title: Effects of aging on mechanical efficiency and muscle activation during level and uphill walking.
abstract: OBJECTIVE
  The metabolic cost of walking is greater in old compared to young adults. This study examines the relation between metabolic cost, muscular efficiency, and leg muscle co-activation during level and uphill walking in young and older adults.
  
  
  METHODS
  Metabolic cost and leg muscle activation were measured in young (22.3 ± 3.6 years) and older adults (74.5 ± 2.9 years) walking on a treadmill at six different slopes (0.0-7.5% grade) and a speed of 1.3 ms(-1). Across the range of slopes, 'delta mechanical efficiency' of the muscular system and antagonist muscle co-activation were quantified.
  
  
  RESULTS
  Across all slopes, older adults walked with a 13-17% greater metabolic cost, 12% lower efficiency, and 25% more leg muscle co-activation than young adults. Among older adults, co-activation was weakly correlated to metabolic cost (r=.233) and not correlated to the lower delta efficiency.
  
  
  CONCLUSIONS
  Lower muscular efficiency and increased leg muscle co-activation contribute to the greater metabolic cost of uphill slope walking among older adults but are unrelated to one another.
authors.affiliation: Biomechanics Laboratory, Department of Kinesiology and Recreation Administration, Humboldt State University, CA, United States. Electronic address: jdo1@humboldt.edu.
authors.forename: Justus D
authors.initials: JD
authors.lastname: Ortega
authors.affiliation: Locomtion Laboratory, Department of Integrative Physiology, University of Colorado, CO, United States.
authors.forename: Claire T
authors.initials: CT
authors.lastname: Farley
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D005684:Gait; D006801:Humans; D007866:Leg / Q000254:growth & development / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption; D016138:Walking / Q000502:physiology*
keywords: Aging; Co-activation; Efficiency; Gait; Walking