title: A new device to estimate VO2 during incline walking by accelerometry and barometry.
abstract: OBJECTIVE
  To examine whether the biased estimation of oxygen consumption rate (VO2, mL x kg(-1) x min(-1)) by accelerometry during incline walking can be improved by the addition of altitude changes as measured by barometry.
  
  
  METHODS
  We measured VO2 by respiratory gas analysis and vector magnitude (VM, G) from triaxial accelerations in 42 healthy people (mean +/- SD age = 63 +/- 7 yr) during graded walking on a treadmill while the incline was varied from -15% to +15%. They walked at subjectively slow, moderate, and fast speeds on level and uphill inclines and, in addition to these, at their fastest speed at 0% incline. They then walked at approximately 3, 4, and 5 km x h(-1) on downhill inclines for 3 min each. We determined a regression equation to estimate VO2 from VM and theoretical vertical upward (Hu, m x min(-1)) and downward speeds (Hd, m x min(-1)) for the last 1 min of each trial. To validate the precision of the equation, we measured VM and altitude changes with a portable device equipped with a triaxial accelerometer and a barometer in 11 of the 42 subjects walking on an outdoor hill and compared the estimated VO2 with the value simultaneously measured by respiratory gas analysis.
  
  
  RESULTS
  VO2 above resting was estimated from VO2 = 0.044 VM + 1.365 Hu + 0.553 Hd (r = 0.93, P < 0.001) and the estimated V O2(y) was almost identical to the measured VO2(x) (y = 0.97x, r = 0.88, P < 0.001) with a mean difference of -0.20 +/- 3.47 (mean +/- SD) by Bland-Altman analysis in the range of 2.0-33.0 mL x kg(-1) x min(-1).
  
  
  CONCLUSIONS
  VO2 during walking on various inclines can be precisely estimated by using the device equipped with a triaxial accelerometer and a barometer.
authors.affiliation: Department of Sports Medical Sciences, Shinshu University Graduate School of Medicine, Asahi, Matsumoto, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Gen-No
authors.forename: Yoshi-Ichiro
authors.initials: Y
authors.lastname: Kamijo
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Okazaki
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nose
mesh_terms: D000054:Acceleration; D000368:Aged; D000465:Algorithms; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D016138:Walking / Q000502:physiology*