title: Evaluation of low-intensity physical activity by triaxial accelerometry.
abstract: OBJECTIVE
  To develop regression-based equations that estimate physical activity ratios [energy expenditure (EE) per minute/sleeping metabolic rate] for low-to-moderate intensity activities using total acceleration obtained by triaxial accelerometry.
  
  
  METHODS
  Twenty-one Japanese adults were fitted with a triaxial accelerometer while also in a whole-body human calorimeter for 22.5 hours. The protocol time was composed of sleep (8 hours), four structured activity periods totaling 4 hours (sitting, standing, housework, and walking on a treadmill at speeds of 71 and 95 m/min, 2 x 30 minutes for each activity), and residual time (10.5 hours). Acceleration data (milligausse) from the different periods and their relationship to physical activity ratio obtained from the human calorimeter allowed for the development of EE equations for each activity. The EE equations were validated on the residual times, and the percentage difference for the prediction errors was calculated as (predicted value - measured value)/measured value x 100.
  
  
  RESULTS
  Using data from triaxial accelerations and the ratio of horizontal to vertical accelerations, there was relatively high accuracy in identifying the four different periods of activity. The predicted EE (882 +/- 150 kcal/10.5 hours) was strongly correlated with the actual EE measured by human calorimetry (846 +/- 146 kcal/10.5 hours, r = 0.94 p < 0.01), although the predicted EE was slightly higher than the measured EE.
  
  
  CONCLUSIONS
  Triaxial accelerometry, when total, vertical, and horizontal accelerations are utilized, can effectively evaluate different types of activities and estimate EE for low-intensity physical activities associated with modern lifestyles.
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan. taishi@aoni.waseda.jp
authors.forename: Taishi
authors.initials: T
authors.lastname: Midorikawa
authors.forename: Shigeho
authors.initials: S
authors.lastname: Tanaka
authors.forename: Kayoko
authors.initials: K
authors.lastname: Kaneko
authors.forename: Kayo
authors.initials: K
authors.lastname: Koizumi
authors.forename: Kazuko
authors.initials: K
authors.lastname: Ishikawa-Takata
authors.forename: Jun
authors.initials: J
authors.lastname: Futami
authors.forename: Izumi
authors.initials: I
authors.lastname: Tabata
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D002153:Calorimetry, Indirect; D004734:Energy Metabolism / Q000502:physiology*; D004864:Equipment and Supplies; D005080:Exercise Test; D005260:Female; D006796:Household Work; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D012044:Regression Analysis; D012146:Rest / Q000502:physiology; D012680:Sensitivity and Specificity; D016138:Walking / Q000502:physiology