Smoothness metrics for reaching performance after stroke. Part 1: which one to choose?
Mohamed Irfan Mohamed Refai, Mique Saes, Bouke L Scheltinga and 8 others
PMID 34702281WHAT IT FOUND
SPARC is the only smoothness metric that consistently worked across simulations of stroke reaching.
Many common metrics failed to detect tremors or were skewed by movement speed. Use SPARC to accurately measure arm movement quality after stroke.
Key findings
01SPARC was the only metric that responded as expected to changes in movement shape, harmonic disturbances, and measurement noise.
02Many other metrics failed to detect tremors, were sensitive to movement duration or distance, or were not robust to measurement noise.
03The study recommends using SPARC to measure the smoothness of upper limb reaching after stroke.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The review was limited to English-language articles. The metrics were tested on computer simulations, not on real patients, so they might not perfectly reflect actual clinical movement patterns. The study only looked at arm reaching movements, so the results may not apply to other tasks like walking or fine motor skills. SPARC may not be sensitive enough to detect very small improvements in movement smoothness in patients who have already recovered significantly.
Declared interests
The study was funded by the European Research Council and the Dutch Technology Foundation. The authors declared no other conflicts of interest.
The easy way to misread this
Do not assume that SPARC can be measured using standard wearable sensors like IMUs without special processing. These sensors measure acceleration, not velocity, and converting the data can introduce errors that make the smoothness score inaccurate.