Robert Morton

Population Health Research Institute | PHIRI · Genetic & Molecular Epidemiology

Objective We performed a systematic review, meta-analysis and meta-regression to determine if dietary protein supplementation augments resistance exercise training (RET)-induced gains in muscle mass and strength. Data sources A systematic search of Medline, Embase, CINAHL and SportDiscus. Eligibility criteria Only randomised controlled trials wit...

Purpose of review: Skeletal muscle mass with aging, during critical care, and following critical care is a determinant of quality of life and survival. In this review, we discuss the mechanisms that underpin skeletal muscle atrophy and recommendations to offset skeletal muscle atrophy with aging and during, as well as following, critical care. Re...

Resistance exercise training (RET)-induced increases in voluntary 1RM strength are greater with higher loads and training by replicating (or close) the strength test. In contrast, RET-induced muscular hypertrophy is primarily mediated by intensity of effort, which is achieved by performing RET to volitional fatigue and with an internal focus on con...

Key points Performing resistance exercise with heavier loads is often proposed to be necessary for the recruitment of larger motor units and activation of type II muscle fibres, leading to type II fibre hypertrophy. Indirect measures [surface electromyography (EMG)] have been used to support this thesis, although we propose that lighter loads lifte...

Background Low buffy coat mitochondrial DNA copy number (mtDNA-CN) is associated with incident risk of stroke and post-stroke mortality; however, its prognostic utility has not been extensively explored. Objective To investigate whether low buffy coat mtDNA-CN is a marker and causal determinant of post-stroke outcomes using epidemiological and gen...

A majority of human genes produce non-protein-coding RNA (ncRNA), and some have roles in development and disease. Neither ncRNA nor human skeletal muscle is ideally studied using short-read sequencing, so we used a customised RNA pipeline and network modelling to study cell-type specific ncRNA responses during muscle growth at scale. We completed f...

A majority of human genes produce non protein-coding RNA (ncRNA) and some have important roles in development and disease. Neither ncRNA nor multinucleated adult human skeletal muscle is ideally studied using sequencing technologies, so using a customised RNA profiling pipeline and quantitative network modelling we studies cell-type specific ncRNA...

It has been postulated that rare coding variants (RVs; MAF < 0.01) contribute to the “missing” heritability of complex traits. We developed a framework, the Rare variant heritability (RARity) estimator, to assess RV heritability (h²RV) without assuming a particular genetic architecture. We applied RARity to 31 complex traits in the UK Biobank (n =...

Importance Body mass index (BMI) is an easily obtained adiposity surrogate. However, there is variability in body composition and adipose tissue distribution between individuals with the same BMI, and there is controversy regarding the BMI associated with the lowest mortality risk. Objective To evaluate which of BMI, fat mass index (FMI), and wais...

Identification of gene-by-environment interactions (GxE) is crucial to understand the interplay of environmental effects on complex traits. However, current methods evaluating GxE on biobank-scale datasets have limitations. We introduce MonsterLM, a multiple linear regression method that does not rely on model specification and provides unbiased es...

It has been postulated that rare coding variants (RVs; MAF<0.01) contribute to the “missing” heritability of complex traits. We developed a novel framework, the Rare variant heritability (RARity) estimator, to assess RV heritability (h2RV) without assuming a particular genetic architecture. We applied RARity to 31 complex traits in the UK Biobank (...

Importance: Body mass index (BMI) is an easily obtainable surrogate for adiposity. However, there is substantial variability in body composition and adipose tissue distribution between individuals with the same BMI. Furthermore, previous literature is conflicting regarding the optimal BMI linked with the lowest mortality risk. Objective: To determi...

Background: Mitochondrial DNA copy number (mtDNA-CN) is an accessible blood-based measurement believed to capture underlying mitochondrial function. The specific biological processes underpinning its regulation, and whether those processes are causative for disease, is an area of active investigation. Methods: We developed a novel method for array-...

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...

Mitochondrial DNA copy number (mtDNA-CN) is an accessible blood-based measurement believed to capture underlying mitochondrial function. The specific biological processes underpinning its regulation, and whether those processes are causative for disease, is an area of active investigation. We developed a novel method for array-based mtDNA-CN estima...

Magnetic resonance imaging (MRI) is the current gold standard for measuring changes in muscle size (cross-sectional area [CSA] and volume) but can be cost-prohibitive and resource-intensive. We evaluated the validity of B-mode ultrasonography (US) as a low-cost alternative to MRI for measuring muscle hypertrophy and atrophy in response to resistanc...

Testosterone products are prescribed to males for a variety of possible health benefits, but causal effects are unclear. Evidence from randomized trials are difficult to obtain, particularly regarding effects on long-term or rare outcomes. Mendelian randomization analyses were performed to infer phenome-wide effects of free testosterone on 461 outc...

Testosterone products are prescribed to males for a variety of possible health benefits, but causal effects are unclear. Evidence from randomized trials are difficult to obtain, particularly regarding effects on long-term or rare outcomes. Mendelian randomization analyses were performed to infer phenome-wide effects of free testosterone on 461 outc...

Testosterone products are prescribed to males for a variety of possible health benefits, but causal effects are unclear. Evidence from randomized trials are difficult to obtain, particularly regarding effects on long-term or rare outcomes. Mendelian randomization analyses were performed to infer phenome-wide effects of free testosterone on 461 outc...

Loading of skeletal muscle changes the tissue phenotype reflecting altered metabolic and functional demands. In humans, heterogeneous adaptation to loading complicates the identification of the underpinning molecular regulators. A within-person differential loading and analysis strategy reduces heterogeneity for changes in muscle mass by ~40% and u...

β-hydroxy-β-methylbutyrate (HMB) is a leucine metabolite that is purported to increase fat-free mass (FFM) gain and performance in response to resistance exercise training (RET). The aim of this systematic review and meta-analysis was to determine the efficacy of HMB supplementation in augmenting FFM and strength gains during RET in young adults. O...

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...

Carotid artery longitudinal wall motion (CALM) exhibits reduced magnitude in older adults and in individuals with chronic diseases, although longitudinal data are lacking to indicate how changes in CALM might develop over time. Therefore, the aim of this study was to investigate the impact of exercise training in healthy men on CALM using a retrosp...

BACKGROUND: Testosterone products are increasingly being prescribed to males for a variety of possible health benefits but the causal relationship between testosterone and health-related outcomes is unclear. Evidence from well-powered randomized controlled trials are difficult to obtain, particularly regarding effects on long-term or adverse outcom...

Introduction: Lower-load (LL), higher-repetition resistance exercise training (RET) can increase muscle mass similar degree as higher-load (HL), lower-repetition RET. However, little is known about how LL and HL RET modulate other aspects of the RET phenotype such as satellite cells, myonuclei, and mitochondrial proteins. We aimed to investigate c...

Leucine metabolites may reduce training-induced inflammation; however, there is scant evidence for this assertion. We conducted a double-blind randomized controlled pragmatic trial where 40 male participants were allocated into 4 groups: α-hydroxyisocaproic acid group ([α-HICA], n = 10, Fat-free mass [FFM] = 62.0 ± 7.1 kg), β-hydroxy-β-methylbutyra...

Objective To determine the effects of multi-ingredient protein (MIP) supplements on resistance exercise training (RT)-induced gains in muscle mass and strength compared with protein-only (PRO) or placebo supplementation. Data sources Systematic search of MEDLINE, Embase, CINAHL and SPORTDiscus. Eligibility criteria Randomised controlled trials wi...

Previous longitudinal studies suggest that left ventricular (LV) structure is unaltered with resistance exercise training (RT) in young men. However, evidence from aerobic exercise training suggests that early changes in functional LV wall mechanics may occur prior to and independently of changes in LV size, although short-term changes in LV mechan...

Background Higher-protein (HP) diets are advocated for several reasons, including mitigation of sarcopenia, but their effects on kidney function are unclear. Objective This meta-analysis was conducted to determine the effect of HP intakes on kidney function in healthy adults. Methods We conducted a systematic review and meta-analysis of trials co...

Transient periods of physical inactivity can result in losses of skeletal muscle mass and reductions in insulin sensitivity. These metabolic impairments may not be fully recovered, particularly in older individuals. ¹ We aimed to examine the impact of two weeks of reduced steps followed by two weeks of recovery, on lean body mass (LBM), integrated...

Recent evidence has established that repetition load determines neither acute rates of muscle protein synthesis or resistance training‐induced hypertrophy. Our objective was to extend on these findings by examining if skeletal muscle hypertrophy following resistance exercise training is instead determined by the degree of motor unit activation. Ten...

The factors that underpin heterogeneity in muscle hypertrophy following resistance exercise training (RET) remain largely unknown. We examined circulating hormones, intramuscular hormones, and intramuscular hormone-related variables in resistance-trained men before and after 12 weeks of RET. Backward elimination and principal component regression e...

Ingestion of proteins with high leucine content during resistance training (RT) can augment hypertrophy. Some data suggest that a leucine metabolite, β-hydroxy, β-methylbutyrate (HMB), is substantially more anabolically efficacious than leucine. Purpose: We aimed to test whether supplementation with HMB versus leucine, added to whey protein, woul...

Resistance training promotes microvasculature expansion; however, it remains unknown how different resistance training programs contribute to angiogenesis. Thus, we recruited experienced resistance trained participants and determined the effect of 12 wk of either high-repetition/low-load or low-repetition/high-load resistance training performed to...

Skeletal muscle supports locomotion and serves as the largest site of postprandial glucose disposal; thus it is a critical organ for physical and metabolic health. Skeletal muscle mass is regulated by the processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB), both of which are sensitive to external loading and aminoacidemia...

Background Physical inactivity impairs insulin sensitivity, which is exacerbated with aging. We examined the impact of two weeks of acute inactivity and recovery on glycemic control, integrated rates of muscle protein synthesis (MPS) in older men and women. Methods Twenty-two overweight, pre-diabetic older adults (12 men, 10 women, 69 ± 4 yr) unde...

Purpose: Discrepancies regarding the effect of resistance exercise training (RET) on arterial stiffness have led to uncertainty regarding the effect of RET on cardiovascular health. Confounding our understanding in this area are the roles of the following: load (heavier vs lighter), participant cardiovascular health, and arterial stiffness assessm...

We reported, using a unilateral resistance training (RT) model, that training with high or low loads (mass per repetition) resulted in similar muscle hypertrophy and strength improvements in RT-naïve subjects. Here we aimed to determine whether the same was true in men with previous RT experience using a whole-body RT program and whether post-exerc...

Purpose: Self-myofascial release (SMR) is a common exercise and therapeutic modality shown to induce acute improvements in joint range of motion (ROM) and recovery; however, no long-term studies have been conducted. Static stretching (SS) is the most common method used to increase joint ROM and decrease muscle stiffness. We hypothesized that SMR p...

Skeletal muscle mass is regulated by a balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). In healthy humans, MPS is more sensitive (varying 4–5 times more than MPB) to changes in protein feeding and loading rendering it the primary locus determining gains in muscle mass. Performing resistance exercise (RE) followed b...