The role of the pressure information from the heel on the perception of the backward-leaning standing position

The effects of the pressure on the coccygeal skin on the perception of backward-leaning sitting positions in stroke patients

The present study investigated the effects of an additional pressure stimulus on coccygeal skin using an original tool to evaluate the perceptibility of sitting while leaning backward in 13 chronic stroke patients who were able to walk independently and 12 age-matched healthy subjects. Each participant's perception of the trunk reference angle at which they felt the highest-pressure stimulation of the coccygeal skin while leaning backward from a quiet sitting position was evaluated based on the accuracy of each reproduction under both normal and additional pressure conditions. The absolute error under the pressure condition was significantly smaller than that under the normal condition in the control group, while no marked difference between conditions was found in the stroke group. The relationship between the absolute error under the normal condition and the pressure effect index showed a significant negative correlation in the stroke group. In stroke patients with a high trunk position perceptibility under the normal condition, the additional pressure information may have functioned as a disturbance and reduced the position perceptibility. In contrast, stroke patients with a low perceptibility in the normal condition may have been able to re-weight and prioritize the additional pressure information in the reference frame. In the control group, the added pressure information may have been re-weighted as prior position information in the reference frame.