Criterion and discriminant validity of accelerometer-based analysis of step time and step time variability during treadmill walking in people with bilateral vestibulopathy

Background: Gait and balance impairments, including increased gait variability, are prevalent in people with bilateral vestibulopathy (BVP). Wearable accelerometers may provide a clinically feasible method to objectively assess gait variability but have not yet been explored in BVP. Research question: Does an accelerometer-based assessment of step time variability during treadmill walking show criterion and discriminant validity in people with BVP?Methods: 30 adults with BVP and 30 age-sex-matched healthy controls walked at 0.6m/s, 0.8m/s, and 1.0m/s on the treadmill of the Computer Assisted Rehabilitation Environment. We examined differences in step time means and coefficients of variation (CoV) between accelerometery (single lower back sensor; MOX1) and 3D motion capture and force plates (Vicon). Criterion validity was assessed using intraclass correlation coefficients (ICC3,1) and Bland-Altman analyses to determine agreement and consistency between the methods. Discriminant validity was assessed by comparing the results of independent t-tests and the effect size between the groups using each method. Results: Mean step time showed moderate to excellent agreement between methods, while step time CoV showed poor agreement and proportional bias. Discriminant validity of accelerometery was supported by consistent between-group significance and effect size values, particularly at 0.6m/s, although effect sizes were larger in motion capture data than in accelerometer data.Significance: An accelerometer-based assessment is valid for assessing mean step time in people with BVP and demonstrates discriminant (particularly at slower speeds) but not criterion validity for assessing step time variability. Before clinical application, test-retest reliability and sensitivity to change should be assessed in BVP.