Directional Measures of Postural Sway Applied to the Diagnostic of Postural Stability in the Population of Adult Women with Different Body Mass Index

Abstract

An impact of body anthropometry on postural stability was assessed in 145 adult women with different body mass indexes (BMI). Center-of-pressure (COP) trajectories were recorded during quiet stance in two 60-second trials, first with eyes open (EO) and then with eyes closed (EC). The data were analyzed using two novel measures of postural sway, the directional indices, and stability vector, that have been proven to be reliable standards for postural stability. Results showed a significant impact of BMI and visual feedback on both the anteroposterior (DIAP) and mediolateral (DIML) directional indices. Significant changes in the stability vector azimuth (SVa) due to vision exclusion, ranged between 0.99 ± 0.04 rad (EO) and 0.96 ± 0.05 rad (EC). The SV azimuth was additionally affected by BMI (0.8 ± 0.05 radians (EO) and 0.66 ± 0.05 rad (EC) in the group of women with the highest BMI). The DIML exhibited a positive correlation with BMI (0.6 and 0.71 for EO and EC, respectively), while the DIAP correlated negatively with BMI (-0.55 and-0.68 for EO and EC, respectively). In the control subjects the SV magnitude i.e., the mean velocity of sway, during EO trials remained at the level of 14.9 ± 2.8 mm/s while in the group with the highest BMI, it was reduced to 8.2 ± 0.8 mm/s. Both directional measures were also affected by the subjects' age. The results document the progressive decline in the postural stability control in adult women caused by excess body weight.