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 (VO 2 , 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 VO 2 from the sum of total impulse (I total , N · min), theoretical potential energy gain (P g , m/min · kg) and loss (P l , m/min · kg) for last one minute of each trial, as VO 2 =0.047I total +0.0014P g +0.0006P l , where I total was determined from a square root of summed accelerations of each direction, and P g or P l from a product of body weight and theoretical height changes. Second, to validate the precision of the equation, we measured VO 2 , I total 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 VO 2 (y) and measured VO 2 (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.