The Self-Efficacy Scale (SES) has been found to predict isokinetic performance better than anthropometric variables. This study tests the predictive power of SES further against other measures of efficacy expectancies as well as measures of depression and perceived disability. A group of 105 chronic back pain patients was administered Beck's Depression Inventory (BDI), SES, the Pain Self-Efficacy Questionnaire (PSEQ), and the Oswestry low back pain disability questionnaire (OSWESTRY). Total isokinetic work done was measured at slow, medium and high speeds, for which multiple regression models were fitted controlling for sex, age, weight and height. The results confirmed SES to be the best overall predictor of isokinetic performance. BDI was not significant as a predictor of isokinetic performance. The models also revealed that SES predicts less well with increases in the test speed, particularly in extension. These results provide further evidence of the diagnostic value of SES relative to OSWESTRY and PSEQ.