Agreements and Discrepancies between the Estimated Walking Distance, Nongraded and Graded Treadmill Testing, and Outside Walking in Patients with Intermittent Claudication

Background: Disease severity in patients with intermittent claudication (IC) is often assessed using walking distances and treadmill tests. The aim of this study was to determine the agreement between walking distance as estimated by the patient, as measured during outside walking, and as determined using a nongraded treadmill protocol (NGTP), and an incremental graded (Gardner-Skinner) treadmill protocol (GSP). Methods: In this prospective observational study, 30 patients with IC estimated their maximal walking distance (MWD) and completed a "Walking Impairment Questionnaire" (WIQ). Outside walking was determined using a measuring wheel and a GSP controlled device. Primary outcomes were differences in MWD and variability (coefficient of variation, COV). Secondary outcomes were results of WIQ and differences in walking speed. Results: Estimated walking distance was significantly higher than MWD as objectively measured during outside walking (400 m vs. 309 m, respectively, P = 0.02). A substantial variability (COV = 55%) was found between both parameters. A small 35-m MWD difference between outside walking and GSP was found with a substantial scatter (COV = 42%). In contrast, a much larger 122-m MWD difference was present between outside walking and NGTP (COV = 89%). Patients walked significantly faster in the open air than on treadmills (median outside walking speed = 3.8 km/hr, GSP = 3.2 km/hr, NGTP = 2.8 km/hr; P < 0.001). Conclusions: An incremental graded (Gardner-Skinner) treadmill protocol demonstrated the best agreement to outside walking. Discrepancies between treadmill tests and outside walking may be explained by a difference in walking speed. A single determination of a walking distance is a poor reflection of true walking capacity.