Perception of trunk inclination during sitting with feet in contact with the floor.

[Purpose] To clarify the sitting postural control, the influences of several reference sitting positions on the perception of the trunk position while sitting with the feet in contact with the floor and keeping the eyes closed were investigated. [Participants and Methods] Fifteen young healthy volunteers participated in the present study. The perception of the trunk position was evaluated by calculating the absolute error (error magnitude) and constant error (error direction) between the reference trunk position (which the subjects memorized; the reference position) and the position that they adopted when reproducing the reference position (the reproduced position). Eight reference positions were set at 5° increments (from 15° backward inclination [-] to 20° forward inclination [+]). [Results] The reference positions had a significant effect on the absolute error, and the absolute error values at -15° and -10° were significantly smaller than at 20°. However, the reference positions had no effect on the constant error. [Conclusion] The present study revealed that the perception of the trunk position while sitting with the feet in contact with the floor is better when inclining backward than when inclining forward. The perception of the trunk position may be higher in a low-stability position and lower in a high-stability position.