title: Overcoming the limitations of the Harmonic Ratio for the reliable assessment of gait symmetry.
abstract: The Harmonic Ratio (HR) is an index based on the spectral analysis of lower trunk accelerations that is commonly used to assess the quality of gait. However, it presents several issues concerning reliability and interpretability. As a consequence, the literature provides very different values albeit corresponding to the same populations. In the present work, an improved harmonic ratio (iHR) was defined, relating the power of the intrinsic harmonics (i.e. associated with the symmetric component of gait) to the total power of the signal for each stride, leading to a normalised index ranging from 0 to 100%. The effect of the considered number of harmonics and strides on the estimate of both HR and iHR was assessed. The gait of three groups of volunteers was investigated: young healthy adults, elderly women and male trans-femoral amputees. Both HR and iHR were able to discriminate gait deviations from the gait of young healthy adults. Moreover, iHR proved to be more robust with respect to the number of considered harmonics and strides, and to exhibit a lower inter-stride variability. Additionally, using a normalised index as iHR led to a more straightforward interpretation and improved comparability. The importance of standardised conditions for the index evaluation was unveiled, and, in order to enhance the future comparability of the index, the following guidelines were presented: considering at least 20 harmonics and 20 strides; expressing the acceleration components in a repeatable, anatomical, local system of reference; and evaluating the iHR index, rather than the traditional HR.
authors.affiliation: Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System (BOHNES), Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Pasciuto
authors.affiliation: Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System (BOHNES), Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Bergamini
authors.affiliation: Clinical Laboratory of Experimental Neurorehabilitation, Santa Lucia Foundation, IRCCS, Rome, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Iosa
authors.affiliation: Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System (BOHNES), Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy. Electronic address: giuseppe.vannozzi@uniroma4.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Vannozzi
authors.affiliation: Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System (BOHNES), Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy.
authors.forename: Aurelio
authors.initials: A
authors.lastname: Cappozzo
mesh_terms: D000054:Acceleration; D000369:Aged, 80 and over; D000674:Amputees; D005260:Female; D005269:Femur / Q000601:surgery; D005684:Gait / Q000502:physiology*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D060726:Torso / Q000502:physiology; D016138:Walking / Q000502:physiology; D055815:Young Adult
keywords: Gait quality indices; Inertial sensors; Locomotion; Reliability; Spectral analysis; Trunk acceleration