, and functional performance.

METHODS

Twenty-two male volunteers (68.1 ± 6.1 years) were randomly assigned to one of three groups: RT plus supplementation (RTS, n = 7); RT only (RT, n = 7); or control (C, n = 8). RTS consumed 0.3 g/kg/day of creatine for 5 days followed by 0.07 g/kg/day. RTS also consumed one 35 g liquid protein ready-to-drink daily. RT and RTS trained 3 days/week.

RESULTS

Following 12 weeks of training, there were no significant differences in the main measured outcome variables between RT and RTS. RTS increased relative (% change) lean body mass (LBM, 3.3 ± 3.1 %) compared with C (p = 0.01). Compared to baseline, RT increased LBM at week 6 (60.2 ± 8.3 to 61.6 ± 9.4 kg; p < 0.05), and decreased fat mass (20.8 ± 4.2 to 19.0 ± 3.9 kg; p = 0.05) and percentage body fat at week 12 (25.7 ± 3.8 to 23.8 ± 4.0 %; p = 0.05); RTS increased LBM at week 6 (p < 0.01) and week 12 (56.4 ± 4.3 to 58.2 ± 3.4 kg; p < 0.01), and decreased percentage body fat at week 12 (23.9 ± 4.4 to 22.0 ± 4.4 %; p < 0.01). In addition, compared to C, relative bench press 1-RM increased for RTS (72.4 ± 62.2 %; p < 0.01) and RT (50.1 ± 21.5 %; p = 0.05); relative leg press 1-RM increased for RTS (129.6 ± 39.4 %; p < 0.0001) and RT (112.9 ± 22.7 %; p < 0.0001); RTS increased relative Margaria stair-climbing power (38.3 ± 30.4 %; p < 0.05); and, relative 400-m walk time decreased for RT (-11 ± 9.2 %; p < 0.05) and RTS (-9.6 ± 9.4 %; p = 0.05). RT increased estimated VO2Max at week 6 (p < 0.01) and 12 (34.6 ± 1.9 to 36.4 ± 2.7 ml/kg/min; p = 0.01) compared to baseline. Lastly, RTS increased estimated VO2Max at week 12 (36.3 ± 2.7 to 37.5 ± 3.3 ml/kg/min; p = 0.05) compared to baseline.

CONCLUSION

Creatine and whey protein supplementation may not provide additional benefits in older adults performing periodized RT to augment muscular and functional performance.

Influence of divergent exercise contraction mode and whey protein supplementation on atrogin-1, MuRF1, and FOXO1/3A in human skeletal muscle

Knowledge from human exercise studies on regulators of muscle atrophy is lacking, but it is important to understand the underlying mechanisms influencing skeletal muscle protein turnover and net protein gain. This study examined the regulation of muscle atrophy-related factors, including atrogin-1 and MuRF1, their upstream transcription factors FOXO1 and FOXO3A and the atrogin-1 substrate eIF3-f, in response to unilateral isolated eccentric (ECC) vs. concentric (CONC) exercise and training. Exercise was performed with whey protein hydrolysate (WPH) or isocaloric carbohydrate (CHO) supplementation. Twenty-four subjects were divided into WPH and CHO groups and completed both single-bout exercise and 12 wk of training. Single-bout ECC exercise decreased atrogin-1 and FOXO3A mRNA compared with basal and CONC exercise, while MuRF1 mRNA was upregulated compared with basal. ECC exercise downregulated FOXO1 and phospho-FOXO1 protein compared with basal, and phospho-FOXO3A was downregulated compared with CONC. CONC single-bout exercise mediated a greater increase in MuRF1 mRNA and increased FOXO1 mRNA compared with basal and ECC. CONC exercise downregulated FOXO1, FOXO3A, and eIF3-f protein compared with basal. Following training, an increase in basal phospho-FOXO1 was observed. While WPH supplementation with ECC and CONC training further increased muscle hypertrophy, it did not have an additional effect on mRNA or protein levels of the targets measured. In conclusion, atrogin-1, MuRF1, FOXO1/3A, and eIF3-f mRNA, and protein levels, are differentially regulated by exercise contraction mode but not WPH supplementation combined with hypertrophy-inducing training. This highlights the complexity in understanding the differing roles these factors play in healthy muscle adaptation to exercise.

Synergistic effects of resistance training and protein intake: practical aspects

Resistance training is a potent stimulus to increase skeletal muscle mass. The muscle protein accretion process depends on a robust synergistic action between protein intake and overload. The intake of protein after resistance training increases plasma amino acids, which results in the activation of signaling molecules leading to increased muscle protein synthesis (MPS) and muscle hypertrophy. Although both essential and non-essential amino acids are necessary for hypertrophy, the intake of free L-leucine or high-leucine whole proteins has been specifically shown to increase the initiation of translation that is essential for elevated MPS. The literature supports the use of protein intake following resistance-training sessions to enhance MPS; however, less understood are the effects of different protein sources and timing protocols on MPS. The sum of the adaptions from each individual training session is essential to muscle hypertrophy, and thus highlights the importance of an optimal supplementation protocol. The aim of this review is to present recent findings reported in the literature and to discuss the practical application of these results. In that light, new speculations and questions will arise that may direct future investigations. The information and recommendations generated in this review should be of benefit to clinical dietitians as well as those engaged in sports.

Whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in human skeletal muscle

PURPOSE

Protein ingestion after resistance exercise increases muscle protein synthesis (MPS) in a dose-dependent manner. However, the molecular mechanism(s) for the dose-dependency of MPS remains unclear. This study aimed to determine the dose response of mammalian target of rapamycin (mTOR) signaling in muscle with ingestion of protein after resistance exercise.

METHODS

Fifteen male subjects performed four sets of six unilateral isokinetic concentric knee extensions. Immediately after exercise, eight subjects consumed water only. The other seven subjects, in a randomized-order crossover design, took either a 10 [3.6 g essential amino acids (EAA)] or 20 g (7.1 g EAA) solution of whey protein. Muscle biopsies from the vastus lateralis muscle were taken 30 min before and 1 h after resistance exercise. Phosphorylation of Akt (Ser473), mTOR (Ser2448), 4E-BP1 (Thr37/46), and S6K1 (Thr389) was measured by western blotting.

RESULTS

Concentric knee extension exercise alone did not increase phosphorylation of Akt and mTOR 1 h after exercise, but ingesting protein after exercise significantly increased the phosphorylation of Akt and mTOR in a dose-dependent manner (P < 0.05). 4E-BP1 phosphorylation significantly decreased after resistance exercise (P < 0.05), but subjects who took 10 or 20 g of protein after exercise showed increased 4E-BP1 from post-exercise dephosphorylation (P < 0.05). S6K1 phosphorylation significantly increased after resistance exercise (P < 0.05), and 20 g of protein further increased S6K1 phosphorylation compared with ingestion of 10 g (P < 0.05).

CONCLUSIONS

These findings suggest that whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in untrained men.

The effect of protein timing on muscle strength and hypertrophy: a meta-analysis

Protein timing is a popular dietary strategy designed to optimize the adaptive response to exercise. The strategy involves consuming protein in and around a training session in an effort to facilitate muscular repair and remodeling, and thereby enhance post-exercise strength- and hypertrophy-related adaptations. Despite the apparent biological plausibility of the strategy, however, the effectiveness of protein timing in chronic training studies has been decidedly mixed. The purpose of this paper therefore was to conduct a multi-level meta-regression of randomized controlled trials to determine whether protein timing is a viable strategy for enhancing post-exercise muscular adaptations. The strength analysis comprised 478 subjects and 96 ESs, nested within 41 treatment or control groups and 20 studies. The hypertrophy analysis comprised 525 subjects and 132 ESs, nested with 47 treatment or control groups and 23 studies. A simple pooled analysis of protein timing without controlling for covariates showed a small to moderate effect on muscle hypertrophy with no significant effect found on muscle strength. In the full meta-regression model controlling for all covariates, however, no significant differences were found between treatment and control for strength or hypertrophy. The reduced model was not significantly different from the full model for either strength or hypertrophy. With respect to hypertrophy, total protein intake was the strongest predictor of ES magnitude. These results refute the commonly held belief that the timing of protein intake in and around a training session is critical to muscular adaptations and indicate that consuming adequate protein in combination with resistance exercise is the key factor for maximizing muscle protein accretion.

Nutrient Timing

As the incidence rate of lifestyle-related chronic conditions such as cardiovascular disease, obesity, and type 2 diabetes continues to increase, the importance of regular exercise and a healthy diet for improving or maintaining good health is critical. Exercise training is known to improve fitness and many health risk factors, as well as to improve the performance of competitive athletes. It has become increasingly clear, however, that nutrient intake before, during, and after exercise sessions has a powerful influence on the adaptive response to the exercise stimuli. In this review, the science behind nutrient timing will be discussed as it relates to exercise performance, recovery, and training adaptation. Evidence will be provided that validates intake of appropriate nutrients before, during, and immediately after exercise not only to improve exercise performance but also to maximize the training response. Ultimately, the combined response to exercise and proper nutrient intake leads to not only better performance in athletes but also greater health benefits for all exercisers.

Are skeletal muscle FNDC5 gene expression and irisin release regulated by exercise and related to health?

Recently, contradictory findings have been reported concerning the function of irisin and its precursor gene, skeletal muscle FNDC5, in energy homeostasis, and the associated regulatory role of exercise and PGC-1α. We therefore evaluated whether muscle FNDC5 mRNA and serum irisin are exercise responsive and whether PGC-1α expression is associated with FNDC5 expression. The male subjects in the study performed single exercises: (1) 1 h low-intensity aerobic exercise (AE) (middle-aged, n = 17), (2) a heavy-intensity resistance exercise (RE) bout (young n = 10, older n = 11) (27 vs. 62 years), (3) long-term 21 weeks endurance exercise (EE) training alone (twice a week, middle-aged, n = 9), or (4) combined EE and RE training (both twice a week, middle-aged, n = 9). Skeletal muscle mRNA expression was analysed by quantitative PCR and serum irisin by ELISA. No significant changes were observed in skeletal muscle PGC-1α, FNDC5 and serum irisin after AE, EE training or combined EE + RE training. However, a single RE bout increased PGC-1α by 4-fold in young and by 2-fold in older men, while FNDC5 mRNA only increased in young men post-RE, by 1.4-fold. Changes in PGC-1α or serum irisin were not consistently accompanied by changes in FNDC5. In conclusion, for the most part, neither longer-term nor single exercise markedly increases skeletal muscle FNDC5 expression or serum irisin. Therefore their changes in response to exercise are probably random and not consistent excluding the confirmation of any definitive link between exercise and FNDC5 expression and irisin release in humans. Moreover, irisin and FNDC5 were not associated with glucose tolerance and being overweight, or with metabolic disturbances, respectively. Finally, factor(s) other than PGC-1α and transcription may regulate FNDC5 expression.

Resistance exercise and the mechanisms of muscle mass regulation in humans: acute effects on muscle protein turnover and the gaps in our understanding of chronic resistance exercise training adaptation

Increasing muscle mass is important when attempting to maximize sports performance and achieve physique augmentation. However, the preservation of muscle mass is essential to maintaining mobility and quality of life with aging, and also impacts on our capacity to recover from illness. Nevertheless, our understanding of the processes that regulate muscle mass in humans during resistance exercise training, chronic disuse and rehabilitation training following atrophy remains very unclear. Here, we report on some of the recent developments in the study of those processes thought to be responsible for governing human muscle protein turnover in response to intense physical activity. Specifically, the effects of acute and chronic resistance exercise in healthy volunteers and also in response to rehabilitation resistance exercise training following muscle atrophy will be discussed, with discrepancies and gaps in our understanding highlighted. In particular, ubiquitin-proteasome mediated muscle proteolysis (Muscle Atrophy F-box/Atrogin-1 and Muscle RING Finger 1), translation initiation of muscle protein synthesis (mammalian target of rapamycin signaling), and satellite cell mediated myogenesis are highlighted as pathways of special relevance to muscle protein metabolism in response to acute resistance exercise. Furthermore, research focused on quantifying signaling and molecular events that modulate muscle protein synthesis and protein degradation under conditions of chronic resistance training is highlighted as being urgently needed to improve knowledge gaps. These studies need to include multiple time-point measurements over the course of any training intervention and must include dynamic measurements of muscle protein synthesis and degradation and sensitive measures of muscle mass. This article is part of a Directed Issue entitled Molecular basis of muscle wasting.

Whey protein does not enhance the adaptations to elbow flexor resistance training

PURPOSE

It is unclear whether protein supplementation augments the gains in muscle strength and size observed after resistance training (RT) because limitations to previous studies include small cohorts, imprecise measures of muscle size and strength, and no control of prior exercise or habitual protein intake. We aimed to determine whether whey protein supplementation affected RT-induced changes in elbow flexor muscle strength and size.

METHODS

We pair-matched 33 previously untrained, healthy young men for their habitual protein intake and strength response to 3-wk RT without nutritional supplementation (followed by 6 wk of no training) and then randomly assigned them to protein (PRO, n = 17) or placebo (PLA, n = 16) groups. Participants subsequently performed elbow flexor RT 3 d · wk(-1) for 12 wk and consumed PRO or PLA immediately before and after each training session. We assessed elbow flexor muscle strength (unilateral 1-repetition maximum and isometric maximum voluntary force) and size (total volume and maximum anatomical cross-sectional area determined with magnetic resonance imaging) before and after the 12-wk RT.

RESULTS

PRO and PLA demonstrated similar increases in muscle volume (PRO 17.0% ± 7.1% vs PLA 14.9% ± 4.6%, P = 0.32), anatomical cross-sectional area (PRO 16.2% ± 7.1% vs PLA 15.6% ± 4.4%, P = 0.80), 1-repetition maximum (PRO 41.8% ± 21.2% vs PLA 41.4% ± 19.9%, P = 0.97), and maximum voluntary force (PRO 12.0% ± 9.9% vs PLA 14.5% ± 8.3%, P = 0.43).

CONCLUSIONS

In the context of this study, protein supplementation did not augment elbow flexor muscle strength and size changes that occurred after 12 wk of RT.

Effect of resistance exercise contraction mode and protein supplementation on members of the STARS signalling pathway

The striated muscle activator of Rho signalling (STARS) pathway is suggested to provide a link between external stress responses and transcriptional regulation in muscle. However, the sensitivity of STARS signalling to different mechanical stresses has not been investigated. In a comparative study, we examined the regulation of the STARS signalling pathway in response to unilateral resistance exercise performed as either eccentric (ECC) or concentric (CONC) contractions as well as prolonged training; with and without whey protein supplementation. Skeletal muscle STARS, myocardian-related transcription factor-A (MRTF-A) and serum response factor (SRF) mRNA and protein, as well as muscle cross-sectional area and maximal voluntary contraction, were measured. A single-bout of exercise produced increases in STARS and SRF mRNA and decreases in MRTF-A mRNA with both ECC and CONC exercise, but with an enhanced response occurring following ECC exercise. A 31% increase in STARS protein was observed exclusively after CONC exercise (P < 0.001), while pSRF protein levels increased similarly by 48% with both CONC and ECC exercise (P < 0.001). Prolonged ECC and CONC training equally stimulated muscle hypertrophy and produced increases in MRTF-A protein of 125% and 99%, respectively (P < 0.001). No changes occurred for total SRF protein. There was no effect of whey protein supplementation. These results show that resistance exercise provides an acute stimulation of the STARS pathway that is contraction mode dependent. The responses to acute exercise were more pronounced than responses to accumulated training, suggesting that STARS signalling is primarily involved in the initial phase of exercise-induced muscle adaptations.

Skeletal muscle molecular responses to resistance training and dietary supplementation in COPD

BACKGROUND

Skeletal muscle dysfunction is a systemic feature of chronic obstructive pulmonary disease (COPD), contributing to morbidity and mortality. Physical training improves muscle mass and function in COPD, but the molecular regulation therein is poorly understood.

METHODS

Candidate genes and proteins regulating muscle protein breakdown (ubiquitin proteasome pathway), muscle protein synthesis (phosphatidylinositol 3 kinase/Akt/mammalian target of rapamycin pathway), myogenesis (MyoD, myogenin and myostatin) and transcription (FOXO1, FOXO3 and RUNX1) were determined in quadriceps muscle samples taken at four time points over 8 weeks of knee extensor resistance training (RT) in patients with COPD and healthy controls (HCs). Patients with COPD were randomly allocated to receive protein/carbohydrate or placebo supplements during RT.

RESULTS

59 patients with COPD (mean (SD) age 68.0 (9.3) years, forced expiratory volume in 1 s (FEV1) 46.9 (17.8) % predicted) and 21 HCs (66.1 (4.8) years, 105.0 (21.6) % predicted) were enrolled. RT increased lean mass (~5%) and strength (~20%) in all groups. Absolute work done during RT was lower throughout in patients with COPD compared with HCs. RT resulted in increases (from basal) in catabolic, anabolic, myogenic and transcription factor protein expression at 24 h, 4 weeks and 8 weeks of exercise in HCs. This response was blunted in patients with COPD, except for myogenic signalling, which was similar. Nutritional supplementation did not augment functional or molecular responses to RT.

CONCLUSIONS

The potential for muscle rehabilitation in response to RT is preserved in COPD. Except for markers of myogenesis, molecular responses to RT are not tightly coupled to lean mass gains but reflect the lower work done during RT, suggesting some caution when identifying molecular targets for intervention. Increasing post-exercise protein and carbohydrate intake is not a prerequisite for a normal training response in COPD.

Effects of whey proteins and carbohydrates on the efficacy of resistance training in elderly people: double blind, randomised controlled trial

BACKGROUND/OBJECTIVES

A few previous studies indicate that protein supplementation increases gains in muscle mass and strength during a resistance exercise program. The purpose of this study was to investigate whether whey protein supplementation results in greater increases in lean body mass, muscle strength and physical function in elderly individuals during 12 weeks of resistance exercise when compared to isocaloric carbohydrate supplementation.

SUBJECTS/METHODS

A total of 161 men and women, 65-91 years old, participated in a randomized, controlled, double-blind intervention study, involving dietary supplementation and a 12-week resistance exercise program, designed to increase muscle mass and strength of all major muscle groups. Participants exercised three times a week and received either 20 g of whey protein (n=83) or isocaloric carbohydrate (n=78) in liquid form immediately after each workout. Data were obtained at baseline and end point.

RESULTS

The primary outcomes, lean body mass, strength and physical function increased significantly during the course of the study. Type of dietary supplementation did not influence gains in lean body mass (P=0.365), quadriceps strength (P=0.776) or performance during a 6-min walk (P=0.726) or a timed up-and-go test (P=0.151). Twenty participants discontinued the intervention.

CONCLUSIONS

Ingestion of 20 g of whey protein immediately after resistance exercise three times per week, does not lead to greater gains in lean body mass, strength and physical function in elderly people with sufficient energy and protein intakes when compared to isocaloric carbohydrate.

Nutrient timing revisited: is there a post-exercise anabolic window?

Nutrient timing is a popular nutritional strategy that involves the consumption of combinations of nutrients--primarily protein and carbohydrate--in and around an exercise session. Some have claimed that this approach can produce dramatic improvements in body composition. It has even been postulated that the timing of nutritional consumption may be more important than the absolute daily intake of nutrients. The post-exercise period is widely considered the most critical part of nutrient timing. Theoretically, consuming the proper ratio of nutrients during this time not only initiates the rebuilding of damaged muscle tissue and restoration of energy reserves, but it does so in a supercompensated fashion that enhances both body composition and exercise performance. Several researchers have made reference to an anabolic “window of opportunity” whereby a limited time exists after training to optimize training-related muscular adaptations. However, the importance - and even the existence - of a post-exercise ‘window’ can vary according to a number of factors. Not only is nutrient timing research open to question in terms of applicability, but recent evidence has directly challenged the classical view of the relevance of post-exercise nutritional intake with respect to anabolism. Therefore, the purpose of this paper will be twofold: 1) to review the existing literature on the effects of nutrient timing with respect to post-exercise muscular adaptations, and; 2) to draw relevant conclusions that allow practical, evidence-based nutritional recommendations to be made for maximizing the anabolic response to exercise.

High-intensity interval training increases in vivo oxidative capacity with no effect on P(i)→ATP rate in resting human muscle

Mitochondrial ATP production is vital for meeting cellular energy demand at rest and during periods of high ATP turnover. We hypothesized that high-intensity interval training (HIT) would increase ATP flux in resting muscle (VPi→ATP) in response to a single bout of exercise, whereas changes in the capacity for oxidative ATP production (Vmax) would require repeated bouts. Eight untrained men (27 ± 4 yr; peak oxygen uptake = 36 ± 4 ml·kg(-1)·min(-1)) performed six sessions of HIT (4-6 × 30-s bouts of all-out cycling with 4-min recovery). After standardized meals and a 10-h fast, VPi→ATP and Vmax of the vastus lateralis muscle were measured using phosphorus magnetic resonance spectroscopy at 4 Tesla. Measurements were obtained at baseline, 15 h after the first training session, and 15 h after completion of the sixth session. VPi→ATP was determined from the unidirectional flux between Pi and ATP, using the saturation transfer technique. The rate of phosphocreatine recovery (kPCr) following a maximal contraction was used to calculate Vmax. While kPCr and Vmax were unchanged after a single session of HIT, completion of six training sessions resulted in a ∼14% increase in muscle oxidative capacity (P ≤ 0.004). In contrast, neither a single nor six training sessions altered VPi→ATP (P = 0.74). This novel analysis of resting and maximal high-energy phosphate kinetics in vivo in response to HIT provides evidence that distinct aspects of human skeletal muscle metabolism respond differently to this type of training.

Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training

The purpose of this review was to determine whether past research provides conclusive evidence about the effects of type and timing of ingestion of specific sources of protein by those engaged in resistance weight training. Two essential, nutrition-related, tenets need to be followed by weightlifters to maximize muscle hypertrophy: the consumption of 1.2-2.0 g protein.kg -1 of body weight, and ≥44-50 kcal.kg-1 of body weight. Researchers have tested the effects of timing of protein supplement ingestion on various physical changes in weightlifters. In general, protein supplementation pre- and post-workout increases physical performance, training session recovery, lean body mass, muscle hypertrophy, and strength. Specific gains, differ however based on protein type and amounts. Studies on timing of consumption of milk have indicated that fat-free milk post-workout was effective in promoting increases in lean body mass, strength, muscle hypertrophy and decreases in body fat. The leucine content of a protein source has an impact on protein synthesis, and affects muscle hypertrophy. Consumption of 3-4 g of leucine is needed to promote maximum protein synthesis. An ideal supplement following resistance exercise should contain whey protein that provides at least 3 g of leucine per serving. A combination of a fast-acting carbohydrate source such as maltodextrin or glucose should be consumed with the protein source, as leucine cannot modulate protein synthesis as effectively without the presence of insulin. Such a supplement post-workout would be most effective in increasing muscle protein synthesis, resulting in greater muscle hypertrophy and strength. In contrast, the consumption of essential amino acids and dextrose appears to be most effective at evoking protein synthesis prior to rather than following resistance exercise. To further enhance muscle hypertrophy and strength, a resistance weight- training program of at least 10-12 weeks with compound movements for both upper and lower body exercises should be followed.

Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis

BACKGROUND

Protein ingestion after a single bout of resistance-type exercise stimulates net muscle protein accretion during acute postexercise recovery. Consequently, it is generally accepted that protein supplementation is required to maximize the adaptive response of the skeletal muscle to prolonged resistance-type exercise training. However, there is much discrepancy in the literature regarding the proposed benefits of protein supplementation during prolonged resistance-type exercise training in younger and older populations.

OBJECTIVE

The objective of the study was to define the efficacy of protein supplementation to augment the adaptive response of the skeletal muscle to prolonged resistance-type exercise training in younger and older populations.

DESIGN

A systematic review of interventional evidence was performed through the use of a random-effects meta-analysis model. Data from the outcome variables fat-free mass (FFM), fat mass, type I and II muscle fiber cross-sectional area, and 1 repetition maximum (1-RM) leg press strength were collected from randomized controlled trials (RCTs) investigating the effect of dietary protein supplementation during prolonged (>6 wk) resistance-type exercise training.

RESULTS

Data were included from 22 RCTs that included 680 subjects. Protein supplementation showed a positive effect for FFM (weighted mean difference: 0.69 kg; 95% CI: 0.47, 0.91 kg; P < 0.00001) and 1-RM leg press strength (weighted mean difference: 13.5 kg; 95% CI: 6.4, 20.7 kg; P < 0.005) compared with a placebo after prolonged resistance-type exercise training in younger and older subjects.

CONCLUSION

Protein supplementation increases muscle mass and strength gains during prolonged resistance-type exercise training in both younger and older subjects.

Dietary protein to maximize resistance training: a review and examination of protein spread and change theories

An appreciable volume of human clinical data supports increased dietary protein for greater gains from resistance training, but not all findings are in agreement. We recently proposed "protein spread theory" and "protein change theory" in an effort to explain discrepancies in the response to increased dietary protein in weight management interventions. The present review aimed to extend "protein spread theory" and "protein change theory" to studies examining the effects of protein on resistance training induced muscle and strength gains. Protein spread theory proposed that there must have been a sufficient spread or % difference in g/kg/day protein intake between groups during a protein intervention to see muscle and strength differences. Protein change theory postulated that for the higher protein group, there must be a sufficient change from baseline g/kg/day protein intake to during study g/kg/day protein intake to see muscle and strength benefits. Seventeen studies met inclusion criteria. In studies where a higher protein intervention was deemed successful there was, on average, a 66.1% g/kg/day between group intake spread versus a 10.2% g/kg/day spread in studies where a higher protein diet was no more effective than control. The average change in habitual protein intake in studies showing higher protein to be more effective than control was +59.5% compared to +6.5% when additional protein was no more effective than control. The magnitudes of difference between the mean spreads and changes of the present review are similar to our previous review on these theories in a weight management context. Providing sufficient deviation from habitual intake appears to be an important factor in determining the success of additional protein in enhancing muscle and strength gains from resistance training. An increase in dietary protein favorably effects muscle and strength during resistance training.

Resistance training induced increase in muscle fiber size in young and older men

Muscle strength and mass decline in sedentary individuals with aging. The present study investigated the effects of both age and 21 weeks of progressive hypertrophic resistance training (RT) on skeletal muscle size and strength, and on myostatin and myogenin mRNA expression in 21 previously untrained young men (26.0 ± 4.3 years) and 18 older men (61.2 ± 4.1 years) and age-matched controls. Vastus lateralis muscle biopsies were taken before and after RT. Type I and type II muscle fiber cross-sectional areas increased more in young men than in older men after RT (P < 0.05). Concentric leg extension increased (P < 0.05) more after 10.5 weeks in young men compared to older men, but after 21 weeks no statistical differences existed. The daily energy and protein intake were greater (P < 0.001) in young subjects. Both myostatin and myogenin mRNA expression increased in older when compared with young men after RT (P < 0.05). In conclusion, after RT, muscle fiber size increased less in older compared to young men. This was associated with lower protein and energy intake and increases in myostatin gene expression in older when compared to young men.