Comparison of hip and low back worn Axivity AX3 and GT3X+ activity monitors

Publikation: Konferencebidrag uden forlag/tidsskriftPosterForskning


For accurate estimates of average PA, specific PA intensity levels, or individual PA behavior, continuous long-term monitoring is needed. However, poor wear compliance is not unusual with activity monitors worn around the waist using an elastic belt and contributes to significant loss of data. Various algorithms have been proposed to handle non-wear periods a posteriori, but without satisfactory results. Fixation of the activity monitor directly on the skin using medical adhesive tape could be a solution to improve compliance, but compromise wear comfort at the hip. A previous study investigating two different monitor placement within an elastic belt around the waist has shown that positioning does not influence the interpretation of the data at group level (3). Moving the monitor to the low back improves fixation and wear comfort but may affect the recordings of PA, and thus jeopardize the validity and comparability of the PA measure. Bibliography A 9 subject convenient sample was selected for wearing an Actigraph GT3X+ with an Axivity AX3 glued back to back in an elastic belt at the hip and an Axivity AX3 on the low back using adhesive tape. All monitors were worn during free living for 24 Hours. The Actigraph GT3X + monitors was initialized to record 30 Hz raw and the Axivity AX3 was initialized to record 100Hz +-8g. The AX3 data was downloaded, resampled and calibrated (1) using the AX3 OMGUI (V1.0.0.28) and further resampled using Matlab into 30 Hz to account for the potential sample frequency dependency (4). After manually aligning the 30 Hz raw data it was saved into GT3X+ binary files for PA processing. All AX3 and GT3X+ data were processed into 10 seconds epoch activity counts using Actilife V.6.11.4. Statistical analysis and post data processing was done in Matlab (V8.5.0 R2015a) and scaled adult cut points from Freedson et al. (2) was used to estimate the relative time spent in sedentary, light, moderate, and vigorous intensity levels. Sleep time was manually excluded from the analysis based on subjects' logs. Autocalibration of accelerometer data for free-living physical activity assessment using local gravity and temperature: an evaluation on four continents. An Axivity AX3 worn at the hip seems to generate similar daily average activity count, time spent in different intensity levels and also epoch by epoch assessed activity count compared with an GT3X+ instrument worn at the same location and using the same PA estimation algorithm. An Axivity AX3 worn on the low back using adhesive tape also seems to generate analogous daily average activity count information compared with a hip worn device. But, further research is needed to investigate various sources affecting the deviations observed in estimated time spent in selected PA intensity levels, and also the relatively large variation observed in epoch by epoch assessed activity counts.
Publikationsdato11. jun. 2015
StatusUdgivet - 11. jun. 2015
BegivenhedICAMPAM 2015: The International Society for the Measurement of Physical Behaviour - Limerich, Irland
Varighed: 9. jun. 201512. jun. 2015


KonferenceICAMPAM 2015