title: Do neural factors underlie age differences in rapid ankle torque development?
abstract: OBJECTIVE
  Rapid torque development is substantially slower in healthy old adults compared with young adults, but the underlying cause of this age-related loss remains unclear. Measurements of myoelectric signals in ankle dorsi- and plantarflexor muscles during rapid exertions were used to explore the extent to which the loss might be attributed to neural factors.
  
  
  METHODS
  Myoelectric signals were measured in a laboratory setting in 24 healthy young and 24 healthy old adult volunteers during rapid isometric and isokinetic torque development. Premotor times, muscle activation rates, and myoelectric activity levels of agonistic and antagonistic muscles were quantified.
  
  
  RESULTS
  There were few marked age differences in the premotor times or in the onset rates or magnitudes of agonistic muscles activities during maximum isometric and during isokinetic exertions. Premotor times were statistically associated with age but, in the mean, were only approximately 10 to 25 ms longer in the old. Age effects on agonist muscle activity magnitudes were significant only in the lateral gastrocnemius. Small decreases in antagonistic muscle activity levels with age were found.
  
  
  CONCLUSIONS
  Given the outcomes of this study, the differences observed previously in rapid torque development abilities in healthy older adults, compared with healthy younger adults, seem attributable largely to differences in muscle contraction mechanisms rather than to differences in speeds of stimulus sensing or central processing of motor commands, or to differences in muscle recruitment strategies.
authors.affiliation: Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor 48109-2125, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Thelen
authors.forename: J A
authors.initials: JA
authors.lastname: Ashton-Miller
authors.forename: A B
authors.initials: AB
authors.lastname: Schultz
authors.forename: N B
authors.initials: NB
authors.lastname: Alexander
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000842:Ankle; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D012727:Sex Characteristics; D013997:Time Factors