INTRODUCTION: Accelerometer-based physical activity monitoring has become the method of choice in many large-scale physical activity (PA) studies. However, there is an ongoing debate regarding the placement of the device, the determination of device wear time, and how to solve a lack of participant compliance. The aim of this study was to assess the compliance of Axivity AX3 accelerometers taped directly to the skin of 9- to 13-yr-old children.
METHODS: Children in 46 school classes (53.4% girls, age 11.0 ± 1.0 yr, BMI 17.7 ± 2.8 kg·m) across Denmark wore two Axivity AX3 accelerometers, one taped on the thigh (n = 903) and one on the lower back (n = 856), for up to 10 consecutive days. Participants were instructed not to reattach an accelerometer should it fall off. Simple and multiple linear regressions were used to determine associations between accelerometer wear time and age, sex, BMI percentiles, and PA level.
RESULTS: More than 65% had >7 d of uninterrupted, 24-h wear time for the thigh location and 59.5% for the lower back location. From multiple linear regressions, PA levels showed the strongest association with lower wear time (thigh: β = -0.231, R = 0.066; lower back: β = -0.454, R = 0.126). In addition, being a boy, being older (only for lower back), and having higher BMI percentile were associated with lower wear time.
CONCLUSION: Using skin-taped Axivity accelerometers, we obtained 7 d of uninterrupted accelerometer data with 24-h wear time per day with a compliance rate of more than 65%. Thigh placement resulted in higher compliance than lower back placement. Achieving days with 24-h wear time reduces the need for arbitrary decisions regarding wear time validation and most likely improves the validity of daily life PA measurements.