Interdevice baseline signal magnitude variability of the ActivPAL3 activity monitor

The aim of this study was to evaluate the interdevice variability in baseline signal magnitude of the ActivPAL3 (PALTechnologies, Glasgow, UK) activity monitor. Twenty consecutively numbered ActivPAL3 triaxial physical activity monitors were assessed for baseline signal magnitudes oriented in the X(vertical standing), Y (side lying), and Z (lying flat) planes. Data was recorded for 60 s in each orientation and the three orthogonal axes were analysed for baseline signal magnitude each orientation. Our batch of devices demonstrated approximately 6.6% difference in raw acceleration calibration values comparedto manufacturer specifications. Analysis of interdevice variability revealed three devices which exhibited baseline signal variability greater than 1.96 SD of the group mean. The impact of interdevice variability in baseline signal magnitude on data collection is unknown, however, supports the argument in the literature for the systematic checking of interdevice variability as routine maintenance.