Methodological factors affecting test performance
The 6MWD is highly sensitive to changes in methodology (table 2). Given the impact of encouragement on
6MWD [33] and the use of encouraged tests in the generation of reference equations [1], it is recommended
that standardised phrases of encouragement are used (see later section on the testing protocol for 6MWT).
Provision of supplemental oxygen [26–29], method for carrying the supplemental oxygen [31, 32] and use
of wheeled walkers [20–25] also have an important impact on 6MWD. These factors must be kept constant
on repeat testing. The 6MWD generated using an externally paced treadmill is substantially lower than in a
hallway [14, 15], which is probably the result of the poor walking efficiency during treadmill walking in
subjects unaccustomed to this activity. Externally paced treadmill testing is not recommended. Track layout
and length may also affect performance on the test, especially when very short track lengths are used [19];
these factors should be kept constant where within-subject comparison of 6MWD on subsequent occasions