| Research Abstract |
Our objective was to establish a sensitive and reliable method of assessing physical activity. We designed a portable apparatus using two accelerometers that could detect body movement during physical activity by measuring vertical and horizontal gravitational acceleration forces. To evaluate the relationship between the output of the accelerometers and physical activity, a graded treadmill exercise test was given to 27 healthy Japanese children, during which gas exchanges were also measured. We studied the relationships among oxygen uptake, heart rate, and output from the accelerometers of the apparatus, which was attached to the back of each child's waist belt. The time integrals of vertical acceleration vector, horizontal acceleration vector and mean vector of both were calculated. The ratio of vertical to horizontal vector integral was a good indication of the type of activity being performed (i.e., jogging or walking). There was a strong correlation between the mean vector integrals and oxygen uptake. The products of the mean vector integral and the ratio of both vectors also correlated with oxygen uptake. The intensity and the method of exercise were estimated by analysis of the output from the accelerometers. This apparatus therefore appears to be a useful tool for assessing physical activity in children.
Because the subject was attached by a flexible cable to the data recorder and the gas exchange analyzer, the exercise testing of this study was only performed under laboratory conditions. We are now developing and testing a new apparatus equipped with a long-life data recording unit to evaluate physical activity under free-living conditions. Further research should be undertaken to validate the relationship between the accelerometer output and the intensity of physicla activity under free-living conditions.
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