The harmonic ratio (HR), derived from the Fourier analysis of trunk accelerations, has been described in various ways as a measure of walking smoothness, walking rhythmicity, or dynamic stability. There is an increasing interest in applying the HR technique to investigate the impact of various pathologies on locomotion; however, explanation of the method has been limited. The aim here is to present a clear description of the mathematical basis of HRs and an understanding of their interpretation. We present harmonic theory, the interpretation of the HR using sinusoidal signals, and an example using actual trunk accelerations and harmonic analyses during limb-loading conditions. We suggest that the HR method may be better defined, not as a measure of rhythmicity or stability, but as a measure of step-tostep symmetry within a stride.
Bellanca et al. REF suggested that the harmonic ratio (ratio of the sum of the amplitudes of the even and uneven harmonics, computing over the PSD of a single stride) could be used as a measure of step symmetry.
Harmonic Ratios: A quantification of step to step symmetry
Journal of biomechanics
Journal of biomechanics
Mathematics Medicine