SPECTRAL AND BOUT DETECTION ANALYSIS OF PHYSICAL-ACTIVITY PATTERNS INHEALTHY, PREPUBERTAL BOYS AND GIRLS

Little is known about the frequency-intensity patterns of naturally oc curring 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 algorit hms were used to characterize the number of exercise bouts, their dura tion and relative intensity. Spectral analysis revealed that physical activity bouts were frequent, pulsatile, and random with no significan t frequencies detected during many 24-min periods of observation. An a verage 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 wa s 21 +/- 5 sec for boys and 20 +/- 4 sec for girls (NS). While high-in tensity exercise bouts comprised less than 20% of the time spent in ph ysical activity, duration of high intensity exercise bouts tended to b e longer and accounted for about 40% of the energy expenditure associa ted with physical activity. Spontaneous physical activity in prepubert al children is characterized by frequent bouts of brief, mostly low in tensity exercise, randomly interspersed with less frequent, but metabo lically substantial high intensity bouts. These findings are potential ly useful in assessing the impact of disease on quality of life in chi ldren, investigating the relationship between physical activity and me chanisms of growth and development, and creating new approaches for in -laboratory exercise testing in children. (C) 1998 Wiley-Liss, Inc.