Responsiveness and validity of the six-minute walk test in individuals with traumatic brain injury

Background. A simple test of aerobic fitness for patients with traumatic brain injury (TBI) that is valid, reliable, and responsive to change is needed to provide clinicians a functional measure of cardiorespiratory capacity. Objective. The purpose of this study was to examine the validity and responsiveness to change of the Six-Minute Walk Test (6MWT) in individuals with TBI. Design. A cohort, pretest-posttest, comparison study was conducted. Methods. Twenty-one patients performed the 6MWT upon admission to and prior to discharge from a postacute rehabilitation facility. Heart rate and distance traveled were recorded. A physiologic cost index (PCI) (beats per meter) was calculated based on steady-state heart rate. At discharge, all participants were able to perform a graded treadmill exercise test to exhaustion during which peak oxygen consumption (V̇O ₂) was measured. Results. Between admission and discharge, mean total distance increased from 342.6 m (SD=127.0) to 408.9 m (SD=124.2), and work increased from 27,185 kg·m (SD=10,528) to 34,114 kg·m (SD=12,057). The effect size indexes were 1.10 and 1.12 for distance and work, respectively. Correlations (r) between the discharge peak V̇O ₂ and the discharge 6MWT distance, PCI, and work were.58, -.61, and.47, respectively. Limitations. Stratification by gait speed may have improved responsiveness, especially for the slow ambulators. Conclusions. All measures correlated well with peak V̇O ₂, establishing an acceptable level of criterion-related (concurrent) validity. The addition of heart rate and calculating the PCI was only slightly better at predicting peak V̇O ₂, albeit nonsignificant, than a simple measure of total distance. The 6MWT provides a good estimate of peak aerobic capacity, and some measures are more responsive to change than others in patients recovering from TBI.