NORMAL VARIABILITY OF POSTURAL, MEASURES - IMPLICATIONS FOR THE RELIABILITY OF RELATIVE BALANCE PERFORMANCE OUTCOMES

The reliability of outcome measures obtained using the Balance Master( TM) and the limits of stability in anterior, posterior, and lateral di rections were evaluated in 70 healthy subjects aged 20 to 32 years. Da ta relating to static sway and the ability to shift the centre of grav ity to preset targets were collected on three occasions one week apart , The centre of gravity position and limits of stability were determin ed over three trials and data converted from a relative reference syst em to absolute displacements from vertical, Intraclass correlation coe fficients revealed fair to poor reliability of static and dynamic sway measures (coefficients less than or equal to 0.55) and excellent reli ability of limits of stability measures and the position of the centre of gravity (coefficients greater than or equal to 0.75). The variabil ity in outcome measures from tests which do not maximally challenge th e postural control system may be a hallmark of normal balance performa nce. Further, the intersubject variation in resting centre of gravity position and in limits of stability supports the use of absolute perfo rmance measures as the interpretive value of data expressed relative t o standard norms is limited.