Anteroposterior perception of the trunk position while seated without the feet touching the floor

[Purpose] The purpose of this study was to investigate the trunk position perception in the anteroposterior direction in young participants sitting without their feet touching the floor to avoid the influence of the hamstrings tension and the feet pressure on the perception. [Subjects and Methods] Fourteen healthy volunteers were seated on a chair fitted with an original manual goniometer. There were 7 reference positions set at 5° increments, from −15° to 15°, and reproductions of each position were conducted 5 times. Trunk position perception was evaluated by the absolute error between the reproduced trunk angle and the reference position angle. [Results] The results revealed a significant effect of reference position on the absolute error. The absolute error at the −5° reference position was significantly larger than at the −15° and 15° positions, and the absolute error at the 0° position was significantly larger than at the −15°, 10°, and 15° positions. [Conclusion] These results suggest that the perception of extreme forward- and backward-leaning trunk positions while sitting without the feet touching the floor would be higher than in a neutral sitting position. The relationship between the stability of the posture and the perception may be involved in the sitting position.