Submovement overlap as a measure of movement smoothness

Many measures have been employed to quantify an aspect of healthy, skilled movement, which has been termed “movement smoothness” of which jerk is the most common. We propose a new, biologicallymotivated quantification of “movement smoothness”: submovement overlap. In previous work, changes in submovements have been linked to changes in movement smoothness. Further investigation revealed that in stroke patients, submovements consistently tend to grow closer over the course of recovery. While jerk analysis showed some patients’ movements growing significantly less smooth, submovement blending provided a remarkably consistent metric of recovery, despite wide variations in subject age, lesion territory, and stroke severity. In stroke patients, it is not average jerk but submovement blending that meaningfully quantifies the movement smoothing that accompanies recovery. The strength and consistency with which it quantified patients’ recovery indicates that analysis of submovement overlap may be a useful tool for measuring learning or other changes in motor behavior in future human movement studies.