title: Detection of lying down, sitting, standing, and stepping using two activPAL monitors.
abstract: 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.
  
  
  OBJECTIVE
  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.
authors.affiliation: 1Department of Kinesiology, Recreation, and Sport Studies, University of Tennessee, Knoxville, TN; and 2Department of Health Sciences, Northeastern University, Boston, MA.
authors.forename: David R
authors.initials: DR
authors.lastname: Bassett
authors.forename: Dinesh
authors.initials: D
authors.lastname: John
authors.forename: Scott A
authors.initials: SA
authors.lastname: Conger
authors.forename: Brian C
authors.initials: BC
authors.lastname: Rider
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Passmore
authors.forename: Justin M
authors.initials: JM
authors.lastname: Clark
mesh_terms: D000293:Adolescent; D000328:Adult; D006801:Humans; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009068:Movement; D011187:Posture; D016684:Prone Position; D015203:Reproducibility of Results; D013848:Thigh; D060726:Torso; D055815:Young Adult