Testing lifting capacity: validity of determining effort level by means of observation

Study Design. Video observation study. Objectives. To establish the validity of determining effort level by visual observation of a lifting test. Summary of Background Data. Determining effort level during a lifting test is critical for interpretation of test performance, yet the validity of these determinations has not been established in patients with chronic nonspecific low back pain. Methods. Fifteen healthy subjects and 16 patients with chronic nonspecific low back pain performed a standardized lifting test as outlined in the Isernhagen Work System Functional Capacity Evaluation. The lifts were videotaped and independently observed by 9 trained observers, who rated effort levels using an Isernhagen Work System categorical scale (Appendix 1) and a Borg Category Ratio scale (Appendix 2). External effort indexes were established to control for effort at group level. Validity of the observer ratings was analyzed by means of a sensitivity and specificity analysis and correlations between performances and observer ratings. Interrater reliability was analyzed by means of intraclass correlation coefficients and Cohen kappa. Results. External indexes differ significantly between patients with chronic low back pain and healthy subjects, indicating that at group level, patients did not perform maximally. Submaximal performances were correctly rated in 85% to 90% (healthy subjects) and in 100% (patients with chronic nonspecific low back pain) of the cases. "Maximal" performances were correctly rated in 46% to 53% (healthy subjects) and in 5% to 7% (patients with chronic nonspecific low back pain) of the cases. Correlations between performances and observer ratings were r=0.90 to r=0.92 (healthy subjects) and r=0.82 (patients with chronic nonspecific low back pain). Reliability: intraclass correlation coefficient, r=0.76 (patients with chronic nonspecific low back pain) to r=0.87 (healthy), Kappa K=0.50 (patients with chronic nonspecific low back pain) to r=0.58 (healthy subjects). Conclusions. Effort level can be determined validly by means of visual observation