Inclinometer Validation and Sedentary Threshold Evaluation in University Students

Sedentary behavior (SB) is a major contributing factor to obesity and significant morbidity and mortality in adolescence and into adulthood, yet measuring SB is difficult. The purpose of this study was to assess the degree of construct validity of the ActiGraph GT3X+ inclinometer function and accelerometry metrics in objectively measuring SB and physical activity in young adult university students while performing semi-structured activities: lying, sitting, reading, playing seated video gaming, video watching, seated conversation, standing, stationary biking, and walking. These nine activities were objectively assessed using inclinometry and four output metrics from the ActiGraph based on the axis used to detect activity. Considering overall accuracy in measuring both sedentary behavior and physical activity, all four accelerometer metrics (94.7%-97.8%) outperformed the inclinometer function (70.9%). While accelerometry was overall more accurate at detecting the behaviors tested, inclinometry had similar or better accuracy than some accelerometry methods at detecting walking, biking, and standing. Using vector magnitude accelerometry with a sedentary threshold of 150 counts per minute was superior to other methods. The findings support use of accelerometry as a valid objective measure of body movement while use of inclinometry as a sole measure is not recommended. Additional research would be beneficial to improve the inclinometer and explore ways of combining this with accelerometer data for objectively measuring SB and physical activity.