Table 1.
Accelerometer variables
| Variable name | Description |
|---|---|
| Time | |
| Isolated non-paretic limb activity [31] | Time, in hours, that the non-paretic limb is moving, while the paretic limb is still |
| Isolated paretic limb activity [31] | Time, in hours, that the paretic limb is moving, while the non-paretic limb is still |
| Bilateral activity [13, 31] | Time, in hours, that both upper limbs are moving together |
| Use ratio [16, 28, 47] | Ratio of hours of paretic limb movement, relative to hours of non-paretic limb movement |
| Magnitude | |
| Paretic limb magnitude [48, 49] | Magnitude of accelerations of the paretic limb, in activity counts* |
| Bilateral magnitude [13, 31] | Intensity, or magnitude of accelerations, of movement across both arms, in activity counts* |
| Magnitude ratio [13, 31, 49] | Ratio of the magnitude of paretic UL accelerations relative to the magnitude of the non-paretic UL accelerations. This ratio reflects the contribution of each limb to activity, expressed as a natural log |
| Variability | |
| Variability of paretic movement [48, 49] | Standard deviation of the magnitude of accelerations across the paretic limb, reflecting the variability of paretic limb movement, in activity counts* |
| Variability of bilateral movement [48, 49] | Standard deviation of the magnitude of accelerations across both limbs, reflecting the variability of bilateral upper limb movement, in activity counts* |
| Variation ratio [48, 49] | Ratio of the variability of paretic limb accelerations relative to the variability of the non-paretic limb accelerations, reflecting the relative variability in the paretic limb |
| Smoothness | |
| Unimanual Jerk Asymmetry Index [34] | Ratio of the average jerk magnitude between the paretic upper limb and the nonparetic upper limb. Higher jerk represents less smooth movement, and an index value of 0 represents similar smoothness of movement in the paretic and non-paretic limbs. Values are bounded between − 1 to + 1 |
| Spectral arc length [35, 36] | A measure of movement smoothness that quantifies movement intermittencies independent of the movement’s amplitude and duration. Longer spectral arc lengths are reflective of less smooth or less coordinated movement |
*Activity counts are computed by the Actilife proprietary software such that 1 activity count = 0.001664 g