Michael D Roberts

Auburn University | AU · Department of Kinesiology

Objective: The objective of this study was to compare the chronic effects of different whey protein forms on body composition and performance when supplemented with resistance training. Methods: Resistance-trained men (N = 56, 21.4 ± 0.4 years, 79.5 ± 1.0 kg) participated in an 8-week resistance training regimen (2 upper-body sessions and 2 lowe...

We sought to determine the effects of L-leucine (LEU) or different protein supplements standardized to LEU (~3.0 g/serving) on changes in body composition, strength, and histological attributes in skeletal muscle and adipose tissue. Seventy-five untrained, college-aged males (mean ± standard error of the mean (SE); age = 21 ± 1 years, body mass = 7...

Introduction We aimed to determine if candidate genetic polymorphisms were associated with resistance training‐induced changes in skeletal muscle hypertrophy variables. Methods Two cohorts of predominantly Caucasian college‐aged male participants (N=109; n=66: Auburn, AL, USA; n=43: Hamilton, Ontario, Canada) performed 12 weeks of progressive full...

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...

We recently reported that resistance trained (T, n=10) and untrained (UT, n=11) young adults experience vastus lateralis (VL) muscle atrophy following two weeks of disuse, and 8 weeks of recovery resistance training (RT) promotes VL hypertrophy in both participant cohorts. However, angiogenesis targets and muscle capillary number were not examined...

We examined changes in skeletal muscle protein lactylation and acetylation in response to acute resistance exercise, chronic resistance training (RT), and a single endurance cycling bout. Additionally, we performed in vitro experiments to determine if different sodium lactate treatments affect myotube protein lactylation and acetylation. The acute...

Background It is unclear whether chronically training close to volitional failure influences motor unit recruitment strategies during fatigue. Purpose We compared resistance training to near volitional failure vs . non-failure on individual motor unit action potential amplitude (MUAP) and surface electromyographic excitation (sEMG) during fatiguin...

Cellular and tissue total RNA concentrations have been widely reported to represent ribosome content, a metric that reflects the trophic state of skeletal muscle. Although various assays are used to assess total RNA concentrations, there is a need to homologize the various quantification approaches. Thus, we analyzed C2C12 myotubes and mouse skelet...

We examined changes in skeletal muscle protein lactylation and acetylation in response to acute resistance exercise, chronic resistance training (RT), and a single endurance cycling bout. Additionally, we performed in vitro experiments to determine if different sodium lactate treatments affect myotube protein lactylation and acetylation. The acute...

We examined how resistance exercise (RE), cycling exercise and disuse atrophy affect myosin heavy chain (MyHC) protein fragmentation. The 1boutRE study involved younger men (n = 8; 5 ± 2 years of RE experience) performing a lower body RE bout with vastus lateralis (VL) biopsies being obtained prior to and acutely following exercise. With the 10week...

The aim of this study was to investigate whether baseline values and acute and chronic changes in androgen receptors (AR) markers, including total AR, cytoplasmic (cAR) and nuclear (nAR) fractions, as well as DNA-binding activity (AR-DNA), are involved in muscle hypertrophy responsiveness by comparing young nonresponder and responder individuals. A...

In this issue, Burke et al. discuss the utility of the rodent synergist ablation (SA) model for examining mechanisms associated with skeletal muscle hypertrophy. In this invited perspective, we aim to complement their original perspective by discussing limitations to the model along with alternative mechanical overload models that have strengths an...

Skeletal muscle wasting is the hallmark pathophysiological adaptation to unloading or disuse that demonstrates the dependency on frequent mechanical stimulation (e.g. muscle activation and subsequent loading) for homeostasis of normally load‐bearing muscles. In the absence of mitigation strategies, no mammalian organism is resistant to muscle atrop...

We sought to examine how resistance training (RT) status in young healthy individuals, either well-trained (T, n=10 (8 males)) or untrained (UT, n=11 (8 males)), affected muscle size and molecular markers with leg immobilization followed by recovery RT. All participants underwent two weeks of left leg immobilization via the use of crutches and a lo...

Ribosomal DNA (rDNA) copies exist across multiple chromosomes and inter-individual variation in copy number is speculated to influence the hypertrophic response to resistance training. Thus, we examined if rDNA copy number was associated with resistance training-induced skeletal muscle hypertrophy. Participants (n=53 males, 21±1 years old; n=29 fem...

Purpose Androgen receptor (AR) expression and signaling has been regarded as a mechanism for regulating muscle hypertrophy. However, little is known about the associations between acute and chronic changes in skeletal muscle total AR, cytoplasmic AR (cAR), nuclear AR (nAR) and AR DNA-binding (AR-DNA) induced by resistance training (RT) and hypertro...

ABSTRACT Position statement: The International Society of Sports Nutrition (ISSN) provides an objective and critical review of the use of a ketogenic diet in healthy exercising adults, with a focus on exercise performance and body composition. However, this review does not address the use of exogenous ketone supplements. The following points summar...

Our laboratory has performed various experiments examining the proteomic alterations that occur with mechanical overload (MOV)-induced skeletal muscle hypertrophy. In the current study we first sought to determine how 10 weeks of resistance training in 15 college-aged females affected protein concentrations in different tissue fractions. Training,...

We sought to examine how resistance exercise (RE), cycling exercise, and disuse atrophy affect myosin heavy chain (MyHC) protein fragmentation in humans. In the first study (1boutRE), younger adult men (n=8; 5+/-2 years of RE experience) performed a lower body RE bout with vastus lateralis (VL) biopsies obtained immediately before, 3-, and 6-hours...

Introduction: Vimentin (VIM) is an intermediate filament that plays a key role in development and regeneration of various tissue types. However, the expression of VIM during skeletal muscle hypertrophy has not been fully elucidated. Therefore, the purpose of this study was to determine the response of VIM following mechanical overload (MOV) with or...

Introduction: The effects of higher-load (HL; sets of 5 repetitions at 80% of 1-RM) versus higher-volume (HV; sets of 10 repetitions at 60% of 1-RM) resistance training (RT) on various molecular outcomes has proven to be similar between the two paradigms. However, the mitochondrial response to such training paradigms remains understudied. Therefore...

Aging and disuse can impair skeletal muscle responses to stimuli and are key drivers in dysregulated proteostasis. Such dysfunction can lead to an accumulation of misfolded proteins resulting in endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR). While the UPR blunts global translation and enhances the production of chaperon...

Limb immobilization causes rapid declines in muscle strength and mass. Given the role of the nervous system in immobilization‐induced weakness, targeted interventions may be able to preserve muscle strength, but not mass, and vice versa. The purpose of this study was to assess the effects of two distinct interventions during 1 week of knee joint im...

Peripheral quantitative computed tomography (pQCT) has recently expanded to quantifying skeletal muscle, however its validity to determine muscle cross‐sectional area (mCSA) compared to magnetic resonance imaging (MRI) is unknown. Eleven male participants (age: 22 ± 3 y) underwent pQCT and MRI dual‐leg mid‐thigh imaging before (PRE) and after (POST...

Purpose Resistance training (RT) induces muscle growth at varying rates across RT phases, and evidence suggests that the muscle-molecular responses to training bouts become refined or attenuated in the trained state. This study examined how proteolysis-related biomarkers and extracellular matrix (ECM) remodeling factors respond to a bout of RT in t...

Denervated myofibers and senescent cells are hallmarks of skeletal muscle aging. However, sparse research has examined how resistance training affects these outcomes. We investigated the effects of unilateral leg extensor resistance training (2 days/week for 8 weeks) on denervated myofibers, senescent cells, and associated protein markers in appare...

The skeletal muscle proteome alterations to aging and resistance training have been reported in prior studies. However, conventional proteomics in skeletal muscle typically yields wide protein abundance ranges that mask the detection of lowly expressed proteins. Thus, we adopted a novel deep proteomics approach whereby myofibril (MyoF) and non-MyoF...

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e. an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e. myofibril hypertrophy) and/or the numbe...

Ribosomal DNA (rDNA) copies are organized in tandem repeats across multiple chromosomes, and inter-individual variation in rDNA copy number has been speculated to be a modifier of the hypertrophic responses to resistance training. In the current study, 82 apparently healthy participants (n=53 males, 21±1 years old; n=29 females, 21±2 years old) per...

Blood flow restriction applied during low-load resistance training (LL-BFR) induces a similar increase in the cross-sectional area of muscle fibers (fCSA) compared to traditional high-load resistance training (HL-RT). However, it is unclear whether LL-BFR leads to differential changes in myofibrillar spacing in muscle fibers and/or extracellular ar...

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the num...

Through decades of empirical data, it has become evident that resistance training (RT) can improve strength/power and skeletal muscle hypertrophy. Yet, until recently, vascular outcomes have historically been underemphasized in RT studies, which is underscored by several exercise-related reviews supporting the benefits of endurance training on vasc...

The aim of this study was to compare the effects of progressive overload in resistance training, specifically comparing the impact of increasing load (LOADprog) versus an increase in repetitions (REPSprog), on muscle strength and cross-sectional area (CSA). We used a within-subject experimental design in which 39 previously untrained young (20 men...

Acute exercise has been shown to improve scores on tests of cognitive function. The cognitive variables that improve with acute exercise are also associated with esport performance. This randomized control trial examined whether performing a high-intensity interval training (HIIT) exercise bout prior to esport competitions produced improvement in S...

Objective The purpose of this study was to examine the acute effects of a multi-ingredient, low calorie dietary supplement (MIDS, XTEND® Healthy Hydration) on 5-kilometer (5-km) time trial performance and blood electrolyte concentrations compared to a carbohydrate-electrolyte beverage (CE, GATORADE® Thirst Quencher) and distilled water (W). Method...

Evolutionary physiologists have long been interested in physiological mechanisms underpinning variation in life-history performance. Recent efforts to elucidate these mechanisms focused on bioenergetics and oxidative stress. One underappreciated area that could play a role in mediating variation in performance is the unfolded protein response (UPR)...

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the num...

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the num...

We examined how set-volume equated resistance training using either the back squat (SQ) or hip thrust (HT) affected hypertrophy and various strength outcomes. Untrained college-aged participants were randomized into HT (n = 18) or SQ (n = 16) groups. Surface electromyograms (sEMG) from the right gluteus maximus and medius muscles were obtained duri...

Position Statement: The International Society of Sports Nutrition (ISSN) presents this position based on a critical examination of literature surrounding the effects of essential amino acid (EAA) supplementation on skeletal muscle maintenance and performance. This position stand is intended to provide a scientific foundation to athletes, dietitians...

Denervated myofibers and senescent cells are hallmarks of skeletal muscle aging. However, sparse research has examined how resistance training affects these outcomes. We investigated the effects of unilateral leg extensor resistance training on denervated myofibers, senescent cells, and associated protein markers in middle-aged participants (MA, 55...

Tumor necrosis factor (TNF) binding to endothelial TNF receptor-I (TNFR-I) facilitates monocyte recruitment and chronic inflammation, leading to the development of atherosclerosis. In vitro data show a heightened inflammatory response and atherogenic potential in endothelial cells (ECs) from African American (AA) donors. High laminar shear stress (...

Although several reports have hypothesized that exercise may increase skeletal muscle protein lactylation, empirical evidence in humans is lacking. Thus, we adopted a multi-faceted approach to examine if acute and subchronic resistance training (RT) altered skeletal muscle protein lactylation levels. In mice, we also sought to examine if surgical a...

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the num...

Purpose of review: The purpose of this opinion paper is to provide current-day and evidence-based information regarding dietary supplements that support resistance training adaptations or acutely enhance strength-power or endurance performance. Recent findings: Several independent lines of evidence support that higher protein diets, which can be...

We recently reported that vastus lateralis (VL) cross‐sectional area (CSA) increases after 7 weeks of resistance training (RT, 2 days/week), with declines occurring following 7 weeks of subsequent treadmill high‐intensity interval training (HIIT) (3 days/week). Herein, we examined the effects of this training paradigm on skeletal muscle proteolytic...

Measures of neuromuscular function are commonly obtained in the research disciplines of aging, disease physiology, and exercise science. The methods used to assess neuromuscular function range in sophistication. Here, we provide comprehensive overviews of strength testing, dynamometer assessments, the use of force plates, and evoked potentials. Our...

Godwin, JS, Telles, GD, Vechin, FC, Conceição, MS, Ugrinowitsch, C, Roberts, MD, and Libardi, CA. Time course of proteolysis biomarker responses to resistance, high-intensity interval, and concurrent exercise bouts. J Strength Cond Res XX(X): 000-000, 2023-Concurrent exercise (CE) combines resistance exercise (RE) and high-intensity interval exerci...

We investigated the effects of performing a period of resistance training (RT) on the performance and molecular adaptations to a subsequent period of endurance training (ET). Twenty‐five young adults were divided into an RT+ET group (n = 13), which underwent 7 weeks of RT followed by 7 weeks of ET, and an ET‐only group (n = 12), which performed 7 w...

Trained individuals may require variations in training stimuli and advanced resistance training paradigms (ADV) to increase skeletal muscle hypertrophy. However, no meta-analysis has examined how ADV versus traditional (TRAD) approaches may diferentially afect hypertrophic outcomes in trained populations. Te aim of this review was to determine whet...

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill-trained. Much of the pre-clinical rodent and human resistance training research to date supports that involved mechanisms include enhanc...

Purpose: We examined how set-volume equated resistance training using either the back squat (SQ) or hip thrust (HT) affected hypertrophy and various strength outcomes. Methods: Untrained college-aged participants were randomized into HT (n=18) or SQ (n=16) groups. Surface electromyograms (sEMG) from the right gluteus maximus and medius muscles were...

We examined the myofibrillar (MyoF) and non-myofibrillar (non-MyoF) proteomic profiles of the vastus lateralis (VL) muscle of younger (Y, 22+/-2 years old; n=5) and middle-aged participants (MA, 56+/-8 years old; n=6), and MA following eight weeks of knee extensor resistance training (RT, 2d/week). Shotgun/bottom-up proteomics in skeletal muscle ty...

Objectives: To investigate the gut-brain axis, we explored the relationships among mood disturbance (MD), diet quality (DQ), and fecal microbiota in free-living adults. Methods: A cross-sectional analysis was conducted with data from 75 healthy adults enrolled in two studies. Anthropometrics, 16s rRNA gene sequencing of fecal microbes, DQ as ass...

Abstract Limited research exists examining how resistance training to failure affects applied outcomes and single motor unit characteristics in previously trained individuals. Herein, resistance‐trained adults (24 ± 3 years old, self‐reported resistance training experience was 6 ± 4 years, 11 men and 8 women) were randomly assigned to either a low‐...

Although several resistance exercise studies have used bioinformatics platforms to identify the biological relevance of gene expression changes, these platforms seldom provide in-depth information on genes that have been mechanistically linked to skeletal muscle hypertrophy. Thus, we sought to perform a secondary analysis on a muscle transcriptomic...

Herein, we determined if a multi-ingredient supplement (NAD3; 312 mg of combined Wasabia japonica extract, theacrine, and copper (I)niacin chelate) versus a placebo (CTL) affected peripheral blood mononuclear (PMBC) transcriptomic, DNA methylation, and sirtuin activity profiles in middle-aged adults after 12 weeks of supplementation. Several mRNAs...

The effects of low load resistance training with blood flow restriction (BFR) on hypertrophy of type I/II myofibers remains unclear, especially in females. The purpose of the present study is to examine changes in type I/II myofiber cross-sectional area (fCSA) and muscle CSA (mCSA) of the vastus lateralis (VL) pre- to post-6 weeks of high load resi...

We investigated the effects of performing a period of resistance training (RT) on the performance and molecular adaptations to a subsequent period of endurance training (ET). Twenty-five young adults were divided into RT+ET (n=13), which underwent seven weeks of RT followed by seven weeks of ET, and ET-only (n=12), which performed seven weeks of ET...

Although transcriptome profiling has been used in several resistance training studies, the associated analytical approaches seldom provide in-depth information on individual genes linked to skeletal muscle hypertrophy. Therefore, a secondary analysis was performed herein on a muscle transcriptomic dataset we previously published involving trained c...

We determined if skeletal muscle extracellular matrix (ECM) content and remodeling markers adapted with resistance training or were associated with hypertrophic outcomes. Thirty-eight untrained males (21±3 yrs.) participated in whole-body resistance training (10 weeks, 2x weekly). Participants completed testing (ultrasound, peripheral quantitative...