Frequency analysis of gait signals to assess symmetry

Human gait is a complex cyclic spatio-temporally movement that requires human joints coordination and involves several biomechanical structures. Some neurological and musculoskeletal pathologies might cause motion disorders and gait impairments, which play an important role for the quality of life and for the independence in performing daily activities. Several researches dealt with the objective assessment and biomechanical description of human gait characteristics, such as symmetry, variability and smoothness. Previous studies proposed different methods and approaches for the investigation of gait symmetry. Despite the several symmetry indexes validated in physiological gait, some challenges are still opened for the identification of robust and suitable methodology in pathological patterns. Recent analysis suggested the application of frequency analysis to biological signals to evaluate characteristics and components that cannot be detected in time domain. This thesis focuses on the characterization of the human gait examining the Body Centre of Mass (BCoM) trajectory using the spectral analysis of the Fourier series. In the thesis, the study has been focused on the vertical displacement of the BCoM trajectory. Two literature symmetry indexes based on combinations of the Fourier series coefficients, developed respectively for the assessment of the gait symmetry of amputee and non-amputee subjects by Ochoa-Diaz & Padilha (2020) and the gait symmetry of healthy subjects at different speeds by Minetti et al. (2011), have been studied to verify their feasibility when applied to hemiparetic gait. Preliminary analysis concentrated on the assessment of algorithm robustness through the investigation of synthetic data. Then, the algorithms have been applied to experimental data of the BCoM trajectory acquired in a previous study. These data refer to two groups of subjects (5 healthy young subjects and 14 pathological patients). Tests with healthy subjects were conducted in the POLITO BIOMed LAB of Politecnico di Torino, Italy. Tests with patients were performed in the specialized Movement Disorders Center of Unità Spinale Unipolare – Città della Salute e della Scienza, Italy. In healthy subjects both indexes (Ochoa-Diaz & Padilha index: 0.94±0.016, Minetti index: 0.77±0.025) provide values closed to 1, that is the value representing a symmetrical gait. These results are in good agreement with those obtained by the authors that proposed the indexes applied to healthy gait. The pathological subjects were divided in two groups: under and over 65 years. When considering all the pathological subjects, the Ochoa-Diaz & Padilha index reported an average value of 0.31±0.233, while the Minetti index provides an average value of 0.39±0.125. These values are lower than those of healthy subjects and show that hemiparetic subjects have a walking alteration, as expected. Younger subjects have higher values (even if lower than the healthy ones) for both symmetry indexes. In conclusion, these indexes have shown to be efficacious to detect hemiparetic gait asymmetry and could be adopted in clinic analysis. Further development of the proposed methodology could be applied to different pathological conditions and the obtained results can be compared, taking into account the pathology and how it affects the gait. The same procedure of spectral analysis might be carried out considering different types of biomechanical signals.