Lumbar muscle fatigue : Analysis of electromyography, endurance time and subjective factors in patients with lumbar disc herniation and healthy subjects

The overall aim of the thesis was to investigate the relation between objectively and subjectively assessed lumbar muscle fatigue and subjective factors in patients with lumbar disc herniation and in healthy subjects. Eighty healthy subjects and 43 patients undergoing surgery for lumbar disc herniation and selected consecutively for the study participated. Muscle fatigue in the lower back was assessed during a modified Sorensen test, an isometric prone holding test for the back extensors against gravity and until exhaustion, or a staircase protocol (20%, 40%, 60%, and 80% of maximum voluntary contraction). Concomitantly, EMG was detected from the lumbar extensor muscles and subjects rated their perceived fatigue - and the patients also their pain - on a Borg CR- 10 scale. Recovery was assessed after the modified Sorensen test during 5-second contractions at 1-5 minutes of recovery then examined using an exponential time dependence model. To measure activity, participation, self-efficacy and health, the patients also filled in questionnaires. The reliability of the modified Sorensen test was also assessed. The modified Sorensen test with concomitant measures of EMG provided useful reliability (ICC>0.60) for evaluation purposes. Borg scale ratings correlated highly (r>0.7) with endurance time. The EMG median frequency slopes correlated low-to-moderately (r