Gait analysis is commonly performed in standardized environments, but there is a growing interest in assessing gait also in ecological conditions. In this regard, an important limitation is the lack of an accurate mobile gold standard for validating any wearable system, such as continuous monitoring devices mounted on the trunk or wrist. This study therefore deals with the development and validation of a new wearable multi-sensor-based system for digital gait assessment in free-living conditions. In particular, results obtained from five healthy subjects during lab-based and realworld experiments were presented and discussed. The in-lab validation, which assessed the accuracy and reliability of the proposed system, shows median percentage errors smaller than 2% in the estimation of spatio-temporal parameters. The system also proved to be easy to use, comfortable to wear and robust during the out-of-lab acquisitions, showing its feasibility for free-living applications.
I. INTRODUCTIONRecent literature has shown the relevance of characterising an individual's mobility in real-world conditions for a complete assessment of typical motor abilities [1,2]. This requires the use of activity monitors, e.g. devices including a single inertial measurement unit (IMU), that can be used without causing discomfort thanks to its limited invasivity. In this sense, the most convenient body positionings are trunk and wrist [3]. However, those locations present criticalities for the analysis of gait in terms of reliability, since the farther from the contact point the IMU is placed, the more difficult the estimation of gait-related parameters is. In this respect, the trunk is far from the ground but near to the centre of mass while the wrist is far from both ground and centre of mass. Although the scientific community is actively working on developing and improving algorithms for the above-mentioned solutions, algorithms validation is still performed in the laboratory while capturing simple gait tasks in spatially and temporally limited observation windows [4,5]. Testing single-sensor algorithms outside the laboratory would require a wearable system that is robust and accurate enough to be used as reference in validating other wearable technologies, i.e. a mobile gold standard