Real-time estimation of daily physical activity intensity by a triaxial accelerometer and a gravity-removal classification algorithm

• Published in: British journal of nutrition Vol. 105; no. 11; pp. 1681 - 1691
• Main Authors: Ohkawara, Kazunori, Oshima, Yoshitake, Hikihara, Yuki, Ishikawa-Takata, Kazuko, Tabata, Izumi, Tanaka, Shigeho
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 14.06.2011; CABI Pub
• Subjects: Acceleration; Accelerometers; Activities of Daily Living; Adult; Algorithms; Biological and medical sciences; Calorimetry; Calorimetry, Indirect; Classification; energy expenditure; equations; Exercise; Female; Field tests; Fundamental and applied biological sciences. Psychology; Gravitation; Humans; Innovative Technique; instrumentation; linear models; Male; methods; Middle Aged; Models, Biological; Monitoring, Physiologic; Monitoring, Physiologic - instrumentation; Monitoring, Physiologic - methods; Motor Activity; Motor Activity - physiology; Movement; physical activity; physiology; regression analysis; Sex Characteristics; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Household activity; Locomotive activity; Non-exercise activity thermogenesis; Accelerometry; Metabolic equivalents; Physical exercise; Human; Intensity; Household; Real time; Algorithm; Daily; Classification; Measurement method
• ISSN: 0007-1145; 1475-2662; 1475-2662
• DOI: 10.1017/S0007114510005441

We have recently developed a simple algorithm for the classification of household and locomotive activities using the ratio of unfiltered to filtered synthetic acceleration (gravity-removal physical activity classification algorithm, GRPACA) measured by a triaxial accelerometer. The purpose of the present study was to develop a new model for the immediate estimation of daily physical activity intensities using a triaxial accelerometer. A total of sixty-six subjects were randomly assigned into validation (n 44) and cross-validation (n 22) groups. All subjects performed fourteen activities while wearing a triaxial accelerometer in a controlled laboratory setting. During each activity, energy expenditure was measured by indirect calorimetry, and physical activity intensities were expressed as metabolic equivalents (MET). The validation group displayed strong relationships between measured MET and filtered synthetic accelerations for household (r 0·907, P < 0·001) and locomotive (r 0·961, P < 0·001) activities. In the cross-validation group, two GRPACA-based linear regression models provided highly accurate MET estimation for household and locomotive activities. Results were similar when equations were developed by non-linear regression or sex-specific linear or non-linear regressions. Sedentary activities were also accurately estimated by the specific linear regression classified from other activity counts. Therefore, the use of a triaxial accelerometer in combination with a GRPACA permits more accurate and immediate estimation of daily physical activity intensities, compared with previously reported cut-off classification models. This method may be useful for field investigations as well as for self-monitoring by general users.