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Qaisar R, Bhaskaran S, Van Remmen H. Muscle fiber type diversification during exercise and regeneration. Free Radic Biol Med 2016; 98:56-67. [PMID: 27032709 DOI: 10.1016/j.freeradbiomed.2016.03.025] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 03/01/2016] [Accepted: 03/24/2016] [Indexed: 01/15/2023]
Abstract
The plasticity of skeletal muscle can be traced down to extensive metabolic, structural and molecular remodeling at the single fiber level. Skeletal muscle is comprised of different fiber types that are the basis of muscle plasticity in response to various functional demands. Resistance and endurance exercises are two external stimuli that differ in their duration and intensity of contraction and elicit markedly different responses in muscles adaptation. Further, eccentric contractions that are associated with exercise-induced injuries, elicit varied muscle adaptation and regenerative responses. Most adaptive changes are fiber type-specific and are highly influenced by diverse structural, metabolic and functional characteristics of individual fiber types. Regulation of signaling pathways by reactive oxygen species (ROS) and oxidative stress also plays an important role in muscle fiber adaptation during exercise. This review focuses on cellular and molecular responses that regulate the adaptation of skeletal muscle to exercise and exercise-related injuries.
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Affiliation(s)
- Rizwan Qaisar
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, OK 73104, USA
| | - Shylesh Bhaskaran
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, OK 73104, USA
| | - Holly Van Remmen
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, OK 73104, USA.
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Karlsen A, Couppé C, Andersen JL, Mikkelsen UR, Nielsen RH, Magnusson SP, Kjaer M, Mackey AL. Matters of fiber size and myonuclear domain: Does size matter more than age? Muscle Nerve 2015; 52:1040-6. [DOI: 10.1002/mus.24669] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 03/12/2015] [Accepted: 03/25/2015] [Indexed: 12/20/2022]
Affiliation(s)
- Anders Karlsen
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Christian Couppé
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Jesper L. Andersen
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Ulla R. Mikkelsen
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Rie H. Nielsen
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - S. Peter Magnusson
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Michael Kjaer
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
| | - Abigail L. Mackey
- Institute of Sports Medicine; Department of Orthopaedic Surgery M; Bispebjerg Hospital; Building 8, Bispebjerg Bakke 23 2400 Copenhagen NV Denmark
- Department of Biomedical Sciences; Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen; Copenhagen Denmark
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Muscle stem cells contribute to myofibres in sedentary adult mice. Nat Commun 2015; 6:7087. [PMID: 25971691 PMCID: PMC4435732 DOI: 10.1038/ncomms8087] [Citation(s) in RCA: 178] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 03/31/2015] [Indexed: 12/12/2022] Open
Abstract
Skeletal muscle is essential for mobility, stability, and whole body metabolism, and muscle loss, for instance during sarcopenia, has profound consequences. Satellite cells (muscle stem cells) have been hypothesized, but not yet demonstrated, to contribute to muscle homeostasis and a decline in their contribution to myofiber homeostasis to play a part in sarcopenia. To test their role in muscle maintenance, we genetically labeled and ablated satellite cells in adult sedentary mice. We demonstrate via genetic lineage experiments that even in the absence of injury, satellite cells contribute to myofibers in all adult muscles, although the extent and timing differs. However, genetic ablation experiments showed that satellite cells are not globally required to maintain myofiber cross-sectional area of uninjured adult muscle.
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Grounds MD. Therapies for sarcopenia and regeneration of old skeletal muscles: more a case of old tissue architecture than old stem cells. BIOARCHITECTURE 2014; 4:81-7. [PMID: 25101758 DOI: 10.4161/bioa.29668] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Age related loss of skeletal muscle mass and function (sarcopenia) reduces independence and the quality of life for individuals, and leads to falls and fractures with escalating health costs for the rapidly aging human population. Thus there is much interest in developing interventions to reduce sarcopenia. One area that has attracted recent attention is the proposed use of myogenic stem cells to improve regeneration of old muscles. This mini-review challenges the fundamental need for myogenic stem cell therapy for sarcopenia. It presents evidence that demonstrates the excellent capacity of myogenic stem cells from very old rodent and human muscles to form new muscles after experimental myofiber necrosis. The many factors required for successful muscle regeneration are considered with a strong focus on integration of components of old muscle bioarchitecture. The fundamental role of satellite cells in homeostasis of normal aging muscles and the incidence of endogenous regeneration in old muscles is questioned. These issues, combined with problems for clinical myogenic stem cell therapies for severe muscle diseases, raise fundamental concerns about the justification for myogenic stem cell therapy for sarcopenia.
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Affiliation(s)
- Miranda D Grounds
- School of Anatomy, Physiology and Human Biology; University of Western Australia; Crawley, Australia
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Verdijk LB, Snijders T, Drost M, Delhaas T, Kadi F, van Loon LJC. Satellite cells in human skeletal muscle; from birth to old age. AGE (DORDRECHT, NETHERLANDS) 2014; 36:545-7. [PMID: 24122288 PMCID: PMC4039250 DOI: 10.1007/s11357-013-9583-2] [Citation(s) in RCA: 257] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 08/23/2013] [Indexed: 05/20/2023]
Abstract
Changes in satellite cell content play a key role in regulating skeletal muscle growth and atrophy. Yet, there is little information on changes in satellite cell content from birth to old age in humans. The present study defines muscle fiber type-specific satellite cell content in human skeletal muscle tissue over the entire lifespan. Muscle biopsies were collected in 165 subjects, from different muscles of children undergoing surgery (<18 years; n = 13) and from the vastus lateralis muscle of young adult (18–49 years; n = 50), older (50–69 years; n = 53), and senescent subjects (70–86 years; n = 49). In a subgroup of 51 aged subjects (71 ± 6 years), additional biopsies were collected after 12 weeks of supervised resistance-type exercise training. Immunohistochemistry was applied to assess skeletal muscle fiber type-specific composition, size, and satellite cell content. From birth to adulthood, muscle fiber size increased tremendously with no major changes in muscle fiber satellite cell content, and no differences between type I and II muscle fibers. In contrast to type I muscle fibers, type II muscle fiber size was substantially smaller with increasing age in adults (r = −0.56; P < 0.001). This was accompanied by an age-related reduction in type II muscle fiber satellite cell content (r = −0.57; P < 0.001). Twelve weeks of resistance-type exercise training significantly increased type II muscle fiber size and satellite cell content. We conclude that type II muscle fiber atrophy with aging is accompanied by a specific decline in type II muscle fiber satellite cell content. Resistance-type exercise training represents an effective strategy to increase satellite cell content and reverse type II muscle fiber atrophy.
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Affiliation(s)
- Lex B. Verdijk
- />Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, P.O. Box 616, 6200 MD Maastricht, The Netherlands
| | - Tim Snijders
- />Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, P.O. Box 616, 6200 MD Maastricht, The Netherlands
| | - Maarten Drost
- />Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, P.O. Box 616, 6200 MD Maastricht, The Netherlands
| | - Tammo Delhaas
- />Department of Biomedical Engineering, Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre+, Maastricht, The Netherlands
- />Department of Pediatric Cardiology, University Hospital Gasthuisberg, Leuven, Belgium
| | - Fawzi Kadi
- />Division of Sport Sciences, School of Health and Medical Sciences, Örebro University, Örebro, Sweden
| | - Luc J. C. van Loon
- />Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, P.O. Box 616, 6200 MD Maastricht, The Netherlands
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Mackey AL, Karlsen A, Couppé C, Mikkelsen UR, Nielsen RH, Magnusson SP, Kjaer M. Differential satellite cell density of type I and II fibres with lifelong endurance running in old men. Acta Physiol (Oxf) 2014; 210:612-27. [PMID: 24219628 DOI: 10.1111/apha.12195] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 09/23/2013] [Accepted: 11/08/2013] [Indexed: 12/13/2022]
Abstract
AIM To investigate the influence of lifelong endurance running on the satellite cell pool of type I and type II fibres in healthy human skeletal muscle. METHODS Muscle biopsies were collected from 15 healthy old trained men (O-Tr) who had been running 43 ± 16 (mean ± SD) kilometres a week for 28 ± 9 years. Twelve age-matched untrained men (O-Un) and a group of young trained and young untrained men were recruited for comparison. Frozen sections were immunohistochemically stained for Pax7, type I myosin and laminin, from which fibre area, the number of satellite cells, and the relationship between these variables were determined. RESULTS In O-Un and O-Tr, type II fibres were smaller and contained fewer satellite cells than type I fibres. However, when expressed relative to fibre area, the difference in satellite cell content between fibre types was eliminated in O-Tr, but not O-Un. A strong positive relationship between fibre size and satellite cell content was detected in trained individuals. In line with a history of myofibre repair, a greater number of fibres with centrally located myonuclei were detected in O-Tr. CONCLUSION Lifelong endurance training (i) does not deplete the satellite cell pool and (ii) is associated with a similar density of satellite cells in type I and II fibres despite a failure to preserve the equal fibre type distribution of satellite cells observed in young individuals. Taken together, these data reveal a differential regulation of satellite cell content between fibre types, in young and old healthy men with dramatically different training histories.
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Affiliation(s)
- A. L. Mackey
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - A. Karlsen
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - C. Couppé
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - U. R. Mikkelsen
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - R. H. Nielsen
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - S. P. Magnusson
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - M. Kjaer
- Department of Orthopaedic Surgery M; Institute of Sports Medicine Copenhagen; Bispebjerg Hospital; Copenhagen Denmark
- Center for Healthy Aging; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
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Stevenson JL, Song H, Cooper JA. Age and sex differences pertaining to modes of locomotion in triathlon. Med Sci Sports Exerc 2014; 45:976-84. [PMID: 23247717 DOI: 10.1249/mss.0b013e31827d17eb] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PURPOSE The magnitude of change in sex differences across age groups in triathlon performance for the Ironman distance has been established. However, the influence of age on sex differences at shorter-distance triathlons is yet to be determined. The aim of this study was to compare sex differences across age groups for the different modes of locomotion among varying triathlon distances (Sprint, Olympic, and Ironman 70.3) in amateur triathletes from the 2009-2011 triathlon World Championship. METHODS Data for the top 10 male and female amateur triathletes for the age groups between 18 and 64 yr were collected from the 2009-2011 World Championships for Sprint, Olympic, and Ironman 70.3 triathlons. Sex differences across age groups were compared using time performances for swimming, cycling, running, transition time, overall race time, and estimated power output. RESULTS Total time differences between sexes were largest in 55-59 yr age groups for Sprint (18.7%, P < 0.05) and in 60-64 yr age groups for Olympic and Ironman 70.3 (14.8% and 21.7%, P < 0.05). Mean sex difference in performance time was smallest for cycling in Sprint (11.8% ± 0.41%) and in Ironman 70.3 (11.2% ± 0.41%), whereas running showed the smallest sex difference in Olympic (7.5% ± 0.33%, P < 0.05). Mean sex differences in estimated power output were significantly greater for swimming in Sprint (41.0% ± 1.47%), Olympic (39.8% ± 1.24%), and Ironman 70.3 (37.%5 ± 1.67%, P < 0.05). CONCLUSIONS Sex differences for total performance time were greatest in the youngest age groups and older age groups for Sprint, Olympic, and Ironman 70.3 distances. Sex differences varied among the modes of locomotion for the three distances of triathlons; however, for short- to mid-distance triathlons, both performance time and estimated power output seem to indicate that the largest sex differences exist for swimming.
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Affiliation(s)
- Jada L Stevenson
- Department of Nutrition, Hospitality, and Retailing, Texas Tech University, Lubbock, TX 79409, USA
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58
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Demontis F, Piccirillo R, Goldberg AL, Perrimon N. Mechanisms of skeletal muscle aging: insights from Drosophila and mammalian models. Dis Model Mech 2013; 6:1339-52. [PMID: 24092876 PMCID: PMC3820258 DOI: 10.1242/dmm.012559] [Citation(s) in RCA: 162] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A characteristic feature of aged humans and other mammals is the debilitating, progressive loss of skeletal muscle function and mass that is known as sarcopenia. Age-related muscle dysfunction occurs to an even greater extent during the relatively short lifespan of the fruit fly Drosophila melanogaster. Studies in model organisms indicate that sarcopenia is driven by a combination of muscle tissue extrinsic and intrinsic factors, and that it fundamentally differs from the rapid atrophy of muscles observed following disuse and fasting. Extrinsic changes in innervation, stem cell function and endocrine regulation of muscle homeostasis contribute to muscle aging. In addition, organelle dysfunction and compromised protein homeostasis are among the primary intrinsic causes. Some of these age-related changes can in turn contribute to the induction of compensatory stress responses that have a protective role during muscle aging. In this Review, we outline how studies in Drosophila and mammalian model organisms can each provide distinct advantages to facilitate the understanding of this complex multifactorial condition and how they can be used to identify suitable therapies.
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Affiliation(s)
- Fabio Demontis
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
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59
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Qaisar R, Renaud G, Hedstrom Y, Pöllänen E, Ronkainen P, Kaprio J, Alen M, Sipilä S, Artemenko K, Bergquist J, Kovanen V, Larsson L. Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs. J Physiol 2013; 591:2333-44. [PMID: 23459759 DOI: 10.1113/jphysiol.2012.250092] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Ageing is associated with a decline in muscle mass and strength leading to increased physical dependency in old age. Postmenopausal women experience a greater decline than men of similar age in parallel with the decrease in female sex steroid hormone production. We recruited six monozygous female twin pairs (55-59 years old) where only one twin pair was on hormone replacement therapy (HRT use = 7.8 ± 4.3 years) to investigate the association of HRT with the cytoplasmic volume supported by individual myonuclei (myonuclear domain (MND) size,) together with specific force at the single fibre level. HRT use was associated with a significantly smaller (∼27%; P < 0.05) mean MND size in muscle fibres expressing the type I but not the IIa myosin heavy chain (MyHC) isoform. In comparison to non-users, higher specific force was recorded in HRT users both in muscle fibres expressing type I (∼27%; P < 0.05) and type IIa (∼23%; P < 0.05) MyHC isoforms. These differences were fibre-type dependent, i.e. the higher specific force in fast-twitch muscle fibres was primarily caused by higher force per cross-bridge while slow-twitch fibres relied on both a higher number and force per cross-bridge. HRT use had no effect on fibre cross-sectional area (CSA), velocity of unloaded shortening (V0) and relative proportion of MyHC isoforms. In conclusion, HRT appears to have significant positive effects on both regulation of muscle contraction and myonuclei organization in postmenopausal women.
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Affiliation(s)
- Rizwan Qaisar
- Department of Neuroscience, Clinical Neurophysiology, Uppsala University, Sweden
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Feng X, Todd T, Lintzenich CR, Ding J, Carr JJ, Ge Y, Browne JD, Kritchevsky SB, Butler SG. Aging-related geniohyoid muscle atrophy is related to aspiration status in healthy older adults. J Gerontol A Biol Sci Med Sci 2012; 68:853-60. [PMID: 23112114 DOI: 10.1093/gerona/gls225] [Citation(s) in RCA: 113] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND Age-related muscle weakness due to atrophy and fatty infiltration in orofacial muscles may be related to swallowing deficits in older adults. An important component of safe swallowing is the geniohyoid (GH) muscle, which helps elevate and stabilize the hyoid bone, thus protecting the airway. This study aimed to explore whether aging and aspiration in older adults were related to GH muscle atrophy and fatty infiltration. METHOD Eighty computed tomography scans of the head and neck from 40 healthy older (average age 78 years) and 40 younger adults (average age 32 years) were analyzed. Twenty aspirators and 20 nonaspirators from the 40 older adults had been identified previously. Two-dimensional views in the sagittal and coronal planes were used to measure the GH cross-sectional area and fatty infiltration. RESULTS GH cross-sectional area was larger in men than in women (p < .05). Decreased cross-sectional area was associated with aging (p < .05), and cross-sectional area was significantly smaller in aspirators compared with nonaspirators, but only among the older men (p < .01). Increasing fatty infiltration was associated with aging in the middle (p < .05) and posterior (p < .01) portions of the GH muscle. There was no significant difference in fatty infiltration of the GH muscle among aspirators and nonaspirators. CONCLUSION GH muscle atrophy was associated with aging and aspiration. Fatty infiltration in the GH muscle was increased with aging but not related to aspiration status. These findings suggest that GH muscle atrophy may be a component of decreased swallowing safety and aspiration in older adults and warrants further investigation.
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Affiliation(s)
- Xin Feng
- Department of Otolaryngology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157, USA.
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Mitchell WK, Williams J, Atherton P, Larvin M, Lund J, Narici M. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Front Physiol 2012; 3:260. [PMID: 22934016 PMCID: PMC3429036 DOI: 10.3389/fphys.2012.00260] [Citation(s) in RCA: 775] [Impact Index Per Article: 64.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Accepted: 06/21/2012] [Indexed: 12/21/2022] Open
Abstract
Changing demographics make it ever more important to understand the modifiable risk factors for disability and loss of independence with advancing age. For more than two decades there has been increasing interest in the role of sarcopenia, the age-related loss of muscle or lean mass, in curtailing active and healthy aging. There is now evidence to suggest that lack of strength, or dynapenia, is a more constant factor in compromised wellbeing in old age and it is apparent that the decline in muscle mass and the decline in strength can take quite different trajectories. This demands recognition of the concept of muscle quality; that is the force generating per capacity per unit cross-sectional area (CSA). An understanding of the impact of aging on skeletal muscle will require attention to both the changes in muscle size and the changes in muscle quality. The aim of this review is to present current knowledge of the decline in human muscle mass and strength with advancing age and the associated risk to health and survival and to review the underlying changes in muscle characteristics and the etiology of sarcopenia. Cross-sectional studies comparing young (18–45 years) and old (>65 years) samples show dramatic variation based on the technique used and population studied. The median of values of rate of loss reported across studies is 0.47% per year in men and 0.37% per year in women. Longitudinal studies show that in people aged 75 years, muscle mass is lost at a rate of 0.64–0.70% per year in women and 0.80–00.98% per year in men. Strength is lost more rapidly. Longitudinal studies show that at age 75 years, strength is lost at a rate of 3–4% per year in men and 2.5–3% per year in women. Studies that assessed changes in mass and strength in the same sample report a loss of strength 2–5 times faster than loss of mass. Loss of strength is a more consistent risk for disability and death than is loss of muscle mass.
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Affiliation(s)
- W Kyle Mitchell
- Division of Surgery, School of Postgraduate Entry Medicine and Health, University of Nottingham Derby, UK
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Qaisar R, Renaud G, Morine K, Barton ER, Sweeney HL, Larsson L. Is functional hypertrophy and specific force coupled with the addition of myonuclei at the single muscle fiber level? FASEB J 2011; 26:1077-85. [PMID: 22125316 DOI: 10.1096/fj.11-192195] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Muscle force is typically proportional to muscle size, resulting in constant force normalized to muscle fiber cross-sectional area (specific force). Mice overexpressing insulin-like growth factor-1 (IGF-1) exhibit a proportional gain in muscle force and size, but not the myostatin-deficient mice. In an attempt to explore the role of the cytoplasmic volume supported by individual myonuclei [myonuclear domain (MND) size] on functional capacity of skeletal muscle, we have investigated specific force in relation to MND and the content of the molecular motor protein, myosin, at the single muscle fiber level from myostatin-knockout (Mstn(-/-)) and IGF-1-overexpressing (mIgf1(+/+)) mice. We hypothesize that the addition of extra myonuclei is a prerequisite for maintenance of specific force during muscle hypertrophy. A novel algorithm was used to measure individual MNDs in 3 dimensions along the length of single muscle fibers from the fast-twitch extensor digitorum longus and the slow-twitch soleus muscle. A significant effect of the size of individual MNDs in hypertrophic muscle fibers on both specific force and myosin content was observed. This effect was muscle cell type specific and suggested there is a critical volume individual myonuclei can support efficiently. The large MNDs found in fast muscles of Mstn(-/-) mice were correlated with the decrement in specific force and myosin content in Mstn(-/-) muscles. Thus, myostatin inhibition may not be able to maintain the appropriate MND for optimal function.
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Affiliation(s)
- Rizwan Qaisar
- Department of Neuroscience, Uppsala University, SE-751 85 Uppsala, Sweden
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Robinson MM, Turner SM, Hellerstein MK, Hamilton KL, Miller BF. Long-term synthesis rates of skeletal muscle DNA and protein are higher during aerobic training in older humans than in sedentary young subjects but are not altered by protein supplementation. FASEB J 2011; 25:3240-9. [PMID: 21613572 DOI: 10.1096/fj.11-186437] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Consuming protein following exercise has been shown to stimulate protein synthesis acutely in skeletal muscle and has been recommended to prevent sarcopenia. It is not known, however, whether acute stimulation persists long term or includes muscle cell division. We asked here whether consuming protein following exercise during aerobic training increases long-term protein and DNA synthesis rates in skeletal muscle of adult humans. Sixteen previously untrained participants (50 ± 8 yr) consumed either a carbohydrate or carbohydrate and protein drink following each session during 6 wk of treadmill training. A younger untrained group provided a nonexercising comparison. Participants were administered heavy water (²H₂O; deuterium oxide) continuously for 6 wk to isotopically label newly synthesized skeletal muscle proteins and DNA. Muscle biopsies were performed after 6 wk of training. Contrary to acute studies, consuming protein after exercise did not increase skeletal muscle protein synthesis rates. In contrast, muscle protein synthesis, DNA, and phospholipid synthesis were significantly higher in the older exercise groups than the younger sedentary group. The higher DNA replication rate could not be attributed to mitochondrial DNA and may be due to satellite cell activation. We conclude that postexercise protein supplementation does not increase rates of mixed protein synthesis over 6 wk and that aerobic exercise may stimulate long-term cell division (DNA synthesis) in skeletal muscle of humans. Measurements of long-term synthesis rates provide important insights into aging and exercise adaptations.
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Affiliation(s)
- Matthew M Robinson
- Department of Health and Exercise Science, Colorado State University, Fort Collins, CO 80523-1582, USA
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