A TRIAXIAL ACCELEROMETER AND PORTABLE DATA-PROCESSING UNIT FOR THE ASSESSMENT OF DAILY PHYSICAL-ACTIVITY

The present study describes the development of a triaxial acceleromete r (TA) and a portable data processing unit for the assessment of daily physical activity. The TA is composed of three orthogonally mounted u niaxial piezoresistive accelerometers and can be used to register acce lerations covering the amplitude and frequency ranges of human body ac celeration, Interinstrument and test-retest experiments showed that th e offset and the sensitivity of the TA were equal for each measurement direction and remained constant on two measurement days, Transverse s ensitivity was significantly different for each measurement direction, but did not influence accelerometer output (<3% of the sensitivity al ong the main axis), The data unit enables the on-line processing of ac celerometer output to a reliable estimator of physical activity over e ight-day periods, Preliminary evaluation of the system in 13 male subj ects during standardized activities in the laboratory demonstrated a s ignificant relationship between accelerometer output and energy expend iture due to physical activity, the standard reference for physical ac tivity (r = 0.89), Shortcomings of the system are its low sensitivity to sedentary activities and the inability to register static exercise. The validity of the system for the assessment of normal daily physica l activity and specific activities outside the laboratory should be st udied in free-living subjects.