pISSN 2288-6982
eISSN 2288-7105




Phys. Ther. Korea 2020; 27(2): 126-132

Published online May 20, 2020

© Korean Research Society of Physical Therapy

The Effects of Augmented Somatosensory Feedback on Postural Sway and Muscle Co-contraction in Different Sensory Conditions

Seo-hyun Kim1, BPT, PT, Kyung-eun Lee1, BPT, PT, One-bin Lim2, PhD, PT, Chung-hwi Yi2 , PhD, PT

1Department of Physical Therapy, The Graduate School, Yonsei University, 2Department of Physical Therapy, College of Health Science,
Yonsei University, Wonju, Korea

Correspondence to: Chung-hwi Yi

Received: January 22, 2020; Revised: February 27, 2020; Accepted: March 13, 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background: Augmented somatosensory feedback stimulates the mechanoreceptor to deliver information on bodily position, improving the postural control. The various types of such feedback include ankle-foot orthoses (AFOs) and vibration. The optimal feedback to mitigate postural sway remains unclear, as does the effect of augmented somatosensory feedback on muscle co-contraction.
Objects: We compared postural sway and ankle muscle co-contraction without feedback (control) and with either of two forms of somatosensory feedback (AFOs and vibration).
Methods: We recruited 15 healthy subjects and tested them under three feedback conditions (control, AFOs, vibration) with two sensory conditions (eyes open, or eyes closed and the head tilted back), in random order. Postural sway was measured using a force platform; the mean sway area of the 95% confidence ellipse (AREA) and the mean velocity of the center-of-pressure displacement (VEL) were assessed. Co-contraction of the tibialis anterior and gastrocnemius muscles was measured using electromyography and converted into a cocontraction index (CI).
Results: We found significant main effects of the three feedback states on postural sway (AREA, VEL) and the CI. The two sensory conditions exerted significant main effects on postural sway (AREA and VEL). AFOs reduced postural sway to a level significantly lower than that of the control (p = 0.014, p < 0.001) or that afforded by vibration (p = 0.024, p < 0.001). In terms of CI amelioration, the AFOs condition was significantly better than the control (p = 0.004). Vibration did not significantly improve either postural sway or the CI compared to the control condition. There was no significant interaction effect between the three feedback conditions and the two sensory conditions.
Conclusion: Lower-extremity devices such as AFOs enhance somatosensory perception, improving postural control and decreasing the CI during static standing.

Keywords: Feedback, Postural balance, Posture, Proprioception