Six-minute walking test done in a hallway or on a treadmill: how close do the two methods agree?

Background: The 6-min walking test (6-MWT) is probably the most widely used test to measure the functional capacity in cardiac rehabilitation. Although the American Thoracic Society recommends testing on a flat surface, treadmills are also used for testing. Therefore, we want to investigate the interchangeability of results of treadmill and hallway 6-MWT in a population of patients participating in a cardiac rehabilitation programme.