Abstract
Smoothness is a main characteristic of goal-directed human movements. The suitability of approaches quantifying movement smoothness is dependent on the analyzed signal's structure. Recently, activities of daily living (ADL) received strong interest in research on aging and neurorehabilitation. Such tasks have complex signal structures and kinematic parameters need to be adapted. In the present study we examined four different approaches to quantify movement smoothness in ADL. We tested the appropriateness of these approaches, namely the number of velocity peaks per meter (NoP), the spectral arc length (SAL), the speed metric (SM) and the log dimensionless jerk (LDJ), by comparing movement signals from eight healthy elderly (67.1a ± 7.1a) with eight healthy young (26.9a ± 2.1a) participants performing an activity of daily living (making a cup of tea). All approaches were able to identify group differences in smoothness (Cohen's d NoP = 2.53, SAL = 1.95, SM = 1.69, LDJ = 4.19), three revealed high to very high sensitivity (z-scores: NoP = 1.96 ± 0.55, SAL = 1.60 ± 0.64, SM = 3.41 ± 3.03, LDJ = 5.28 ± 1.52), three showed low within-group variance (NoP = 0.72, SAL = 0.60, SM = 0.11, LDJ = 0.71), two showed strong correlations between the first and the second half of the task execution (intra-trial R2s: NoP = 0.22 n.s., SAL = 0.33, SM = 0.36, LDJ = 0.91), and one was independent of other kinematic parameters (SM), while three showed strong models of multiple linear regression (R2s: NoP = 0.61, SAL = 0.48, LDJ = 0.70). Based on our results we make suggestion toward use examined smoothness measures. In total the log dimensionless jerk proved to be the most appropriate in ADL, as long as trial durations are controlled.
Highlights
Despite the great importance of analyzing ecologically valid activities in clinical research and diagnostics, the quantification of activities of daily living (ADL) was typically limited to subjective scorings of videos [1, 2] or timed trials [3,4,5], a parametric quantification of movement quality was not feasible
Three of the parameters showed a within-group variance index above or equal 0.6, meaning that within group variability was low in the number of velocity peaks per meter, the spectral arc length, and the log dimensionless jerk, while it was very high in the speed metric
We tested only one ADL task and the question is how much our findings can be extended to ADL in general
Summary
Despite the great importance of analyzing ecologically valid activities in clinical research and diagnostics, the quantification of activities of daily living (ADL) was typically limited to subjective scorings of videos [1, 2] or timed trials [3,4,5], a parametric quantification of movement quality was not feasible. With technologies like advanced motion-tracking devices, it recently became more feasible to investigate human behavior in a natural, ecological valid setting. Certain actions, like phases of inactivity, transporting, grasping, rotating, circling, or balancing, repeatedly appear in ADL. Smoothness is a main characteristic of goal-directed movements. It is suggested that the planning of movement dynamics are based on smoothness [7].
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