Motor unit number estimates and neuromuscular transmission in the tibialis anterior of master athletes: evidence that athletic older people are not spared from age-related motor unit remodeling.
Muscle motor unit numbers decrease markedly in old age, while remaining motor units are enlarged and can have reduced neuromuscular junction transmission stability. However, it is possible that regular intense physical activity throughout life can attenuate this remodeling. The aim of this study was to compare the number, size, and neuromuscular junction transmission stability of tibialis anterior (TA) motor units in healthy young and older men with those of exceptionally active master runners. The distribution of motor unit potential (MUP) size was determined from intramuscular electromyographic signals recorded in healthy male Young (mean ± SD, 26 ± 5 years), Old (71 ± 4 years) and Master Athletes (69 ± 3 years). Relative differences between groups in numbers of motor units was assessed using two methods, one comparing MUP size and muscle cross-sectional area (CSA) determined with MRI, the other comparing surface recorded MUPs with maximal compound muscle action potentials and commonly known as a "motor unit number estimate (MUNE)". Near fiber (NF) jiggle was measured to assess neuromuscular junction transmission stability. TA CSA did not differ between groups. MUNE values for the Old and Master Athletes were 45% and 40%, respectively, of the Young. Intramuscular MUPs of Old and Master Athletes were 43% and 56% larger than Young. NF jiggle was slightly higher in the Master Athletes, with no difference between Young and Old. These results show substantial and similar motor unit loss and remodeling in Master Athletes and Old individuals compared with Young, which suggests that lifelong training does not attenuate the age-related loss of motor units.
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
Mathew
M
Piasecki
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
Alex
A
Ireland
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
Jessica
J
Coulson
Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada.
Dan W
DW
Stashuk
Mathematics and Computer Science, Mount Allison University, Sackville, New Brunswick, Canada.
Andrew
A
Hamilton-Wright
Andrology Research Unit, Cardiovascular, Metabolic and Nutritional Sciences Domain, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.
Agnieszka
A
Swiecicka
Manchester Diabetes Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK.
Martin K
MK
Rutter
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK j.s.mcphee@mmu.ac.uk.
Jamie S
JS
McPhee
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
David A
DA
Jones
D000200:Action Potentials; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D056352:Athletes; D004576:Electromyography / Q000379:methods; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009473:Neuronal Plasticity; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012420:Running; D009435:Synaptic Transmission / Q000502:physiology*; D013977:Tibia / Q000033:anatomy & histology / Q000294:innervation / Q000502:physiology*
Aging; electromyography; master athletes; motor unit; skeletal muscle
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