Stability and convergent validity of three physical activity assessments

PURPOSE: The purpose of this study was to examine the stability and convergent validity of heart rate (HR) monitoring, Caltrac accelerometer, and physical activity recall (PAR) in sixth-grade girls during normal weekday activities. METHODS: 46 sixth-grade girls (age 12 +/- 0.6) wore HR monitors and Caltrac accelerometers for 3 d during school, after school, and evenings. We also obtained a PAR for each day. Data were compared on the basis of kcal x h(-1). RESULTS: Two days' worth of data were analyzed for each participant. Intraclass correlation coefficients obtained by use of repeated measures ANOVA revealed that HR monitoring (r = 0.99) and PAR (r = 0.98) were extremely stable across 2 d, whereas Caltrac was moderately stable (r = 0.76). Pearson correlations between techniques were HR versus PAR, r = 0.50 (P < 0.01), HR versus Caltrac, r = 0.28, and Caltrac versus PAR, r = 0.76 (P < 0.01). Methods comparison plots showed poor individual subject agreement between all three types of assessment. CONCLUSION: HR and PAR were stable across 2 d. PAR underestimated caloric expenditure by approximately 14%. Caltrac showed the least utility in both reliability and validity.