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 non- (NGTP) and an incremental graded (Gardner Skinner) treadmill protocol (GSP).
In this prospective observational study, 30 patients with IC estimated their maximum walking distance (MWD) and completed a 'Walking Impairment Questionnaire' (WIQ). Outside walking was determined using a measuring wheel and a GPS 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.
Estimated walking distance was significantly higher than MWD as objectively measured during outside walking (400m vs 309m, respectively P=.02). A substantial variability (COV=55%) was found between both parameters. A small 35m MWD difference between outside walking and GSP was found with a substantial scatter (COV=42%). In contrast, a much larger 122m 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/h, GSP=3.2 km/h, NGTP=2.8 km/h; P<.001).
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.