UC Irvine

Little is known about the frequency-intensity patterns of naturally occurring physical activity in children. A data set obtained previously by direct observation of physical activity in 8 girls and 7 boys (all prepubertal, ages 6-10) was analyzed with spectral analysis to detect significant frequency-intensity relationships. Pulse detection algorithms were used to characterize the number of exercise bouts, their duration and relative intensity. Spectral analysis revealed that physical activity bouts were frequent, pulsatile, and random with no significant frequencies detected during many 24-min periods of observation. An average of 83 ± 11 bouts per hour were observed in boys and 89 ± 12 bouts per hour in girls, and the mean duration of an exercise bout was 21 ± 5 sec for boys and 20 ± 4 sec for girls (NS). While high-intensity exercise bouts comprised less than 20% of the time spent in physical activity, duration of high intensity exercise bouts tended to be longer and accounted for about 40% of the energy expenditure associated with physical activity. Spontaneous physical activity in prepubertal children is characterized by frequent bouts of brief, mostly low intensity exercise, randomly interspersed with less frequent, but metabolically substantial high intensity bouts. These findings are potentially useful in assessing the impact of disease on quality of life in children, investigating the relationship between physical activity and mechanisms of growth and development, and creating new approaches for in-laboratory exercise testing in children. Am. J. Hum. Biol. 10:289-297, 1998. © 1998 Wiley-Liss, Inc.