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

We investigated the repeatability and validity of the incremental shuttle walk test (ISWT) distance compared to peak oxygen uptake (VO_2pk ) during maximal incremental cycle ergometer (ICE) and treadmill (ITM) tests in adults with severe asthma.

Adults with severe asthma, Medical Research Council (MRC) dyspnoea ≥2, were recruited from specialists caring for patients with severe asthma. All participants performed three ISWT (familiarization and two subsequent tests on the same day), an ICE and an ITM in a randomized order, on separate days, to intolerance with expiratory gas analysis.

A total of 50 patients (32 females, mean (SD), age: 54 (13) years, forced expiratory volume in 1 s (FEV₁ ): 1.9 (0.8) L and body mass index (BMI): 32 (6) kg/m² ) completed all five tests. The mean (SD) ISWT distance for each test was 400 (156), 418 (142) and 438 (157) m (P = 0.001), respectively. There was a strong correlation between the ISWT distance with VO_2pk derived from ITM (r = 0.74, P < 0.001) and ICE (r = 0.75, P < 0.001).

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 VO_2pk on both ICE and ITM, but they are not interchangeable.