Fig. 3

a Time functions of the vertical acceleration (blue) and the reconstruction error (red) for a Fourier partial series of 20 terms are shown superimposed (subject #1, walking speed: 5 km/h); b Time functions of the vertical displacement estimated by OMCS and by the proposed Fourier-based method, together with the time function of the difference. a shows the jumps occurring at the detected stride times and the oscillations due to Gibbs phenomenon on either side of the boundary between successive gait strides. b shows the mild effects of discontinuity jumps due to spline interpolation across boundaries and the presence of small-amplitude Gibbs oscillations on the estimated VT displacement