[Show abstract][Hide abstract] ABSTRACT: Dear Editor:
Morphological adaptations of skeletal muscle to resistance exercise training (RET) have been the subject of many studies: essentially, muscle hypertrophy is achieved by a structural remodelling of the contractile machinery, which can be assessed macroscopically by investigating changes in muscle architecture (i.e. fascicle length, Lf; pennation angle, PA; muscle thickness, MT) (Gans ; Narici ; Lieber and Fridén , ; Reeves et al. , ). A thorough understanding of muscle architecture is indeed fundamental when interpreting training-induced changes in muscle function given its key role as determinant of muscle mechanical properties (Narici et al. ; Lieber and Fridén ).
In a recent study by Fukutani and Kurihara () published in SpringerPlus (, 4:341), the authors investigated differences in Lf between resistance trained and untrained individuals using a cross-sectional design: the main conclusion being made was that Lf was not associated with muscle hypertrophy on the basis that no significant differences in Lf were found between the groups. The authors claimed that fascicle length does not increase with resistance training.
Some fundamental considerations arise from these findings. Skeletal muscle hypertrophy in response to RET is mainly accomplished with the addition of new contractile material as a result of enhanced muscle myofibrillar protein synthesis after exercise (Glass ; Atherton and Smith ). Moreover, it is well established that the longitudinal post-natal growth of mammal muscle is associated with the increased in length and size of muscle fibres (Goldspink ; Williams and Goldspink ; Russell et al. ). Seminal pre-clinical studies previously showed that skeletal muscle responds to passive and intermittent stretch by adding new sarcomeres in-series (Holly et al. ; Goldspink ; Williams et al. ; Williams ), a phenomenon that occurs also in response to exercise regimes/overload, especially when including lengthening muscle actions (Goldspink ; Proske and Morgan ). Greater addition of serial sarcomeres was found in rats after downhill compared to uphill running (Lynn and Morgan ; Butterfield et al. ), reinforcing the concept of muscle longitudinal growth being intimately related to lengthening contractions. Indeed, the addition of sarcomeres in series (and thus increased Lf) appears to be one of the main “protective” mechanisms after eccentric exercise induced muscle damage (Morgan and Talbot ).
Further support to these observations on animal muscle can be found in numerous studies investigating architectural responses to RET, directly in humans. Interestingly, Fukutani and Kurihara stated it as controversial as to whether Lf increases after RET: however the number of reports showing no increases in Lf in response to exercise is limited (Blazevich et al. [2007b]; Erskine et al. ; Ema et al. ) compared to those that demonstrated an increase in Lf after either conventional resistance, isokinetic, isoinertial or even marathon training (Morgan and Proske ; Seynnes et al. ; Blazevich et al. [2007a]; Potier et al. ; Reeves et al. ; Baroni et al. ; Franchi et al. , ; Sharifnezhad et al. ; McMahon et al. ; Murach et al. ). But, most importantly, it was recently reported by our group that, in both young and older populations, architectural changes, such as increases in Lf, are somewhat contraction-specific (Reeves et al. ; Franchi et al. , ). That is, concentric loading promotes increases in PA, reflecting preferential addition of sarcomeres in parallel, whereas eccentric training favours the increase of Lf through the addition of sarcomeres in series. It is our opinion that these investigations should have been cited in Fukutani and Kurihara’s manuscript. Furthermore, considering the substantial number of longitudinal studies that have showed significant changes in Lf and muscle architecture after RET, the adoption of such a cross-sectional study design calls into question the validity of these conclusions. Moreover, the investigation was performed on recreationally active volunteers (the untrained group, with “no experience in regular RET”) compared to a group of “resistance exercise trained” participants, either body builders or rugby players (i.e. the number of bodybuilders/rugby players was not specified). Taking into account the aforementioned considerations on the contraction-specificity of architectural responses, the individual history of resistance training in both groups should have been accounted for. Kawakami and colleagues () previously reported that PA and MT are greater in bodybuilders compared to untrained and moderately trained subjects (Lf was not investigated), but Abe et al. (, ), showed that Lf is greater in elite male 100 m-sprinters compared to elite long-distance runners and to non-sprinters. Rather than being innate factors, as Fukutani and Kurihara argue, architectural adaptations such as increases in Lf are indeed detectable longitudinally and are training/contraction-specific (Blazevich et al. ; Franchi et al. , ). In addition, Lf was measured as a straight line in Fukutani and Kurihara’s study: while this might not represent a problem in the untrained group, in hypertrophied muscle, instead, fascicles show a significantly greater curvature, which partially explains the increased pennation occurring with hypertrophy (clearly visible in bodybuilders muscle) (Kawakami et al. ). Since the fascicle curvature was neglected by the methodological approach used to measure Lf, the true Lf values could have been underestimated in the resistance-trained group. Therefore, Lf may have gone undetected as a result of the simplicity of the morphometric analyses implemented. Thus, the chances are that Fukutani and Kurihara’s results were biased by the non-longitudinal study design and by the possible underestimation of Lf due to specific methodological approach. We agree that in some cases “muscle hypertrophy is not necessarily accompanied with increase in Lf” (Fukutani and Kurihara ), but these cases can only be truly determined by tightly controlled longitudinal studies.
We are of the opinion that the nature of fascicle length (Lf) increase is highly dependent on which type of contraction and mechanical stimulus is predominant in specific RET programmes: thus, data on muscle architecture features should be cautiously interpreted, as crucial in the understanding of muscle structural remodelling and its functional characteristics.
[Show abstract][Hide abstract] ABSTRACT: Skeletal muscles exhibit radical changes in physiology and metabolism in response to exercise. While exercise induces highly specific physiological changes, e.g., hypertrophy, associated with weightlifting or oxygen utilization associated with aerobic-type exercises, the foundation of these changes is driven by the summation of exercise-induced alterations in muscle protein metabolism. Practically, any type of exercise stimulates muscle protein turnover, the purpose being both to renew, and also modify, the myocellular composition of proteins in line with adaptations according to the mechanical and metabolic demands imposed. The mechanism(s) by which exercise stimulates protein turnover has been the subset of intense study. These studies have been led by the use of stable isotopically labeled amino acids. Essentially, use of these heavier variants (e.g., 13C AA vs. 12C) coupled to mass spectrometry has enabled study of the dynamic responses of muscle protein turnover to exercise. Using these techniques, it has become patently clear that exercise stimulates muscle protein turnover, i.e., muscle protein synthesis (MPS) and breakdown (MPB). Moreover, intake of specific nutrients (i.e., dietary proteins) potentiates MPS while attenuating MPB, facilitating maintenance of proteostasis and exercise adaptation. The mechanisms driving these protein metabolic responses to exercise include the coordinated activation of mRNA translation pathways (e.g., mechanistic target of rapamycin) and multiple MPB pathways (e.g., autophagy and ubiquitin-proteasome). These processes are triggered by exercise-induced hormone, auto/paracrine-acting growth factors, mechanical transduction, and intramyocellular second messenger pathways. Finally, there remains poor understanding of how distinct exercise modes (e.g., resistance vs. endurance) lead to such distinct adaptations from a protein metabolic and molecular standpoint.
No preview · Article · Dec 2015 · Progress in molecular biology and translational science
[Show abstract][Hide abstract] ABSTRACT: We recently reported that the greatest distinguishing feature between eccentric (ECC) and concentric (CON) muscle loading lays in architectural adaptations: ECC favors increases in fascicle length (Lf), associated with distal vastus lateralis muscle (VL) hypertrophy, and CON increases in pennation angle (PA). Here, we explored the interactions between structural and morphological remodeling, assessed by ultrasound and dual x-ray absorptiometry (DXA), and long-term muscle protein synthesis (MPS), evaluated by deuterium oxide (D2O) tracing technique. Ten young males (23 ± 4 years) performed unilateral resistance exercise training (RET) three times/week for 4 weeks; thus, one-leg trained concentrically while the contralateral performed ECC exercise only at 80% of either CON or ECC one repetition maximum (1RM). Subjects consumed an initial bolus of D2O (150 mL), while a 25-mL dose was thereafter provided every 8 days. Muscle biopsies from VL midbelly (MID) and distal myotendinous junction (MTJ) were collected at 0 and 4-weeks. MPS was then quantified via GC–pyrolysis–IRMS over the 4-week training period. Expectedly, ECC and CON RET resulted in similar increases in VL muscle thickness (MT) (7.5% vs. 8.4%, respectively) and thigh lean mass (DXA) (2.3% vs. 3%, respectively), albeit through distinct remodeling: Lf increasing more after ECC (5%) versus CON (2%) and PA increasing after CON (7% vs. 3%). MPS did not differ between contractile modes or biopsy sites (MID-ECC: 1.42 vs. MID-CON: 1.4% day−1; MTJ-ECC: 1.38 vs. MTJ-CON: 1.39% day−1). Muscle thickness at MID site increased similarly following ECC and CON RET, reflecting a tendency for a contractile mode-independent correlation between MPS and MT (P = 0.07; R2 = 0.18). We conclude that, unlike MT, distinct structural remodeling responses to ECC or CON are not reflected in MPS; the molecular mechanisms of distinct protein deposition, and/or the role of protein breakdown in mediating these responses remain to be defined.
[Show abstract][Hide abstract] ABSTRACT: Aims/hypothesis:
We aimed to investigate the role of insulin in regulating human skeletal muscle metabolism in health and diabetes.
We conducted a systematic review and meta-analysis of published data that examined changes in skeletal muscle protein synthesis (MPS) and/or muscle protein breakdown (MPB) in response to insulin infusion. Random-effects models were used to calculate weighted mean differences (WMDs), 95% CIs and corresponding p values. Both MPS and MPB are reported in units of nmol (100 ml leg vol.)(-1) min(-1).
A total of 104 articles were examined in detail. Of these, 44 and 25 studies (including a total of 173 individuals) were included in the systematic review and meta-analysis, respectively. In the overall estimate, insulin did not affect MPS (WMD 3.90 [95% CI -0.74, 8.55], p = 0.71), but significantly reduced MPB (WMD -15.46 [95% CI -19.74, -11.18], p < 0.001). Overall, insulin significantly increased net balance protein acquisition (WMD 20.09 [95% CI 15.93, 24.26], p < 0.001). Subgroup analysis of the effect of insulin on MPS according to amino acid (AA) delivery was performed using meta-regression analysis. The estimate size (WMD) was significantly different between subgroups based on AA availability (p = 0.001). An increase in MPS was observed when AA availability increased (WMD 13.44 [95% CI 4.07, 22.81], p < 0.01), but not when AA availability was reduced or unchanged. In individuals with diabetes and in the presence of maintained delivery of AA, there was a significant reduction in MPS in response to insulin (WMD -6.67 [95% CI -12.29, -0.66], p < 0.05).
This study demonstrates the complex role of insulin in regulating skeletal muscle metabolism. Insulin appears to have a permissive role in MPS in the presence of elevated AAs, and plays a clear role in reducing MPB independent of AA availability.
[Show abstract][Hide abstract] ABSTRACT: Skeletal muscle mass plays a vital role in locomotion, whole-body metabolic health, and is a positive predictor of longevity. It is well established the mammalian target of rapamycin (mTOR) is a central regulator of skeletal muscle protein turnover. The pursuit to find novel nutrient compounds or functional food sources that possess the ability to activate mTOR and promote skeletal muscle protein accretion has been on going. Over the last decade, a key role has been proposed for the phospholipid phosphatidic acid (PA) in mTOR activation. Mechanical load-induced (i.e., resistance exercise) intramuscular PA can directly bind to and activate mTOR. In addition, PA provided exogenously in cell culture heightens mTOR activity, albeit indirectly. Thus, endogenously generated PA and exogenous provision of PA appear to act through distinct mechanisms that converge on mTOR and, potentially, may amplify muscle protein synthesis. In support of this notion, limited evidence from humans suggests that resistance exercise training combined with oral supplemental PA enhances strength gains and muscle hypertrophy. However, the precise mechanisms underpinning the augmented muscle remodelling response with supplemental PA remain elusive. In this review, we will critically examine available evidence from cell cultures and animal and human experimental models to provide an overview of the mechanisms through which endogenous and exogenous PA may act to promote muscle anabolism, and discuss the potential for PA as a therapeutic tool to maintain or restore skeletal muscle mass in the context of ageing and disease.
No preview · Article · Sep 2015 · Applied Physiology Nutrition and Metabolism
[Show abstract][Hide abstract] ABSTRACT: Background:
Diagnostics of the human ageing process may help predict future healthcare needs or guide preventative measures for tackling diseases of older age. We take a transcriptomics approach to build the first reproducible multi-tissue RNA expression signature by gene-chip profiling tissue from sedentary normal subjects who reached 65 years of age in good health.
One hundred and fifty probe-sets form an accurate classifier of young versus older muscle tissue and this healthy ageing RNA classifier performed consistently in independent cohorts of human muscle, skin and brain tissue (n = 594, AUC = 0.83-0.96) and thus represents a biomarker for biological age. Using the Uppsala Longitudinal Study of Adult Men birth-cohort (n = 108) we demonstrate that the RNA classifier is insensitive to confounding lifestyle biomarkers, while greater gene score at age 70 years is independently associated with better renal function at age 82 years and longevity. The gene score is 'up-regulated' in healthy human hippocampus with age, and when applied to blood RNA profiles from two large independent age-matched dementia case-control data sets (n = 717) the healthy controls have significantly greater gene scores than those with cognitive impairment. Alone, or when combined with our previously described prototype Alzheimer disease (AD) RNA 'disease signature', the healthy ageing RNA classifier is diagnostic for AD.
We identify a novel and statistically robust multi-tissue RNA signature of human healthy ageing that can act as a diagnostic of future health, using only a peripheral blood sample. This RNA signature has great potential to assist research aimed at finding treatments for and/or management of AD and other ageing-related conditions.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Resistance exercise training (RET) is widely used to increase muscle mass in athletes and also aged/cachectic populations. However, the time course and metabolic and molecular control of hypertrophy remain poorly defined. Using newly developed deuterium oxide (D2O)-tracer techniques, we investigated the relationship between long-term muscle protein synthesis (MPS) and hypertrophic responses to RET. A total of 10 men (2361 yr) undertook 6 wk of unilateral (1-legged) RET [6 x 8 repetitions, 75% 1 repetition maximum (1-RM) 3/wk], rendering 1 leg untrained (UT) and the contralateral, trained (T). After baseline bilateral vastus lateralis (VL) muscle biopsies, subjects consumed 150 ml D2O (70 atom percentage; thereafter 50 ml/wk) with regular body water monitoring in saliva via high-temperature conversion elemental analyzer:isotope ratio mass spectrometer. Further bilateral VL muscle biopsies were taken at 3 and 6 wk to temporally quantify MPS via gas chromatography: pyrolysis: isotope ratio mass spectrometer. Expectedly, only the T leg exhibited marked increases in function [i.e., 1-RM/maximal voluntary contraction (60 degrees)] and VL thickness (peaking at 3 wk). Critically, whereas MPS remained unchanged in the UT leg (e.g., similar to 1.35 +/- 0.08%/d), the T leg exhibited increased MPS at 0-3wk(1.6 +/- 0.01%/d), but not at3-6wk(1.29 +/- 0.11%/d); this was reflected by dampened acute mechanistic target of rapamycin complex 1 signaling responses to RET, beyond 3 wk. Therefore, hypertrophic remodeling is most active during the early stages of RET, reflecting longer-term MPS. Moreover, D2O heralds promise for coupling MPS and muscle mass and providing insight into the control of hypertrophy and efficacy of anabolic interventions.
No preview · Article · Jul 2015 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: The anabolic effects of dietary protein on skeletal muscle depend on adequate skeletal muscle perfusion, which is impaired in older people.
To explore fed-state muscle microvascular blood flow, protein metabolism and exercise-training status in older men.
We measured leg blood flow (LBF), muscle microvascular blood volume (MBV) and muscle protein turnover under postabsorptive and fed-state (IV Glamin to double AA, dextrose to sustain glucose ∼7-7.5 mmol·l(-1) ) conditions in two groups: 10 untrained men (72.3 ± 1.4 y; BMI 26.5 ± 1.15 kg·m(2) ) and 10 men who had undertaken 20-weeks fully-supervised, whole-body resistance-exercise training (RET) (72.8 ± 1.4 y; BMI 26.3 ± 1.2 kg·m(2) ). We measured LBF by Doppler ultrasound and muscle MBV by contrast enhanced ultrasound (CEUS). Muscle protein synthesis (MPS) was measured using [1, 2-(13) C2 ] leucine with breakdown (MPB) and net protein balance (NPB) by ring-[D5 ] phenylalanine tracers. Plasma insulin was measured via ELISA and indices of anabolic signalling (e.g. Akt/mTORC1) by immunoblotting from muscle biopsies.
Whereas older untrained men did not exhibit fed-state increases in LBF or MBV, the RET group exhibited increases in both LBF and MBV. Despite our hypothesis that enhanced fed-state circulatory responses would improve anabolic responses to nutrition, fed-sate increases in MPS (∼50-75%; P<0.001), were identical in both groups. Finally, whereas only the RET group exhibited fed-state suppression of MPB (∼-38%; P<0.05), positive net protein balance (NPB) achieved was similar in both groups.
We conclude that RET enhances fed-state LBF and MBV and restores nutrient-dependent attenuation of MPB without robustly enhancing MPS or NPB. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
No preview · Article · Apr 2015 · The Journal of Physiology
[Show abstract][Hide abstract] ABSTRACT: Background: The anabolic response of skeletal muscle to essential amino acids (EAAs) is dose dependent, maximal at modest doses, and short lived, even with continued EAA availability, a phenomenon termed “muscle-full.” However, the effect of EAA ingestion profile on muscle metabolism remains undefined.
Objective: We determined the effect of Bolus vs. Spread EAA feeding in young men and hypothesized that muscle-full is regulated by a dose-, not delivery profile–, dependent mechanism.
Methods: We provided 16 young healthy men with 15 g mixed-EAA, either as a single dose (“Bolus” n = 8) or in 4 fractions at 45-min intervals (“Spread” n = 8). Plasma insulin and EAA concentrations were assayed by ELISA and ion-exchange chromatography, respectively. Limb blood flow by was determined by Doppler ultrasound, muscle microvascular flow by Sonovue (Bracco) contrast-enhanced ultrasound, and phosphorylation of mammalian target of rapamycin complex 1 substrates by immunoblotting. Intermittent muscle biopsies were taken to quantify myofibrillar-bound 13C6-phenylalanine to determine muscle protein synthesis (MPS).
Results: Bolus feeding achieved rapid insulinemia (13.6 μIU ⋅ mL−1, 25 min after commencement of feeding), aminoacidemia (∼2500 μM at 45 min), and capillary recruitment (+45% at 45 min), whereas Spread feeding achieved attenuated insulin responses, gradual low-amplitude aminoacidemia (peak: ∼1500 μM at 135 min), and no detectable capillary recruitment (all P < 0.01 vs. Bolus). Despite these differences, identical anabolic responses were observed; fasting fractional synthetic rates of 0.054% ⋅ h−1 (Bolus) and 0.066% ⋅ h−1 (Spread) increased to 0.095% and 0.104% ⋅ h−1 (no difference in increment or final values between regimens). With both Spread and Bolus feeding strategies, a latency of at least 90 min was observed before an upswing in MPS was evident. Similarly with both feeding strategies, MPS returned to fasting rates by 180 min despite elevated circulating EAAs.
Conclusion: These data do not support EAA delivery profile as an important determinant of anabolism in young men at rest, nor rapid aminoacidemia/leucinemia as being a key factor in maximizing MPS. This trial was registered at clinicaltrials.gov as NCT01735539.
Full-text · Article · Jan 2015 · Journal of Nutrition
[Show abstract][Hide abstract] ABSTRACT: Aging is associated with a gradual loss of muscle mass termed sarcopenia, which has significant impact on quality-of-life. Because oxidative stress is proposed to negatively impact upon musculoskeletal aging, we investigated links between human aging and markers of oxidative stress, and relationships to muscle mass and strength in young and old nonsarcopenic and sarcopenic adults. Sixteen young and 16 old males (further subdivided into “old” and “old sarcopenic”) were studied. The abundance of protein carbonyl adducts within skeletal muscle sarcoplasmic, myofibrillar, and mitochondrial protein subfractions from musculus vastus lateralis biopsies were determined using Oxyblot immunoblotting techniques. In addition, concentrations of recognized cytoprotective proteins (eg, heat shock proteins [HSP], αβ-crystallin) were also assayed. Aging was associated with increased mitochondrial (but not myofibrillar or sarcoplasmic) protein carbonyl adducts, independently of (stage-I) sarcopenia. Correlation analyses of all subjects revealed that mitochondrial protein carbonyl abundance negatively correlated with muscle strength ([1-repetition maximum], p = .02, r
2 = −.16), but not muscle mass (p = .13, r
2 = −.08). Abundance of cytoprotective proteins, including various HSPs (HSP 27 and 70), were unaffected by aging/sarcopenia. To conclude, these data reveal that mitochondrial protein carbonylation increases moderately with age, and that this increase may impact upon skeletal muscle function, but is not a hallmark of (stage-I) sarcopenia, per se.
Full-text · Article · Mar 2014 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Muscle hypertrophy following resistance training (RT) involves activation of myofibrillar protein synthesis (MPS) to expand the myofibrillar protein pool. The degree of hypertrophy following RT is, however, highly variable and thus we sought to determine the relationship between the acute activation of MPS and RT-induced hypertrophy. We measured MPS and signalling protein activation after the first session of resistance exercise (RE) in untrained men (n = 23) and then examined the relation between MPS with magnetic resonance image determined hypertrophy. To measure MPS, young men (24±1 yr; body mass index = 26.4±0.9 kg•m(2)) underwent a primed constant infusion of L-[ring-(13)C6] phenylalanine to measure MPS at rest, and acutely following their first bout of RE prior to 16 wk of RT. Rates of MPS were increased 235±38% (P<0.001) above rest 60-180 min post-exercise and 184±28% (P = 0.037) 180-360 min post exercise. Quadriceps volume increased 7.9±1.6% (-1.9-24.7%) (P<0.001) after training. There was no correlation between changes in quadriceps muscle volume and acute rates of MPS measured over 1-3 h (r = 0.02), 3-6 h (r = 0.16) or the aggregate 1-6 h post-exercise period (r = 0.10). Hypertrophy after chronic RT was correlated (r = 0.42, P = 0.05) with phosphorylation of 4E-BP1(Thr37/46) at 1 hour post RE. We conclude that acute measures of MPS following an initial exposure to RE in novices are not correlated with muscle hypertrophy following chronic RT.