Reliability of unconventional centre of pressure measures of quiet standing balance in people with chronic stroke

Background: People with stroke often have asymmetric motor impairment. Investigating asymmetries in, and dynamic properties of, centre of pressure movement during quiet standing can inform how balance is controlled. Research question: What are the test-retest reliabilities of unconventional measures of quiet standing balance control in people with chronic stroke?Methods: Twenty people with chronic stroke (>6 months post-stroke), who were able to stand for at least 30 s without support, were recruited. Participants completed two 30-second quiet standing trials in a standardized position. Unconventional measures of quiet standing balance control included: symmetry of variability in centre of pressure displacement and velocity, between-limb synchronization, and sample entropy. Root mean square of centre of pressure displacement and velocity in the antero-posterior and medio-lateral directions were also calculated. Intraclass correlation coefficients (ICCs) were used to determine test-retest reliability, and Bland -Altman plots were created to examine proportional biases. Results: ICC3,2 were between 0.79 and 0.95 for all variables, indicating 'good' to 'excellent' reliability (>0.75). However, ICC3,1 for symmetry indices and between-limb synchronization were < 0.75. Bland-Altman plots revealed possible proportional biases for root mean square of medio-lateral centre of pressure displacement and velocity and between-limb synchronization, with larger between-trial differences for participants with worse values.Significance: These findings suggest that centre of pressure measures extracted from a single 30-second quiet standing trial may have sufficient reliability for some research studies in chronic stroke. However, for clinical applications, the average of at least two trials may be required.