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      Motor unit number and transmission stability in octogenarian world class athletes: Can age-related deficits be outrun?

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          Abstract

          World champion master athletes in their ninth decade of life had a greater number of surviving motor units, reduced collateral reinnervation, better neuromuscular transmission stability, and a greater amount of excitable muscle mass compared with age-matched controls. The presumed better maintenance of motor units occurs at a time point when motor unit loss is greatest and the loss of muscle mass becomes functionally relevant, potentially maintaining function and attenuating the deleterious effects of sarcopenia .

          Abstract

          Our group has shown a greater number of functioning motor units (MU) in a cohort of highly active older (∼65 yr) masters runners relative to age-matched controls. Because of the precipitous loss in the number of functioning MUs in the eighth and ninth decades of life it is unknown whether older world class octogenarian masters athletes (MA) would also have greater numbers of functioning MUs compared with age-matched controls. We measured MU numbers and neuromuscular transmission stability in the tibialis anterior of world champion MAs (∼80 yr) and compared the values with healthy age-matched controls (∼80 yr). Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular electromyography signals during dorsiflexion at ∼25% of maximum voluntary isometric contraction. Near fiber (NF) MU potential analysis was used to assess neuromuscular transmission stability. For the MAs compared with age-matched controls, the amount of excitable muscle mass (compound muscle action potential) was 14% greater ( P < 0.05), there was a trend ( P = 0.07) toward a 27% smaller surface-detected MU potential representative of less collateral reinnervation, and 28% more functioning MUs ( P < 0.05). Additionally, the MAs had greater MU neuromuscular stability than the controls, as indicated by lower NF jitter and jiggle values ( P < 0.05). These results demonstrate that high-performing octogenarians better maintain neuromuscular stability of the MU and mitigate the loss of MUs associated with aging well into the later decades of life during which time the loss of muscle mass and strength becomes functionally relevant. Future studies may identify the concomitant roles genetics and exercise play in neuroprotection.

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          Author and article information

          Journal
          J Appl Physiol (1985)
          J. Appl. Physiol
          jap
          jap
          JAPPLPHYSIOL
          Journal of Applied Physiology
          American Physiological Society (Bethesda, MD )
          8750-7587
          1522-1601
          24 March 2016
          1 October 2016
          1 October 2017
          : 121
          : 4
          : 1013-1020
          Affiliations
          1Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph Ontario, Canada;
          2School of Medicine and School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada;
          3Faculty of Health Sciences, School of Kinesiology, Canadian Centre for Activity and Aging, The University of Western Ontario, Ontario, Canada;
          4Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada;
          5Department of Physical Medicine and Rehabilitation, The University of Western Ontario, London, Ontario, Canada;
          6Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada;
          7Department of Medicine, McGill University, Montreal, Quebec, Canada;
          8Meakins Christie Laboratories, McGill University, Montreal, Quebec, Canada; and
          9Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada
          Author notes
          Address for reprint requests and other correspondence: G. A. Power, Neuromechanical Performance Research Laboratory, Dept. of Human Health and Nutritional Sciences, College of Biological Sciences, Univ. of Guelph, Ontario, Canada (e-mail: gapower@ 123456uoguelph.ca ).
          Article
          PMC5142311 PMC5142311 5142311 JAPPL-00149-2016
          10.1152/japplphysiol.00149.2016
          5142311
          27013605
          Copyright © 2016 the American Physiological Society
          Funding
          Funded by: http://doi.org/10.13039/501100000024 Gouvernement du Canada | Canadian Institutes of Health Research (Instituts de recherche en santé du Canada)
          Award ID: 84408
          Award ID: 125986
          Funded by: http://doi.org/10.13039/501100000038 Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada (Conseil de Recherches en Sciences Naturelles et en Génie du Canada)
          Award ID: 180970-2011
          Categories
          Highlighted Topic
          Aging and Exercise

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