Understanding the measurement properties of the incremental shuttle walk test in patients with severe asthma.

There was a small increase in the mean ISWT distance on sequential testing. In clinical practice, the coefficient of repeatability and heteroscedasticity need to be considered when assessing whether a true change has occurred within an individual patient. The ISWT has validity compared to VO2pk on both ICE and ITM, but they are not interchangeable.