Background-The purpose of this study was to provide some evidence of the validity of a modified shuttle test (MST) by comparing performance on the MST with peak oxygen consumption (Ṽ O 2 peak) measured during a treadmill test in a group of adult patients with cystic fibrosis. Method-Twenty patients with stable cystic fibrosis performed a ramped maximal treadmill test (STEEP protocol) and the MST using a randomised balanced design. (Thorax 1999;54:437-439) Keywords: modified shuttle test; cystic fibrosis Exercise testing is useful in determining prognosis, exercise prescription, and in the evaluation of new and existing treatments in patients with cystic fibrosis. The most precise method of assessing exercise capacity is by formal laboratory tests with online analysis of expired air. However, formal tests are not widely available to clinicians working in cystic fibrosis centres, and there is debate as to the most appropriate protocol for testing. Furthermore, many patients with cystic fibrosis find these tests excessively stressful and are reluctant to perform such tests on a routine basis. Some centres have attempted to use informal tests to assess and monitor exercise capacity in patients with cystic fibrosis, but some studies have highlighted the controversy surrounding the reliability, validity, and sensitivity of many of these tests. The shuttle walking test is an incremental externally paced informal exercise test which overcomes many of the problems associated with existing informal exercise tests. The original authors of the shuttle walking test have shown this test to be a reliable (after just one practice test), valid, and sensitive measure of exercise capacity in patients with chronic obstructive pulmonary disease. [3][4][5] We have carried out preliminary work with the shuttle walking test in adult patients with cystic fibrosis, and have shown that the walking speeds in the original test (up to a maximum of 2.37 m/s) do not elicit a maximal response in adult patients with cystic fibrosis and minimal disability as well as in patients with more severe disability. On the basis of these preliminary findings the original test was modified by the addition of three levels and, further, by permitting the patients to run. The additional stages to the original 12 stage test were: level 13, 5.63 mph, 15 shuttles; level 14, 6.00 mph, 16 shuttles; and level 15, 6.38 mph, 17 shuttles. It was hypothesised that this modified shuttle test (MST) could be used to measure peak exercise capacity objectively in adult patients with cystic fibrosis. The aim of this study was therefore to compare patients' performance on the MST with peak oxygen consumption (Ṽ O 2 peak) measured directly during a treadmill test. Results-The MethodsTwenty patients (14 men) of mean (SD) age 25 (7) years, weight 58 (8) kg, height 1.68 (0.08) metres volunteered for the study. All patients had been familiarised with the MST and the treadmill test prior to entry into the study. Patients undertook the treadmill test on one visit to the h...

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