Influence of feet position on COP measures in post-stroke patients in quiet standing

Foot placement is an important methodological parameter in experiments for analyzing the behavior of the center of pressure (CoP) duringquiet standing. In the case of stroke patients, this is a relevant issue, as the standardized position, usually adopted is not ecological.

Do between-limb synchronization, weight-bearing symmetry, and amplitude of the postural sway of post-stroke individuals differ between standardized and comfortable foot positions during quiet standing?

A total of 36 volunteers (20 with stroke and 16 healthy) stood barefoot, for 60 s, on two force plates with feet in a comfortable and standardized position (14° of external rotation and heels 17 cm apart). Three trials were performed in each position, and the average values obtained were analyzed.

The comfortable position adopted by stroke individuals was characterized by heels kept 17 cm apart and with 21° of external rotation. None of the measures of the healthy group were influenced by feet position. In the stroke group, the lag to maximal between-feet correlation in the mediolateral direction (ML ρ_max lag) was higher (0.45 s) and the weight-bearing symmetry was better in the comfortable (38%) than in the standardized conditions (0.19 s and 32%, respectively). Neither the other CoP measures nor the intra-subject variability was sensitive to feet position.

The assumption that standardization leads to reduced variability might not be valid to the post-stroke and healthy individuals age around 55 years. Therefore, adoption of a comfortable condition might be advantageous, once it allows for a more practical and realistic evaluation of postural control.