THE STABILITY OF CHILDRENS PHYSICAL-ACTIVITY AS MEASURED BY ACCELEROMETRY AND SELF-REPORT

The Computer Science Application (CSA) accelerometer uses integrated c ircuitry and memory to provide a continuous recording of minute-by-min ute movement counts. It has been previously validated as an objective monitor of children's physical activity in field and laboratory settin gs. Our purpose was to derive accelerometry summary variables reflecti ve of different physical activity intensity levels, evaluate the stabi lity of these summary variables, and define the number of days needed to adequately measure usual physical activity. A secondary study purpo se was to compare three self-report questionnaires to accelerometry. T hirty children (7-15 yr) wore accelerometers for 12 h . d(-1) for 6 d. Daily summary variables of average movement count (total physical act ivity) and dairy frequency of sedentary through vigorous activity were constructed. Intraclass correlation coefficients (R) and 95% confiden ce intervals (CI) were used to analyze the data. Accelerometry stabili ty using 1 monitored day to represent usual physical activity was R = 0.42-0.47. When 6 d were used, stability increased to R = 0.81-0.84. A cceptable intraclass correlations and CI were achieved with 4 d of mon itoring (R = 0.75-0.78, CI = 0.60-0.88). The self-report questionnaire s were poorly to moderately correlated to accelerometry variables (r = -0.03-0.51). Data indicate that in field settings: 1) accelerometry c an be used to assess the intensity of children's activity and 2) 4 or more days of activity monitoring are needed to achieve satisfactory re liability.