Background: The ability to objectively assess physical activity and inactivity in free living individuals is important in understanding activity patterns and the dose response relationship with health. Currently, a large number of research tools exist, but little evidence has examined the validity/utility of the Research Tracker 6 (RT6) monitor. Questions remain in regard to the best placements, positions, and cut-points in young adults to determine activity intensity across a range of activities. This study sought to address this gap in young adults. The study aims were 1) to examine criterion validity of RT6 in comparison to breath-by-breath gas analysis; 2) convergent validity of RT6 in comparison to ActiGraph and GENEActiv; 3) development of RT6 tri-axial vector magnitude cut-points to classify physical activity at different intensities (i.e., for sedentary, moderate, and vigorous); 4) to compare the generated cut-points of the RT6 in comparison to other tools. Methods: Following ethics approval and informed consent, 31 young adults (age = 22±3 years: BMI = 23±3 kg/m2) undertook five modes of physical activity/sedentary behaviors while wearing three different accelerometers at hip and wrist locations (ActiGraph GT9X Link, GENEActiv, RT6). Expired gas was sampled during the five activities (MetaMax 3B). Correlational analysis assessed the relationship between accelerometer devices and METs/VO2. Receiver Operating Characteristic Curves analysis were used to calculate area under the curve and define cut-points for physical activity intensities. Results: The RT6 demonstrated criterion and convergent validity (r = 0.662–0.966, P < .05). RT6 generally performed good to excellent across activity intensities and monitor position (sedentary [AUC = 0.862–0.911], moderate [AUC = 0.849–0.830], vigorous [AUC = 0.872–0.877]) for non-dominant and dominant position, respectively. Cut-points were derived across activity intensities for non-dominant- and dominant-worn RT6 devices. Comparison of the RT6 derived cut-points identified appropriate agreement with comparative tools but yields the strongest agreement with the ActiGraph monitor at the hip location during sedentary, light, and moderate activity. Conclusion: The RT6 performed similar to the ActiGraph and GENEActiv and is capable of classifying the intensity of physical activity in young adults. As such this may offer a more useable tool for understanding current physical activity levels and in intervention studies to monitor and track changes without the excessive need for downloading and making complex analysis, especially given the option to view energy expenditure data while wearing it. The RT6 should be placed on the dominant hip when determining activities that are sedentary, moderate, or vigorous intensity.
Validity of ActiGraph 2-Regression Model, Matthews Cut-Points, and NHANES Cut-Points for Assessing Free-Living Physical Activity
