Electromyographic and Kinematic Analysis of Trunk and Limb Muscles During a Holding Task in Individuals With Chronic Low Back Pain and Healthy Controls

Background: Chronic low back pain (CLBP) affects a large proportion of the population and has been associated with different muscle dysfunctions. However, there is no consensus regarding muscle electromyography and kinematic patterns during fatiguing tasks. Objective: To examine whether trunk and limb muscle fatigability and activation patterns of individuals suffering CLBP differ from those of healthy participants during a holding task. Design: Cross-sectional study. Setting: Clinical research laboratory. Participants: Twenty-four participants with CLBP and 26 matched healthy controls. Methods: Both groups performed a static holding task, in a semisquat position, until exhaustion. The performance variable was time to failure. Electromyography signs, such as median frequency and root mean square, were used to quantify fatigability by applying linear regression to each of the 3 successive test periods. Kinematic variables were monitored throughout the holding task. Main Outcome Measurements: Independent t tests were used to compare time to failure. Electromyography-based measures of muscle fatigability were examined through a two-way, repeated-measures analysis of variance (mixed-model), whereas kinematic analysis was based on 2 multivariate analyses of variance. Results: Although the groups differed in time to failure (healthy group: mean 201.6 seconds, SD 98.9 seconds; CLBP: mean 132.4 seconds, SD 78.9 seconds; P = .009), no statistically significant differences were found in electromyography-based measures of muscle fatigability, except for the internal oblique muscle. Kinematic variables were similar in the 2 groups. Conclusion: Despite similar electromyography fatigability in the 2 groups, individuals with CLBP seem to be more sensitive to certain effects of back muscle fatigue. Significant differences in electromyography measurements in the internal oblique muscle, both between groups and across periods, suggest that individuals with CLBP trigger a subtly different activation pattern to control the spine. In a holding task, compared with healthy people, this may represent a compensatory behavior aimed at adapting to certain deficits in spine control or pain.