An accelerometry-based methodology for assessment of real-world bilateral upper extremity activity

Abstract

Background: The use of both upper extremities (UE) is necessary for the completion of many everyday tasks. Few clinical assessments measure the abilities of the UEs to work together; rather, they assess unilateral function and compare it between affected and unaffected UEs. Furthermore, clinical assessments are unable to measure function that occurs in the real-world, outside the clinic. This study examines the validity of an innovative approach to assess real-world bilateral UE activity using accelerometry.

Methods: Seventy-four neurologically intact adults completed ten tasks (donning/doffing shoes, grooming, stacking boxes, cutting playdough, folding towels, writing, unilateral sorting, bilateral sorting, unilateral typing, and bilateral typing) while wearing accelerometers on both wrists. Two variables, the Bilateral Magnitude and Magnitude Ratio, were derived from accelerometry data to distinguish between high- and low-intensity tasks, and between bilateral and unilateral tasks. Estimated energy expenditure and time spent in simultaneous UE activity for each task were also calculated.

Results: The Bilateral Magnitude distinguished between high- and low-intensity tasks, and the Magnitude Ratio distinguished between unilateral and bilateral UE tasks. The Bilateral Magnitude was strongly correlated with estimated energy expenditure (ρ = 0.74, p<0.02), and the Magnitude Ratio was strongly correlated with time spent in simultaneous UE activity (ρ = 0.93, p<0.01) across tasks.

Conclusions: These results demonstrate face validity and construct validity of this methodology to quantify bilateral UE activity during the performance of everyday tasks performed in a laboratory setting, and can now be used to assess bilateral UE activity in real-world environments.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Example of data processing for one participant and one task, Grooming.

A. Vector magnitude (measured in activity counts) for the dominant and nondominant UEs. B. Vector magnitudes were smoothed using a 5-sample moving average, resulting in decreased amplitudes. C. The Bilateral Magnitude (measured in activity counts) was calculated for each second of activity. D. The Magnitude Ratio was calculated for each second of activity. E & F. Histograms of Bilateral Magnitude and Magnitude Ratio values, respectively. The median values are identified by arrows.

Figure 2. Example data for a single participant.

A. Scatterplot illustrating the relationship between the Magnitude Ratio and Bilateral Magnitude (measured in activity counts) for each second of data (filled circles) for one task, Grooming. The median value of both variables is indicated by the red ‘X.’ B. Scatterplot illustrating how the different tasks compare to Grooming with respect to median Bilateral Magnitude and median Magnitude Ratio values. The median Magnitude Ratio for Bilateral Sorting and Bilateral Typing deviated from 0, despite these being bilateral tasks. For Bilateral Sorting, the participant used her nondominant UE to complete half of the task before using both UEs together. For Bilateral Typing, the participant frequently used her dominant UE to press the “Backspace” key, even though she used both UEs to type in a hunt-and-peck fashion.

Figure 3. Sample data across all tasks.

Values are the middle 50% (25–75 percentiles) of median Bilateral Magnitude (vertical bars, measured in activity counts) and median Magnitude Ratio (horizontal bars) values. Differences between tasks and variability within tasks are evident.