Patterns in anticipatory postural adjustment onset timing across multiple trunk muscles: Psychological correlates and participant clustering along the low back pain continuum

Abstract

Background: Feedforward activation of trunk muscles is crucial for spinal control and can be quantified by assessing anticipatory postural adjustments (APA). Few studies have examined time-dependent changes in APA onset times across the low back pain (LBP) continuum and their association with psychological factors. Objectives: 1) Investigate variations in APA onset times along the LBP continuum; 2) identify participant clusters based on APA onset timing patterns across trunk muscles; 3) compare these clusters on psychological factors. Method: This cross-sectional study assessed APA onset times of trunk muscles using surface electromyography in 30 pain-free, 20 recurrent LBP (in remission), and 28 chronic LBP participants. Fear of movement, pain vigilance/awareness, and pain-related worry were evaluated using self-reported measures. Mixed linear models compared APA onset times between groups, while K-means clustering identified participant subgroups with similar APA onset timing patterns. Between-cluster differences in psychological factors were analyzed using oneway ANOVAs and Kruskal-Wallis tests. Results: No significant group-by-muscle interaction was found (p = 0.362), nor between-group differences in APA onset timing (p = 0.832). Cluster analysis identified three subgroups, independent of LBP-status, characterized by a pattern of early, similar, or delayed APA onsets across trunk muscles. Pain vigilance/awareness scores differed between clusters (p = 0.029), with highest scores in the delayed APA cluster, while differences in other psychological factors were nonsignificant despite moderate/large effect sizes. Conclusions: APA onset times did not progressively differ along the LBP-continuum. A pattern of delayed APA onset timing across trunk muscles was associated with higher levels of pain vigilance/awareness.