title: Characterization of the human quadriceps muscle in active elders.
abstract: OBJECTIVE
  To compare muscle activation deficits and muscle physiology in older versus younger adults.
  
  
  METHODS
  A maximal volitional isometric contraction of the quadriceps muscle with burst-superimposition was used to assess strength and activation. In addition, force-frequency testing during fresh, fatigue, and recovery conditions and electrically elicited fatigue testing were performed.
  
  
  METHODS
  Muscle performance laboratory.
  
  
  METHODS
  Healthy, active young (age range, 20-28 yr) and older (age range, 66-83 yr) subjects.
  
  
  METHODS
  Torque production, activation of the quadriceps, F50 values from the force-frequency relationships (frequency at which 50% of the maximum normalized force is produced), and the average amount of fatigue.
  
  
  RESULTS
  Older subjects were weaker (574.4 +/- 156 N) than younger subjects (900.9 +/- 295 N) and had significantly greater deficits in central activation in the quadriceps muscles (elderly = 95.5% activation; younger = 98.1% activation). The force-frequency curves for the elderly were to the left of the younger subjects for all 3 testing conditions. Aged muscles fatigued to the same extent as younger muscle (young = 49.8% +/- 2.6%, elderly = 51.1% +/- 2.8%).
  
  
  CONCLUSIONS
  These results can be used to modify high-intensity strength training protocols designed to optimize sustainable strength gains in the elderly during rehabilitation.
authors.affiliation: Department of Physical Therapy, University of Delaware, Newark, DE 19716, USA. jensteve@udel.edu
authors.forename: J E
authors.initials: JE
authors.lastname: Stevens
authors.forename: S
authors.initials: S
authors.lastname: Binder-Macleod
authors.forename: L
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007866:Leg / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque