22
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Failure to expand the motor unit size to compensate for declining motor unit numbers distinguishes sarcopenic from non‐sarcopenic older men

      research-article

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Key points

          • The age‐related loss of muscle mass is related to the loss of innervating motor neurons and denervation of muscle fibres.

          • Not all denervated muscle fibres are degraded; some may be reinnervated by an adjacent surviving neuron, which expands the innervating motor unit proportional to the numbers of fibres rescued.

          • Enlarged motor units have larger motor unit potentials when measured using electrophysiological techniques.

          • We recorded much larger motor unit potentials in relatively healthy older men compared to young men, but the older men with the smallest muscles (sarcopenia) had smaller motor unit potentials than healthy older men.

          • These findings suggest that healthy older men reinnervate large numbers of muscle fibres to compensate for declining motor neuron numbers, but a failure to do so contributes to muscle loss in sarcopenic men.

          Abstract

          Sarcopenia results from the progressive loss of skeletal muscle mass and reduced function in older age. It is likely to be associated with the well‐documented reduction of motor unit numbers innervating limb muscles and the increase in size of surviving motor units via reinnervation of denervated fibres. However, no evidence exists to confirm the extent of motor unit remodelling in sarcopenic individuals. The aim of the present study was to compare motor unit size and number between young ( n = 48), non‐sarcopenic old ( n = 13), pre‐sarcopenic ( n = 53) and sarcopenic ( n = 29) men. Motor unit potentials (MUPs) were isolated from intramuscular and surface EMG recordings. The motor unit numbers were reduced in all groups of old compared with young men (all P < 0.001). MUPs were higher in non‐sarcopenic and pre‐sarcopenic men compared with young men ( P = 0.039 and 0.001 respectively), but not in the vastus lateralis of sarcopenic old ( P = 0.485). The results suggest that extensive motor unit remodelling occurs relatively early during ageing, exceeds the loss of muscle mass and precedes sarcopenia. Reinnervation of denervated muscle fibres probably expands the motor unit size in the non‐sarcopenic and pre‐sarcopenic old, but not in the sarcopenic old. These findings suggest that a failure to expand the motor unit size distinguishes sarcopenic from pre‐sarcopenic muscles.

          Key points

          • The age‐related loss of muscle mass is related to the loss of innervating motor neurons and denervation of muscle fibres.

          • Not all denervated muscle fibres are degraded; some may be reinnervated by an adjacent surviving neuron, which expands the innervating motor unit proportional to the numbers of fibres rescued.

          • Enlarged motor units have larger motor unit potentials when measured using electrophysiological techniques.

          • We recorded much larger motor unit potentials in relatively healthy older men compared to young men, but the older men with the smallest muscles (sarcopenia) had smaller motor unit potentials than healthy older men.

          • These findings suggest that healthy older men reinnervate large numbers of muscle fibres to compensate for declining motor neuron numbers, but a failure to do so contributes to muscle loss in sarcopenic men.

          Related collections

          Most cited references43

          • Record: found
          • Abstract: not found
          • Article: not found

          Sarcopenia Is Recognized as an Independent Condition by an International Classification of Disease, Tenth Revision, Clinical Modification (ICD-10-CM) Code.

            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Innervation and neuromuscular control in ageing skeletal muscle.

            Changes in the neuromuscular system affecting the ageing motor unit manifest structurally as a reduction in motor unit number secondary to motor neuron loss; fibre type grouping due to repeating cycles of denervation-reinnervation; and instability of the neuromuscular junction that may be due to either or both of a gradual perturbation in postsynaptic signalling mechanisms necessary for maintenance of the endplate acetylcholine receptor clusters or a sudden process involving motor neuron death or traumatic injury to the muscle fibre. Functionally, these changes manifest as a reduction in strength and coordination that precedes a loss in muscle mass and contributes to impairments in fatigue. Regular muscle activation in postural muscles or through habitual physical activity can attenuate some of these structural and functional changes up to a point along the ageing continuum. On the other hand, regular muscle activation in advanced age (>75 years) loses its efficacy, and at least in rodents may exacerbate age-related motor neuron death. Transgenic mouse studies aimed at identifying potential mechanisms of motor unit disruptions in ageing muscle are not conclusive due to many different mechanisms converging on similar motor unit alterations, many of which phenocopy ageing muscle. Longitudinal studies of ageing models and humans will help clarify the cause and effect relationships and thus, identify relevant therapeutic targets to better preserve muscle function across the lifespan.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Epidemiology of sarcopenia and insight into possible therapeutic targets

              With the ageing population, sarcopenia is becoming a public health concern. However, controversy remains over how it can best be defined. In this Review, the authors discuss the various approaches to defining sarcopenia, its prevalence and potential lifestyle modifications and potential therapeutic strategies.
                Bookmark

                Author and article information

                Contributors
                j.s.mcphee@mmu.ac.uk
                Journal
                J Physiol
                J. Physiol. (Lond.)
                10.1111/(ISSN)1469-7793
                TJP
                jphysiol
                The Journal of Physiology
                John Wiley and Sons Inc. (Hoboken )
                0022-3751
                1469-7793
                23 March 2018
                01 May 2018
                23 March 2018
                : 596
                : 9 ( doiID: 10.1113/tjp.2018.596.issue-9 )
                : 1627-1637
                Affiliations
                [ 1 ] School of Healthcare Science Manchester Metropolitan University Manchester M15GD UK
                [ 2 ] Department of Systems Design Engineering University of Waterloo Ontario N2L 3G1 Canada
                [ 3 ] Andrology Research Unit, Cardiovascular, Metabolic and Nutritional Sciences Domain, Faculty of Biology, Medicine and Health University of Manchester Manchester UK
                [ 4 ] Manchester Diabetes Centre, Central Manchester University Hospitals NHS Foundation Trust Manchester Academic Health Science Centre Manchester UK
                Author notes
                [*] [* ] Corresponding author J. S. McPhee: School of Healthcare Science, Manchester Metropolitan University, Manchester M1 5GD, UK. Email:  j.s.mcphee@ 123456mmu.ac.uk
                Author information
                http://orcid.org/0000-0002-7804-4631
                Article
                TJP12865
                10.1113/JP275520
                5924831
                29527694
                f9639212-be96-4c8f-ad10-d2378f5c646e
                © 2018 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 03 November 2017
                : 07 February 2018
                Page count
                Figures: 3, Tables: 1, Pages: 11, Words: 7495
                Funding
                Funded by: Medical Research Council
                Award ID: MR/K025252/1
                Categories
                Research Paper
                Muscle
                Editor's Choice
                Custom metadata
                2.0
                tjp12865
                1 May 2018
                Converter:WILEY_ML3GV2_TO_NLMPMC version:version=5.3.7.2 mode:remove_FC converted:30.04.2018

                Human biology
                sarcopenia,muscle,motor unit,denervation,electromyography
                Human biology
                sarcopenia, muscle, motor unit, denervation, electromyography

                Comments

                Comment on this article