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Table 2 Differences in speed and VO2 calibration regression equation estimates between treadmill- and track-calibration methods

From: Validity of treadmill- and track-based individual calibration methods for estimating free-living walking speed and VO2 using the Actigraph accelerometer

Regression estimates Speed (km · h−1) VO2 (ml · kg−1 · min−1)
  Mean ∆ treadmill – track (95 % CI) Mean ∆ treadmill – track (95 % CI)
Intercepts of calibration equations −0.02 (−0.16, 0.12) 2.00 (1.18, 2.82)***
Slopes of Actigraph countsa 1.5·10−4 (1.1·10−4, 1.9·10−4)*** 2.9·10−4 (4.1·10−4, 9.8·10−4)
Estimated speed or VO2 at specific Actigraph counts
 … 2000 counts · min−1 0.29 (0.19, 0.39)*** 2.85 (0.42, 3.28)***
 … 3300 counts · min−1 0.49 (0.37, 0.61)*** 3.71 (3.18, 4.24)***
 … 4600 counts · min−1 0.70 (0.54, 0.86)*** 4.79 (3.87, 5.71)***
  1. aWhile the relationship between Actigraph counts and speed was linear and quantified by one slope, the relationship between Actigraph counts and VO2 was quadratic and quantified with two slopes (one for the linear and the other for quadratic term). Consequently, for VO2, between-method differences were tested for the sum of the slopes of the linear and quadratic terms of Actigraph counts (representing the total ‘effect’ of Actigraph counts). ∆ treadmill – track = difference between regression estimates of treadmill and track calibration equations; CI = confidence interval; ***p < .001