Lumbar muscle fatigue and subjective health measurements in patients with lumbar disc herniation 2 years after surgery

In this prospective study the purpose was to evaluate patients with lumbar-disc herniation regarding changes in back-muscle fatigue and subjective health measurements 2 years after surgery. Endurance time, EMG median frequency and ratings of lumbar-muscle fatigue and pain were measured before surgery, 4 weeks after and 2 years after surgery in 26 patients (19 men and 7 women) with lumbar-disc herniation. A modified Sorensen test was performed with concurrent recordings of electromyography from the lumbar muscles at four recording sites. The questionnaires Oswestry disability index, Roland-Morris disability questionnaire, Self-efficacy scale, SF-36, Back beliefs questionnaire, Odom and a 6-grade physical activity scale were used. Two years after surgery the patients had longer endurance times (increase from 178 s to 231 s, p < 0.001), a non-significant tendency for flatter L5 slopes (decrease from -0.20 to -0.16 Hz/s, p < 0.066), higher initial median frequency (L1 increase from 58 to 64 Hz p < 0.001, L5 increase from 76 to 84 Hz p = 0.001) and improved questionnaire scores. The questionnaires Oswestry, Roland-Morris and SF-36 physical functioning correlated with the endurance time 0.69-0.93 and with L5 slope 0.01-0.93 and the highest correlations were found in women. Both EMG and endurance time measurements are needed for evaluating fatigue in lumbar-disc herniation.