Table 4.
Summary and definition of the main outcome parameters of the reviewed papers.
| Measure | Type | Definition | References |
|---|---|---|---|
| Number of steps | Event | Local maximum of the filtered acceleration signal | [38] |
| Number of U-turns | Event | Threshold at 95th percentile of vertical acceleration lower RMS curve | [38] |
| Distance | Spatio-temporal | Distance walked within 6MWT | [47,49,50] |
| Gait speed | Spatio-temporal | Distance traveled divided by time taken (m/s) | [37,52] |
| Cadence | Spatio-temporal | Steps taken divided by given time interval (steps/s) | [37,42,43,44,45,46,51,52,63] |
| Stance time | Spatio-temporal | Time between heel strike and toe-off | [52] |
| Stride time SD | Spatio-temporal | Stride time is defined as the time between two consecutive heel-strikes of the same foot | [46,60] |
| Stride time variability | Spatio-temporal | Stride time SD divided by mean stride time (%) | [37,60] |
| Swing time variability | Spatio-temporal | Swing time SD divided by mean swing time (%). Swing time is defined as the time interval between toe-off and the subsequent heel-strike of the same foot | [37] |
| Step length | Spatio-temporal | Number of steps between 2 consecutive U-turns divided by time taken | [38] |
| Stance ratio | Spatio-temporal | Percentage of the gait cycle during which the foot is in stance phase (%) | [39] |
| Load ratio | Spatio-temporal | Percentage of the stance corresponding to loading phase defined as the time between heel strike and toe strike (%) | [39] |
| Foot flat ratio | Spatio-temporal | Percentage of the stance corresponding to the foot-flat phase (%) | [39] |
| Push ratio | Spatio-temporal | Percentage of the stance corresponding to push phase defined as the time between heel off and toe off (%) | [39] |
| Symmetry of foot pitch angular velocity | Spatio-temporal | Pearson correlation coefficient (-) | [39] |
| Symmetry of foot pitch angular velocity | Spatio-temporal | Mean absolute difference between each left and right signal sample of cycle n divided by the mean range of the signals in the cycle (-) | [39] |
| Coefficient of stride cycle repetition | Spatio-temporal | Sum of positive autocorrelation coefficients of the three axes as a function of t (-) | [39] |
| Coefficient of step repetition | Spatio-temporal | Norm of autocorrelation coefficients as a function of t (-) | [39] |
| Gait asymmetry | Spatio-temporal | Percentage difference between left and right leg gait cycles (%) | [43] |
| Width and length of Poincaré plots | Spatio-temporal | Width and length of the long and short axis of the stride duration elliptical data plots between successive gait cycles (-) | [60] |
| Flat foot ratio | Spatio-temporal | Foot flat time as a percentage of the whole gait cycle (s) | [52] |
| Minimal toe clearance | Spatio-temporal | Minimal toe clearance during the swing phase (m) | [52] |
| Stride regularity | Frequency | Unbiased and normalized autocorrelation coefficient at the second dominant period (-) | [37] |
| Step regularity | Frequency | Unbiased and normalized autocorrelation coefficient at the first dominant period (-) | [37] |
| First quartile of Fourier transform (FQFFT) | Frequency | Percentage of acceleration frequencies within the first quartile of an FFT frequency plot (%) | [44,63] |
| Ratio of even/odd harmonics (REOH) | Frequency | Ratio of acceleration signal in phase with stride frequency (-) | [44,60,63] |
| Peak frequency | Frequency | Frequency of greatest magnitude in spectrum (Hz) | [57,64] |
| Shannon enthropy | Frequency | Expected value of signal information | [57,64] |
| Root mean square (RMS) | Acceleration descriptive statistics | RMS of the accelerations in anteroposterior, mediolateral and vertical directions | [46,57,64] |
| Acceleration maximum | Acceleration descriptive statistics | Acceleration maximum of positive and negative axis direction | [44,63] |
| Acceleration mean | Acceleration descriptive statistics | Acceleration mean of positive and negative axis direction | [44,57,63] |
| Acceleration standard deviation | Acceleration descriptive statistics | Acceleration standard deviation of positive and negative axis direction | [44,57,63] |
| Acceleration coefficient of variance | Acceleration descriptive statistics | Acceleration mean divided by standard deviation | [57,64] |
| Interstride trunk variability | Acceleration descriptive statistics | Mean values of the unbiased autocorrelation coefficients of the three acceleration components | [46,51] |
| Initial peak acceleration | Acceleration descriptive statistics | Peak tibial acceleration after foot contact | [48] |
| Absolute symmetry index | Acceleration descriptive statistics | Absolute differences in initial peak acceleration between limbs (%) | [48] |
| Walking intensity | Acceleration descriptive statistics | Integral of the modulus accelerometer output | [51] |
| Resultant acceleration | Acceleration descriptive statistics | Square root of the sum of squared acceleration signals in AP, ML an V directions | [53] |
| Euclidean norm minus one | Acceleration descriptive statistics | Resultant acceleration minus one | [55] |
| Short-term lyapunov exponents | Non-linear indexes | Quantifies stride-to-stride local dynamic stability of walking | [60,63] |
| Recurrence quantification analysis | Non-linear indexes | Provides a characterization of a variety of features of a given time series, including a quantification of deterministic structure and non-stationarity, based on the construction of recurrence plots. | [60] |
| Multiscale entropy | Non-linear indexes | Quantifies the complexity or irregularity of a time series | [60] |
| Index of harmonicity | Non-linear indexes | Quantifies the contribution of the stride frequency to the signal power relative to higher harmonics | [60] |
| Sample entropy | Non-linear indexes | Negative logarithm of the probability that if two sets of simultaneous data points of length m have distance <r then two sets of simultaneous data points of length m + 1 also have distance <r | [37] |
| Path length | Kinematics | Ratio between the length of the real path of the foot in 3D space (including both stride length and width) and stride length of one cycle (% stride length) | [39] |
| Strike angle | Kinematics | Angle between the foot and the ground at heel strike in sagittal plane (deg) | [39] |
| Lift off angle | Kinematics | Angle between the foot and the ground at toe off in sagittal plane (deg) | [39] |
| Max angular velocity | Kinematics | Maximum pitch foot angular velocity during swing phase (deg/s) | [39] |
| Hip, knee, ankle joint, and pelvis angles | Kinematics | Joint angles using Euler angle decomposition (deg) | [41,45,54,58] |
| Causality index | Other | Sum of the number of significant relationships remaining after thresholding the pairwise causality matrix | [56] |
| Kernel density estimation (KDE) peak | Other | Peak of the density functions at 100 equally spaced inertial gait data amplitude values | [56] |
| Dynamic time warping (DTW) score | Other | Summarizes the degree of similarity between sequences following alignment | [56] |
| Warp score | Other | Summarizes the number of “warps”, or repetitions of samples, needed to achieve an optimal alignment between sequences. | [56,62] |
| Change in acceleration pattern between two conditions (δM) | Other | Difference between two attractors | [40] |
| Change in variability around the attractor (δD) | Other | Change in acceleration variability between conditions | [40] |
| Attractor-based index | Other | Product of δM and δD | [40] |