title: Comparison of raw acceleration from the GENEA and ActiGraph™ GT3X+ activity monitors.
abstract: OBJECTIVE
  To compare raw acceleration output of the ActiGraph™ GT3X+ and GENEA activity monitors.
  
  
  METHODS
  A GT3X+ and GENEA were oscillated in an orbital shaker at frequencies ranging from 0.7 to 4.0 Hz (ten 2-min trials/frequency) on a fixed radius of 5.08 cm. Additionally, 10 participants (age = 23.8 ± 5.4 years) wore the GT3X+ and GENEA on the dominant wrist and performed treadmill walking (2.0 and 3.5 mph) and running (5.5 and 7.5 mph) and simulated free-living activities (computer work, cleaning a room, vacuuming and throwing a ball) for 2-min each. A linear mixed model was used to compare the mean triaxial vector magnitude (VM) from the GT3X+ and GENEA at each oscillation frequency. For the human testing protocol, random forest machine-learning technique was used to develop two models using frequency domain (FD) and time domain (TD) features for each monitor. We compared activity type recognition accuracy between the GT3X+ and GENEA when the prediction model was fit using one monitor and then applied to the other. Z-statistics were used to compare the proportion of accurate predictions from the GT3X+ and GENEA for each model.
  
  
  RESULTS
  GENEA produced significantly higher (p < 0.05, 3.5 to 6.2%) mean VM than GT3X+ at all frequencies during shaker testing. Training the model using TD input features on the GENEA and applied to GT3X+ data yielded significantly lower (p < 0.05) prediction accuracy. Prediction accuracy was not compromised when interchangeably using FD models between monitors.
  
  
  CONCLUSIONS
  It may be inappropriate to apply a model developed on the GENEA to predict activity type using GT3X+ data when input features are TD attributes of raw acceleration.
authors.affiliation: Health Sciences, Northeastern University, 316D Robinson Hall, 360 Huntington Ave., Boston, MA 02115, USA. d.john@neu.edu.
authors.forename: Dinesh
authors.initials: D
authors.lastname: John
authors.forename: Jeffer
authors.initials: J
authors.lastname: Sasaki
authors.forename: John
authors.initials: J
authors.lastname: Staudenmayer
authors.forename: Marianna
authors.initials: M
authors.lastname: Mavilia
authors.forename: Patty S
authors.initials: PS
authors.lastname: Freedson
mesh_terms: D000054:Acceleration; D000328:Adult; D003020:Clothing; D006801:Humans; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000379:methods*; D009043:Motor Activity / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D055815:Young Adult