Superior Aerobic Capacity and Indices of Skeletal Muscle Morphology in Chronically Trained Master Endurance Athletes Compared With Untrained Older Adults

Mitigating disuse-induced skeletal muscle atrophy in ageing: Resistance exercise as a critical countermeasure

The gradual deterioration of physiological systems with ageing makes it difficult to maintain skeletal muscle mass (sarcopenia), at least partly due to the presence of 'anabolic resistance', resulting in muscle loss. Sarcopenia can be transiently but markedly accelerated through periods of muscle disuse-induced (i.e., unloading) atrophy due to reduced physical activity, sickness, immobilisation or hospitalisation. Periods of disuse are detrimental to older adults' overall quality of life and substantially increase their risk of falls, physical and social dependence, and early mortality. Disuse events induce skeletal muscle atrophy through various mechanisms, including anabolic resistance, inflammation, disturbed proteostasis and mitochondrial dysfunction, all of which tip the scales in favour of a negative net protein balance and subsequent muscle loss. Concerningly, recovery from disuse atrophy is more difficult for older adults than their younger counterparts. Resistance training (RT) is a potent anabolic stimulus that can robustly stimulate muscle protein synthesis and mitigate muscle losses in older adults when implemented before, during and following unloading. RT may take the form of traditional weightlifting-focused RT, bodyweight training and lower- and higher-load RT. When combined with sufficient dietary protein, RT can accelerate older adults' recovery from a disuse event, mitigate frailty and improve mobility; however, few older adults regularly participate in RT. A feasible and practical approach to improving the accessibility and acceptability of RT is through the use of resistance bands. Moving forward, RT must be prescribed to older adults to mitigate the negative consequences of disuse atrophy.

Single- Versus Double-Leg Cycling: Small Muscle Mass Exercise Improves Exercise Capacity to a Greater Extent in Older Compared With Younger Population

Manipulating the amount of muscle mass engaged during exercise can noninvasively inform the contribution of central cardiovascular and peripheral vascular-oxidative functions to endurance performance. To better understand the factors contributing to exercise limitation in older and younger individuals, exercise performance was assessed during single-leg and double-leg cycling. 16 older (67 ± 5 years) and 14 younger (35 ± 5 years) individuals performed a maximal exercise using single-leg and double-leg cycling. The ratio of single-leg to double-leg cycling power (RatioPower SL/DL) was compared between age groups. The association between fitness (peak oxygen consumption, peak power output, and physical activity levels) and RatioPower SL/DL was explored. The RatioPower SL/DL was greater in older compared with younger individuals (1.14 ± 0.11 vs. 1.06 ± 0.08, p = .041). The RatioPower SL/DL was correlated with peak oxygen consumption (r = .886, p < .001), peak power output relative to body mass (r = .854, p < .001), and levels of physical activity (r = .728, p = .003) in the younger but not older subgroup. Reducing the amount of muscle mass engaged during exercise improved exercise capacity to a greater extent in older versus younger population and may reflect a greater reduction in central cardiovascular function compared with peripheral vascular-oxidative function with aging.

Analysis of Common Exercise Modalities in Improving Athletic Performance in Older Adults: A Narrative Review

ABSTRACT

Exercise leads to robust cardiovascular, musculoskeletal, and psychological benefits that improve quality of life and longevity for older adults, but accompanying improvements in athletic parameters are less well explored. The aim of this review is to summarize some of the most common exercise modalities, namely, Pilates, martial arts (tai chi, Japanese-style karate, hard martial arts), locomotion (brisk walking/jogging and running), Masters sports, resistance training, and high-intensity interval training, in improving athletic performance for older adults. Regular participation in these activities can have robust yet unique impacts on physical performance that prolong exercise participation. In particular, this review will explore benefits in cardiorespiratory fitness, power, strength, flexibility, and balance, thereby hopefully improving endurance, exercise adherence, and overall fall risk. A narrative literature review was performed to explore benefits, pitfalls, and recommendations for some of the most popular exercise modalities for older adults.

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes

INTRODUCTION

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance.

METHODS

Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8 ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue.

RESULTS

Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9 s; P = 0.017), and respiratory muscle force development decreased during inspiration (- 22.8 ± 11.6%, P < 0.001) and expiration (- 10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions.

CONCLUSIONS

Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

Age-Related Study of Anthropometry Indicators, Body Composition, Strength and Vital Capacity at Masters Athletics: How to Postpone Sarcopenia

Purpose

The purpose of this study was to compare the anthropometric indicators of sports veterans, former athletes who stopped training, and non-sports people aged 40 years and older to assess the impact of regular sports on the stability of the body.

Patients and Methods

100 athletes and 31 people non-sports were included in the study. Athletes were divided into two groups depending on the mode of motor activity. The first group (n=75) continued their regular sports activities. The second group (n=25) stopped training. Height, weight, chest circumference, mobility, waist, shoulder circumference, forearm, hip, ankle, fat mass, and muscle mass were measured, and dynamometry was performed.

Results

Body weight is statistically significantly (p<0.05) less in those who continue sports (70.7±10.2) classes after 60 years compared with the control group (82.4±9.3). In sports veterans, the chest excursion and the shoulder circumference is statistically significantly (p<0.05) greater than in the control group. In the subjects of the first group aged from 40 to 49 (4551±612) and from 50 to 59 (4242±416), the FVC index was statistically significantly (p<0.05) higher than in the control group (3890±344 and 3786±401, respectively). The body composition of veterans is characterized by a high level of muscle mass and a low level of fat mass. At the age of 40-49, the percentage of muscle tissue in sports veterans was statistically significantly higher (46.32±2.74) (p<0.05) than in the group of athletes who stopped sports activities (44.09±5.29).

Conclusion

Veterans of sports demonstrate higher indicators of limb girth and muscle strength compared to untrained people of the same age. In addition, sports veterans have a lower content of adipose tissue and a greater expression of muscle mass. Thus, the data obtained by us show that sports prevent the development of sarcopenia and can also affect cardiovascular risk.

The Impact of Sport-discipline and Sex on Physical Fitness and Bone Markers in Athletes

This study was performed to determine the impact of sex and sport-discipline on physical fitness and bone markers in young sub-elite track and field athletes. One hundred and forty-four track and field sub-elite athletes (78 males aged 17.8±1.6 years; 66 females aged 17.2±1.9 years) volunteered to participate in this study and were categorized according to their disciplines in endurance (EG: n=67) or power athletes (PG: n=77). A significant main effect of sex was observed for C-telopeptide type I collagen (CTx) (F=11.37; p<0.001; η2=0.10, moderate), for osteocalcin (OC) (F=8.58; p<0.004; η2=0.09, moderate) and for N-terminal propeptide of procollagen type I (PINP) (F=7.96; p<0.05; η2=0.07, moderate). The average CTx, OC and P1NP levels were significantly higher in males compared with females (0.05 Collapse

Key Words Collapse

MESH Headings

• Female
• Humans
• Male
• Sports
• Athletes
• Collagen Type I
• Exercise
• Physical Fitness
• Biomarkers
• Peptide Fragments

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Grants Collapse

Affiliation(s)

Ammar Nebigh Research Laboratory Education, Motricity, Sports and Health, High Institute of Sport and Physical Education, Sfax University, Sfax, Tunisia Higher Institute of Sport and Physical Education of Ksar Saîd, University of "La Manouba", Tunis, Tunisia
Imed Touhami National Center of Medicine and Science in Sports, Tunisian Research Laboratory "Sports Performance Optimization", National Center of Medicine and Science in Sports (CNMSS), Tunis, Tunisia
Mokhtar Chtara Unit Head, Science Studies and Research, Sharjah Women's Sports, UAE Tunisian Research Laboratory "Sport Performance Optimization", National Center of Medicine and Science in Sports, Tunis, Tunisia
Karuppasamy Govindasamy Department of Physical Education & Sports Science, SRM Institute of Science and Technology, Kattankulathur, Tamilnadu, India
Chandrababu Surech Department of Physical Education & Sports Science, SRM Institute of Science and Technology, Kattankulathur, Tamilnadu, India
Rawad El Hage Department of Physical Education, University of Balamand, Balamand, Lebanon
Ayoub Saeidi Department of Physical Education and Sport Sciences, Faculty of Humanities and Social Sciences, University of Kurdistan, Sanandaj, Kurdistan, Iran
Daniel Boullosa INISA, Federal University of Mato Grosso do Sul, Campo Grande, Brazil Faculty of Physical Activity and Sports Sciences, Universidad de León, León, Spain
Cain C T Clark Centre for Intelligent Healthcare, Coventry University, Coventry, United Kingdom of Great Britain and Northern Ireland
Urs Granacher University of Freiburg, Department of Sport and Sport Science, Exercise and Human Movement Science, Freiburg, Germany
Hassane Zouhal UFR APS, laboratoire Mouvement Sport Sante, Rennes, France Institut International des Sciences du Sport (2I2S), Irodouer, France

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Chronic training status affects muscle excitation of the vastus lateralis during repeated contractions

This study examined electromyographic amplitude (EMG_RMS)-force relationships during repeated submaximal knee extensor muscle actions among chronic aerobically-(AT), resistance-trained (RT), and sedentary (SED) individuals. Fifteen adults (5/group) attempted 20 isometric trapezoidal muscle actions at 50% of maximal strength. Surface electromyography (EMG) was recorded from vastus lateralis (VL) during the muscle actions. For the first and last successfully completed contractions, linear regression models were fit to the log-transformed EMG_RMS-force relationships during the linearly increasing and decreasing segments, and the b terms (slope) and a terms (antilog of y-intercept) were calculated. EMG_RMS was averaged during steady force. Only the AT completed all 20 muscle actions. During the first contraction, the b terms for RT (1.301 ​± ​0.197) were greater than AT (0.910 ​± ​0.123; p ​= ​0.008) and SED (0.912 ​± ​0.162; p ​= ​0.008) during the linearly increasing segment, and in comparison to the linearly decreasing segment (1.018 ​± ​0.139; p ​= ​0.014), respectively. For the last contraction, the b terms for RT were greater than AT during the linearly increasing (RT ​= ​1.373 ​± ​0.353; AT ​= ​0.883 ​± ​0.129; p ​= ​0.018) and decreasing (RT ​= ​1.526 ​± ​0.328; AT ​= ​0.970 ​± ​0.223; p ​= ​0.010) segments. In addition, the b terms for SED increased from the linearly increasing (0.968 ​± ​0.144) to decreasing segment (1.268 ​± ​0.126; p ​= ​0.015). There were no training, segment, or contraction differences for the a terms. EMG_RMS during steady force increased from the first- ([64.08 ​± ​51.68] ​μV) to last-contraction ([86.73 ​± ​49.55] ​μV; p ​= ​0.001) collapsed across training statuses. The b terms differentiated the rate of change for EMG_RMS with increments in force among training groups, indicating greater muscle excitation to the motoneuron pool was necessary for the RT than AT during the linearly increasing and decreasing segments of a repetitive task.

The Impact of Training on the Loss of Cardiorespiratory Fitness in Aging Masters Endurance Athletes

Elite masters endurance athletes are considered models of optimal healthy aging due to the maintenance of high cardiorespiratory fitness (CRF) until old age. Whereas a drop in VO₂max in masters athletes has been broadly investigated, the modifying impact of training still remains a matter of debate. Longitudinal observations in masters endurance athletes demonstrated VO₂max declines between -5% and -46% per decade that were closely related to changes in training volume. Here, using regression analyses, we show that 54% and 39% of the variance in observed VO₂max decline in male and female athletes, respectively is explained by changes in training volume. An almost linear VO₂max decrease was observed in studies on young and older athletes, as well as non-athletes, starting a few days after training cessation, with a decline of as much as -20% after 12 weeks. Besides a decline in stroke volume and cardiac output, training cessation was accompanied by considerable reductions in citrate synthase and succinate dehydrogenase activity (reduction in mitochondrial content and oxidative capacity). This reduction could largely be rescued within similar time periods of training (re)uptake. It is evident that training reduction or cessation leads to a considerably accelerated VO₂max drop, as compared to the gradual aging-related VO₂max decline, which can rapidly nullify many of the benefits of preceding long-term training efforts.

Preserved stem cell content and innervation profile of elderly human skeletal muscle with lifelong recreational exercise

Abstract

Muscle fibre denervation and declining numbers of muscle stem (satellite) cells are defining characteristics of ageing skeletal muscle. The aim of this study was to investigate the potential for lifelong recreational exercise to offset muscle fibre denervation and compromised satellite cell content and function, both at rest and under challenged conditions. Sixteen elderly lifelong recreational exercisers (LLEX) were studied alongside groups of age‐matched sedentary (SED) and young subjects. Lean body mass and maximal voluntary contraction were assessed, and a strength training bout was performed. From muscle biopsies, tissue and primary myogenic cell cultures were analysed by immunofluorescence and RT‐qPCR to assess myofibre denervation and satellite cell quantity and function. LLEX demonstrated superior muscle function under challenged conditions. When compared with SED, the muscle of LLEX was found to contain a greater content of satellite cells associated with type II myofibres specifically, along with higher mRNA levels of the beta and gamma acetylcholine receptors (AChR). No difference was observed between LLEX and SED for the proportion of denervated fibres or satellite cell function, as assessed in vitro by myogenic cell differentiation and fusion index assays. When compared with inactive counterparts, the skeletal muscle of lifelong exercisers is characterised by greater fatigue resistance under challenged conditions in vivo, together with a more youthful tissue satellite cell and AChR profile. Our data suggest a little recreational level exercise goes a long way in protecting against the emergence of classic phenotypic traits associated with the aged muscle.

Key points

The detrimental effects of ageing can be partially offset by lifelong self‐organized recreational exercise, as evidence by preserved type II myofibre‐associated satellite cells, a beneficial muscle innervation status and greater fatigue resistance under challenged conditions.

Satellite cell function (in vitro), muscle fibre size and muscle fibre denervation determined by immunofluorescence were not affected by recreational exercise.

Individuals that are recreationally active are far more abundant than master athletes, which sharply increases the translational perspective of the present study. Future studies should further investigate recreational activity in relation to muscle health, while also including female participants.

Exercise in Octogenarians: How Much Is Too Little?

The global population is rapidly aging, with predictions of many more people living beyond 85 years. Age-related physiological adaptations predispose to decrements in physical function and functional capacity, the rate of which can be accelerated by chronic disease and prolonged physical inactivity. Decrements in physical function exacerbate the risk of chronic disease, disability, dependency, and frailty with advancing age. Regular exercise positively influences health status, physical function, and disease risk in adults of all ages. Herein, we review the role of structured exercise training in the oldest old on cardiorespiratory fitness and muscular strength and power, attributes critical for physical function, mobility, and independent living. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A mycoprotein-based high-protein vegan diet supports equivalent daily myofibrillar protein synthesis rates compared with an isonitrogenous omnivorous diet in older adults: a randomised controlled trial

Animal-derived dietary protein ingestion and physical activity stimulate myofibrillar protein synthesis rates in older adults. We determined whether a non-animal-derived diet can support daily myofibrillar protein synthesis rates to the same extent as an omnivorous diet. Nineteen healthy older adults (aged 66 (sem 1) years; BMI 24 (sem 1) kg/m2; twelve males, seven females) participated in a randomised, parallel-group, controlled trial during which they consumed a 3-d isoenergetic high-protein (1·8 g/kg body mass per d) diet, where the protein was provided from predominantly (71 %) animal (OMNI; n 9; six males, three females) or exclusively vegan (VEG; n 10; six males, four females; mycoprotein providing 57 % of daily protein intake) sources. During the dietary control period, participants conducted a daily bout of unilateral resistance-type leg extension exercise. Before the dietary control period, participants ingested 400 ml of deuterated water, with 50-ml doses consumed daily thereafter. Saliva samples were collected throughout to determine body water 2H enrichments, and muscle samples were collected from rested and exercised muscle to determine daily myofibrillar protein synthesis rates. Deuterated water dosing resulted in body water 2H enrichments of approximately 0·78 (sem 0·03) %. Daily myofibrillar protein synthesis rates were 13 (sem 8) (P = 0·169) and 12 (sem 4) % (P = 0·016) greater in the exercised compared with rested leg (1·59 (sem 0·12) v. 1·77 (sem 0·12) and 1·76 (sem 0·14) v. 1·93 (sem 0·12) %/d) in OMNI and VEG groups, respectively. Daily myofibrillar protein synthesis rates did not differ between OMNI and VEG in either rested or exercised muscle (P > 0·05). Over the course of a 3-d intervention, omnivorous- or vegan-derived dietary protein sources can support equivalent rested and exercised daily myofibrillar protein synthesis rates in healthy older adults consuming a high-protein diet.

Resistance Exercise, Aging, Disuse, and Muscle Protein Metabolism

Skeletal muscle is the organ of locomotion, its optimal function is critical for athletic performance, and is also important for health due to its contribution to resting metabolic rate and as a site for glucose uptake and storage. Numerous endogenous and exogenous factors influence muscle mass. Much of what is currently known regarding muscle protein turnover is owed to the development and use of stable isotope tracers. Skeletal muscle mass is determined by the meal- and contraction-induced alterations of muscle protein synthesis and muscle protein breakdown. Increased loading as resistance training is the most potent nonpharmacological strategy by which skeletal muscle mass can be increased. Conversely, aging (sarcopenia) and muscle disuse lead to the development of anabolic resistance and contribute to the loss of skeletal muscle mass. Nascent omics-based technologies have significantly improved our understanding surrounding the regulation of skeletal muscle mass at the gene, transcript, and protein levels. Despite significant advances surrounding the mechanistic intricacies that underpin changes in skeletal muscle mass, these processes are complex, and more work is certainly needed. In this article, we provide an overview of the importance of skeletal muscle, describe the influence that resistance training, aging, and disuse exert on muscle protein turnover and the molecular regulatory processes that contribute to changes in muscle protein abundance. © 2021 American Physiological Society. Compr Physiol 11:2249-2278, 2021.

Nutrition for Older Athletes: Focus on Sex-Differences

Regular physical exercise and a healthy diet are major determinants of a healthy lifespan. Although aging is associated with declining endurance performance and muscle function, these components can favorably be modified by regular physical activity and especially by exercise training at all ages in both sexes. In addition, age-related changes in body composition and metabolism, which affect even highly trained masters athletes, can in part be compensated for by higher exercise metabolic efficiency in active individuals. Accordingly, masters athletes are often considered as a role model for healthy aging and their physical capacities are an impressive example of what is possible in aging individuals. In the present review, we first discuss physiological changes, performance and trainability of older athletes with a focus on sex differences. Second, we describe the most important hormonal alterations occurring during aging pertaining regulation of appetite, glucose homeostasis and energy expenditure and the modulatory role of exercise training. The third part highlights nutritional aspects that may support health and physical performance for older athletes. Key nutrition-related concerns include the need for adequate energy and protein intake for preventing low bone and muscle mass and a higher demand for specific nutrients (e.g., vitamin D and probiotics) that may reduce the infection burden in masters athletes. Fourth, we present important research findings on the association between exercise, nutrition and the microbiota, which represents a rapidly developing field in sports nutrition.

Influence of sex on the age-related adaptations of neuromuscular function and motor unit properties in elite masters athletes

KEY POINTS

Masters athletes maintain high levels of activity into older age and allow an examination of the effects of aging dissociated from the effects of increased sedentary behaviour. Evidence suggests masters athletes are more successful at motor unit remodelling, the reinnervation of denervated fibres acting to preserve muscle fibre number, but little data are available in females. Here we used intramuscular electromyography to demonstrate that motor units sampled from the tibialis anterior show indications of remodelling from middle into older age and which does not differ between males and females. The age-related trajectory of motor unit discharge characteristic differs according to sex, with female athletes progressing to a slower firing pattern that was not observed in males. Our findings indicate motor unit remodelling from middle to older age occurs to a similar extent in male and female athletes, with discharge rates progressively slowing in females only.

ABSTRACT

Motor unit (MU) remodelling acts to minimise loss of muscle fibres following denervation in older age, which may be more successful in masters athletes. Evidence suggests performance and neuromuscular function decline with age in this population, although the majority of studies have focused on males, with little available data on female athletes. Functional assessments of strength, balance and motor control were performed in 30 masters athletes (16 male) aged 44-83 years. Intramuscular needle electrodes were used to sample individual motor unit potentials (MUPs) and near-fibre MUPs in the tibialis anterior (TA) during isometric contractions at 25% maximum voluntary contraction, and used to determine discharge characteristics (firing rate, variability) and biomarkers of peripheral MU remodelling (MUP size, complexity, stability). Multilevel mixed-effects linear regression models examined effects of age and sex. All aspects of neuromuscular function deteriorated with age (P < 0.05) with no age × sex interactions, although males were stronger (P < 0.001). Indicators of MU remodelling also progressively increased with age to a similar extent in both sexes (P < 0.05), whilst MU firing rate progressively decreased with age in females (p = 0.029), with a non-significant increase in males (p = 0.092). Masters athletes exhibit age-related declines in neuromuscular function that are largely equal across males and females. Notably, they also display features of MU remodelling with advancing age, probably acting to reduce muscle fibre loss. The age trajectory of MU firing rate assessed at a single contraction level differed between sexes, which may reflect a greater tendency for females to develop a slower muscle phenotype.

High-dose leucine supplementation does not prevent muscle atrophy or strength loss over 7 days of immobilization in healthy young males

BACKGROUND

Unavoidable periods of disuse lead to muscle atrophy and functional decline. Preventing such declines can reduce the risk of re-injury and improve recovery of normal physiological functioning.

OBJECTIVES

We aimed to determine the effectiveness of high-dose leucine supplementation on muscle morphology and strength during 7 d of unilateral lower-limb immobilization, and the role of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis in disuse atrophy.

METHODS

Sixteen healthy males (mean ± SEM age: 23 ± 1 y) underwent 7 d of unilateral lower-limb immobilization, with thrice-daily leucine (LEU; n = 8) or placebo (PLA; n = 8) supplementation (15 g/d). Before and after immobilization, muscle strength and compartmental tissue composition were assessed. A primed continuous infusion of l-[ring-13C6]-phenylalanine with serial muscle biopsies was used to determine postabsorptive and postprandial (20 g milk protein) MyoPS and MitoPS, fiber morphology, markers of protein turnover, and mitochondrial function between the control leg (CTL) and the immobilized leg (IMB).

RESULTS

Leg fat-free mass was reduced in IMB (mean ± SEM: -3.6% ± 0.5%; P = 0.030) but not CTL with no difference between supplementation groups. Isometric knee extensor strength declined to a greater extent in IMB (-27.9% ± 4.4%) than in CTL (-14.3% ± 4.4%; P = 0.043) with no difference between groups. In response to 20 g milk protein, postprandial MyoPS rates were significantly lower in IMB than in CTL (-22% ± 4%; P < 0.01) in both LEU and PLA. Postabsorptive MyoPS rates did not differ between legs or groups. Postabsorptive MitoPS rates were significantly lower in IMB than in CTL (-14% ± 5%; P < 0.01) and postprandial MitoPS rates significantly declined in response to 20 g milk protein ingestion (CTL: -10% ± 8%; IMB: -15% ± 10%; P = 0.039), with no differences between legs or groups. There were no significant differences in measures of mitochondrial respiration between legs, but peroxisome proliferator-activated receptor γ coactivator 1-α and oxidative phosphorylation complex II and III were significantly lower in IMB than in CTL (P < 0.05), with no differences between groups.

CONCLUSIONS

High-dose leucine supplementation (15 g/d) does not appear to attenuate any functional declines associated with 7 d of limb immobilization in young, healthy males.This trial was registered at clinicaltrials.gov as NCT03762278.

Immobilization leads to alterations in intracellular phosphagen and creatine transporter content in human skeletal muscle

The role of dysregulated intracellular creatine (Cr) metabolism in disuse atrophy is unknown. In this study, skeletal muscle biopsy samples were obtained after 7 days of unilateral leg immobilization (IMMOB) and from the nonimmobilized control limb (CTRL) of 15 healthy men (23.1 ± 3.5 yr). Samples were analyzed for fiber type cross-sectional area (CSA) and creatine transporter (CreaT) at the cell membrane periphery (MEM) or intracellular (INT) areas, via immunofluorescence microscopy. Creatine kinase (CK) and AMP-activated protein kinase (AMPK) were determined via immunoblot. Phosphocreatine (PCr), Cr, and ATP were measured via enzymatic analysis. Body composition and maximal isometric knee extensor strength were assessed before and after disuse. Leg strength and fat-free mass were reduced in IMMOB (~32% and 4%, respectively; P < 0.01 for both). Type II fiber CSA was smaller (~12%; P = 0.028) and intramuscular PCr lower (~13%; P = 0.015) in IMMOB vs. CTRL. CreaT protein was greater in type I fibers in both limbs (P < 0.01). CreaT was greater in IMMOB vs. CTRL (P < 0.01) and inversely associated with PCr concentration in both limbs (P < 0.05). MEM CreaT was greater than INT CreaT in type I and II fibers of both limbs (~14% for both; P < 0.01 for both). Type I fiber CreaT tended to be greater in IMMOB vs. CTRL (P = 0.074). CK was greater and phospho-to-total AMPKThr172 tended to be greater, in IMMOB vs. CTRL (P = 0.013 and 0.051, respectively). These findings suggest that modulation of intracellular Cr metabolism is an adaptive response to immobilization in young healthy skeletal muscle.

Single-muscle fiber contractile properties in lifelong aerobic exercising women

The purpose of this study was to examine the effects of lifelong aerobic exercise on single-muscle fiber performance in trained women (LLE; n = 7, 72 ± 2 yr) by comparing them to old healthy nonexercisers (OH; n = 10, 75 ± 1 yr) and young exercisers (YE; n = 10, 25 ± 1 yr). On average, LLE had exercised ~5 days/wk for ~7 h/wk over the past 48 ± 2 yr. Each subject had a vastus lateralis muscle biopsy to examine myosin heavy chain (MHC) I and IIa single-muscle fiber size and function (strength, speed, power). MHC I fiber size was similar across all three cohorts (YE = 5,178 ± 157, LLE = 4,983 ± 184, OH = 4,902 ± 159 µm2). MHC IIa fiber size decreased (P < 0.05) 36% with aging (YE = 4,719 ± 164 vs. OH = 3,031 ± 153 µm2), with LLE showing a similar 31% reduction (3,253 ± 189 µm2). LLE had 17% more powerful (P < 0.05) MHC I fibers and offset the 18% decline in MHC IIa fiber power observed with aging (P < 0.05). The LLE contractile power was driven by greater strength (+11%, P = 0.056) in MHC I fibers and elevated contractile speed (+12%, P < 0.05) in MHC IIa fibers. These data indicate that lifelong exercise did not benefit MHC I or IIa muscle fiber size. However, LLE had contractile function adaptations that enhanced MHC I fiber power and preserved MHC IIa fiber power through different contractile mechanisms (strength vs. speed). The single-muscle fiber contractile properties observed with lifelong aerobic exercise are unique and provide new insights into aging skeletal muscle plasticity in women at the myocellular level.NEW & NOTEWORTHY This is the first investigation to examine the effects of lifelong exercise on single-muscle fiber physiology in women. Nearly 50 yr of moderate to vigorous aerobic exercise training resulted in enhanced slow-twitch fiber power primarily by increasing force production, whereas fast-twitch fiber power was preserved primarily by increasing contractile speed. These unique muscle fiber power profiles helped offset the effects of fast-twitch fiber atrophy and highlight the benefits of lifelong aerobic exercise for myocellular health.

Comparable Rates of Integrated Myofibrillar Protein Synthesis Between Endurance-Trained Master Athletes and Untrained Older Individuals

Background

An impaired muscle anabolic response to exercise and protein nutrition is thought to underpin age-related muscle loss, which may be exacerbated by aspects of biological aging that may not be present in older individuals who have undertaken long-term high-level exercise training, or master athletes (MA). The aim of this study was to compare rested-state and exercise-induced rates of integrated myofibrillar protein synthesis (iMyoPS) and intracellular signaling in endurance trained MA and healthy age-matched untrained individuals (Older Controls).

Methods

In a parallel study design, iMyoPS rates were determined over 48 h in the rested-state and following a bout of unaccustomed resistance exercise (RE) in OC (n = 8 males; 73.5 ± 3.3 years) and endurance-trained MA (n = 7 males; 68.9 ± 5.7 years). Intramuscular anabolic signaling was also determined. During the iMyoPS measurement period, physical activity was monitored via accelerometry and dietary intake was controlled.

Results

Anthropometrics, habitual activity, and dietary intake were similar between groups. There was no difference in rested-state rates of iMyoPS between OC (1.47 ± 0.06%⋅day^–1) and MA (1.46 ± 0.08%⋅day^–1). RE significantly increased iMyoPS above rest in both OC (1.60 ± 0.08%⋅day^–1, P < 0.01) and MA (1.61 ± 0.08%⋅day^–1, P < 0.01), with no difference between groups. Akt^Thr308 phosphorylation increased at 1 h post-RE in OC (P < 0.05), but not MA. No other between-group differences in intramuscular signaling were apparent at any time-point.

Conclusion

While our sample size is limited, these data suggest that rested-state and RE-induced iMyoPS are indistinguishable between MA and OC. Importantly, the OC retain a capacity for RE-induced stimulation of skeletal muscle remodeling.