Vertical displacement of the approximated body center of mass during typical daily activities: A transition-based complementary filter method using barometric and inertial data

By monitoring the movement of the body's centre of mass during daily-living activities, it is possible to gather information on an individual's functional capacity and quantify key abilities such as lower limb strength, postural control and dynamic stability. To this end, a wearable inertial measurement unit attached to the lower back can offer a practical solution for analysing CoM movement in real-world conditions. However, accelerometer-based measurements are prone to drift, limiting their suitability for long-term monitoring. To mitigate these effects, miniaturized high-resolution barometers can be integrated to provide stable direct height measurements. In this study, we developed and validated a method for the reconstruction of the vertical displacement of the centre of mass during daily activities (Transition-Based Complementary Filter). The method consisted of two steps: first, the transition intervals within which vertical displacements of the centre of mass occur are identified, then, within these intervals, the complementary filter is applied to estimate the vertical displacement. Validation was carried out on twenty healthy subjects wearing an inertial unit and a barometer on the lower back, while a marker-based stereophotogrammetry system served as reference. Participants performed a series of motor tasks replicating typical home-based activities, including standing, sitting, lying, squatting, and stair climbing. The method demonstrated high accuracy, achieving a median root mean square error of 0.02 m and a median concordance correlation coefficient of 98 %. These findings underscore its robustness and clinical utility, paving the way for improved rehabilitation strategies and enhanced patient outcomes.