title: The reliability and validity of the physiological cost index in healthy subjects while walking on 2 different tracks.
abstract: OBJECTIVE
  To investigate the reliability and validity of the Physiological Cost Index (PCI) scores, as a measure of energy expenditure, when healthy subjects walk on 2 different tracks (20-m and 12-m figure eight tracks).
  
  
  METHODS
  Intra- and interrater reliability and construct validity.
  
  
  METHODS
  Physiotherapy division of a university in London, UK.
  
  
  METHODS
  Forty healthy subjects (15 men, 25 women; mean age +/- standard deviation, 34.5+/-12.6 y).
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  Heart rate (in beats/min) and speed (in m/min) were used to calculate the PCI (in beats/m). Rate of oxygen consumption (VO2, in mL x kg(-1) x min(-1)) and oxygen cost (EO2, in mL x kg(-1) x m(-1)) were used as criterion estimates of energy cost EO2. Pearson correlation coefficients between the PCI, components of the PCI, EO2, and VO2 were used to quantify validity. Intrarater reliability was assessed in all participants and interrater reliability was assessed on a subset of 13 subjects using intraclass correlation coefficients and Bland-Altman plots.
  
  
  RESULTS
  Intrarater (r=.73, r=.79) and interrater (r=.62, r=.66) reliability were acceptable between PCI scores from 20-m and 12-m tracks, respectively. Correlations between VO2 and EO2 with PCI were weak. PCI scores from the 20-m track were significantly lower than those on the 12-m track (P=.002). Subjects walked significantly faster on the 20-m track (P<.001). Results suggest a large difference in PCI scores would be necessary to indicate a "true" alteration in performance (52% for 20-m track, 43.4% for the 12-m track).
  
  
  CONCLUSIONS
  The PCI is reliable but not valid as a measure of the energy cost of walking in healthy subjects, on either track. The 20-m track is recommended for clinical use because it enables subjects to walk at a faster pace.
authors.affiliation: Physiotherapy Division, King's College London, London, England.
authors.forename: Rachel C
authors.initials: RC
authors.lastname: Graham
authors.forename: Nicola M
authors.initials: NM
authors.lastname: Smith
authors.forename: Claire M
authors.initials: CM
authors.lastname: White
mesh_terms: D000328:Adult; D000368:Aged; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D013686:Telemetry; D016138:Walking / Q000502:physiology*