A method to determine validity and reliability of activity sensors

METHOD Four sensors were securely fastened to a mechanical oscillator (Vibration Exciter, type 4809, Bruel & Kjaer) and moved at various frequencies (6.67Hz; 13.45Hz; 19.88Hz) within the range of human physical activity. For each of the three sensor axes, the sensors were simultaneously moved for five minutes per defined frequency. The acceleration of each movement was expressed by its RMS value (RMSinput). Raw sensor output (sample frequency 200 Hz) was converted to IMA counts per minute (cpm, in [ms-2]), according to Bouten et al. (1997) [3]. Linear regression analysis was used to examine the relationship between the RMS and IMA. Factors taken into account were the four sensors and the three axes. The device tested in this study was the ProMove2 (Inertia Technology), containing the 3D MEMS inertial sensor (type: LIS3LV02DL, ST Microsystems).