title: Motor unit number and transmission stability in octogenarian world class athletes: Can age-related deficits be outrun?
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.
authors.affiliation: Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph Ontario, Canada; gapower@uoguelph.ca.
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Power
authors.affiliation: School of Medicine and School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada.
authors.forename: Matti D
authors.identifier: 0000-0002-0755-3164
authors.initials: MD
authors.lastname: Allen
authors.affiliation: Faculty of Health Sciences, School of Kinesiology, Canadian Centre for Activity and Aging, The University of Western Ontario, Ontario, Canada.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Gilmore
authors.affiliation: Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Stashuk
authors.affiliation: Faculty of Health Sciences, School of Kinesiology, Canadian Centre for Activity and Aging, The University of Western Ontario, Ontario, Canada.|Department of Physical Medicine and Rehabilitation, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Doherty
authors.affiliation: Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada.|Department of Medicine, McGill University, Montreal, Quebec, Canada.|Meakins Christie Laboratories, McGill University, Montreal, Quebec, Canada; and.
authors.forename: Russell T
authors.initials: RT
authors.lastname: Hepple
authors.affiliation: Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada.
authors.forename: Tanja
authors.initials: T
authors.lastname: Taivassalo
authors.affiliation: Faculty of Health Sciences, School of Kinesiology, Canadian Centre for Activity and Aging, The University of Western Ontario, Ontario, Canada.|Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Rice
mesh_terms: D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology* / Q000502:physiology*; D054874:Athletic Performance / Q000502:physiology; D002452:Cell Count; D005260:Female; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000166:cytology* / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000502:physiology; D009469:Neuromuscular Junction / Q000166:cytology / Q000502:physiology; D013177:Sports / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*
keywords: aging; dynapenia; electromyography; master athletes; muscle function; physical activity; sarcopenia