A Shimmer 9DoF wireless kinematic sensor module
comprising mutually orthogonal tri-axial accelerometers, rate
gyroscopes and magnetometers, was used as the sensing
platform [21]. For our experiments we only use the tri-axial
accelerometer with ±1.5 g range selected and exclude the
magnetometer since it can be affected by the presence of
ferromagnetic materials which are expected to be present in
the natural environment [22]. We also leave out the gyroscope
in view of using a minimal number of sensors aimed at
reducing the amount of data processing involved. The dorsal
side of the forearm proximal to the wrist on the dominant arm
was chosen as the sensing position since it was likely to
produce significant sensor responses to the arm movements
being investigated. The dorsal side was in contact with the XY
plane of the sensor with the X-axis pointing towards the hand
and the Z-axis pointing away from the dorsal aspect. Sensor
data was collected at a rate of 50 Hz, deemed sufficient for
assessing habitual limb movement, which is on the higher side
compared to assessing holistic activity as in [13, 16].