Towards clinical application: repetitive sensor position re-calibration for improved reliability of gait parameters.

While camera-based motion tracking systems are considered to be the gold standard for kinematic analysis, these systems are not practical in clinical practice. However, the collection of gait parameters using inertial sensors is feasible in clinical settings and less expensive, but suffers from drift error that excludes accurate analyses. The goal of this study was to apply a combination of repetitive sensor position re-calibration techniques in order to improve the intra-day and inter-day reliability of gait parameters using inertial sensors. Kinematic data of nineteen healthy elderly individuals were captured twice within the first day and once on a second day after one week using inertial sensors fixed on the subject's forefoot during gait. Parameters of walking speed, minimum foot clearance (MFC), minimum toe clearance (MTC), stride length, stance time and swing time, as well as their corresponding measures of variability were calculated. Intra-day and inter-day differences were rated using intra-class correlation coefficients (ICC(3,1)), as well as the bias and limits of agreement. The results indicate excellent reliability for all intra-day and inter-day mean parameters (ICC: MFC 0.83-stride length 0.99). While good to excellent reliability was observed during intra-day parameters of variability (ICC: walking speed 0.71-MTC 0.98), corresponding inter-day reliability ranged from poor to excellent (ICC: walking speed 0.32-MTC 0.95). In conclusion, the system is suitable for reliable measurement of mean temporo-spatial parameters and the variability of MFC and MTC. However, the system's accuracy needs to be improved before remaining parameters of variability can reliably be collected.