Dysequilibrium Reaction Time and “Long-Loop” Recruitment Deficits in Subjects with Hemiplegia

Abstract

Gaps in the recruitment of postural muscles to correct body sway may be a limiting factor in the rehabilitation of patients with stroke. The purpose of this study was to determine how the onset of a postural reflex compares to the conscious identification of body sway in patients with hemiplegia and in a comparison group of able-bodied subjects. All subjects stood on a movable force platform that was unexpectedly displaced backwards inducing a forward body sway. The excursion and velocity of the platform displacements were varied systematically and the frequency of activation of postural muscles was recorded. A hand held response key was used to measure the time required to react to the postural disturbance (RT). In addition, the onset time of a long-loop “stretch” reflex was measured in the gastrocnemius muscles bilaterally. Subjects with hemiplegia failed to recruit a reflex response in 53% of the trials, whereas able-bodied subjects had an absent response in only 3% of the trials. The upper extremity RT for subjects with hemiplegia was not significantly delayed compared to able-bodied subjects, and the onset of a stretch reflex response in the gastrocnemius muscles was not different between groups. In addition, there was no correlation between reflex onset and conscious reaction time for control or disabled groups. These results have implications for the practice of occupational therapy because lower extremity recruitment deficits may persist and require treatment even though the recognition of body sway and the onset of reflex muscle discharge (when recruited) was similar to that of able-bodied subjects.

Keywords

cognition balance EMG

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