title: Evaluation of a theoretical model to quantify the sources of metabolic cost in walking.
abstract: OBJECTIVE
  To evaluate the validity of a theoretical model of walking in which the oxygen uptake (V(O2)) is described as a function of speed by an equation in the form y = ax + b, with constant a representing the metabolic cost for performing the walking movement, and constant b representing the sum of the metabolic costs for basal metabolism and maintaining balance and posture.
  
  
  METHODS
  Repeated-measures analysis of variance was used to analyze our theoretical model. In a human exercise research laboratory, 12 healthy male subjects walked on a level treadmill at speeds of 0.39-1.83 m/sec under a control condition, while wearing "instability" shoes with peripheral vision obstructed, and with 2-kg weights around each wrist. Total transported mass was the same under each condition through the carriage of 4 kg in a back pack during the control and instability conditions. Outcome was determined by equations describing (V(O2)) as a function of speed and by kinematics of the center of mass.
  
  
  RESULTS
  The constant b was higher (P < 0.01) for the instability condition than the other conditions, but constant a did not differ among the conditions. However, external work was greatest (P < 0.05) for the instability condition.
  
  
  CONCLUSIONS
  Because the kinematic data demonstrate that the instability condition increased the metabolic cost for performing the walking movement compared with the control condition, and there was no difference among conditions in constant a, the theoretical model seems invalid.
authors.affiliation: Department of Physical Medicine and Rehabilitation, VA Northern California Health Care System and University of California-Davis Medical Center, Sacramento, California 95655-1200, USA.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Hoffman
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
authors.forename: Robin B
authors.initials: RB
authors.lastname: Candau
authors.forename: Jean-Denis
authors.initials: JD
authors.lastname: Rouillon
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001944:Breath Tests; D004734:Energy Metabolism / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology*; D016138:Walking / Q000502:physiology*