Background: Standing postural sway is often quantified from center of pressure trajectories. During assessments of longer durations, children may fidget, thus limiting the feasibility and validity of sway recordings.
Research Question: Do postural sway sample durations less than 30 s maintain construct and concurrent validity?
Methods: In this case-control, observational study, we measured postural sway in 41 children (age 5-12 years, 23 typically developing (TD); 18 with spastic cerebral palsy (CP), 13 diplegic and 5 hemiplegic, 11 GMFCS level I and 7 level II) for 30-second eyes-opened and eyes-closed conditions. From a single recording, 5-second incremental durations of 5 to 30 seconds were considered in this analysis. We quantified anteroposterior, mediolateral, and transverse-plane sway using seven time-domain variables: root-mean-square error, total excursion, mean frequency, mean distance, sway area, and 95% confidence circle and ellipse areas. Variables were calculated in eyes-opened and eyes-closed conditions, as well as the ratio of the two. Construct validity was evaluated by the persistence of large effect sizes (Glass’s Δ ≥ 0.80) between CP and TD participants at shorter durations than 30 seconds. Concurrent validity was evaluated by the correlations of shorter duration measures to the 30-second measure.
Results: Seven sway measures had large between-group effects (Glass’s Δ ≥ 1.02) for the 30-second measure that persisted (Glass’s Δ ≥ 0.81) at shorter durations (5-25 seconds) and also maintained concurrent validity (r ≥ 0.83). Six of these seven measures were taken in the eyes-closed condition, and all seven measures were in the mediolateral direction or transverse plane.
Significance: Our analysis suggests that sway durations less than 30 seconds can uphold construct and concurrent validity. These measures were primarily in the eyes-closed conditions and mediolateral direction. These results are a promising indicator that shorter-duration sway measures may be of utility when fidgeting prevents longer recordings.
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