Physical activity monitoring in extremely obese adolescents from the Teen-LABORATORIES study

Abstract

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

Methods: 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.

Results: 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.

Conclusion: 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.

Figures

Figure 1

Bland-Altman analysis for observed versus SAM steps for 400MWT. The regression line is represented as a solid black line, and the mean difference is represented by a solid, bold line with ± 1.96 standard deviations represented by the dashed lines.

Figure 2

Bland-Altman analysis for observed versus AC steps for 400MWT. The regression line is represented as a solid black line, and the mean difference is represented by a solid, bold line with ± 1.96 standard deviations represented by the dashed lines.

Figure 3

Heart rate recorded by the AH monitor across activity bouts. a=significantly different from longer duration activity (p

Figure 4

Ability of step- and count-based monitors to differentiate across activity bouts: (A) SAM steps; (B) AC steps; (C) AC activity counts; (D) AH activity counts. a=significantly different from low activity (p