Which field walking test should be used to assess functional exercise capacity in lung cancer? an observational study

Background: There is emerging evidence regarding the efficacy of exercise training to improve exercise capacity for individuals with non-small cell lung cancer (NSCLC). Cardiopulmonary exercise testing (CPET) is the gold standard measure of exercise capacity; however this laboratory test has limitations for use in research and clinical practice. Alternative field walking tests are the six-minute walk test (6MWT), incremental-shuttle walk test (ISWT) and endurance-shuttle walk test (ESWT); however there is limited information about their clinimetric properties in NSCLC. Aims: In NSCLC to determine the 1) criterion validity of the 6MWT, ISWT and ESWT against CPET; 2) construct validity of the 6MWT, ISWT and ESWT against measures of function, strength, respiratory function and health-related quality of life (HRQoL); and 3) clinical applicability of the tests. Methods: Twenty participants (40 % male, mean +/- SD age 66.1 +/- 6.5 years) with stage I-IIIb NSCLC completed the 6MWT, ISWT, ESWT and CPET within six months of treatment. Testing order was randomised. Additional measures included Eastern Cooperative Oncology Group Performance-Status (ECOG-PS, function), respiratory function, hand-grip dynamometry and HRQoL. Correlations and regression analyses were used to assess relationships. Results: The ISWT demonstrated criterion validity with a moderate relationship between ISWT distance and CPET peak oxygen consumption (r = 0.61, p = 0.007). Relationships between CPET and six minute walk distance (6MWD) (r = 0.24, p = 0.329) or ESWT time (r = 0.02, p = 0.942) were poor. Moderate construct validity existed for the 6MWD and respiratory function (forced vital capacity % predicted r = 0.53, p = 0.019; forced expiratory volume in the first second % predicted r = 0.55, p = 0.015). There were no relationships between the walking tests and measures of function, strength or HRQoL. The ESWT had a ceiling effect with 18 % reaching maximum time. No floor effects were seen in the tests. The mean +/- SD time required to perform the individual 6MWT, ISWT and ESWT was 12.8 +/- 2.5, 14.7 +/- 3.7 and 16.3 +/- 5.0 min respectively; in comparison to CPET which was 51.2 +/- 12.7 min. Only one assessor was required to perform all field walking tests and no adverse events occurred. Conclusions: The ISWT is a promising measure of functional exercise capacity in lung cancer. Findings need to be confirmed in a larger sample prior to translation into practice.