Molecular Differences in Skeletal Muscle After 1 Week of Active vs. Passive Recovery From High-Volume Resistance Training.

ABSTRACT: Vann, CG, Haun, CT, Osburn, SC, Romero, MA, Roberson, PA, Mumford, PW, Mobley, CB, Holmes, HM, Fox, CD, Young, KC, and Roberts, MD. Molecular differences in skeletal muscle after 1 week of active vs. passive recovery from high-volume resistance training. J Strength Cond Res 35(8): 2102-2113, 2021-Numerous studies have evaluated how deloading after resistance training (RT) affects strength and power outcomes. However, the molecular adaptations that occur after deload periods remain understudied. Trained, college-aged men (n = 30) performed 6 weeks of whole-body RT starting at 10 sets of 10 repetitions per exercise per week and finishing at 32 sets of 10 repetitions per exercise per week. After this period, subjects performed either active (AR; n = 16) or passive recovery (PR; n = 14) for 1 week where AR completed ∼15% of the week 6 training volume and PR ceased training. Variables related to body composition and recovery examined before RT (PRE), after 6 weeks of RT (POST), and after the 1-week recovery period (DL). Vastus lateralis (VL) muscle biopsies and blood samples were collected at each timepoint, and various biochemical and histological assays were performed. Group × time interactions (p < 0.05) existed for skeletal muscle myosin heavy chain (MHC)-IIa mRNA (AR > PR at POST and DL) and 20S proteasome activity (post-hoc tests revealed no significance in groups over time). Time effects (P < 0.05) existed for total mood disturbance and serum creatine kinase and mechano growth factor mRNA (POST > PRE &D L), VL pressure to pain threshold and MHC-IIx mRNA (PRE&DL > POST), Atrogin-1 and MuRF-1 mRNA (PRE < POST < DL), MHC-I mRNA (PRE < POST & DL), myostatin mRNA (PRE & POST < DL), and mechanistic target of rapamycin (PRE > POST & DL). No interactions or time effects were observed for barbell squat velocity, various hormones, histological metrics, polyubiquitinated proteins, or phosphorylated/pan protein levels of 4E-BP1, p70S6k, and AMPK. One week of AR after a high-volume training block instigates marginal molecular differences in skeletal muscle relative to PR. From a practical standpoint, however, both paradigms elicited largely similar responses.

An intron variant of the GLI family zinc finger 3 (GLI3) gene differentiates resistance training-induced muscle fiber hypertrophy in younger men.

We examined the association between genotype and resistance training-induced changes (12 wk) in dual x-ray energy absorptiometry (DXA)-derived lean soft tissue mass (LSTM) as well as muscle fiber cross-sectional area (fCSA; vastus lateralis; n = 109; age = 22 ± 2 y, BMI = 24.7 ± 3.1 kg/m2 ). Over 315 000 genetic polymorphisms were interrogated from muscle using DNA microarrays. First, a targeted investigation was performed where single nucleotide polymorphisms (SNP) identified from a systematic literature review were related to changes in LSTM and fCSA. Next, genome-wide association (GWA) studies were performed to reveal associations between novel SNP targets with pre- to post-training change scores in mean fCSA and LSTM. Our targeted investigation revealed no genotype-by-time interactions for 12 common polymorphisms regarding the change in mean fCSA or change in LSTM. Our first GWA study indicated no SNP were associated with the change in LSTM. However, the second GWA study indicated two SNP exceeded the significance level with the change in mean fCSA (P = 6.9 × 10-7 for rs4675569, 1.7 × 10-6 for rs10263647). While the former target is not annotated (chr2:205936846 (GRCh38.p12)), the latter target (chr7:41971865 (GRCh38.p12)) is an intron variant of the GLI Family Zinc Finger 3 (GLI3) gene. Follow-up analyses indicated fCSA increases were greater in the T/C and C/C GLI3 genotypes than the T/T GLI3 genotype (P < .05). Data from the Auburn cohort also revealed participants with the T/C and C/C genotypes exhibited increases in satellite cell number with training (P < .05), whereas T/T participants did not. Additionally, those with the T/C and C/C genotypes achieved myonuclear addition in response to training (P < .05), whereas the T/T participants did not. In summary, this is the first GWA study to examine how polymorphisms associate with the change in hypertrophy measures following resistance training. Future studies are needed to determine if the GLI3 variant differentiates hypertrophic responses to resistance training given the potential link between this gene and satellite cell physiology.

Frequent Manipulation of Resistance Training Variables Promotes Myofibrillar Spacing Changes in Resistance-Trained Individuals.

We sought to determine if manipulating resistance training (RT) variables differentially altered the expression of select sarcoplasmic and myofibril proteins as well as myofibrillar spacing in myofibers. Resistance-trained men (n = 20; 26 ± 3 years old) trained for 8 weeks where a randomized leg performed either a standard (CON) or variable RT protocol (VAR: manipulation of load, volume, muscle action, and rest intervals at each RT session). A pre-training (PRE) vastus lateralis biopsy was obtained from a randomized single leg, and biopsies were obtained from both legs 96 h following the last training bout. The sarcoplasmic protein pool was assayed for proteins involved in energy metabolism, and the myofibril protein pool was assayed for relative myosin heavy chain (MHC) and actin protein abundances. Sections were also histologically analyzed to obtain myofibril spacing characteristics. VAR resulted in ~12% greater volume load (VL) compared to CON (p < 0.001). The mean fiber cross-sectional area increased following both RT protocols [CON: 14.6% (775.5 µm2), p = 0.006; VAR: 13.9% (743.2 µm2), p = 0.01 vs. PRE for both], but without significant differences between protocols (p = 0.79). Neither RT protocol affected a majority of assayed proteins related to energy metabolism, but both training protocols increased hexokinase 2 protein levels and decreased a mitochondrial beta-oxidation marker (VLCAD protein; p < 0.05). Citrate synthase activity levels increased with CON RT (p < 0.05), but not VAR RT. The relative abundance of MHC (summed isoforms) decreased with both training protocols (p < 0.05). However, the relative abundance of actin protein (summed isoforms) decreased with VAR only (13.5 and 9.0%, respectively; p < 0.05). A decrease in percent area occupied by myofibrils was observed from PRE to VAR (-4.87%; p = 0.048), but not for the CON (4.53%; p = 0.979). In contrast, there was an increase in percent area occupied by non-contractile space from PRE to VAR (10.14%; p = 0.048), but not PRE to CON (0.72%; p = 0.979). In conclusion, while both RT protocols increased muscle fiber hypertrophy, a higher volume-load where RT variables were frequently manipulated increased non-contractile spacing in resistance-trained individuals.

The effects of resistance training with or without peanut protein supplementation on skeletal muscle and strength adaptations in older individuals.

Several studies suggest resistance training (RT) while supplementing with various protein supplements can enhance strength and muscle mass in older individuals. However, to date, no study has examined the effects of RT with a peanut protein powder (PP) supplement on these outcomes. Herein, 39 older, untrained individuals (n = 17 female, n = 22 male; age = 58.6 ± 8.0 years; body mass index =28.7 ± 5.8) completed a 6-week (n = 22) or 10-week (n = 17) RT program, where full-body training was implemented twice weekly (ClinicalTrials.gov trial registration NCT04015479; registered July 11, 2019). Participants in each program were randomly assigned to consume either a PP supplement once per day (75 total g powder providing 30 g protein, > 9.2 g essential amino acids, ~ 315 kcal; n = 20) or no supplement (CTL; n = 19). Right leg vastus lateralis (VL) muscle biopsies were obtained prior to and 24 h following the first training bout in all participants to assess the change in myofibrillar protein synthetic rates (MyoPS) as measured via the deuterium-oxide (D2O) tracer method. Pre- and Post-intervention testing in all participants was conducted using dual energy x-ray absorptiometry (DXA), VL ultrasound imaging, a peripheral quantitative computed tomography (pQCT) scan at the mid-thigh, and right leg isokinetic dynamometer assessments. Integrated MyoPS rates over a 24-h period were not significantly different (p < 0.05) between supplement groups following the first training bout. Regarding chronic changes, there were no significant supplement-by-time interactions in DXA-derived fat mass, lean soft tissue mass or percent body fat between supplementation groups. There was, however, a significant increase in VL thickness in PP versus CTL participants when the 6- and 10-week cohorts were pooled (interaction p = 0.041). There was also a significant increase in knee flexion torque in the 10-week PP group versus the CTL group (interaction p = 0.032). In conclusion, a higher-protein, defatted peanut powder supplement in combination with RT positively affects select markers of muscle hypertrophy and strength in an untrained, older adult population. Moreover, subanalyses indicated that gender did not play a role in these adaptations.

A Theacrine-Based Supplement Increases Cellular NAD+ Levels and Affects Biomarkers Related to Sirtuin Activity in C2C12 Muscle Cells In Vitro.

There is evidence in rodents to suggest that theacrine-based supplements modulate tissue sirtuin activity as well as other biological processes associated with aging. Herein, we examined if a theacrine-based supplement (termed NAD3) altered sirtuin activity in vitro while also affecting markers of mitochondrial biogenesis. The murine C2C12 myoblast cell line was used for experimentation. Following 7 days of differentiation, myotubes were treated with 0.45 mg/mL of NAD3 (containing ~2 mM theacrine) for 3 and 24 h (n = 6 treatment wells per time point). Relative to control (CTL)-treated cells, NAD3 treatments increased (p < 0.05) Sirt1 mRNA levels at 3 h, as well as global sirtuin activity at 3 and 24 h. Follow-up experiments comparing 24 h NAD3 or CTL treatments indicated that NAD3 increased nicotinamide phosphoribosyltransferase (NAMPT) and SIRT1 protein levels (p < 0.05). Cellular nicotinamide adenine dinucleotide (NAD+) levels were also elevated nearly two-fold after 24 h of NAD3 versus CTL treatments (p < 0.001). Markers of mitochondrial biogenesis were minimally affected. Although these data are limited to select biomarkers in vitro, these preliminary findings suggest that a theacrine-based supplement can modulate select biomarkers related to NAD+ biogenesis and sirtuin activity. However, these changes did not drive increases in mitochondrial biogenesis. While promising, these data are limited to a rodent cell line and human muscle biopsy studies are needed to validate and elucidate the significance of these findings.

Acute and chronic effects of resistance training on skeletal muscle markers of mitochondrial remodeling in older adults.

We investigated the acute and chronic effects of resistance training (RT) on skeletal muscle markers of mitochondrial content and remodeling in older, untrained adults. Sixteen participants (n = 6 males, n = 10 females; age = 59 ± 4 years) completed 10 weeks of full-body RT (2 day/week). Muscle biopsies from the vastus lateralis were obtained prior to RT (Pre), 24 hr following the first training session (Acute), and 72 hr following the last training session (Chronic). Protein levels of mitochondrial electron transport chain complexes I-V (+39 to +180%, p ≤ .020) and markers of mitochondrial fusion Mfn1 (+90%, p = .003), Mfn2 (+110%, p < .001), and Opa1 (+261%, p = .004) increased following chronic RT. Drp1 protein levels also increased (+134%, p = .038), while Fis1 protein levels did not significantly change (-5%, p = .584) following chronic RT. Interestingly, protein markers of mitochondrial biogenesis (i.e., PGC-1α, TFAM, and NRF1) or mitophagy (i.e., Pink1 and Parkin) were not significantly altered (p > .050) after 10 weeks of RT. In summary, chronic RT promoted increases in content of electron transport chain proteins (i.e., increased protein levels of all five OXPHOS complexes) and increase in the levels of proteins related to mitochondrial dynamics (i.e., increase in fusion protein markers) in skeletal muscle of older adults. These results suggest that chronic RT could be a useful strategy to increase mitochondrial protein content in older individuals.

Resistance training increases muscle NAD+ and NADH concentrations as well as NAMPT protein levels and global sirtuin activity in middle-aged, overweight, untrained individuals.

We examined if resistance training affected muscle NAD+ and NADH concentrations as well as nicotinamide phosphoribosyltransferase (NAMPT) protein levels and sirtuin (SIRT) activity markers in middle-aged, untrained (MA) individuals. MA participants (59±4 years old; n=16) completed 10 weeks of full-body resistance training (2 d/wk). Body composition, knee extensor strength, and vastus lateralis muscle biopsies were obtained prior to training (Pre) and 72 hours following the last training bout (Post). Data from trained college-aged men (22±3 years old, training age: 6±2 years old; n=15) were also obtained for comparative purposes. Muscle NAD+ (+127%, p<0.001), NADH (+99%, p=0.002), global SIRT activity (+13%, p=0.036), and NAMPT protein (+15%, p=0.014) increased from Pre to Post in MA participants. Additionally, Pre muscle NAD+ and NADH in MA participants were lower than college-aged participants (p<0.05), whereas Post values were similar between cohorts (p>0.10). Interestingly, muscle citrate synthase activity levels (i.e., mitochondrial density) increased in MA participants from Pre to Post (+183%, p<0.001), and this increase was significantly associated with increases in muscle NAD+ (r2=0.592, p=0.001). In summary, muscle NAD+, NADH, and global SIRT activity are positively affected by resistance training in middle-aged, untrained individuals. Whether these adaptations facilitated mitochondrial biogenesis remains to be determined.

Higher doses of a green tea-based supplement increase post-exercise blood flow following an acute resistance exercise bout in recreationally resistance-trained college-aged men.

BACKGROUND: There are animal data suggesting green tea can enhance blood flow. However, human data are lacking. Thus, the purpose of this study was to examine the acute effects of low and high doses of a green tea-based supplement (GBS) on brachial artery blood flow before and following a resistance exercise bout. METHODS: In this, double-blinded placebo-controlled trial, college-aged males (n = 18) who self-reported recreationally resistance training for the previous 6 ± 3 years were assigned to one of two studies including a low (300 mg serving) (n = 9) or high dose (600 mg serving) (n = 8; 1 drop) GBS study. During testing sessions, participants reported to the laboratory following an overnight fast and rested in a supine position for 15 min. Thereafter, baseline measurements for resting heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), brachial artery diameter (BAD) and blood flow (BBF) were obtained (PRE). Participants then consumed either their respective GBS dose or a similar placebo dose (microcrystalline cellulose) in a supine resting state. HR, SBP, DBP, BAD and BBF were measured 45 min after placebo or GBS ingestion (PRE2). Participants were then placed in a recumbent position and performed 4 sets of 10 arm curl repetitions using an 11 kg dumbbell. Participants returned to a supine position and HR, SBP, DBP, BAD and BBF were obtained within the first 3 min following exercise (POST), 15 min after exercise (15POST), and 45 min after exercise (45POST). Participants returned to the laboratory 24-48 h later to repeat the same protocol with either GBS or the placebo depending on randomization. Two-way (supplement x time) repeated measures ANOVAs were used to compare dependent variables between testing sessions for Study 1 (300 mg of GBS and placebo) and Study 2 (600 mg of GBS and placebo), and statistical significance was set at p < 0.05. No statistical comparisons were made between studies. RESULTS: As expected, exercise increased BAD and BBF compared to resting baseline measured irrespective of supplementation. In addition, BAD and BBF did not differ between GBS and placebo at any time point after exercise in Study 1. In study 2, however, 600 mg GBS increased baseline-normalized BBF at immediately post exercise compared to placebo (placebo = 211 ± 155% increase, GBS = 349 ± 156% increase; p = 0.012) but not BAD. CONCLUSIONS: These data suggest a higher dose of GBS can enhance localized blood flow acutely following a resistance exercise bout. However, the long-term implications of these data are unclear, and more well-powered studies are needed to validate efficacy and elucidate potential mechanisms.

Skeletal Muscle Protein Composition Adaptations to 10 Weeks of High-Load Resistance Training in Previously-Trained Males.

While high-load resistance training increases muscle hypertrophy, the intramuscular protein responses to this form of training remains largely unknown. In the current study, recreationally resistance-trained college-aged males (N = 15; mean ± SD: 23 ± 3 years old, 6 ± 5 years training) performed full-body, low-volume, high-load [68-90% of one repetition maximum (1RM)] resistance training over 10 weeks. Back squat strength testing, body composition testing, and a vastus lateralis biopsy were performed before (PRE) and 72 h after the 10-week training program (POST). Fiber type-specific cross-sectional area (fCSA), myofibrillar protein concentrations, sarcoplasmic protein concentrations, myosin heavy chain and actin protein abundances, and muscle tissue percent fluid were analyzed. The abundances of individual sarcoplasmic proteins in 10 of the 15 participants were also assessed using proteomics. Significant increases (p < 0.05) in type II fCSA and back squat strength occurred with training, although whole-body fat-free mass paradoxically decreased (p = 0.026). No changes in sarcoplasmic protein concentrations or muscle tissue percent fluid were observed. Myosin heavy chain protein abundance trended downward (-2.9 ± 5.8%, p = 0.069) and actin protein abundance decreased (-3.2 ± 5.3%, p = 0.034) with training. Proteomics indicated only 13 sarcoplasmic proteins were altered with training (12 up-regulated, 1 down-regulated, p < 0.05). Bioinformatics indicated no signaling pathways were affected, and proteins involved with metabolism (e.g., ATP-PCr, glycolysis, TCA cycle, or beta-oxidation) were not affected. These data comprehensively describe intramuscular protein adaptations that occur following 10 weeks of high-load resistance training. Although previous data from our laboratory suggests high-volume resistance training enhances the ATP-PCr and glycolytic pathways, we observed different changes in metabolism-related proteins in the current study with high-load training.

An optimized procedure for isolation of rodent and human skeletal muscle sarcoplasmic and myofibrillar proteins.

Several published protocols exist for isolating contractile or myofibrillar (MF) proteins from skeletal muscle, however, achieving complete resuspension of the myofibril pellet can be technically challenging. We performed several previously published MF isolation methods with the intent of determining which method was most suitable for MF protein isolation and solubilization. Here, we provide an optimized protocol to isolate sarcoplasmic and solubilized MF protein fractions from mammalian skeletal muscle suitable for several downstream assays.

Skeletal Muscle Myofibrillar Protein Abundance Is Higher in Resistance-Trained Men, and Aging in the Absence of Training May Have an Opposite Effect.

Resistance training generally increases skeletal muscle hypertrophy, whereas aging is associated with a loss in muscle mass. Interestingly, select studies suggest that aging, as well as resistance training, may lead to a reduction in the abundance of skeletal muscle myofibrillar (or contractile) protein (per mg tissue). Proteomic interrogations have also demonstrated that aging, as well as weeks to months of resistance training, lead to appreciable alterations in the muscle proteome. Given this evidence, the purpose of this small pilot study was to examine total myofibrillar as well as total sarcoplasmic protein concentrations (per mg wet muscle) from the vastus lateralis muscle of males who were younger and resistance-trained (denoted as YT, n = 6, 25 ± 4 years old, 10 ± 3 self-reported years of training), younger and untrained (denoted as YU, n = 6, 21 ± 1 years old), and older and untrained (denoted as OU, n = 6, 62 ± 8 years old). The relative abundances of actin and myosin heavy chain (per mg tissue) were also examined using SDS-PAGE and Coomassie staining, and shotgun proteomics was used to interrogate the abundances of individual sarcoplasmic and myofibrillar proteins between cohorts. Whole-body fat-free mass (YT > YU = OU), VL thickness (YT > YU = OU), and leg extensor peak torque (YT > YU = OU) differed between groups (p < 0.05). Total myofibrillar protein concentrations were greater in YT versus OU (p = 0.005), but were not different between YT versus YU (p = 0.325). The abundances of actin and myosin heavy chain were greater in YT versus YU (p < 0.05) and OU (p < 0.001). Total sarcoplasmic protein concentrations were not different between groups. While proteomics indicated that marginal differences existed for individual myofibrillar and sarcoplasmic proteins between YT versus other groups, age-related differences were more prominent for myofibrillar proteins (YT = YU > OU, p < 0.05: 7 proteins; OU > YT = YU, p < 0.05: 11 proteins) and sarcoplasmic proteins (YT = YU > OU, p < 0.05: 8 proteins; OU > YT&YU, p < 0.05: 29 proteins). In summary, our data suggest that modest (~9%) myofibrillar protein packing (on a per mg muscle basis) was evident in the YT group. This study also provides further evidence to suggest that notable skeletal muscle proteome differences exist between younger and older humans. However, given that our n-sizes are low, these results only provide a preliminary phenotyping of the reported protein and proteomic variables.

Skeletal muscle LINE-1 ORF1 mRNA is higher in older humans but decreases with endurance exercise and is negatively associated with higher physical activity.

The long interspersed nuclear element-1 (L1) is a retrotransposon that constitutes 17% of the human genome and is associated with various diseases and aging. Estimates suggest that ~100 L1 copies are capable of copying and pasting into other regions of the genome. Herein, we examined if skeletal muscle L1 markers are affected by aging or an acute bout of cycling exercise in humans. Apparently healthy younger (23 ± 3 y, n = 15) and older participants (58 ± 8 y, n = 15) donated a vastus lateralis biopsy before 1 h of cycling exercise (PRE) at ~70% of heart rate reserve. Second (2 h) and third (8 h) postexercise muscle biopsies were also obtained. L1 DNA and mRNA expression were quantified using three primer sets [5' untranslated region (UTR), L1.3, and ORF1]. 5'UTR and L1.3 DNA methylation as well as ORF1 protein expression were also quantified. PRE 5'UTR, ORF1, or L1.3 DNA were not different between age groups (P > 0.05). ORF1 mRNA was greater in older versus younger participants (P = 0.014), and cycling lowered this marker at 2 h versus PRE (P = 0.027). 5'UTR and L1.3 DNA methylation were higher in younger versus older participants (P < 0.05). Accelerometry data collected during a 2-wk period before the exercise bout indicated higher moderate-to-vigorous physical activity (MVPA) levels per day was associated with lower PRE ORF1 mRNA in all participants (r = -0.398, P = 0.032). In summary, skeletal muscle ORF1 mRNA is higher in older apparently healthy humans, which may be related to lower DNA methylation patterns. ORF1 mRNA is also reduced with endurance exercise and is negatively associated with higher daily MVPA levels.NEW & NOTEWORTHY The long interspersed nuclear element-1 (L1) gene is highly abundant in the genome and encodes for an autonomous retrotransposon, which is capable of copying and pasting itself into other portions of the genome. This is the first study in humans to demonstrate that certain aspects of skeletal muscle L1 activity are altered with aging. Additionally, this is the first study in humans to demonstrate that L1 ORF1 mRNA levels decrease after a bout of endurance exercise, regardless of age.

Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy.

Cellular adaptations that occur during skeletal muscle hypertrophy in response to high-volume resistance training are not well-characterized. Therefore, we sought to explore how actin, myosin, sarcoplasmic protein, mitochondrial, and glycogen concentrations were altered in individuals that exhibited mean skeletal muscle fiber cross-sectional area (fCSA) hypertrophy following 6 weeks of high-volume resistance training. Thirty previously resistance-trained, college-aged males (mean ± standard deviation: 21±2 years, 5±3 training years) had vastus lateralis (VL) muscle biopsies obtained prior to training (PRE), at week 3 (W3), and at week 6 (W6). Muscle tissue from 15 subjects exhibiting PRE to W6 VL mean fCSA increases ranging from 320-1600 µm2 was further interrogated using various biochemical and histological assays as well as proteomic analysis. Seven of these individuals donated a VL biopsy after refraining from training 8 days following the last training session (W7) to determine how deloading affected biomarkers. The 15 fCSA hypertrophic responders experienced a +23% increase in mean fCSA from PRE to W6 (p<0.001) and, while muscle glycogen concentrations remained unaltered, citrate synthase activity levels decreased by 24% (p<0.001) suggesting mitochondrial volume decreased. Interestingly, repeated measures ANOVAs indicated that p-values approached statistical significance for both myosin and actin (p = 0.052 and p = 0.055, respectively), and forced post hoc tests indicated concentrations for both proteins decreased ~30% from PRE to W6 (p<0.05 for each target). Phalloidin-actin staining similarly revealed actin concentrations per fiber decreased from PRE to W6. Proteomic analysis of the sarcoplasmic fraction from PRE to W6 indicated 40 proteins were up-regulated (p<0.05), KEGG analysis indicated that the glycolysis/gluconeogenesis pathway was upregulated (FDR sig. <0.001), and DAVID indicated that the following functionally-annotated pathways were upregulated (FDR value <0.05): a) glycolysis (8 proteins), b) acetylation (23 proteins), c) gluconeogenesis (5 proteins) and d) cytoplasm (20 proteins). At W7, sarcoplasmic protein concentrations remained higher than PRE (+66%, p<0.05), and both actin and myosin concentrations remained lower than PRE (~-50%, p<0.05). These data suggest that short-term high-volume resistance training may: a) reduce muscle fiber actin and myosin protein concentrations in spite of increasing fCSA, and b) promote sarcoplasmic expansion coincident with a coordinated up-regulation of sarcoplasmic proteins involved in glycolysis and other metabolic processes related to ATP generation. Interestingly, these effects seem to persist up to 8 days following training.

Pre-training Skeletal Muscle Fiber Size and Predominant Fiber Type Best Predict Hypertrophic Responses to 6 Weeks of Resistance Training in Previously Trained Young Men.

Limited evidence exists regarding differentially expressed biomarkers between previously-trained low versus high hypertrophic responders in response to resistance training. Herein, 30 college-aged males (training age 5 ± 3 years; mean ± SD) partook in 6 weeks of high-volume resistance training. Body composition, right leg vastus lateralis (VL) biopsies, and blood were obtained prior to training (PRE) and at the 3-week (W3) and 6-week time points (W6). The 10 lowest (LOW) and 10 highest (HIGH) hypertrophic responders were clustered based upon a composite hypertrophy score of PRE-to-W6 changes in right leg VL mean muscle fiber cross-sectional area (fCSA), VL thickness assessed via ultrasound, upper right leg lean soft tissue mass assessed via dual x-ray absorptiometry (DXA), and mid-thigh circumference. Two-way ANOVAs were used to compare biomarker differences between the LOW and HIGH clusters over time, and stepwise linear regression was performed to elucidate biomarkers that explained significant variation in the composite hypertrophy score from PRE to W3, W3 to W6, and PRE to W6 in all 30 participants. PRE-to-W6 HIGH and LOW responders exhibited a composite hypertrophy change of +10.7 ± 3.2 and -2.1 ± 1.6%, respectively (p < 0.001). Compared to HIGH responders, LOW responders exhibited greater PRE type II fCSA (+18%, p = 0.022). Time effects (p < 0.05) existed for total RNA/mg muscle (W6 > W3 > PRE), phospho (p)-4EBP1 (PRE > W3&W6), pan-mTOR (PRE > W3 < W6), p-mTOR (PRE > W3 < W6), pan-AMPKα (PRE > W3 < W6), pan-p70s6k (PRE > W3), muscle ubiquitin-labeled proteins (PRE > W6), mechano growth factor mRNA (W6 > W3&PRE), 45S rRNA (PRE > W6), and muscle citrate synthase activity (PRE > W3&W6). No interactions existed for the aforementioned biomarkers and/or other assayed targets (muscle 20S proteasome activity, serum total testosterone, muscle androgen receptor protein levels, muscle glycogen, or serum creatine kinase). Regression analysis indicated PRE type II fiber percentage (R 2 = 0.152, ß = 0.390, p = 0.033) and PRE type II fCSA (R 2 = 0.207, ß = -0.455, p = 0.019) best predicted the PRE-to-W6 change in the composite hypertrophy score. While our sample size is limited, these data suggest: (a) HIGH responders may exhibit more growth potential given that they possessed lower PRE type II fCSA values and (b) possessing a greater type II fiber percentage as a trained individual may be advantageous for hypertrophy in response to resistance training.

Correction to: Ten weeks of branched-chain amino acid supplementation improves select performance and immunological variables in trained cyclists.

For the author R. Mac Thompson, the first name should be R. Mac and the last name should be Thompson. On SpringerLink the name is listed correctly, but on PubMed he is listed as Mac Thompson R.

The Effects of Fortetropin Supplementation on Body Composition, Strength, and Power in Humans and Mechanism of Action in a Rodent Model.

OBJECTIVE: The purpose of this study was to investigate the effects of Fortetropin on skeletal muscle growth and strength in resistance-trained individuals and to investigate the anabolic and catabolic signaling effects using human and rodent models. METHODS: In the rodent model, male Wistar rats (250 g) were gavage fed with either 1.2 ml of tap water control (CTL) or 0.26 g Fortetropin for 8 days. Then rats participated in a unilateral plantarflexion exercise bout. Nonexercised and exercised limbs were harvested at 180 minutes following and analyzed for gene and protein expression relative to mammalian target of rapamycin (mTOR) and ubiquitin signaling. For the human model, 45 (of whom 37 completed the study), resistance-trained college-aged males were divided equally into 3 groups receiving a placebo macronutrient matched control, 6.6 or 19.8 g of Fortetropin supplementation during 12 weeks of resistance training. Lean mass, muscle thickness, and lower and upper body strength were measured before and after 12 weeks of training. RESULTS: The human study results indicated a Group × Time effect (p ≤ 0.05) for lean mass in which the 6.6 g (+1.7 kg) and 19.8 g (+1.68 kg) but not placebo (+0.6 kg) groups increased lean mass. Similarly, there was a Group × Time effect for muscle thickness (p ≤ 0.05), which increased in the experimental groups only. All groups increased equally in bench press and leg press strength. In the rodent model, a main effect for exercise (p ≤ 0.05) in which the control plus exercise but not Fortetropin plus exercise increased both ubiquitin monomer protein expression and polyubiquitination. mTOR signaling was elevated to a greater extent in the Fortetropin exercising conditions as indicated by greater phosphorylation status of 4EBP1, rp6, and p70S6K for both exercising conditions. CONCLUSIONS: Fortetropin supplementation increases lean body mass (LBM) and decreases markers of protein breakdown while simultaneously increasing mTOR signaling.

Effects of Arachidonic Acid Supplementation on Acute Anabolic Signaling and Chronic Functional Performance and Body Composition Adaptations.

BACKGROUND: The primary purpose of this investigation was to examine the effects of arachidonic acid (ARA) supplementation on functional performance and body composition in trained males. In addition, we performed a secondary study looking at molecular responses of ARA supplementation following an acute exercise bout in rodents. METHODS: Thirty strength-trained males (age: 20.4 ± 2.1 yrs) were randomly divided into two groups: ARA or placebo (i.e. CTL). Then, both groups underwent an 8-week, 3-day per week, non-periodized training protocol. Quadriceps muscle thickness, whole-body composition scan (DEXA), muscle strength, and power were assessed at baseline and post-test. In the rodent model, male Wistar rats (~250 g, ~8 weeks old) were pre-fed with either ARA or water (CTL) for 8 days and were fed the final dose of ARA prior to being acutely strength trained via electrical stimulation on unilateral plantar flexions. A mixed muscle sample was removed from the exercised and non-exercised leg 3 hours post-exercise. RESULTS: Lean body mass (2.9%, p<0.0005), upper-body strength (8.7%, p<0.0001), and peak power (12.7%, p<0.0001) increased only in the ARA group. For the animal trial, GSK-ß (Ser9) phosphorylation (p<0.001) independent of exercise and AMPK phosphorylation after exercise (p-AMPK less in ARA, p = 0.041) were different in ARA-fed versus CTL rats. CONCLUSIONS: Our findings suggest that ARA supplementation can positively augment strength-training induced adaptations in resistance-trained males. However, chronic studies at the molecular level are required to further elucidate how ARA combined with strength training affect muscle adaptation.

A putative low-carbohydrate ketogenic diet elicits mild nutritional ketosis but does not impair the acute or chronic hypertrophic responses to resistance exercise in rodents.

We examined whether acute and/or chronic skeletal muscle anabolism is impaired with a low-carbohydrate diet formulated to elicit ketosis (LCKD) vs. a mixed macronutrient Western diet (WD). Male Sprague-Dawley rats (9-10 wk of age, 300-325 g) were provided isoenergetic amounts of a LCKD or a WD for 6 wk. In AIM 1, basal serum and gastrocnemius assessments were performed. In AIM 2, rats were resistance exercised for one bout and were euthanized 90-270 min following exercise for gastrocnemius analyses. In AIM 3, rats voluntarily exercised daily with resistance-loaded running wheels, and hind limb muscles were analyzed for hypertrophy markers at the end of the 6-wk protocol. In AIM 1, basal levels of gastrocnemius phosphorylated (p)-rps6, p-4EBP1, and p-AMPKα were similar between diets, although serum insulin (P < 0.01), serum glucose (P < 0.001), and several essential amino acid levels (P < 0.05) were lower in LCKD-fed rats. In AIM 2, LCKD- and WD-fed rats exhibited increased postexercise muscle protein synthesis levels (P < 0.0125), but no diet effect was observed (P = 0.59). In AIM 3, chronically exercise-trained LCKD- and WD-fed rats presented similar increases in relative hind limb muscle masses compared with their sedentary counterparts (12-24%, P < 0.05), but there was no between-diet effects. Importantly, the LCKD induced "mild" nutritional ketosis, as the LCKD-fed rats in AIM 2 exhibited ∼1.5-fold greater serum ß-hydroxybutyrate levels relative to WD-fed rats (diet effect P = 0.003). This study demonstrates that the tested LCKD in rodents, while only eliciting mild nutritional ketosis, does not impair the acute or chronic skeletal muscle hypertrophic responses to resistance exercise.

Ten weeks of branched-chain amino acid supplementation improves select performance and immunological variables in trained cyclists.

We examined if supplementing trained cyclists (32 ± 2 year, 77.8 ± 2.6 kg, and 7.4 ± 1.2 year training) with 12 g/day (6 g/day L-Leucine, 2 g/day L-Isoleucine and 4 g/day L-Valine) of either branched-chain amino acids (BCAAs, n = 9) or a maltodextrin placebo (PLA, n = 9) over a 10-week training season affected select body composition, performance, and/or immune variables. Before and after the 10-week study, the following was assessed: (1) 4-h fasting blood draws; (2) dual X-ray absorptiometry body composition; (3) Wingate peak power tests; and (4) 4 km time-trials. No group × time interactions existed for total lean mass (P = 0.27) or dual-leg lean mass (P = 0.96). A significant interaction existed for body mass-normalized relative peak power (19 % increase in the BCAA group pre- to post-study, P = 0.01), and relative mean power (4 % increase in the BCAA group pre- to post-study, P = 0.01). 4 km time-trial time to completion approached a significant interaction (P = 0.08), as the BCAA group improved in this measure by 11 % pre- to post-study, though this was not significant (P = 0.15). There was a tendency for the BCAA group to present a greater post-study serum BCAA: L-Tryptophan ratio compared to the PLA group (P = 0.08). A significant interaction for neutrophil number existed (P = 0.04), as there was a significant 18 % increase within the PLA group from the pre- to post-study time point (P = 0.01). Chronic BCAA supplementation improves sprint performance variables in endurance cyclists. Additionally, given that BCAA supplementation blunted the neutrophil response to intense cycling training, BCAAs may benefit immune function during a prolonged cycling season.

Comparative effects of whey protein versus L-leucine on skeletal muscle protein synthesis and markers of ribosome biogenesis following resistance exercise.

We compared immediate post-exercise whey protein (WP, 500 mg) versus L-leucine (LEU, 54 mg) feedings on skeletal muscle protein synthesis (MPS) mechanisms and ribosome biogenesis markers 3 h following unilateral plantarflexor resistance exercise in male, Wistar rats (~250 g). Additionally, in vitro experiments were performed on differentiated C2C12 myotubes to compare nutrient (i.e., WP, LEU) and 'exercise-like' treatments (i.e., caffeine, hydrogen peroxide, and AICAR) on ribosome biogenesis markers. LEU and WP significantly increased phosphorylated-rpS6 (Ser235/236) in the exercised (EX) leg 2.4-fold (P < 0.01) and 2.7-fold (P < 0.001) compared to the non-EX leg, respectively, whereas vehicle-fed control (CTL) did not (+65 %, P > 0.05). Compared to the non-EX leg, MPS levels increased 32 % and 52 % in the EX leg of CTL (P < 0.01) and WP rats (P < 0.001), respectively, but not in LEU rats (+15 %, P > 0.05). Several genes associated with ribosome biogenesis robustly increased in the EX versus non-EX legs of all treatments; specifically, c-Myc mRNA, Nop56 mRNA, Bop1 mRNA, Ncl mRNA, Npm1 mRNA, Fb1 mRNA, and Xpo-5 mRNA. However, only LEU significantly increased 45S pre-rRNA levels in the EX leg (63 %, P < 0.001). In vitro findings confirmed that 'exercise-like' treatments similarly altered markers of ribosome biogenesis, but only LEU increased 47S pre-rRNA levels (P < 0.01). Collectively, our data suggests that resistance exercise, as well as 'exercise-like' signals in vitro, acutely increase the expression of genes associated with ribosome biogenesis independent of nutrient provision. Moreover, while EX with or without WP appears superior for enhancing translational efficiency (i.e., increasing MPS per unit of RNA), LEU administration (or co-administration) may further enhance ribosome biogenesis over prolonged periods with resistance exercise.