Estimating physical activity in youth using an ankle accelerometer

ABSTRACT

This study developed and validated a vector magnitude (VM) two-regression model (2RM) for use with an ankle-worn ActiGraph accelerometer. For model development, 181 youth (mean ± SD; age, 12.0 ± 1.5 yr) completed 30 min of supine rest and 2–7 structured activities. For cross-validation, 42 youth (age, 12.6 ± 0.8 yr) completed approximately 2 hr of unstructured physical activity (PA). PA data were collected using an ActiGraph accelerometer, (non-dominant ankle) and the VM was expressed as counts/5-s. Measured energy expenditure (Cosmed K4b²) was converted to youth METs (MET_y; activity VO₂ divided by resting VO₂). A coefficient of variation (CV) was calculated for each activity to distinguish continuous walking/running from intermittent activity. The ankle VM sedentary behavior threshold was ≤10 counts/5-s, and a CV≤15 counts/5-s was used to identify walking/running. The ankle VM2RM was within 0.42 MET_y of measured MET_y during the unstructured PA (P > 0.05). The ankle VM2RM was within 5.7 min of measured time spent in sedentary, LPA, MPA, and VPA (P > 0.05). Compared to the K4b², the ankle VM2RM provided similar estimates to measured values during unstructured play and provides a feasible wear location for future studies.

KEYWORDS:

• Motion sensor
• energy expenditure
• activity counts variability
• children
• adolescents

Acknowledgments

The authors would like to thank the research participants and Magdalene Horton, Prince Owusu, Larry Kennard, Katie Dooley, Shawn Pedicini, Rachel Mclellan, and Sarah Sullivan for help with data collection.

Disclosure statement

No potential conflict of interest was reported by the authors SEC or JFO. DRB is a member of the scientific advisory board of ActiGraph, L.L.C.

Additional information

Funding

This work was supported by the National Heart, Lung, and Blood Institute [R21HL093407].