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The hand, one of the most versatile but mechanically redundant parts of the human body, suffers more and longer than other body parts after stroke. One of the rehabilitation paradigms, task-oriented rehabilitation, encourages motor repeatability, the ability to produce similar motor performance over repetitions through compensatory strategies while taking advantage of the motor system's redundancy. The previous studies showed that stroke survivors inconsistently performed a given motor task with limited motor solutions. We hypothesized that stroke survivors would exhibit deficits in motor repeatability and adaptive compensation compared to healthy controls in during repetitive force-pulse (RFP) production tasks using multiple fingers. Seventeen hemiparetic stroke survivors and seven healthy controls were asked to repeatedly press force sensors as fast as possible using the four fingers of each hand. The hierarchical variability decomposition model was employed to compute motor repeatability and adaptive compensation across finger-force impulses, respectively. Stroke survivors showed decreased repeatability and adaptive compensation of force impulses between individual fingers as compared to the control (p < 0.05). The stroke survivors also showed decreased pulse frequency and greater peak-to-peak time variance than the control (p < 0.05). Force-related variables, such as mean peak force and peak force interval variability, demonstrated no significant difference between groups. Our findings indicate that stroke-induced brain injury negatively affects their ability to exploit their redundant or abundant motor system in an RFP task.

The ability to control redundant motor effectors is one of hallmarks in human motor control, and the topic has been studied extensively over several decades since the initial inquiries proposed by Nicholi Bernstein. However, our understanding of the influence of stroke on the control of redundant motor systems is very limited. This study aimed to investigate the effect of stroke-related constraints on multi-finger force control abilities in a visuomotor task. Impaired (IH) and less-impaired hands (LH) of 19 hemiparetic stroke survivors and 19 age-matched control subjects were examined. Each hand repeatedly produced isometric forces to match a target force of 5 N shown on a computer screen using all four fingers. The hierarchical variability decomposition (HVD) model was used to separate force-matching errors (motor performance) into task-relevant measures (accuracy, steadiness, and reproducibility). Task-irrelevant sources of variability in individual finger force profiles within and between trials (flexibility and multiformity) were also quantified. The IH in the stroke survivors showed deficits in motor performance attributed mainly to lower accuracy and reproducibility as compared to control hands (p < 0.05). The LH in stroke survivors showed lower reproducibility and both hands in stroke also had higher multiformity than the control hands (p < 0.05). The findings from our HVD model suggest that accuracy, reproducibility, and multiformity were mainly impaired during force-matching task in the stroke survivors. The specific motor deficits identified through the HVD model with the new conceptual framework may be considered as critical factors for scientific investigation on stroke and evidence-based rehabilitation of this population.

Background and Purpose: Functional capacity is a predictor, as well as a consequence, of stroke. However, little research has been done to examine whether higher-level functional capacity above basic activities of daily living is a predictor of stroke., Methods: We followed 1493 Japanese community-dwelling adults aged ≥60 years (mean age, 70.1 years) who were independent in basic activities of daily living and had no history of stroke. Baseline data were collected using a self-administered questionnaire. Higher-level functional capacity was measured using the total score and 3 subscales (instrumental activities of daily living, intellectual activity, and social role) derived from the Tokyo Metropolitan Institute of Gerontology Index of Competence. Adjusted hazard ratios and 95% confidence intervals were calculated by the Cox proportional hazards model., Results: During a mean follow-up of 10.4 years, 191 participants developed a first stroke. Impaired higher-level functional capacity based on total score of the Tokyo Metropolitan Institute of Gerontology Index of Competence was significantly associated with stroke (hazard ratio, 1.64; 95% confidence interval, 1.15-2.33). Among the 3 subscales, only intellectual activity was significantly associated with stroke (hazard ratio, 1.64; 95% confidence interval, 1.21-2.22). Social role was significantly associated with stroke only among those aged ≥75 years (hazard ratio, 1.78; 95% confidence interval, 1.07-2.98)., Conclusions: Impaired higher-level functional capacity, especially in the domain of intellectual activity, was a predictor of stroke, even among community-dwelling older adults with independent basic activities of daily living at baseline. Monitoring of higher-level functional capacity might be useful to detect those at higher risk of developing stroke in the future., (© 2016 American Heart Association, Inc.)