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Molly S. Bray, James R. Morrow Jr., James M. Pivarnik and John T. Bricker

This study investigated the validity of the Caltrac accelerometer for estimating resting and exercise energy expenditure for children. Seventeen children 9 to 12 years of age participated in the study. Criterion values of energy expenditure were determined from measures of oxygen consumption (VO2) and respiratory exchange ratio (RER), and Caltrac estimates of energy expenditure were obtained concurrently for each experimental condition. Correlations were significant between Caltrac estimates and measured energy expenditure at rest (r = .53, p<.03) and at slow (r = .89, p<.001) and brisk (r = .85, p<.001) treadmill walking. The Caltrac overestimated caloric expenditure for rest (M = 7%; range = −8 to 36%) and also for both slow (M = 17%; range = −3 to 30%) and brisk (M = 25%; range = 5 to 46%) walking. However, because of the high validity coefficients during activity, and because of its practicality in field settings, the Caltrac may be useful in estimating daily resting and walking energy expenditure for groups of children.

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Renee M. Jeffreys, Thomas H. Inge, Todd M. Jenkins, Wendy C. King, Vedran Oruc, Andrew D. Douglas and Molly S. Bray


The accuracy of physical activity (PA) monitors to discriminate between PA, sedentary behavior, and nonwear in extremely obese (EO) adolescents is unknown.


Twenty-five subjects (9 male/16 female; age = 16.5 ± 2.0 y; BMI = 51 ± 8 kg/m2) wore 3 activity monitors (StepWatch [SAM], Actical [AC], Actiheart [AH]) during a 400-m walk test (400MWT), 2 standardized PA bouts of varying duration, and 1 sedentary bout.


For the 400MWT, percent error between observed and monitor-recorded steps was 5.5 ± 7.1% and 82.1 ± 38.6% for the SAM and AC steps, respectively (observed vs. SAM steps: −17.2 ± 22.2 steps; observed vs. AC steps: −264.5 ± 124.8 steps). All activity monitors were able to differentiate between PA and sedentary bouts, but only SAM steps and AH heart rate were significantly different between sedentary behavior and nonwear (P < .001). For all monitors, sedentary behavior was characterized by bouts of zero steps/counts punctuated by intermittent activity steps/counts; nonwear was represented almost exclusively by zero steps/counts.


Of all monitors tested, the SAM was most accurate in terms of counting steps and differentiating levels of PA and thus, most appropriate for EO adolescents. The ability to accurately characterize PA intensity in EO adolescents critically depends on activity monitor selection.