Movement fluency metrics during multi-phase sit-to-walk and reach-to-grasp: Test-retest reliability and agreement between laboratory-based and portable 3D motion analysis systems.

Background: International consensus recommends use of kinematic metrics of movement during standardized functional tasks after stroke to ascertain whether rehabilitation is driving behavioral restitution or compensation. Quality of human movement can be characterized by fluency metrics including smoothness and hesitation. Before using these metrics in stroke rehabilitation it is important to find whether 'reference values', from healthy adults, are repeatable.

Research question: Do kinematic metrics of smoothness and hesitation have test-retest reliability during standardized functional tasks performed by healthy adults?

Methods: a correlational agreement study. Testing sessions separated by 1-4 weeks. Participants, 75 adults reporting no neurological or musculoskeletal diagnosis, performed standardized multi-phase sit-to-walk and reach-to-grasp with kinematic data collected simultaneously by optokinetic and video-based 3D motion analysis systems. Smoothness was derived using the Spectral Arc Length method. Hesitation was the maximum decrease in thorax forward velocity as percentage of peak value. Analysis used the intra-class correlation coefficient (ICC) with 95 % confidence intervals [95 % CI]. The clinically acceptable level of test-retest reliability was set as, ICC 0.75 [lower 95 % CI 0.70 or above].

Findings: of the 75 participants, 72 completed both sessions. Neither smoothness nor hesitation kinematic metrics reached clinically acceptable test-retest reliability for either motion analysis system. Intra-participant variability was observed within sessions, e.g., mean coefficients of variation for sit-to-walk hesitation ranged from 13 % to 22 %.

Significance: Test-retest reliability of smoothness and hesitation kinematic metrics was clinically unacceptable for multi-phase tasks. Intra-participant within-session variation was observed. This intra-participant variation could hamper establishment of reference values for use in stroke rehabilitation.