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Nishikawa Y, Watanabe K, Holobar A, Kitamura R, Maeda N, Hyngstrom AS. Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females. Eur J Appl Physiol 2024; 124:1979-1990. [PMID: 38366213 PMCID: PMC11199256 DOI: 10.1007/s00421-024-05420-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 01/11/2024] [Indexed: 02/18/2024]
Abstract
PURPOSE The purpose of this study was to compare laterality in motor unit firing behavior between females and males. METHODS Twenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC). High-density surface electromyography (HD-sEMG) signals were recorded in the first dorsal interosseous (FDI) muscle and decomposed into individual motor unit (MU) firing behavior using a convolution blind source separation method. RESULTS In total, 769 MUs were detected (females, n = 318 and males, n = 451). Females had a significantly higher discharge rate than males at each relative torque level (10%: male dominant hand, 13.4 ± 2.7 pps vs. female dominant hand, 16.3 ± 3.4 pps; 30%: male dominant hand, 16.1 ± 3.9 pps vs. female dominant hand, 20.0 ± 5.0 pps; and 60%: male dominant hand, 19.3 ± 3.8 vs. female dominant hand, 25.3 ± 4.8 pps; p < 0.0001). The recruitment threshold was also significantly higher in females than in males at 30 and 60% MVC. Furthermore, males exhibited asymmetrical discharge rates at 30 and 60% MVC and recruitment thresholds at 30 and 60% MVC, whereas no asymmetry was observed in females. CONCLUSION In the FDI muscle, compared to males, females exhibited different neuromuscular strategies with higher discharge rates and recruitment thresholds and no asymmetrical MU firing behavior. Notably, the findings that sex differences in neuromuscular activity also occur in healthy individuals provide important information for understanding the pathogenesis of various diseases.
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Affiliation(s)
- Yuichi Nishikawa
- Faculty of Frontier Engineering, Institute of Science & Engineering, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
| | - Kohei Watanabe
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Nagoya, Japan
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Ryoka Kitamura
- Graduate School of Frontier Engineering, Kanazawa University, Kanazawa, Japan
| | - Noriaki Maeda
- Division of Sports Rehabilitation, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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Lecce E, Conti A, Nuccio S, Felici F, Bazzucchi I. Characterising sex-related differences in lower- and higher-threshold motor unit behaviour through high-density surface electromyography. Exp Physiol 2024. [PMID: 38888901 DOI: 10.1113/ep091823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Accepted: 05/28/2024] [Indexed: 06/20/2024]
Abstract
Emerging questions in neuromuscular physiology revolve around whether males and females share similar neural control in diverse tasks across a broad range of intensities. In order to explore these features, high-density electromyography was used to record the myoelectrical activity of biceps brachii during trapezoidal isometric contractions at 35% and 70% of maximal voluntary force (MVF) on 11 male and 13 female participants. Identified motor units were then classified as lower-threshold (recruited at ≤30%MVF) and higher-threshold (recruited at >30%MVF). The discharge rate, interspike interval variability, recruitment and derecruitment thresholds, and estimates of neural drive to motor neurons were assessed. Female lower-threshold motor units showed higher neural drive (P < 0.001), accompanied by higher discharge rate at recruitment (P = 0.006), plateau (P = 0.001) and derecruitment (P = 0.001). On the other hand, male higher-threshold motor units showed greater neural drive (P = 0.04), accompanied by higher discharge rate at recruitment (P = 0.005), plateau (P = 0.04) and derecruitment (P = 0.01). Motor unit discharge rate normalised by the recruitment threshold was significantly higher in female lower-threshold motor units (P < 0.001), while no differences were observed in higher-threshold motor units. Recruitment and derecruitment thresholds are higher in males across all intensities (P < 0.01). However, males and females have similar activation and deactivation strategies, as evidenced by similar recruitment-to-derecruitment ratios (P > 0.05). This study encompasses a broad intensity range to analyse motor unit sex-related differences, highlighting higher neural drive and discharge rates in female lower-threshold motor units, elevated recruitment and derecruitment thresholds in males, and convergences in activation and deactivation strategies. HIGHLIGHTS: What is the central question of the study? Do male and female motor units behave similarly in low- and high-intensity contractions? What is the main finding and its importance? Female motor units show higher discharge rates in low-intensity tasks and lower discharge rates in high-intensity tasks, with no differences in recruitment behaviour. A broader inter-spike interval variability was also observed in females. These findings underline that there are sex-specific differences concern the firing strategies based on task intensity.
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Affiliation(s)
- Edoardo Lecce
- Department of Movement, Human and Health Sciences, Laboratory of Exercise Physiology, University of Rome 'Foro Italico', Rome, Italy
| | - Alessandra Conti
- Department of Movement, Human and Health Sciences, Laboratory of Exercise Physiology, University of Rome 'Foro Italico', Rome, Italy
| | - Stefano Nuccio
- Department of Movement, Human and Health Sciences, Laboratory of Exercise Physiology, University of Rome 'Foro Italico', Rome, Italy
| | - Francesco Felici
- Department of Movement, Human and Health Sciences, Laboratory of Exercise Physiology, University of Rome 'Foro Italico', Rome, Italy
| | - Ilenia Bazzucchi
- Department of Movement, Human and Health Sciences, Laboratory of Exercise Physiology, University of Rome 'Foro Italico', Rome, Italy
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Guo Y, Jones EJ, Smart TF, Altheyab A, Gamage N, Stashuk DW, Piasecki J, Phillips BE, Atherton PJ, Piasecki M. Sex disparities of human neuromuscular decline in older humans. J Physiol 2024. [PMID: 38857412 DOI: 10.1113/jp285653] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 05/07/2024] [Indexed: 06/12/2024] Open
Abstract
Females typically live longer than males but, paradoxically, spend a greater number of later years in poorer health. The neuromuscular system is a critical component of the progression to frailty, and motor unit (MU) characteristics differ by sex in healthy young individuals and may adapt to ageing in a sex-specific manner due to divergent hormonal profiles. The purpose of this study was to investigate sex differences in vastus lateralis (VL) MU structure and function in early to late elderly humans. Intramuscular electromyography signals from 50 healthy older adults (M/F: 26/24) were collected from VL during standardized submaximal contractions and decomposed to quantify MU characteristics. Muscle size and neuromuscular performance were also measured. Females had higher MU firing rate (FR) than males (P = 0.025), with no difference in MU structure or neuromuscular junction transmission (NMJ) instability. All MU characteristics increased from low- to mid-level contractions (P < 0.05) without sex × level interactions. Females had smaller cross-sectional area of VL, lower strength and poorer force steadiness (P < 0.05). From early to late elderly, both sexes showed decreased neuromuscular function (P < 0.05) without sex-specific patterns. Higher VL MUFRs at normalized contraction levels previously observed in young are also apparent in old individuals, with no sex-based difference of estimates of MU structure or NMJ transmission instability. From early to late elderly, the deterioration of neuromuscular function and MU characteristics did not differ between sexes, yet function was consistently greater in males. These parallel trajectories underscore the lower initial level for older females and may offer insights into identifying critical intervention periods. KEY POINTS: Females generally exhibit an extended lifespan when compared to males, yet this is accompanied by a poorer healthspan and higher rates of frailty. In healthy young people, motor unit firing rate (MUFR) at normalized contraction intensities is widely reported to be higher in females than in age-matched males. Here we show in 50 people that older females have higher MUFR than older males with little difference in other MU parameters. The trajectory of decline from early to late elderly does not differ between sexes, yet function is consistently lower in females. These findings highlight distinguishable sex disparities in some MU characteristics and neuromuscular function, and suggest early interventions are needed for females to prevent functional deterioration to reduce the ageing health-sex paradox.
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Affiliation(s)
- Yuxiao Guo
- Institute of Sports Medicine and Health, Chengdu Sport University, Chengdu, China
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Eleanor J Jones
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Thomas F Smart
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Abdulmajeed Altheyab
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
- College of Applied Medical Sciences, King Saud bin Abdulaziz University for Health Science, Riyadh, Saudi Arabia
| | - Nishadi Gamage
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
- Neurophysiology of Human Movement Group, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, Australia
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada
| | - Jessica Piasecki
- Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, Nottingham Trent University, Nottingham, UK
| | - Bethan E Phillips
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Philip J Atherton
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Mathew Piasecki
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
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Marsala MJ, Gabriel DA, Greig Inglis J, Christie AD. How many motor units is enough? An assessment of the influence of the number of motor units on firing rate calculations. J Electromyogr Kinesiol 2024; 75:102872. [PMID: 38458102 DOI: 10.1016/j.jelekin.2024.102872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 02/25/2024] [Accepted: 03/02/2024] [Indexed: 03/10/2024] Open
Abstract
The number of motor units included in calculations of mean firing rates varies widely in the literature. It is unknown how the number of decomposed motor units included in the calculation of firing rate per participant compares to the total number of active motor units in the muscle, and if this is different for males and females. Bootstrapped distributions and confidence intervals (CI) of mean motor unit firing rates decomposed from the tibialis anterior were used to represent the total number of active motor units for individual participants in trials from 20 to 100 % of maximal voluntary contraction. Bootstrapped distributions of mean firing rates were constructed using different numbers of motor units, from one to the maximum number for each participant, and compared to the CIs. A probability measure for each number of motor units involved in firing rate was calculated and then averaged across all individuals. Motor unit numbers required for similar levels of probability increased as contraction intensity increased (p < 0.001). Increased levels of probability also required higher numbers of motor units (p < 0.001). There was no effect of sex (p ≥ 0.97) for any comparison. This methodology should be repeated in other muscles, and aged populations.
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Affiliation(s)
- Michael J Marsala
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada
| | - David A Gabriel
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - J Greig Inglis
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - Anita D Christie
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada.
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Piasecki J, Škarabot J, Spillane P, Piasecki M, Ansdell P. Sex Differences in Neuromuscular Aging: The Role of Sex Hormones. Exerc Sport Sci Rev 2024; 52:54-62. [PMID: 38329342 DOI: 10.1249/jes.0000000000000335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
Males and females experience different trajectories of neuromuscular function across the lifespan, with females demonstrating accelerated deconditioning in later life. We hypothesize that the menopause is a critical period in the female lifespan, during which the dramatic reduction in sex hormone concentrations negatively impacts synaptic input to the motoneuron pool, as well as motor unit discharge properties.
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Affiliation(s)
- Jessica Piasecki
- Sport, Health and Performance Enhancement Research Centre, Nottingham Trent University, Nottingham, UK
| | - Jakob Škarabot
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Padraig Spillane
- Department of Sport, Exercise and Rehabilitation, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, UK
| | - Mathew Piasecki
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, UK
| | - Paul Ansdell
- Department of Sport, Exercise and Rehabilitation, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, UK
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Tøien T, Nielsen JL, Berg OK, Brobakken MF, Nyberg SK, Espedal L, Malmo T, Frandsen U, Aagaard P, Wang E. The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men. J Appl Physiol (1985) 2023; 135:1360-1371. [PMID: 37881849 PMCID: PMC10979801 DOI: 10.1152/japplphysiol.00208.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 10/11/2023] [Accepted: 10/25/2023] [Indexed: 10/27/2023] Open
Abstract
Aging is typically associated with decreased muscle strength and rate of force development (RFD), partly explained by motor unit remodeling due to denervation, and subsequent loss of fast-twitch type II myofibers. Exercise is commonly advocated to counteract this detrimental loss. However, it is unclear how life-long strength versus endurance training may differentially affect markers of denervation and reinnervation of skeletal myofibers and, in turn, affect the proportion and morphology of fast-twitch type II musculature. Thus, we compared fiber type distribution, fiber type grouping, and the prevalence of atrophic myofibers (≤1,494 µm2) in strength-trained (OS) versus endurance-trained (OE) master athletes and compared the results to recreationally active older adults (all >70 yr, OC) and young habitually active references (<30 yr, YC). Immunofluorescent stainings were performed on biopsy samples from vastus lateralis, along with leg press maximal strength and RFD measurements. OS demonstrated similar type II fiber distribution (OS: 52.0 ± 16.4%; YC: 51.1 ± 14.4%), fiber type grouping, maximal strength (OS: 170.0 ± 18.9 kg, YC: 151.0 ± 24.4 kg), and RFD (OS: 3,993 ± 894 N·s-1, YC: 3,470 ± 1,394 N·s-1) as young, and absence of atrophic myofibers (OS: 0.2 ± 0.7%; YC: 0.1 ± 0.4%). In contrast, OE and OC exhibited more atrophic fibers (OE: 1.2 ± 1.0%; OC: 1.1 ± 1.4%), more grouped fibers, and smaller proportion of type II fibers (OE: 39.3 ± 11.9%; OC: 35.0 ± 12.4%) than OS and YC (all P < 0.05). In conclusion, strength-trained master athletes were characterized by similar muscle morphology as young, which was not the case for recreationally active or endurance-trained old. These results indicate that strength training may preserve type II fibers with advancing age in older men, likely as a result of chronic use of high contractile force generation.NEW & NOTEWORTHY Aging is associated with loss of fast-twitch type II myofibers, motor unit remodeling, and grouping of myofibers. This study reveals, for the first time, that strength training preserves neural innervation of type II fibers, resulting in similar myofiber type distribution and grouping in life-long strength-trained master athletes as young moderately active adults. In contrast, life-long endurance-trained master athletes and recreationally active old adults demonstrated higher proportion of type I fibers accompanied by more marked grouping of type I myofibers, and more atrophic fibers compared with strength-trained master athletes and young individuals. Thus, strength training should be utilized as a training modality for preservation of fast-twitch musculature, maximal muscle strength, and rapid force capacity (RFD) with advancing age.
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Affiliation(s)
- Tiril Tøien
- Department of Health and Social Sciences, Molde University College, Molde, Norway
| | - Jakob Lindberg Nielsen
- Department of Sports Science and Clinical Biomechanics, Research Unit for Muscle Physiology and Biomechanics, University of Southern Denmark, Odense, Denmark
| | - Ole Kristian Berg
- Department of Health and Social Sciences, Molde University College, Molde, Norway
| | - Mathias Forsberg Brobakken
- Department of Health and Social Sciences, Molde University College, Molde, Norway
- Department of Psychosis and Rehabilitation, Psychiatry Clinic, St. Olavs University Hospital, Trondheim, Norway
| | - Stian Kwak Nyberg
- Department of Anesthesiology and Intensive Care, Drammen Hospital, Vestre Viken Hospital Trust, Drammen, Norway
| | - Lars Espedal
- Department of Health and Social Sciences, Molde University College, Molde, Norway
| | - Thomas Malmo
- Norwegian Defence University College, Norwegian Armed Forces, Oslo, Norway
| | - Ulrik Frandsen
- Department of Sports Science and Clinical Biomechanics, Research Unit for Muscle Physiology and Biomechanics, University of Southern Denmark, Odense, Denmark
| | - Per Aagaard
- Department of Sports Science and Clinical Biomechanics, Research Unit for Muscle Physiology and Biomechanics, University of Southern Denmark, Odense, Denmark
| | - Eivind Wang
- Department of Health and Social Sciences, Molde University College, Molde, Norway
- Department of Psychosis and Rehabilitation, Psychiatry Clinic, St. Olavs University Hospital, Trondheim, Norway
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Piasecki J, Guo Y, Jones EJ, Phillips BE, Stashuk DW, Atherton PJ, Piasecki M. Menstrual Cycle Associated Alteration of Vastus Lateralis Motor Unit Function. SPORTS MEDICINE - OPEN 2023; 9:97. [PMID: 37874413 PMCID: PMC10597975 DOI: 10.1186/s40798-023-00639-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 09/21/2023] [Indexed: 10/25/2023]
Abstract
BACKGROUND Estrogen and progesterone are the primary female sex hormones and have net excitatory and inhibitory effects, respectively, on neuronal function. Fluctuating concentrations across the menstrual cycle has led to several lines of research in relation to neuromuscular function and performance; however evidence from animal and cell culture models has yet to be demonstrated in human motor units coupled with quantification of circulating hormones. Intramuscular electromyography was used to record motor unit potentials and corresponding motor unit potential trains from the vastus lateralis of nine eumenorrheic females during the early follicular, ovulation and mid luteal phases of the menstrual cycle, alongside assessments of neuromuscular performance. Multi-level regression models were applied to explore effects of time and of contraction level. Statistical significance was accepted as p < 0.05. RESULTS Knee extensor maximum voluntary contraction, jump power, force steadiness, and balance did not differ across the menstrual phases (all p > 0.4). Firing rate of low threshold motor units (10% maximum voluntary contraction) was lower during the ovulation and mid luteal phases (β = - 0.82 Hz, p < 0.001), with no difference in motor unit potentials analysed from 25% maximum voluntary contraction contractions. Motor unit potentials were more complex during ovulation and mid luteal phase (p < 0.03), with no change in neuromuscular junction transmission instability (p > 0.3). CONCLUSIONS Assessments of neuromuscular performance did not differ across the menstrual cycle. The suppression of low threshold motor unit firing rate during periods of increased progesterone may suggest a potential inhibitory effect and an alteration of recruitment strategy; however this had no discernible effect on performance. These findings highlight contraction level-dependent modulation of vastus lateralis motor unit function over the eumenorrheic cycle, occurring independently of measures of performance.
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Affiliation(s)
- Jessica Piasecki
- Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, Nottingham Trent University, Nottingham, UK.
| | - Yuxiao Guo
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Eleanor J Jones
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Bethan E Phillips
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada
| | - Philip J Atherton
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
| | - Mathew Piasecki
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK
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Lulic-Kuryllo T, Benedini M, Cogliati M, Cudicio A, Guarneri B, Gazzina S, Piva S, Latronico N, Orizio C, Negro F. Sex-differences in the longitudinal recovery of neuromuscular function in COVID-19 associated acute respiratory distress syndrome survivors. Front Med (Lausanne) 2023; 10:1185479. [PMID: 37435534 PMCID: PMC10330713 DOI: 10.3389/fmed.2023.1185479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 06/05/2023] [Indexed: 07/13/2023] Open
Abstract
Introduction Patients admitted to the intensive care unit (ICU) following severe acute respiratory syndrome 2 (SARS-CoV-2) infection may have muscle weakness up to 1 year or more following ICU discharge. However, females show greater muscle weakness than males, indicating greater neuromuscular impairment. The objective of this work was to assess sex differences in longitudinal physical functioning following ICU discharge for SARS-CoV-2 infection. Methods We performed longitudinal assessment of physical functioning in two groups: 14 participants (7 males, 7 females) in the 3-to-6 month and 28 participants (14 males, 14 females) in the 6-to-12 month group following ICU discharge and assessed differences between the sexes. We examined self-reported fatigue, physical functioning, compound muscle action potential (CMAP) amplitude, maximal strength, and the neural drive to the tibialis anterior muscle. Results We found no sex differences in the assessed parameters in the 3-to-6-month follow-up, indicating significant weakness in both sexes.Sex differences emerged in the 6-to-12-month follow-up. Specifically, females exhibited greater impairments in physical functioning, including lower strength, walking lower distances, and high neural input even 1 year following ICU-discharge. Discussion Females infected by SARS-CoV-2 display significant impairments in functional recovery up to 1 year following ICU discharge. The effects of sex should be considered in post-COVID neurorehabilitation.
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Affiliation(s)
- Tea Lulic-Kuryllo
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Marco Benedini
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Marta Cogliati
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Alessandro Cudicio
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Bruno Guarneri
- Department of Medical and Surgical Specialities, Radiological Sciences and Public Health, University of Brescia, Brescia, Lombardia, Italy
| | - Stefano Gazzina
- Neurophysiology Unit, ASST Spedali Civili University Hospital, Brescia, Lombardia, Italy
| | - Simone Piva
- Department of Medical and Surgical Specialities, Radiological Sciences and Public Health, University of Brescia, Brescia, Lombardia, Italy
- Department of Anesthesia, Critical Care and Emergency, ASST Spedali Civili University Hospital, Brescia, Italy
| | - Nicola Latronico
- Department of Medical and Surgical Specialities, Radiological Sciences and Public Health, University of Brescia, Brescia, Lombardia, Italy
- Department of Anesthesia, Critical Care and Emergency, ASST Spedali Civili University Hospital, Brescia, Italy
- ‘Alessandra Bono’ University Research Center on Long-Term Outcome (LOTO) in Critical Illness Survivors, University of Brescia, Brescia, Italy
| | - Claudio Orizio
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
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Jones EJ, Guo Y, Martinez‐Valdes E, Negro F, Stashuk DW, Atherton PJ, Phillips BE, Piasecki M. Acute adaptation of central and peripheral motor unit features to exercise-induced fatigue differs with concentric and eccentric loading. Exp Physiol 2023; 108:827-837. [PMID: 37018481 PMCID: PMC10988466 DOI: 10.1113/ep091058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 03/14/2023] [Indexed: 04/07/2023]
Abstract
NEW FINDINGS What is the central question of this study? Conflicting evidence exists on motor unit (MU) firing rate in response to exercise-induced fatigue, possibly due to the contraction modality used: Do MU properties adapt similarly following concentric and eccentric loading? What is the main finding and its importance? MU firing rate increased following eccentric loading only despite a decline in absolute force. Force steadiness deteriorated following both loading methods. Central and peripheral MU features are altered in a contraction type-dependant manner, which is an important consideration for training interventions. ABSTRACT Force output of muscle is partly mediated by the adjustment of motor unit (MU) firing rate (FR). Disparities in MU features in response to fatigue may be influenced by contraction type, as concentric (CON) and eccentric (ECC) contractions demand variable amounts of neural input, which alters the response to fatigue. This study aimed to determine the effects of fatigue following CON and ECC loading on MU features of the vastus lateralis (VL). High-density surface (HD-sEMG) and intramuscular (iEMG) electromyography were used to record MU potentials (MUPs) from bilateral VLs of 12 young volunteers (six females) during sustained isometric contractions at 25% and 40% of the maximum voluntary contraction (MVC), before and after completing CON and ECC weighted stepping exercise. Multi-level mixed effects linear regression models were performed with significance assumed as P < 0.05. MVC decreased in both CON and ECC legs post-exercise (P < 0.0001), as did force steadiness at both 25% and 40% MVC (P < 0.004). MU FR increased in ECC at both contraction levels (P < 0.001) but did not change in CON. FR variability increased in both legs at 25% and 40% MVC following fatigue (P < 0.01). From iEMG measures at 25% MVC, MUP shape did not change (P > 0.1) but neuromuscular junction transmission instability increased in both legs (P < 0.04), and markers of fibre membrane excitability increased following CON only (P = 0.018). These data demonstrate that central and peripheral MU features are altered following exercise-induced fatigue and differ according to exercise modality. This is important when considering interventional strategies targeting MU function.
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Affiliation(s)
- Eleanor J. Jones
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research CentreUniversity of NottinghamNottinghamUK
| | - Yuxiao Guo
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research CentreUniversity of NottinghamNottinghamUK
| | - Eduardo Martinez‐Valdes
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
| | - Francesco Negro
- Department of Clinical and Experimental SciencesUniversità degli Studi di BresciaBresciaItaly
| | - Daniel W. Stashuk
- Department of Systems Design EngineeringUniversity of WaterlooWaterlooOntarioCanada
| | - Philip J. Atherton
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research CentreUniversity of NottinghamNottinghamUK
| | - Bethan E. Phillips
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research CentreUniversity of NottinghamNottinghamUK
| | - Mathew Piasecki
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research CentreUniversity of NottinghamNottinghamUK
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Inns TB, Bass JJ, Hardy EJ, Wilkinson DJ, Stashuk DW, Atherton PJ, Phillips BE, Piasecki M. Motor unit dysregulation following 15 days of unilateral lower limb immobilisation. J Physiol 2022; 600:4753-4769. [PMID: 36088611 PMCID: PMC9827843 DOI: 10.1113/jp283425] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 08/19/2022] [Indexed: 01/12/2023] Open
Abstract
Disuse atrophy, caused by situations of unloading such as limb immobilisation, causes a rapid yet diverging reduction in skeletal muscle function when compared to muscle mass. While mechanistic insight into the loss of mass is well studied, deterioration of muscle function with a focus towards the neural input to muscle remains underexplored. This study aimed to determine the role of motor unit adaptation in disuse-induced neuromuscular deficits. Ten young, healthy male volunteers underwent 15 days of unilateral lower limb immobilisation with intramuscular electromyography (iEMG) bilaterally recorded from the vastus lateralis (VL) during knee extensor contractions normalised to maximal voluntary contraction (MVC), pre and post disuse. Muscle cross-sectional area was determined by ultrasound. Individual MUs were sampled and analysed for changes in motor unit (MU) discharge and MU potential (MUP) characteristics. VL CSA was reduced by approximately 15% which was exceeded by a two-fold decrease of 31% in muscle strength in the immobilised limb, with no change in either parameter in the non-immobilised limb. Parameters of MUP size were reduced by 11% to 24% with immobilisation, while neuromuscular junction (NMJ) transmission instability remained unchanged, and MU firing rate decreased by 8% to 11% at several contraction levels. All adaptations were observed in the immobilised limb only. These findings highlight impaired neural input following immobilisation reflected by suppressed MU firing rate which may underpin the disproportionate reductions of strength relative to muscle size. KEY POINTS: Muscle mass and function decline rapidly in situations of disuse such as bed rest and limb immobilisation. The reduction in muscle function commonly exceeds that of muscle mass, which may be associated with the dysregulation of neural input to muscle. We have used intramuscular electromyography to sample individual motor unit and near fibre potentials from the vastus lateralis following 15 days of unilateral limb immobilisation. Following disuse, the disproportionate loss of muscle strength when compared to size coincided with suppressed motor unit firing rate. These motor unit adaptations were observed at multiple contraction levels and in the immobilised limb only. Our findings demonstrate neural dysregulation as a key component of functional loss following muscle disuse in humans.
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Affiliation(s)
- Thomas B. Inns
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
| | - Joseph J. Bass
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
| | - Edward J.O. Hardy
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
- Department of Surgery and AnaestheticsRoyal Derby HospitalDerbyUK
| | - Daniel J. Wilkinson
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
| | - Daniel W. Stashuk
- Department of Systems Design EngineeringUniversity of WaterlooOntarioCanada
| | - Philip J. Atherton
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
| | - Bethan E. Phillips
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
| | - Mathew Piasecki
- Centre Of Metabolism, Ageing & PhysiologyMRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRCUniversity of NottinghamDerbyUK
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11
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Hayek R, Gottlieb U, Gutman I, Kingma I, Springer S. Can stabilization analysis following a single leg drop jump be compared between young and middle-aged adults. J Biomech 2022; 143:111269. [PMID: 36049385 DOI: 10.1016/j.jbiomech.2022.111269] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 08/09/2022] [Accepted: 08/18/2022] [Indexed: 11/15/2022]
Abstract
We aimed to verify whether the computational approaches previously proposed to analyze stability after a single-leg drop-jump (SLDJ) could be applied to a population of middle-aged adults. Fifteen middle-aged (56.4 ± 4.6 years) and 15 young adults (26.7 ± 3.9 years) performed five SLDJs. Stabilization measurements included (1) time to stabilization (TTS) based on vertical ground reaction force (GRF) (TTSv) and a fixed stabilization threshold; (2) TTS based on medio-lateral GRF (TTSml) using five different methods to preprocess the signal and stabilization threshold; (3) early medio-lateral stabilization- the averaged absolute values of the GRF in 0.2-1.4 s post-landing; (4) late medio-lateral stabilization - the averaged absolute values of the GRF at 1 s-5 s after landing. TTSv showed longer TTS values in middle-aged participants. In addition, middle-aged adults showed greater sway in late stabilization. However, TTSml values varied considerably between calculation methods, and early stabilization showed no significant differences between groups except in the first 0.2 s after landing. The results of the current study suggest that TTS calculations are sensitive to signal and threshold selection, and to the processing method. Calculations based on a fixed threshold are more appropriate for studying dynamic postural stability in middle age. With appropriate method selection, a decreased stabilizing performance can be demonstrated in middle-aged adults compared to young adults.
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Affiliation(s)
- Roee Hayek
- Faculty of Health Sciences, Department of Physical Therapy, The Neuromuscular & Human Performance Laboratory, Ariel University, Ariel, Israel
| | - Uri Gottlieb
- Faculty of Health Sciences, Department of Physical Therapy, The Neuromuscular & Human Performance Laboratory, Ariel University, Ariel, Israel
| | - Itai Gutman
- Faculty of Health Sciences, Department of Physical Therapy, The Neuromuscular & Human Performance Laboratory, Ariel University, Ariel, Israel
| | - Idsart Kingma
- Vrije Universiteit, Department of Human Movement Sciences, Amsterdam Movement Sciences, Amsterdam, The Netherlands
| | - Shmuel Springer
- Faculty of Health Sciences, Department of Physical Therapy, The Neuromuscular & Human Performance Laboratory, Ariel University, Ariel, Israel.
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12
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Ely IA, Jones EJ, Inns TB, Dooley S, Miller SBJ, Stashuk DW, Atherton PJ, Phillips BE, Piasecki M. Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability. Exp Physiol 2022; 107:1061-1070. [PMID: 35923141 PMCID: PMC9542263 DOI: 10.1113/ep090367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 07/28/2022] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? We aimed to determine levels of bilateral knee extensor force accuracy and any subsequent alterations to central and/or peripheral motor unit features, following 4 weeks of unilateral force accuracy training. What is the main finding and its importance? In the trained limb only, knee extensor force tracking accuracy improved with reduced motor unit firing rate variability in the vastus lateralis, and no change to neuromuscular junction transmission instability. Interventional strategies to improve force accuracy may be directed to older/clinical populations where such improvements may aid performance of daily living activities. ABSTRACT Background Muscle force output during sustained submaximal isometric contractions fluctuates around an average value and is partly influenced by variation in motor unit (MU) firing rates. MU firing rate (FR) variability seemingly reduces following exercise training interventions, however, much less is known with respect to peripheral MU properties. We therefore investigated whether targeted force accuracy training could lead to improved muscle functional capacity and control, in addition to determining any alterations of individual MU features. Methods Ten healthy participants (7 females, 3 males, 27±6 years, 170±8 cm, 69±16kg) underwent a 4-week supervised, unilateral knee extensor force accuracy training intervention. The coefficient of variation for force (FORCECoV ) and sinusoidal wave force tracking accuracy (FORCESinu ) were determined at 25% maximal voluntary contraction (MVC) pre- and post-training. Intramuscular electromyography was utilised to record individual MU potentials from the vastus lateralis (VL) muscles at 25% MVC during sustained contractions, pre- and post-training. Results Knee extensor muscle strength remained unchanged following training, with no improvements in unilateral leg-balance. FORCECoV and FORCESinu significantly improved in only the trained knee extensors by ∼13% (p = 0.01) and ∼30% (p<0.0001) respectively. MU FR variability significantly reduced in the trained VL by ∼16% (n = 8; p = 0.001), with no further alterations to MU FR or neuromuscular junction transmission instability. Conclusion Our results suggest muscle force control and tracking accuracy is a trainable characteristic in the knee extensors, which is likely explained by the reduction in MU FR variability which was apparent in the trained limb only. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Isabel A Ely
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
| | - Eleanor J Jones
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
| | - Thomas B Inns
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
| | - Síobhra Dooley
- School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Dublin, Ireland
| | - Sarah B J Miller
- School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Dublin, Ireland
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Canada
| | - Philip J Atherton
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
| | - Bethan E Phillips
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
| | - Mathew Piasecki
- Centre of Metabolism, Ageing and Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Derby, United Kingdom
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13
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Lulic-Kuryllo T, Greig Inglis J. Sex differences in motor unit behaviour: A review. J Electromyogr Kinesiol 2022; 66:102689. [DOI: 10.1016/j.jelekin.2022.102689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 10/15/2022] Open
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14
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Guo Y, Piasecki J, Swiecicka A, Ireland A, Phillips BE, Atherton PJ, Stashuk D, Rutter MK, McPhee JS, Piasecki M. Circulating testosterone and dehydroepiandrosterone are associated with individual motor unit features in untrained and highly active older men. GeroScience 2022; 44:1215-1228. [PMID: 34862585 PMCID: PMC9213614 DOI: 10.1007/s11357-021-00482-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 10/28/2021] [Indexed: 10/31/2022] Open
Abstract
Long-term exercise training has been considered as an effective strategy to counteract age-related hormonal declines and minimise muscle atrophy. However, human data relating circulating hormone levels with motor nerve function are scant. The aims of the study were to explore associations between circulating sex hormone levels and motor unit (MU) characteristics in older men, including masters athletes competing in endurance and power events. Forty-three older men (mean ± SD age: 69.9 ± 4.6 years) were studied based on competitive status. The serum concentrations of dehydroepiandrosterone (DHEA), total testosterone (T) and estradiol were quantified using liquid chromatography mass spectrometry. Intramuscular electromyographic signals were recorded from vastus lateralis (VL) during 25% of maximum voluntary isometric contractions and processed to extract MU firing rate (FR), and motor unit potential (MUP) features. After adjusting for athletic status, MU FR was positively associated with DHEA levels (p = 0.019). Higher testosterone and estradiol were associated with lower MUP complexity; these relationships remained significant after adjusting for athletic status (p = 0.006 and p = 0.019, respectively). Circulating DHEA was positively associated with MU firing rate in these older men. Higher testosterone levels were associated with reduced MUP complexity, indicating reduced electrophysiological temporal dispersion, which is related to decreased differences in conduction times along axonal branches and/or MU fibres. Although evident in males only, this work highlights the potential of hormone administration as a therapeutic interventional strategy specifically targeting human motor units in older age.
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Affiliation(s)
- Yuxiao Guo
- MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRC, School of Medicine, University of Nottingham, Nottingham, UK
| | - Jessica Piasecki
- Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, Nottingham Trent University, Nottingham, UK
| | - Agnieszka Swiecicka
- Division of Diabetes, Endocrinology and Gastroenterology, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
- Department of Basic and Clinical Sciences, University of Nicosia Medical School, Nicosia, Cyprus
| | - Alex Ireland
- Department of Sport and Exercise Sciences, Musculoskeletal Science and Sports Medicine Research Centre, Manchester Metropolitan University, Manchester, UK
| | - Bethan E. Phillips
- MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRC, School of Medicine, University of Nottingham, Nottingham, UK
| | - Philip J. Atherton
- MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRC, School of Medicine, University of Nottingham, Nottingham, UK
| | - Daniel Stashuk
- Department of Systems Design Engineering, University of Waterloo, Waterloo, ON Canada
| | - Martin K. Rutter
- Division of Diabetes, Endocrinology and Gastroenterology, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
- Diabetes, Endocrinology and Metabolism Centre, Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK
| | - Jamie S. McPhee
- Department of Sport and Exercise Sciences, Musculoskeletal Science and Sports Medicine Research Centre, Manchester Metropolitan University, Manchester, UK
| | - Mathew Piasecki
- MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research and NIHR Nottingham BRC, School of Medicine, University of Nottingham, Nottingham, UK
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15
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Guo Y, Jones EJ, Inns TB, Ely IA, Stashuk DW, Wilkinson DJ, Smith K, Piasecki J, Phillips BE, Atherton PJ, Piasecki M. Neuromuscular recruitment strategies of the vastus lateralis according to sex. Acta Physiol (Oxf) 2022; 235:e13803. [PMID: 35184382 PMCID: PMC9286427 DOI: 10.1111/apha.13803] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 02/03/2022] [Accepted: 02/16/2022] [Indexed: 12/19/2022]
Abstract
AIM Despite males typically exhibiting greater muscle strength and fatigability than females, it remains unclear if there are sex-based differences in neuromuscular recruitment strategies e.g. recruitment and modulation of motor unit firing rate (MU FR) at normalized forces and during progressive increases in force. METHODS The study includes 29 healthy male and 31 healthy female participants (18-35 years). Intramuscular electromyography (iEMG) was used to record individual motor unit potentials (MUPs) and near-fibre MUPs from the vastus lateralis (VL) during 10% and 25% maximum isometric voluntary contractions (MVC), and spike-triggered averaging was used to obtain motor unit number estimates (MUNE) of the VL. RESULTS Males exhibited greater muscle strength (P < .001) and size (P < .001) than females, with no difference in force steadiness at 10% or 25% MVC. Females had 8.4% and 6.5% higher FR at 10% and 25% MVC, respectively (both P < .03), while the MUP area was 33% smaller in females at 10% MVC (P < .02) and 26% smaller at 25% MVC (P = .062). However, both sexes showed similar increases in MU size and FR when moving from low- to mid-level contractions. There were no sex differences in any near-fibre MUP parameters or in MUNE. CONCLUSION In the vastus lateralis, females produce muscle force via different neuromuscular recruitment strategies to males which is characterized by smaller MUs discharging at higher rates. However, similar strategies are employed to increase force production from low- to mid-level contractions. These findings of similar proportional increases between sexes support the use of mixed sex cohorts in studies of this nature.
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Affiliation(s)
- Yuxiao Guo
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Eleanor J. Jones
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Thomas B. Inns
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Isabel A. Ely
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Daniel W. Stashuk
- Department of Systems Design Engineering University of Waterloo Waterloo Ontario Canada
| | - Daniel J. Wilkinson
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Kenneth Smith
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Jessica Piasecki
- Musculoskeletal Physiology Research Group Sport, Health and Performance Enhancement Research Centre Nottingham Trent University Nottingham UK
| | - Bethan E. Phillips
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Philip J. Atherton
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
| | - Mathew Piasecki
- Centre of Metabolism Ageing & Physiology (COMAP) MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre School of Medicine University of Nottingham Derby UK
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16
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Jones EJ, Chiou S, Atherton PJ, Phillips BE, Piasecki M. Ageing and exercise-induced motor unit remodelling. J Physiol 2022; 600:1839-1849. [PMID: 35278221 PMCID: PMC9314090 DOI: 10.1113/jp281726] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 02/14/2022] [Indexed: 11/08/2022] Open
Abstract
A motor unit (MU) comprises the neuron cell body, its corresponding axon and each of the muscle fibres it innervates. Many studies highlight age-related reductions in the number of MUs, yet the ability of a MU to undergo remodelling and to expand to rescue denervated muscle fibres is also a defining feature of MU plasticity. Remodelling of MUs involves two coordinated processes: (i) axonal sprouting and new branching growth from adjacent surviving neurons, and (ii) the formation of key structures around the neuromuscular junction to resume muscle-nerve communication. These processes rely on neurotrophins and coordinated signalling in muscle-nerve interactions. To date, several neurotrophins have attracted focus in animal models, including brain-derived neurotrophic factor and insulin-like growth factors I and II. Exercise in older age has demonstrated benefits in multiple physiological systems including skeletal muscle, yet evidence suggests this may also extend to peripheral MU remodelling. There is, however, a lack of research in humans due to methodological limitations which are easily surmountable in animal models. To improve mechanistic insight of the effects of exercise on MU remodelling with advancing age, future research should focus on combining methodological approaches to explore the in vivo physiological function of the MU alongside alterations of the localised molecular environment.
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Affiliation(s)
- Eleanor J. Jones
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC–Versus Arthritis Centre of Excellence for Musculoskeletal Ageing ResearchNottingham NIHR Biomedical Research CentreSchool of MedicineUniversity of NottinghamNottinghamUK
| | - Shin‐Yi Chiou
- School of SportExercise, and Rehabilitation Sciences, MRC‐Versus Arthritis Centre for Musculoskeletal Ageing Research, Centre for Human Brain HealthUniversity of BirminghamBirminghamUK
| | - Philip J. Atherton
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC–Versus Arthritis Centre of Excellence for Musculoskeletal Ageing ResearchNottingham NIHR Biomedical Research CentreSchool of MedicineUniversity of NottinghamNottinghamUK
| | - Bethan E. Phillips
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC–Versus Arthritis Centre of Excellence for Musculoskeletal Ageing ResearchNottingham NIHR Biomedical Research CentreSchool of MedicineUniversity of NottinghamNottinghamUK
| | - Mathew Piasecki
- Centre of Metabolism, Ageing & Physiology (COMAP), MRC–Versus Arthritis Centre of Excellence for Musculoskeletal Ageing ResearchNottingham NIHR Biomedical Research CentreSchool of MedicineUniversity of NottinghamNottinghamUK
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Rippetoe M, Mangi AA. The Impact of Sex on Strength Training in Adults With Cardiovascular Disease. Clin Ther 2022; 44:442-449. [DOI: 10.1016/j.clinthera.2022.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 01/07/2022] [Accepted: 01/09/2022] [Indexed: 02/03/2023]
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18
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Preventing age-related motor unit loss; is exercise the answer? Exp Gerontol 2022; 159:111695. [DOI: 10.1016/j.exger.2022.111695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 09/30/2021] [Accepted: 01/04/2022] [Indexed: 11/23/2022]
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Pethick J, Piasecki M. Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity? Front Sports Act Living 2022; 4:817770. [PMID: 35392594 PMCID: PMC8980913 DOI: 10.3389/fspor.2022.817770] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 02/28/2022] [Indexed: 11/16/2022] Open
Abstract
Recent technological developments have enabled significant advances in our understanding of the ability to voluntarily control muscle force output. The fluctuations inherent to muscle force output can be quantified according to both their magnitude and temporal structure (or "complexity"), with such quantification facilitating comparison of force control between distinct populations. In comparison to young adults, older adults exhibit an increase in the magnitude (i.e., decreased steadiness) and a decrease in the complexity (i.e., decreased adaptability) of force fluctuations, both of which are indicative of a loss of force control. There remain, however, key gaps in knowledge that limit our interpretation of this age-related loss of force control. One such gap relates to the effect of lifelong physical activity on force control. To date, research on aging and force control has largely been conducted on inactive or moderately active older adults. However, high levels of lifelong physical activity, such as that exhibited by Masters athletes, have been shown to have protective effects on the function and morphology of the neuromuscular system. Some of these effects (e.g., on impaired inhibitory transmission in the motor cortex and on motor unit discharge rates) have the potential to attenuate the age-related loss of force control, while others (e.g., greater motor unit remodeling capacity) have the potential to worsen it. We therefore propose that, in order to progress our knowledge of the effects of aging on force control, future studies must consider the potential modulatory effect of lifelong physical activity.
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Affiliation(s)
- Jamie Pethick
- School of Sport, Rehabilitation and Exercise Sciences, University of Essex, Colchester, United Kingdom
- *Correspondence: Jamie Pethick
| | - Mathew Piasecki
- Centre of Metabolism, Ageing and Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, United Kingdom
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20
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Jones EJ, Piasecki J, Ireland A, Stashuk DW, Atherton PJ, Phillips BE, McPhee JS, Piasecki M. Lifelong exercise is associated with more homogeneous motor unit potential features across deep and superficial areas of vastus lateralis. GeroScience 2021; 43:1555-1565. [PMID: 33763775 PMCID: PMC8492837 DOI: 10.1007/s11357-021-00356-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 03/10/2021] [Indexed: 12/12/2022] Open
Abstract
Motor unit (MU) expansion enables rescue of denervated muscle fibres helping to ameliorate age-related muscle atrophy, with evidence to suggest master athletes are more successful at this remodelling. Electrophysiological data has suggested MUs located superficially are larger than those located deeper within young muscle. However, the effects of ageing and exercise on MU heterogeneity across deep and superficial aspects of vastus lateralis (VL) remain unclear. Intramuscular electromyography was used to record individual MU potentials (MUPs) and near fibre MUPs (NFMs) from deep and superficial regions of the VL during 25% maximum voluntary contractions, in 83 males (15 young (Y), 17 young athletes (YA), 22 old (O) and 29 master athletes (MA)). MUP size and complexity were assessed using area and number of turns, respectively. Multilevel mixed effects linear regression models were performed to investigate the effects of depth in each group. MUP area was greater in deep compared with superficial MUs in Y (p<0.001) and O (p=0.012) but not in YA (p=0.071) or MA (p=0.653). MUP amplitude and NF MUP area were greater, and MUPs were more complex in deep MUPs from Y, YA and O (all p<0.05) but did not differ across depth in MA (all p>0.07). These data suggest MU characteristics differ according to depth within the VL which may be influenced by both ageing and exercise. A more homogenous distribution of MUP size and complexity across muscle depths in older athletes may be a result of a greater degree of age-related MU adaptations.
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Affiliation(s)
- Eleanor J Jones
- Clinical, Metabolic and Molecular Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, UK
| | - Jessica Piasecki
- Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, School of Science and Technology, Nottingham Trent University, Nottingham, UK
| | - Alex Ireland
- Department of Life Sciences, Musculoskeletal Science and Sports Medicine Research Centre, Manchester Metropolitan University, Manchester, UK
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada
| | - Philip J Atherton
- Clinical, Metabolic and Molecular Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, UK
| | - Bethan E Phillips
- Clinical, Metabolic and Molecular Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, UK
| | - Jamie S McPhee
- Department of Sport and Exercise Sciences, Musculoskeletal Science and Sports Medicine Research Centre, Manchester Metropolitan University, Manchester, UK
| | - Mathew Piasecki
- Clinical, Metabolic and Molecular Physiology, MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, UK.
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21
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Walker S. Evidence of resistance training-induced neural adaptation in older adults. Exp Gerontol 2021; 151:111408. [PMID: 34022275 DOI: 10.1016/j.exger.2021.111408] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Revised: 05/04/2021] [Accepted: 05/17/2021] [Indexed: 11/25/2022]
Abstract
The deleterious effects of aging on force production are observable from the age of 40 upwards, depending on the measure. Neural mechanisms contributing to maximum force production and rate of force development have been suggested as descending drive from supraspinal centers, spinal motoneuron excitability, and corticospinal inhibition of descending drive; all of which influence motor unit recruitment and/or firing rate. Resistance-trained Master athletes offer a good source of information regarding the inevitable effects of aging despite the countermeasure of systematic resistance-training. However, most evidence of neural adaptation is derived from longitudinal intervention studies in previously untrained (i.e. resistance-training naïve) older adults. There is good evidence for the effect of resistance-training on the end-point of neural activation, i.e. motor unit behavior, but little to no data on the generation of descending drive from e.g. transcranial magnetic stimulation or cortical imaging studies in older adults. This, along with tracking master athletes over several years, would provide valuable information and could be the focus of future research.
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Affiliation(s)
- Simon Walker
- NeuroMuscular Research Center, Faculty of Sport and Health Sciences, University of Jyväskylä, Finland.
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22
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Strasser B, Pesta D, Rittweger J, Burtscher J, Burtscher M. Nutrition for Older Athletes: Focus on Sex-Differences. Nutrients 2021; 13:nu13051409. [PMID: 33922108 PMCID: PMC8143537 DOI: 10.3390/nu13051409] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Revised: 04/08/2021] [Accepted: 04/12/2021] [Indexed: 12/13/2022] Open
Abstract
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.
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Affiliation(s)
- Barbara Strasser
- Medical Faculty, Sigmund Freud Private University, A-1020 Vienna, Austria
- Correspondence: ; Tel.: +43-(0)1-798-40-98
| | - Dominik Pesta
- Institute of Aerospace Medicine, German Aerospace Center (DLR), D-51147 Cologne, Germany; (D.P.); (J.R.)
- Centre for Endocrinology, Diabetes and Preventive Medicine (CEDP), University Hospital Cologne, D-50931 Cologne, Germany
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), D-50931 Cologne, Germany
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich-Heine University Düsseldorf, D-40225 Düsseldorf, Germany
- German Center for Diabetes Research (DZD e.V.), D-85764 Neuherberg, Germany
- Department of Sport Science, University of Innsbruck, A-6020 Innsbruck, Austria;
| | - Jörn Rittweger
- Institute of Aerospace Medicine, German Aerospace Center (DLR), D-51147 Cologne, Germany; (D.P.); (J.R.)
| | - Johannes Burtscher
- Department of Biomedical Sciences, University of Lausanne, CH-1015 Lausanne, Switzerland;
| | - Martin Burtscher
- Department of Sport Science, University of Innsbruck, A-6020 Innsbruck, Austria;
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23
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Near-fiber electromyography. Clin Neurophysiol 2021; 132:1089-1104. [PMID: 33774377 DOI: 10.1016/j.clinph.2021.02.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 01/28/2021] [Accepted: 02/05/2021] [Indexed: 11/23/2022]
Abstract
OBJECTIVE Describe and evaluate the concepts of near fiber electromyography (NFEMG), the features used, including near fiber motor unit potential (NFMUP) duration and dispersion, which relate to motor unit distal axonal branch and muscle fiber conduction time dispersion, and NFMUP segment jitter, a new measure of the temporal variability of neuromuscular junction transmission (NMJ), and axonal branch and muscle fibre conduction for the near fibres (i.e. NF jitter), and the methods for obtaining their values. METHODS Trains of high-pass filtered motor unit potentials (MUPs) (i.e. NFMUP trains) were extracted from needle-detected EMG signals to assess changes in motor unit (MU) morphology and electrophysiology caused by neuromuscular disorders or ageing. Evaluations using simulated needle-detected EMG data were completed and example human data are presented. RESULTS NFEMG feature values can be used to detect axonal sprouting, conduction slowing and NMJ transmission delay as well as changes in MU fiber diameter variability, and NF jitter. These changes can be detected prior to alterations of MU size or numbers. CONCLUSIONS The evaluations clearly demonstrate and the example data support that NFMUP duration and dispersion reflect MU distal axonal branching, conduction slowing and NMJ transmission delay and/or MU fiber diameter variability and that NFMUP jiggle and segment jitter reflect NF jitter. SIGNIFICANCE NFEMG can detect early changes in MU morphology and/or electrophysiology and has the potential to augment clinical diagnosis and tracking of neuromuscular disorders.
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24
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Latella C. Pick me, Pick me! Rationale for investigating persistent inward currents (PICs) and associated exercise effects in the ageing neuromuscular system. J Physiol 2021; 599:1957-1959. [PMID: 33491208 DOI: 10.1113/jp281324] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Christopher Latella
- Neurophysiology Research Laboratory, Edith Cowan University, Joondalup, Australia.,Centre for Exercise and Sports Science Research (CESSR), School of Medical and Health Sciences, Edith Cowan University, Joondalup, Australia
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25
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Molecular and neural adaptations to neuromuscular electrical stimulation; Implications for ageing muscle. Mech Ageing Dev 2020; 193:111402. [PMID: 33189759 PMCID: PMC7816160 DOI: 10.1016/j.mad.2020.111402] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/04/2020] [Accepted: 11/08/2020] [Indexed: 02/07/2023]
Abstract
Muscle atrophy and functional declines observed with advancing age can be minimized via various NMES protocols. Animal models have shown that NMES induces motor axon regeneration and promotes axonal outgrowth and fibre reinnervation. The activation of BDNF-trkB contributes to promotion of nerve growth and survival and mediates neuroplasticity. NMES is able to regulate muscle protein homeostasis and elevate oxidative enzyme activity.
One of the most notable effects of ageing is an accelerated decline of skeletal muscle mass and function, resulting in various undesirable outcomes such as falls, frailty, and all-cause mortality. The loss of muscle mass directly leads to functional deficits and can be explained by the combined effects of individual fibre atrophy and fibre loss. The gradual degradation of fibre atrophy is attributed to impaired muscle protein homeostasis, while muscle fibre loss is a result of denervation and motor unit (MU) remodelling. Neuromuscular electrical stimulation (NMES), a substitute for voluntary contractions, has been applied to reduce muscle mass and functional declines. However, the measurement of the effectiveness of NMES in terms of its mechanism of action on the peripheral motor nervous system and neuromuscular junction, and multiple molecular adaptations at the single fibre level is not well described. NMES mediates neuroplasticity and upregulates a number of neurotropic factors, manifested by increased axonal sprouting and newly formed neuromuscular junctions. Repeated involuntary contractions increase the activity levels of oxidative enzymes, increase fibre capillarisation and can influence fibre type conversion. Additionally, following NMES muscle protein synthesis is increased as well as functional capacity. This review will detail the neural, molecular, metabolic and functional adaptations to NMES in human and animal studies.
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26
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Musci RV, Fitzgerald LF. Evaluating skeletal muscle function across the lifespan: Age as a continuous variable. J Physiol 2020; 599:3-4. [PMID: 33043454 DOI: 10.1113/jp280868] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 10/09/2020] [Indexed: 01/12/2023] Open
Affiliation(s)
- Robert V Musci
- Department of Human Genetics, University of Utah, Salt Lake City, UT, USA
| | - Liam F Fitzgerald
- Department of Physical Therapy, University of Florida, Gainesville, FL, USA
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