ESTIMATING CALORIC EXPENDITURE USING THE PHYSICAL ACTIVITY INDEX (PAI) IN CHILDREN AND ADOLESCENTS PERFORMING A MULTISTAGE MAXIMAL EXERCISE TEST

PURPOSE: The primary purposes of this investigation were (a) to examine the validity of the PAI, (b) to develop a statistical model to predict cumulative Kcal expenditure using PAI as the predictor variable and (c) to develop a statistical model to predict total Kcal expenditure using PAItotal and selected physiological and behavioral measures as the predictor variables for children and adolescents performing load incremented maximal treadmill exercise. The secondary purpose of the study was to develop a prediction model to estimate total Kcal expenditure using the PAI (session) alone and in combination with selected physiological measures as the predictor variables. METHODS: Eighty-four children and adolescents (12.5±2.4 yrs) performed a maximal Bruce treadmill (TM) protocol. During TM, heart rate (HR), oxygen consumption (VO2), rating of perceived exertion (RPE-overall), pedometer step count, and Kcal expenditure were measured. Post-TM, RPE-session was obtained and a physical activity questionnaire administered. The PAI, PAItotal, and PAI (session) were calculated as: PAI = Cumulative step count x RPE-overall PAItotal = Total step count x RPE-overall at test termination PAI (session) = Total step count x RPE-session RESULTS: Multiple regression analyses revealed a strong, positive relation between the PAI score and VO2 in L.min-1(r=0.607, p<0.05), VO2 in mL.kg-1.min-1 (r=0.725, p<0.05) and HR in beats.min-1 (r=0.755, p<0.05). These findings established a high level of concurrent validity for the PAI. The following models to predict Kcal expenditure were developed: Model I : Cumulative Kcal = 21.632 + 0.006(PAI) p<0.05, SEE=17.59, r=0.74, r2=0.54. Model II : Total Kcal = -11.59+0.002(PAItotal)+27.245(VO2max) p<0.05, SEE=15.37, r=0.86, r2=0.739. Model V : Total Kcal = 38.6 + 0.004(PAIsession), p<0.05, SEE=24.23, r=0.36, r2=0.13. Model VI : Total Kcal = -64.759+26.998(VO2max)+0.305(HRmax)+0.001 (PAIsession) p<0.05, SEE=10.46, r = 0.918 , r2 = 0.842. In comparison to the PAI (session), PAI was a stronger predictor of Kcal expenditure during a load incremented treadmill protocol in a sample of children and adolescents. CONCLUSIONS: The PAI has public health implications, provides an easy tool to estimate total physical activity load (i.e. volume x intensity) and predicts Kcal expenditure in children and adolescents performing standard treadmill exercise protocols. Generalizability of findings is limited to healthy children and adolescents performing load incremented maximal treadmill exercise.