Youth Oriented Activity Trackers: Comprehensive Laboratory- and Field-Based Validation

Background: Commercial activity trackers are growing in popularity among adults and some are beginning to be marketed to children. There is, however, a paucity of independent research examining the validity of these devices to detect physical activity of different intensity levels. Objectives: The purpose of this study was to determine the validity of the output from 3 commercial youth-oriented activity trackers in 3 phases: (1) orbital shaker, (2) structured indoor activities, and (3) 4 days of free-living activity. Methods: Four units of each activity tracker (Movband [MB], Sqord [SQ], and Zamzee [ZZ]) were tested in an orbital shaker for 5-minutes at three frequencies (1.3, 1.9, and 2.5 Hz). Participants for Phase 2 (N=14) and Phase 3 (N=16) were 6-12 year old children (50% male). For Phase 2, participants completed 9 structured activities while wearing each tracker, the ActiGraph GT3X+ (AG) research accelerometer, and a portable indirect calorimetry system to assess energy expenditure (EE). For Phase 3, participants wore all 4 devices for 4 consecutive days. Correlation coefficients, linear models, and non-parametric statistics evaluated the criterion and construct validity of the activity tracker output. Results: Output from all devices was significantly associated with oscillation frequency (r=.92-.99). During Phase 2, MB and ZZ only differentiated sedentary from light intensity (PPr=.76, .86, and .59 for the MB, SQ, and ZZ, respectively). Conclusions: Across study phases, the SQ demonstrated stronger validity than the MB and ZZ. The validity of youth-oriented activity trackers may directly impact their effectiveness as behavior modification tools, demonstrating a need for more research on such devices

The Relationship between Aerobic Capacity and Bone Health in Young Women

International Journal of Exercise Science 9(1): 56-63, 2016. The purpose of the present investigation was to examine the relationship between maximal oxygen consumption (VO2max) and bone health in young women. Eighty-three participants (age=21.0±2.2 years; BMI=22.4±3.0 kg/m2) reported for testing on two occasions separated by 48 hours. During visit 1 body composition assessment via dual-energy X-ray absorptiometry (DXA) and during visit 2, a VO2max test performed on a motorized treadmill. Weak correlations were found between absolute VO2max (L/min) and whole-body bone mineral density (WB-BMD: r=0.24, p=0.031) and whole-body bone mineral content (WB-BMC: r=0.37, p\u3c0.001). No relation between variables were observed when VO2max was expressed relative to body mass (mL/kg/min). Moderate correlations were observed between bone variables and body mass (WB-BMD: r=0.36, p\u3c0.001; WB-BMC: r=0.62, p\u3c0.001), fat-free mass (WB-BMD: r=0.45, p\u3c0.001; WB-BMC: r=0.54, p\u3c0.001), and fat mass (WB-BMD: r=0.31, p=0.004; WB-BMC: r=0.60, p\u3c0.001). Body mass, regardless of composition, was a stronger predictor of bone health than aerobic capacity in this sample of young women