Introduction: The activPAL is an accelerometer-based monitor worn on the thigh that classifies daily activities into three categories (sitting/lying down, standing, and stepping). The monitor discriminates between sitting/lying and the upright position by detecting the inclination of the thigh. It detects stepping from the acceleration vs time waveform. However, a current limitation of the ActivPAL is that it does not discriminate between sitting and lying down.
Purpose: To determine if placing a second activPAL monitor on the torso would allow the detection of seated versus lying postures.
Methods: Fifteen healthy adults (18-55 years of age) wore an activPAL on the right thigh, and another activPAL over the right ribcage. Both monitors were synchronized and initialized to record data in 15-sec epochs. Participants performed a semi-structured routine of activities for 3 minutes each. Activities included lying down (while supine, prone, and on the side), sitting, standing, sweeping, treadmill walking at 3 mph, and treadmill running at 6 mph. The spatial orientation of the thigh and chest monitors was used to determine body posture, and the activPAL on the thigh was used to detect ambulation.
Results: The use of two activPAL devices enabled four behaviors to be accurately classified. The percentage of observations that were classified accurately was as follows: lying down (100%), sitting (100%), standing/light activity in the upright position (90.8%), and stepping (100%).
Conclusion: The current method allows researchers to obtain more detailed information on postural allocation, compared to use of a single activPAL on the thigh.
(C) 2014 American College of Sports Medicine