Assessment of postural stability in stable and unstable conditions.

Purpose: The aim of the study was to determine whether it is possible to assess static balance on an unstable surface using center of pressure velocities obtained with a force platform when standing on a wobble board.
Methods: The center of pressure velocities were recorded with a force platform within three days (four trials per day) in thirty young adults in three conditions: standing on a rigid surface, compliant surface, and on a wobble board. Reliability of mean velocities of the center of pressure was examined using intraclass correlation coefficients. Relationships between the three conditions were assessed with Pearson correlation coefficients.
Results: Intra-session reliability was excellent for standing on a rigid surface and on a compliant surface and good for standing on a wobble board. Inter-session reliability was good for all parameters in all conditions, except for poor reliability in the anterior-posterior direction in standing on a wobble board. All correlations between the same parameter in different conditions were statistically significant (P < 0.05), except for velocity of the center of pressure in the anterior-posterior direction between stance on a rigid surface and stance on a wobble board.
Conclusions: Centre of pressure velocity parameters obtained with a force plate when standing on a wobble board can provide valuable information about postural stability in unstable conditions.