Test-retest reliability of psychophysical lift capacity in patients with non-specific chronic low back pain and healthy subjects

Objective: Psychophysical lift capacity tests are lifting tests in which the performance, expressed in Newtons, is divided by the perceived exertion, expressed on a Borg scale. The aim of this study was to analyse test-retest reliability of psychophysical lift capacity tests. Subjects: Patients with non-specific chronic low back pain (n=20) and healthy subjects (n=20). Methods: Psychophysical lift capacity tests were assessed during a back school intake at the Centre for Rehabilitation of the University Medical Centre Groningen. Patients on the waiting list and healthy subjects were assessed twice, with a 2-week interval between assessments. Intra-class correlation (ICC) was calculated as a measure of reliability. An ICC >= 0.75 was considered as an acceptable reliability. Limits of agreement as a measure for natural variation were calculated. Results: The psychophysical static and dynamic lift capacity tests showed good reliability (ICC >= 0.75). The limits of agreement are substantial, indicating a considerable natural variation between test-sessions for all psychophysical tests. Conclusion: The psychophysical static lift capacity and dynamic lifting capacity are reliable instruments for patients with non-specific chronic low back pain and healthy subjects. However, a substantial amount of natural variation should be taken into account between 2 test sessions when interpreting the test results clinically