System identification: a feasible, reliable and valid way to quantify upper limb motor impairments.

This was a measurement feasibility and validation study, not a treatment trial, so it does not show that using system identification improves patient care. Nine of 94 participants were excluded from analysis for poor model fit or incomplete task levels. Reliability was poor for some key parameters, including elbow stiffness with full weight support in patients and slope parameters in healthy controls. Construct validity correlations were weak to moderate and based on relatively small samples, so the method may not reliably distinguish synergy, spasticity, and viscoelasticity. Participants needed some active shoulder abduction and elbow extension, so results may not apply to people with more severe upper limb impairment. The protocol was tested only in chronic stroke and cerebral palsy, not other conditions. Measurements were made at a fixed posture with small elbow movements, not across full active movement, so impairments only present during movement may be missed.

No author conflicts of interest are reported in the supplied text. The article is tagged as supported by non-U.S. government research.

Do not read this as a validated clinical assessment. The elbow stiffness measure for spasticity had poor reliability in patients, and correlations with impairment measures were only weak to moderate.