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Improvements in Force Variability and Structure from Vision- to Memory-Guided Submaximal Isometric Knee Extension in Subacute Stroke.

  • Chow, John W1
  • Stokic, Dobrivoje S1
  • 1 1 Methodist Rehabilitation Center.
Published Article
Journal of Applied Physiology
American Physiological Society
Publication Date
Nov 02, 2017
DOI: 10.1152/japplphysiol.00717.2017
PMID: 29097632


We examined changes in variability, accuracy, frequency composition, and temporal regularity of force signal from vision-guided to memory-guided force-matching tasks in 17 subacute stroke and 17 age-matched healthy subjects. Subjects performed a unilateral isometric knee extension at 10%, 30%, and 50% of peak torque (MVC) for 10 s (3 trials each). Visual feedback was removed at the 5s-mark in the first 2 trials (feedback withdrawal), and 30 s after the second trial the subjects were asked to produce the target force without visual feedback (force recall). The coefficient of variation and constant error were used to quantify force variability and accuracy. Force structure was assessed by the median frequency, relative spectral power in the 0-3 Hz band, and sample entropy of the force signal. At 10% MVC, the force signal in subacute stroke subjects became steadier, more broadband, and temporally more irregular after the withdrawal of visual feedback, with progressively larger error at higher contraction levels. Also, the lack of modulation in the spectral frequency at higher force levels with visual feedback persisted in both the withdrawal and recall conditions. In terms of changes from the visual feedback condition, the feedback withdrawal produced a greater difference between the paretic, non-paretic, and control legs than the force recall. The overall results suggest improvements in force variability and structure from vision- to memory-guided force control in subacute stroke despite decreased accuracy. Different sensory-motor memory retrieval mechanisms seem to be involved in the feedback withdrawal and force recall conditions, which deserves further studies.

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