Validity of Poststroke Gait Spatiotemporal and Joint Excursion Metrics Between Inertial Measurement Units and a Marker-Based System.

People with chronic stroke often walk with altered spatiotemporal parameters and joint excursions, metrics that can serve as intervention targets. Inertial measurement units (IMUs) allow such metrics to be quantified outside of a traditional motion capture laboratory. The purpose of this study was to quantify the validity of common poststroke biomechanical gait metrics between an IMU-based and a marker-based system during treadmill walking, a context that facilitates gait training interventions. For 61 people with chronic stroke, we assessed the validity of stride duration, stride length, and sagittal plane joint excursions of the bilateral hip, knee, and ankle in 2 ways: (1) Across participants, revealing whether both systems similarly characterize participants' average gait parameters; and (2) Within participants, revealing whether both systems similarly quantify stride-by-stride variance. Across participants, all joint metrics had either excellent (Lin correlation coefficient; LCC > .75) or good (LCC .60-.74) validity, suggesting that IMU-derived metrics that are often the target of treatment can be appropriately compared to existing population norms. In contrast, median validity within participants was excellent for stride duration, but only poor (LCC < .40) to fair (LCC .40-.59) for stride length and most joint excursions. Therefore, IMU-derived gait metrics quantified on a stride-by-stride basis should be interpreted cautiously.