Correlations between force plate measures for assessment of balance

Objective. To compare different force plate measures for assessment of postural stability during normal standing. Five types of measures were analysed: (1) The standard deviation of the horizontal ground reaction force, (2) the standard deviation of the centre of pressure, (3) the mean velocity of the centre of pressure, (4) movement strategy measures, and (5) the standard deviation of the vertical ground reaction force. Background. Force plate measures such as types 1–3 are frequently used, but they seem to have limited usefulness for assessment of balance on an individual level. Hence, there is a need to investigate alternative force plate measures (such as types 4 and 5). Methods. Force plate measures for 20 stroke patients were (a) compared to each other, and (b) compared to a clinical balance test, called Berg’s balance test. Results. There was generally a significant correlation (P < 0.01) between measures of types 1–3. The movement strategy measures were not significantly correlated to any of the other measures. The vertical force measure was only significantly correlated to the antero-posterior mean velocity of the centre of pressure. There was a significant correlation between (a) Berg’s balance test and the vertical force measure (rs=−0.76), and (b) the static part of Berg’s balance test and the antero-posterior mean velocity of the centre of pressure (rs=−0.6). Conclusions. Measures of type 1, 2, 4 and 5 seem to quantify different aspects of human standing. The results also indicate that Berg’s balance test and the vertical force measure quantify a similar aspect of the postural stability.