Purpose: To examine whether the biased estimation of oxygen consumption rate (VO2, mL/kg·min) 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 ~3, 4, and 5 km/h on downhill inclines for 3 min each. We determined a regression equation to estimate VO2 from VM and theoretical vertical upward (Hu, m·min-1) and downward speeds (Hd, m/min) 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 VO2(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/kg·min. Conclusions: VO2 during walking on various inclines can be precisely estimated by using the device equipped with a triaxial accelerometer and a barometer.
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