[Postural characteristics of healthy subjects under different thickness of foam]

To investigate the effects of different thickness of foam on the postural control of standing in healthy subjects.

Thirty healthy adult subjects (11 males, 19 females) were taken into examination of computerized posturography measurement under different surface conditions such as the firm surface and 1 to 5 layer foams of medium density with 4.7 cm high respectively in stance of feet together with eye open and eye closed for 30 s. The following time-dominated parameters regarding to the center of pressure (COP) movement were used for the analysis: whole path length (WPL), unit path length (UPL) which means the sway velocity of the COP movement, unit area path length (UAPL), circumference area (CA), effective value area (EVA) and rectangle areas (RA).

All parameters had the increased tendency when the layer of foam was added with both eye open and closed conditions except the UAPL, which had a decreased tendency. The parameters on different layer of foam were significance (P < 0.05) except the following conditions: (1) WPL and UPL on layer 4 and 5 with eyes opened and eyes closed; (2) UAPL on layer 2 and 3, layer 3 and 4, layer 4 and 5 with eyes opened, layer 3 and 4, layer 3 and 5 and layer 4 and 5 with eyes closed, (3) CA on layer 2 and 3, layer 3 and 4, layer 4 and 5 with eyes opened, layer 3 and 4, layer 3 and 5, layer 4 and 5 with eyes closed; (4) RA and EVA on layer 2 and 3, layer 4 and 5 with eyes opened, layer 3 and 4, layer 4 and 5, layer 3 and 5 with eyes closed.

The postural stability of normal subjects decreased when the foam thickness was added in some extent. It was important that the thickness of foam should be considered for interrupting the proprioception of feet in clinical. The whole path length and average velocity of movement of COP can be considered as the stable and sensitivity parameters in the foam posturography.