Objective Measurement of exercise capacity is essential in patients with non-specific chronic low back pain (CLBP). However, the conventional Astrand bicycle test is not feasible in patients with a very poor aerobic capacity. Therefore the Astrand bicycles test for non-specific CLBP patients based on lean body mass (LBM) was developed as an alternative. The aim of this study was to evaluate reliability and validity of the LBM-based Astrand test. Subjects Twenty patients with non-specific CLBP and 20 healthy subjects were included for the reliability evaluation, and 19 healthy subjects for the validity evaluation. Method Patients and healthy subjects were assessed twice. Intra class correlation (ICC), repeatability coefficient (RC) and the limits of agreement (LOA) were calculated as a measure of test re-tests reliability. An ICC >= 0.75 was considered acceptable. Validity was tested by calculating ICC between the LBM-based Astrand test and a maximal bicycle test. Results The LBM-based Astrand test shows good reliability, reflected by an ICC >= 0.91 and 95% of the 20 patients could perform the test. However, differences with the estimated true value reflected by the RC and natural variation reflected by the LOA were substantial in patients. Validity was good, reflected by ICC >= 0.88. Conclusion The present study shows that the LBM-based Astrand test is a reliable, valid, and feasible method for patients with non-specific CLBP. However, a substantial amount of variation should be taken into account in patients when interpreting the test results clinically.