Effects of Light Finger Touch on Postural Sway during Standing and Crouching Tasks

Light touch contact of the fingertip reduces postural sway. The light touch effect was confirmed in several postural orientations. However, the effect on postural control in the crouching posture remains unclear. This study investigated the effect of a light fingertip touch on the perturbation of the center of pressure in bipedal standing and crouching. Twenty-two healthy participants engaged in eight postural control tasks: standing/crouching (Posture) × eyes opened/eyes closed (Vision) × light touch/no touch (Touch). The total trajectory length and root-mean-square of the center of pressure in the anterior-posterior and medio-lateral directions were analyzed. Light touch reduced the sway of the center of pressure in both the standing and crouching postures, particularly in the anterior-posterior direction. Furthermore, the touch effect on the sway of the center of pressure varied between the standing and crouching postures. Consistent effects were observed in the anterior-posterior direction, but differing effects were observed in the medio-lateral direction. These results indicate that somatosensory input from the fingertip reduces postural sway in both directions in a crouched posture. Variations of the center of pressure disturbances in the medio-lateral direction could originate from differences in postural strategies involving the ankle and hip joints between bipedal standing and crouching positions.