Organization of functional postural responses following perturbations in multiple directions in elderly fallers standing quietly.

The objective of the study was to assess functional postural responses by analyzing the center-of-pressure trajectories resulting from perturbations delivered in multiple directions to elderly fallers. Ten elderly individuals were standing quietly on two force platforms while an apparatus delivered controlled perturbations at the level of pelvis in eight directions: 'forward (FW)' and 'backward (BW)' [anterioposterior plane (AP)], 'left (LT)' and 'right (RT)' [mediolateral plane (ML)] and four combinations of these principal directions: forward-left (FL), forward-right (FR), backward-left (BL) and backward-right (BR). Perturbations were repeated randomly four times in each direction. Peak amplitude responses (PAR AP and PAR ML) and times to reach peak amplitude responses (TPAR-AP and TPAR-ML) were extracted for each perturbation direction from acquired center-of-pressure data. One-way analysis of variance was used to test differences between directionally-similar perturbation directions. Balance abilities were assessed by means of Berg Balance Scale. Average Berg Balance Scale for the group resulted in 33.9±5.8 points, which means that the participants were at greater risk of fall. The comparison of the group averaged PARAP and TPAR-AP in all 'forward' directions (FW, FL, FR) as well in all 'backward' directions (BW, BL, BR) have not shown statistically significant differences. The comparison of the group averaged PARML and TPAR-ML in all 'left' directions (LT, FL, BL) as well in all 'right' directions (RT, FR, BR) have not shown statistically significant differences. These results suggest that a principle of decoupled control may to a large extent be preserved also in elderly with clearly diminished balancing abilities, which implies that the accuracy in the assessment of perturbation direction may be well preserved also in very old age.