The digital revolution that characterizes the beginning of the 4.0 Era has already prompted out a variety of smart living technologies, which rely on the pervasive connectivity granted by the Internet of Things. These technologies are having a relevant impact on health systems, working and domestic environments, sports and rehabilitation, by enabling new promising practices for human body kinematic studies. This paper provides a specific discussion on how kinematic studies in clinical diagnosis, rehabilitation and sport, take benefit from the use of the recent smart living technologies. More specifically, in exploring the latest trends in the application of gait analysis using wearable sensors and Machine Learning techniques.

A theoretical framework to implement multi-sensor data fusion methods for kinematic quantities is proposed. All methods defined through the framework allow the combination of signals obtained from position, velocity and acceleration sensors addressing the same target, and improvement in the observation of the kinematics of the target. Differently from several alternative methods, the considered ones need no dynamic and/or error models to operate and can be implemented with low computational burden. In fact, they gain measurements by summing filtered versions of the heterogeneous kinematic quantities. In particular, in the case of position measurement, the use of filters with finite impulse responses, all characterized by finite gain throughout the bandwidth, in place of straightforward time-integrative operators, prevents the drift that is typically produced by the offset and low-frequency noise affecting velocity and acceleration data. A simulated scenario shows that the adopted method keeps the error in a position measurement, obtained indirectly from an accelerometer affected by an offset equal to 1 ppm on the full scale, within a few ppm of the full-scale position. If the digital output of the accelerometer undergoes a second-order time integration, instead, the measurement error would theoretically rise up to 12n(n+1) ppm in the full scale at the n-th discrete time instant. The class of methods offered by the proposed framework is therefore interesting in those applications in which the direct position measurements are characterized by poor accuracy and one has also to look at the velocity and acceleration data to improve the tracking of a target.