Motor unit number estimates in the tibialis anterior muscle of young, old, and very old men.
The rate of motor unit (MU) loss and its influence on the progression of sarcopenia is not well understood. Therefore, the main purpose of this study was to estimate and compare numbers of MUs in the tibialis anterior (TA) of young men ( approximately 25 years) and two groups of older men ( approximately 65 years and >/=80 years). Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular electromyographic signals during isometric dorsiflexions at 25% of maximum voluntary contraction. The mean surface-MU potential size was divided into the maximum M wave to calculate the motor unit number estimate (MUNE). The MUNE was significantly reduced in the old (91) compared to young (150) men, and further reduced in the very old men (59). Despite the smaller MUNE at age 65, strength was not reduced until beyond 80 years. This suggests that age-related MU loss in the TA does not limit function until a critical threshold is reached.
McNeil
Chris J
CJ
Canadian Centre for Activity and Aging, St. Joseph's Health Annex School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, 1490 Richmond Street, London, Ontario N6G 2M3, Canada.
Doherty
Timothy J
TJ
Stashuk
Daniel W
DW
Rice
Charles L
CL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002452:Cell Count / Q000379:methods / Q000706:statistics & numerical data; D003430:Cross-Sectional Studies; D004576:Electromyography / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology*