Post-Stroke Lower Limb Spasticity Alters the Interlimb Temporal Synchronization of Centre of Pressure Displacements Across Multiple Timescales.

Lower limb spasticity is a common sensorimotor consequence post-stroke, which further complicates stability control by altering the temporal relationship between individual-limb centre of pressure (COP) displacements. The present work employed the discrete wavelet transform to better understand the influence of lower limb spasticity on the control of standing balance, which occurs across multiple timescales. An 8-level decomposition of the individual-limb COP was performed, using retrospective data from 91 stroke survivors with (n = 29) and without (n = 56) lower limb spasticity. Inter-limb temporal synchrony and spatial symmetry at each timescale were evaluated by the cross correlation coefficient at zero phase-lag and the root mean square ratio, respectively, using the reconstructed time series at each timescale. Reduced temporal synchrony was observed among individuals with lower limb spasticity at frequencies down to 0.20 Hz. The present results suggest that the additional balance control challenges associated with post-stroke lower limb spasticity may be linked to the ability to temporally co-modulate the more rapid COP displacements. This may be particularly problematic if individuals are faced with balance perturbations, which require rapid reactive balance corrections to regain stability.