title: Step activity monitor: increased accuracy in quantifying ambulatory activity.
abstract: This study compares the accuracy of a two-dimensional accelerometer worn on the ankle (a step activity monitor) with that of an electronic, digital pedometer worn on the belt line. Twenty-nine human subjects were evaluated while they briskly walked 400 M, slowly walked 10 M, and ascended and descended a flight of stairs. The step activity monitor had less error in all activities; its mean absolute error was 0.54%, whereas that of the pedometer was 2.82%. The difference was more pronounced in obese subjects (body mass index greater than 30), with an overall mean absolute error of 0.48% for the step activity monitor and 6.12% for the pedometer (nearly 13 times that of the step activity monitor). For subjects with a body mass index less than 30, the step activity monitor had an overall error of 0.56% and the pedometer had an overall error of 1.56% (less than 3 times that of the step activity monitor). The absolute error of the pedometer was positively correlated with body mass index (r = 0.792, p < 0.0001) and weight (r = 0.753, p < 0.0001), whereas the error of the step activity monitor was not significantly correlated with either. Neither device was significantly biased by age, gender, or the presence of a lower-extremity joint prosthesis. The accuracy and additional capabilities, including a real-time memory record of activity, of the step activity monitor make it well suited for objectively quantifying ambulatory activity, especially for obese subjects.
authors.affiliation: Joint Replacement Institute, Orthopaedic Hospital, Los Angeles, California 90007, USA.
authors.forename: E F
authors.initials: EF
authors.lastname: Shepherd
authors.forename: E
authors.initials: E
authors.lastname: Toloza
authors.forename: C D
authors.initials: CD
authors.lastname: McClung
authors.forename: T P
authors.initials: TP
authors.lastname: Schmalzried
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D000368:Aged; D000843:Ankle Joint / Q000502:physiology*; D001186:Artificial Limbs; D015992:Body Mass Index; D005081:Exercise Therapy / Q000295:instrumentation; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D019876:Sports Equipment; D016138:Walking / Q000502:physiology*