TABLE V.
Features computed from wearable inertial sensor data
| Category | Feature | Units | Description | Reference |
|---|---|---|---|---|
| CAP | Duration | s | Total time to complete the ambulatory circuit or an individual task of the ambulatory circuit. | |
| Floor surface speed ratio | Measures the effect of walking speed on two different floor surfaces. | |||
| Walking speed | m/s | Walking speed as determined by distance divided by time (normalized by leg length). | ||
| WBM | COM peak angular velocity | Maximum rotational velocity of the COM around the Z-axis. | ||
| Root mean square (RMS) | m/s2/s | Square root of the mean of the squares of each COM acceleration signal (normalized by time). Represents acceleration magnitude. Synonymous with movement intensity (MI). | [28] | |
| Smoothness index (harmonic ratio) | Ratio of even to odd harmonics of the vertical Y-axis COM acceleration signal. A higher harmonic ratio represents a smoother walking pattern. | [29] | ||
| Smoothness of RMS | m/s3/s | Square root of the mean of the squares of each COM acceleration signal derivative (normalized by time). Synonymous with RMS of jerk and smoothness of MI. | [28] | |
| GF | Cadence | steps/min | The average number of steps taken per minute. | |
| Double support percent | % | Percentage of the gait cycle that both feet are on the ground. Computed as the sum of the initial double support time and the terminal double support time. | [30] | |
| Gait cycle time | s | Duration to complete one stride (time between two consecutive initial contacts of the same foot). | [30] | |
| Number of gait cycles | Total number of complete gait cycles (strides) that occurred. | |||
| Shank peak angular velocity | °/s | Maximum rotational velocity of the shank around the Z-axis during the gait cycle. This occurs during the swing phase. | ||
| Shank range of motion (ROM) | ° | Range of integrated Z-axis angular velocity for each gait cycle. Provides an estimate of the degrees of shank movement. | [30] | |
| Step length | m | Distance between initial contacts of opposite feet (normalized by leg length). | [31] | |
| Step regularity | % | Regularity of the acceleration of sequential steps. Computed using the autocorrelation of the vertical Y-axis of the COM acceleration. | [23] | |
| Stride regularity | % | Regularity of the acceleration of sequential strides (see step regularity). | [23] | |
| Step symmetry | % | Ratio of step regularity to stride regularity. | [23] |
CAP = clinical assessments of progress, COM = center of mass, GF = gait features, m = meters, MI = movement intensity, min = minute, RMS = root mean square, ROM = range of motion, s = seconds, WBM = whole body movement, ° = degrees.