Abstract
Accelerometer calibration for physical activity (PA) intensity is commonly performed using Metabolic Equivalent of Task (MET) as criterion. However, MET is not an age-equivalent measure of PA intensity, which limits the use of MET-calibrated accelerometers for age-related PA investigations. We investigated calibration using VO2net (VO2gross − VO2stand; mL⋅min−1⋅kg−1) as criterion compared to MET (VO2gross/VO2rest) and the effect on assessment of free-living PA in children, adolescents and adults. Oxygen consumption and hip/thigh accelerometer data were collected during rest, stand and treadmill walk and run. Equivalent speed (Speedeq) was used as indicator of the absolute speed (Speedabs) performed with the same effort in individuals of different body size/age. The results showed that VO2net was higher in younger age-groups for Speedabs, but was similar in the three age-groups for Speedeq. MET was lower in younger age-groups for both Speedabs and Speedeq. The same VO2net-values respective MET-values were applied to all age-groups to develop accelerometer PA intensity cut-points. Free-living moderate-and-vigorous PA was 216, 115, 74 and 71 min/d in children, adolescents, younger and older adults with VO2net-calibration, but 140, 83, 74 and 41 min/d with MET-calibration, respectively. In conclusion, VO2net calibration of accelerometers may provide age-equivalent measures of PA intensity/effort for more accurate age-related investigations of PA in epidemiological research.
Highlights
The use of accelerometers to measure physical activity (PA) in research have expanded tremendously since the millennium shift
We propose VO2net (VO2gross − VO2stand, mL·kg−1 ·min−1 ), instead of Metabolic Equivalent of Task (MET) (VO2gross /VO2rest ), to be a criterion measure for accelerometer calibration in children, adolescents and adults
This conclusion is based on the finding that these age-groups showed similar relationship between Speedeq and VO2net, and VO2net may be considered a measure of absolute PA intensity equivalent by age
Summary
The use of accelerometers to measure physical activity (PA) in research have expanded tremendously since the millennium shift. Sensors 2019, 19, 3377 different intensity levels such as light (LPA), moderate (MPA) and vigorous (VPA) physical activity. These PA intensity measures have been used in cross-sectional and longitudinal epidemiological studies to investigate, for example, the age-related decline in PA from childhood into adulthood and associated factors, in an attempt to identify risk groups for future cardiometabolic disease [2,3,4]. When adults walk and run at these speeds, they reach the MET-value of about 5.0 and 9.0, respectively [7] Despite their lower MET-values, the younger individuals would exert higher degree of effort with higher oxygen consumption per kg body weight compared to the older individuals [8,9] as they are moving with higher step frequency [10,11]
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