Table 1 Variables and type of analysis used in the literature to assess soft tissue vibrations
Type of analysis | Variable (unit) | Description/Computation | References |
|---|---|---|---|
Temporal | Peak acceleration (m s−2) | Maximum of the absolute value of the acceleration signal | Nikooyan and Zadpoor [61] Giandolini et al. [14] |
Root mean square acceleration (m s−2) | Average root mean square of the signal with a 0.01 s window | Ehrström et al. [9] | |
Standard deviation of accelerations (m s−2) | Standard deviation of the acceleration signal | Gellearts et al. [27] | |
Maximal displacement (m) | Difference between the maximum and minimum position of the soft tissue markers relative to the segment of interest | Borràs et al. [29] Broatch et al. [28] | |
Fast Fourier Transform | Normalised Fourier Transform (m s−2/Hz) | Fourier Transform normalised by the frequency resolution Represent the amplitude at each frequency | Enders et al. [39] Khassetarash [36] |
Power Spectral Density (m2 s−4/Hz) | Square of the Fourier Transform normalised by the inverse of the product of the signal length by the sample frequency Represent the power at each frequency | Giandolini et al. [14] Friesenbichler et al. [41] | |
Continuous Wavelet Transform | Time integral of wavelet coefficients for different frequency bands (m s−2/Hz) | Equivalent to the Normalised Fourier Transform | |
Sum of wavelets power | Non-indicated (normalised) | Khassetarash et al. [31] | |
Temporal | Peak frequency estimate | Inverse of the duration between the two first peaks after heel strike | Boyer and Nigg [22] |
Fast Fourier Transform | Peak frequency (Hz) | Frequency with the most amplitude | Enders et al. [6] Giandolini et al. [14] |
Mean frequency (Hz) | Weighted average product of the amplitude of the frequency by the frequency | Friesenbichler et al. [41] Enders et al. [6] | |
Median frequency (Hz) | Frequency that split the amplitude or power spectrum in half | Enders et al. [6] Trama et al. [62] | |
Continuous Wavelet Transform | Peak frequency (Hz) | See above | |
Continuous Wavelet Transform | Damping coefficient (s−1) | Decrement of logarithm power or logarithm decrement of power (estimation via least-square minimisation) | |
Settling time (s) | Time between maximum amplitude and 10% amplitude | Khassetarash et al. [31] Trama et al. [62] | |
Energy dissipation (J kg−1) | Product of the time integral of the square vibration speed by the double of damping coefficient | ||
Partly Ensemble Empirical Mode Decomposition | Damping coefficient (s−1) | See above | Khassetarash et al. [40] |
Damping ratio (ø) | Damping coefficient relative to the critical damping of the frequency damped | ||
Energy dissipation (J kg−1) | See above |