Three-minute Step Test to Assess Exercise Capacity in Children with Cystic Fibrosis with Mild Lung Disease

The information obtained from a simple submaximal test (the 3-min step test) was compared with that from a maximal cycle ergometry study, in a group of children with CF with relatively mild abnormalities of lung function (FEV(1) > 50% predicted). Nineteen subjects with CF undertook both exercise tests on the same day. Measurements included heart rate (HR), oxygen saturations (SaO(2)), visual analogue score of perceived breathlessness (VAS), 15-count breathlessness score (15c), and peak oxygen consumption (VO(2)). There were significant differences in the median changes in HR and VAS during the cycle test compared to the step test, 78 vs. 46 beats per minute (P < 0.05) and 51 mm vs. 42 mm (P < 0.05), respectively. There were no differences between median changes in 15c and SaO(2), but 3 subjects had significant desaturations (>4%) during the cycle test only. Significant exercise desaturations may occur in mild CF lung disease and will not be detected by a 3-min step test. The 15c did not discriminate between a maximal and a submaximal test, and was less useful than VAS. Important information may be missed by the step test which is detected by more complex exercise tests.