Comparing Physiological Cost Index Between the 2-Minute and 6-Minute Walk Tests Across Neurological Rehabilitation Cohorts: Archives of Physical Medicine and Rehabilitation Submission.

Abstract

To compare the Physiological Cost Index (PCI) across stroke, traumatic brain injury (TBI), and non-TBI groups; evaluate within-group changes in PCI during inpatient rehabilitation; assess agreement between PCI derived from the 2-minute and 6-minute walk tests; and estimate a distribution-based minimal clinically important difference (MCID). Retrospective cohort study. Hospital. Two hundred twenty-seven adults undergoing inpatient neurorehabilitation, including individuals with stroke (n = 117), traumatic brain injury (n = 71), and non-traumatic brain injury neurological conditions (n = 39). None MAIN OUTCOME MEASURE(S): Physiological Cost Index (PCI; beats·m⁻¹) derived from the 2MWT and 6MWT at admission and discharge. Individuals with non-TBI showed higher admission 6MWT-derived PCI than individuals with stroke and TBI (global p = 0.0012; ε² = 0.073; post-hoc: non-TBI>stroke (p=0.015); non-TBI>TBI (p=0.002). Stroke improved from admission to discharge (2MWT Δ -0.13 ± 0.41; 6MWT Δ -0.17 ± 0.59), while TBI/non-TBI changes were small/non-significant. Across groups and timepoints, PCI was higher for 2MWT than 6MWT; Bland-Altman mean bias +0.35 (admission) and +0.26 (discharge) beats·m⁻¹. The 2MWT yields systematically higher PCI values than the 6MWT; likely reflecting non-steady-state cardiovascular responses inherent to shorter-duration walking. Stroke patients demonstrated clinically meaningful efficiency gains approaching an exploratory, distribution-based MCID (∼0.2 beats·m⁻¹); anchor-validated thresholds require larger, diagnosis-specific cohorts.