Reliability of Measurements of Endurance Time, Electromyographic Fatigue and Recovery, and Associations to Activity Limitations, in Patients with Lumbar Disc Herniation

Background. Electromyographic (EMG) spectral parameters and endurance tests for back muscles have long been used to estimate low-back muscle fatigue. Purpose. The present purpose was to evaluate the test-retest reliability of a fatigue-testing protocol and to investigate associations between activity limitations and fatigue in patients with lumbar disc herniation. Methods. To evaluate the reliability, endurance time, EMG spectral parameters and ratings of lumbar muscle fatigue and back pain were measured three times in 15 patients with lumbar disc herniation. The patients performed a modified Sorensen test with concurrent recordings of electromyography from the lumbar muscles at four recording sites. Ratings of their perceived fatigue and pain on a Borg scale were collected simultaneously. Recovery over five minutes was recorded. Questionnaires about activity, participation, self-efficacy and health were also used. Results. Endurance time had an ICC of 0.85 indicating good reliability. Initial, end and median frequency recovery had intraclass correlation coefficients (ICCs) over 0.6 that is acceptable but with large standard errors of measurement. The median frequency slopes for the four recording sites had ICCs of 0.19-0.48. Agreement coefficients for the Borg ratings ranged between 0.78 and 0.97. Moderate correlation was found between activity limitations and endurance time. Conclusions. Endurance time measurement and Borg ratings may be recommended for evaluating intervention both with groups of patients, i.e. for research purposes, and for individuals. The median frequency parameters may be recommended for groups only. The study shows the importance of establishing the reliability of the patient category if the results are to be used to evaluate intervention. Copyright (C) 2010 John Wiley & Sons, Ltd.