Adxl362

The MOX Activity Logger (MOX; Maastricht Instruments, Maastricht, NL) (Maastricht Instruments BVa, 2020 ) contains a tri-axial accelerometer (ADXL362, Analog Devices, Norwood, MA, US). This small, light-weight, waterproof device (35 mm × 35 mm × 10 mm, 11 g) measures raw acceleration data (±8 g) in three orthogonal sensor axes (X, Y, and Z) at a 25 Hz sampling rate. The raw data is stored directly on the internal memory. The MOX has storage capacity and battery life for continuous measurements up to 7 days. Device configuration, data transfer and charging of the device are possible via an USB connection. Data analysis is performed offline. The MOX was worn in the front trouser pocket, attached with a clip, to secure a fixed orientation of the device with respect to axial mobility of the upper leg. This wear location is shown in Figure 1.
Two commonly used activity trackers, the activPAL (activPAL3, PAL Technologies Ltd, Glasgow, Scotland, UK) and the Fitbit Alta HR (Fitbit; Fitbit Inc., San Fransisco, CA, US) were used as reference for a more relevant interpretation of the validation results. Based on the recommendations of the manufactures the activPAL is worn on the dominant leg ten centimetres above the patella (activPAL) and the Fitbit is worn on the non-dominant wrist (Fitbit, 2020a ).

The PA levels were assessed with the MOX activity monitor (MOX; Maastricht Instruments B.V., the Netherlands (Figure 1)). The device contained a tri-axial accelerometer sensor (ADXL362; Analog Devices, Norwood, MA, USA) in a small waterproof housing (35 × 35 × 10 mm, 11 g). Raw acceleration data (±8 g) were measured in three orthogonal sensor axes (X, Y and Z) at a 25 Hz sampling rate. The accelerometer was factory calibrated against gravity for each axis. The raw acceleration data were converted to a PA classification using a previously described embedded algorithm [34 (link)]. After sensor noise reduction, the data were segmented in to one-second long windows using a fixed non-overlapping sliding window. Based on the amount of activity, each window was classified as dynamic or static. For the static windows, the sensor orientation was assessed. Based on a cut-off value of 0.8 g the static windows were classified as standing or sedentary. Each minute the classified results were sent to the Hospital Fit smartphone application via a Bluetooth protocol.

The MOX Activity Logger (MOX; Maastricht Instruments, Maastricht, The Netherlands) is the successor of the DAAFB [5 ,24 (link)] and CAM [7 (link),22 (link),25 (link)] activity loggers. The device contains a tri-axial accelerometer sensor (ADXL362; Analog Devices, Norwood, MA, USA) in a small waterproof housing (35 × 35 × 10 mm, 11 g) [26 ]. The MOX uses a custom-made, double-sided, waterproof patch for body attachment. Raw acceleration data (±8 g) is measured in three orthogonal sensor axes (X, Y and Z) at a 25 Hz sampling rate and stored directly on the internal memory. The MOX is capable of measuring and storing data continuously up to seven days. Data analysis is performed offline. The MOX has been successfully used for physical activity monitoring in colorectal cancer survivors and COPD patients [3 (link),27 (link)] worn on an upper leg location.