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

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 one-way 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.