title: Ambulatory measurement of knee motion and physical activity: preliminary evaluation of a smart activity monitor.
abstract: BACKGROUND
  There is currently a paucity of devices available for continuous, long-term monitoring of human joint motion. Non-invasive, inexpensive devices capable of recording human activity and joint motion have many applications for medical research. Such a device could be used to quantify range of motion outside the gait laboratory. The purpose of this study was to test the accuracy of the modified Intelligent Device for Energy Expenditure and Activity (IDEEA) in measuring knee flexion angles, to detect different physical activities, and to quantify how often healthy subjects use deep knee flexion in the ambulatory setting.
  
  
  METHODS
  We compared Biomotion Laboratory (BML) "gold standard" data to simultaneous IDEEA measures of knee motion and gait, step up/down, and stair descent in 5 healthy subjects. In addition, we used a series of choreographed physical activities outside the BML to confirm the IDEEA's ability to accurately measure 7 commonly-performed physical activities. Subjects then continued data collection during ordinary activities outside the gait laboratory.
  
  
  RESULTS
  Pooled correlations between the BML and IDEEA knee flexion angles were .97 +/- .03 for step up/down, .98 +/- .02 for stair descent, and .98 +/- .01 for gait. In the BML protocol, the IDEEA accurately identified gait, but was less accurate in identifying step up/down and stair descent. During sampling outside the BML, the IDEEA accurately detected walking, running, stair ascent, stair descent, standing, lying, and sitting. On average, subjects flexed their knees >120 degrees for 0.17% of their data collection periods outside the BML.
  
  
  CONCLUSIONS
  The modified IDEEA system is a useful clinical tool for evaluating knee motion and multiple physical activities in the ambulatory setting. These five healthy subjects rarely flexed their knees >120 degrees.
authors.affiliation: Harvard Medical School Harris Orthopaedic Biomechanics and Biomaterials Laboratory Massachusetts General Hospital 55 Fruit Street, GRJ 1126 Boston, MA 02114-2696, USA. jhuddleston@stanford.edu
authors.forename: James
authors.initials: J
authors.lastname: Huddleston
authors.forename: Amer
authors.initials: A
authors.lastname: Alaiti
authors.forename: Dov
authors.initials: D
authors.lastname: Goldvasser
authors.forename: Donna
authors.initials: D
authors.lastname: Scarborough
authors.forename: Andrew
authors.initials: A
authors.lastname: Freiberg
authors.forename: Harry
authors.initials: H
authors.lastname: Rubash
authors.forename: Henrik
authors.initials: H
authors.lastname: Malchau
authors.forename: William
authors.initials: W
authors.lastname: Harris
authors.forename: David
authors.initials: D
authors.lastname: Krebs