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Detection of Lying Down, Sitting, Standing, and Stepping Using Two ActivPAL Monitors


Medicine & Science in Sports & Exercise: October 2014 - Volume 46 - Issue 10 - p 2025–2029
doi: 10.1249/MSS.0000000000000326
Applied Sciences

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 versus time wave form. However, a current limitation of the activPAL is that it does not discriminate between sitting and lying down.

Purpose: This study aimed to determine whether placing a second activPAL monitor on the torso would allow the detection of seated versus lying postures.

Methods: Fifteen healthy adults (18–55 yr of age) wore an activPAL on the right thigh and another activPAL over the right rib cage. Both monitors were synchronized and initialized to record data in 15-s epochs. Participants performed a semistructured routine of activities for 3 min 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 percentages of observations that were classified accurately were as follows: lying down (100%), sitting (100%), standing/light activity in the upright position (90.8%), and stepping (100%).

Conclusions: The current method allows researchers to obtain more detailed information on postural allocation compared with that in the use of a single activPAL on the thigh.

1Department of Kinesiology, Recreation, and Sport Studies, University of Tennessee, Knoxville, TN; and 2Department of Health Sciences, Northeastern University, Boston, MA

Address for correspondence: David R. Bassett, Jr., M.D., Department of Kinesiology, Recreation, and Sport Studies, University of Tennessee, 1914 Andy Holt Ave., Knoxville, TN 37919; E-mail:

Submitted for publication October 2013.

Accepted for publication February 2014.

© 2014 American College of Sports Medicine