Haptic stabilization of posture: changes in arm proprioception and cutaneous feedback for different arm orientations

Area of Science:

• Biomechanics
• Human sensorimotor control
• Postural stability

Background:

• Quiet stance involves continuous postural sway.
• Active fingertip contact with a surface can reduce postural sway.
• This stabilization occurs even without significant mechanical support.

Purpose of the Study:

• To investigate how fingertip somatosensory and proprioceptive information contributes to postural control.
• To test the hypothesis that optimal postural stabilization occurs when fingertip contact is in the plane of body sway.

Main Methods:

• Subjects maintained index finger contact with a surface during quiet stance.
• Two stances were used: tandem Romberg (medial-lateral instability) and duck stance (fore-aft instability).
• Fingertip contact was either lateral or frontal relative to the body.

Main Results:

• Postural sway was significantly reduced when fingertip contact was in the plane of instability for each stance.
• Lateral contact was more effective in the tandem stance; frontal contact was more effective in the duck stance.
• Changes in fingertip force preceded changes in center of foot pressure by approximately 250 ms.

Conclusions:

• Fingertip contact acts as an active sensor, utilizing somatosensory and proprioceptive feedback for postural control.
• Optimal stabilization is achieved when the contact surface is aligned with the primary direction of body sway.
• This sensory information provides directional and amplitude cues about body sway.