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A new device to estimate energy expenditure during uphill and downhill walking by accelerometry and barometry

We developed a new device to estimate energy expenditure during uphill and downhill walking. First, we measured oxygen consumption rate (VO2, respiratory gas analysis) and 3 dimensional accelerations in 42 healthy people (63±7(SD) yr) during graded walking on a treadmill while slope was varied from −15% to +15%. They walked for 3 minutes at subjectively slow, moderate, fast and fastest speeds on flat and uphill settings and walked at ∼3, 4 and 5km/h for downhill settings. We determined a regression equation to estimate VO2 from the sum of total impulse (Itotal, N · min), theoretical potential energy gain (Pg, m/min · kg) and loss (Pl, m/min · kg) for last one minute of each trial, as VO2=0.047Itotal+0.0014Pg+0.0006Pl, where Itotal was determined from a square root of summed accelerations of each direction, and Pg or Pl from a product of body weight and theoretical height changes. Second, to validate the precision of the equation, we measured VO2, Itotal and barometric pressure in 11 of 42 subjects walking in the field. The height change was estimated from change in barometric pressure. A regression equation between estimated VO2 (y) and measured VO2 (x) in the range of 0.37∼2.56 l/min was y=0.98x+0.04 (r=0.88, P<0.001) with mean difference of 0.01±0.23 (SD) in Brand‐Altman plot. Thus, energy expenditure during uphill and downhill walking was precisely estimated with a device composed of accelerometers and a barometer.