The influence of weight-bearing asymmetry on postural responses to balance perturbations in individuals with stroke

Abstract

Background: Improvement of postural stability is an important goal during post-stroke rehabilitation. Since weight-bearing asymmetry (WBA) towards the unaffected leg is common, training of weight-bearing symmetry has been a major focus in post-stroke balance rehabilitation. It is assumed that restoration of a more symmetrical weight distribution is associated with improved postural stability. Several studies, however, suggest that a moderate degree of WBA may be used as a compensatory strategy to improve stability. Objective. To investigate the effect of WBA on measures of dynamic postural stability in the chronic phase after stroke i.e.: 1) the threshold for compensatory stepping and 2) the choice of the stepping leg after postural perturbations. Methods. Eight people in the chronic phase after stroke were exposed to translational balance perturbations in four directions while standing on a moveable platform. The stepping threshold and the choice of the stepping leg were determined in each direction and for three conditions of imposed WBA (symmetric loading, 10%, and 20% extra weight on the unaffected leg). The stepping threshold was defined as the highest perturbation intensity that could be sustained without stepping. Results. More WBA tended to increase the stepping threshold for perturbations towards the affected side (P = .065), whereas it decreased the stepping threshold towards the unaffected side (P = .006). Stepping thresholds for forward and backward perturbations were not influenced by WBA (main effect P = .078 and P = .595). Increased WBA resulted in an increased likelihood of stepping with the affected leg (20.8% symmetric loading (WBA 0%), 31.3% (WBA 10%), 44.8% (WBA 20%)) however; predominant stepping with the unaffected leg persisted. Conclusion. WBA may improve the ability to sustain perturbations towards the affected side. The increased likelihood of stepping with the affected leg may, however, result in a higher fall risk, which was most pronounced when as much as 20% extra body weight was borne on the unaffected leg. Therefore, a moderate WBA after stroke may be regarded as a useful strategy to improve stability towards the affected side without adversely affecting stepping responses.