Background
Functional capacity assessment is important in patients with chronic obstructive pulmonary disease (COPD). It can be performed by the six-minute walk test (6MWT) on a 30-meter track. However, such space is not always available in clinical settings. Objectives: To compare the performance between the 6MWT on a 30- (6MWT30) and 20-meter (6MWT20) track; to evaluate the validity and reliability of the 6MWT30 and the 6MWT20; and to determine for which patients track length has the greatest impact on performance.
Conclusions
Performance was higher on the 6MWT30, with the difference increasing as performance improved. Therefore, the 6MWT20 is valid and reliable to evaluate functional capacity but should not be considered interchangeable with the 6MWT30, especially for the less disabled patients with COPD.
Methods
Patients with COPD randomly performed two 6MWT30 and two 6MWT20 on two different days and were also assessed using the COPD Assessment Test (CAT) and modified Medical Research Council (mMRC) scale.
Results
Thirty patients (23 men; mean ± standard deviation FEV1%pred: 45.6 ± 12.1) participated in the study. They walked a greater distance on the 6MWT30 than on the 6MWT20 [mean difference: 22.1 m (95% CI: 12, 32 m)]. The longer the 6MWT30 distance, the greater the difference between the 2 tests (r = 0.51; p = 0.004). The 6MWT20 showed high reliability [ICC: 0.96 (95% CI: 0.77, 0.99)] and the results were associated with the distance walked on the 6MWT30 (r = 0.86), CAT (r = -0.53), and mMRC (r = -0.62). Patients who walked ≥430 m in the 6MWT30 presented a difference between the tests greater than those who walked <430 m (34.5 ± 23.3 m vs. 12.6 ± 24.1 m; respectively; p = 0.01). Conclusions: Performance was higher on the 6MWT30, with the difference increasing as performance improved. Therefore, the 6MWT20 is valid and reliable to evaluate functional capacity but should not be considered interchangeable with the 6MWT30, especially for the less disabled patients with COPD.