Postural effects of the scaled display of visual foot center of pressure feedback under different somatosensory conditions at the foot and the ankle.

OBJECTIVES

To assess the effects of the scaled display of visual foot center of pressure (COP) feedback on upright postural control under different somatosensory conditions at the foot and the ankle.

DESIGN

Before and after intervention trials.

SETTING

University medical bioengineering laboratory.

PARTICIPANTS

Young healthy adults (N=8; mean age, 23+/-2.5 y; mean body weight, 76.8+/-11.2 kg; mean height, 179.8+/-6.8 cm).

INTERVENTIONS

Participants were asked to stand upright, as immobile as possible, in 3 visual conditions: a stationary cross feedback (SC-FB) condition and 2 different foot COP feedback (COP-FB) conditions involving increasing scale displays of 2:1 (COP-FB2) and of 10:1 (COP-FB10). These latter conditions correspond to the ratio between the COP displacement on the screen and the actual COP displacement measured by the force platform. This postural task was executed on 2 (firm, foam) support surface conditions. In the foam condition, a 2-cm thick foam support surface was placed under the participants' feet to alter the quality and/or quantity of somatosensory information at the foot and the ankle.

MAIN OUTCOME MEASURE

COP displacements were recorded using a force platform.

RESULTS

In the firm support surface condition, no significant difference was observed between the COP-FB2 and the SC-FB conditions, whereas the COP-FB10 condition yielded decreased COP displacements relative to the SC-FB condition. In the foam support surface condition, both the COP-FB2 and the COP-FB10 conditions yielded decreased COP displacements relative to the SC-FB condition, with a greater stabilizing effect in the COP-FB10 than COP-FB2 condition.

CONCLUSIONS

The postural effects of the scale display of visual COP feedback differed depending on the somatosensory conditions at the foot and the ankle. These findings suggest that increased reliance on augmented sensory information for controlling upright posture in conditions of altered somatosensory input from the foot and ankle could have implications in clinical and rehabilitative areas.