title: Muscle performance and physical function are associated with voluntary rate of neuromuscular activation in older adults.
abstract: BACKGROUND
  Muscle power is related to mobility function in older adults, and effective power production requires rapid neuromuscular activation. Accordingly, this study examines the association of neuromuscular activation rate with muscle performance in persons of different age and mobility function.
  
  
  METHODS
  Participants were recruited to three experimental groups: middle-aged healthy adults (MH), older healthy adults (OH), and older adults with mobility limitations (OML). OH and OML were primarily differentiated by performance on the Short Physical Performance Battery (SPPB). Muscle performance (acceleration and power) and electromyography (EMG) were recorded during a maximal-effort leg press task at an absolute resistance (260 N) and at a relative resistance (70% of the one-repetition maximum [1 RM]). Neuromuscular activation rate was quantified as pre-movement time (duration between EMG onset and movement onset) and the rate of EMG rise.
  
  
  RESULTS
  Pre-movement time, rate of EMG rise, leg press acceleration, and leg press power were lower in OML relative to MH and OH but did not differ between OH and MH, with the exception of power at 70% 1RM. Across all older participants, rate of EMG rise was positively associated with acceleration, power, and the SPPB score.
  
  
  CONCLUSIONS
  Slowing of neuromuscular activation rate is associated with compromised dynamic muscle performance, which may contribute to mobility limitations in some older adults. Future research should identify the precise neurophysiological impairments that contribute to declines in neuromuscular activation rate and mobility function with aging.
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington St, Boston, MA 02111, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Clark
authors.forename: Carolynn
authors.initials: C
authors.lastname: Patten
authors.forename: Kieran F
authors.initials: KF
authors.lastname: Reid
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Carabello
authors.forename: Edward M
authors.initials: EM
authors.lastname: Phillips
authors.forename: Roger A
authors.initials: RA
authors.lastname: Fielding
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D004185:Disability Evaluation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D051346:Mobility Limitation; D018482:Muscle, Skeletal / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*