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 > or = 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 > or = 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.