Task-specific abdominal muscle recruitment and relative activation onset during core stabilization exercises in adults with and without chronic low back pain

Background Altered motor control in chronic low back pain (CLBP) may depend on task demands, but coordinated recruitment of deep and superficial abdominal muscles across core-stabilization tasks remains unclear. Objective To compare abdominal muscle activation and relative activation onset of the transversus abdominis/internal oblique (TrA/IO) and rectus abdominis (RA) between healthy adults and adults with CLBP across core-stabilization postures. Methods Sixty adults (30 healthy controls and 30 with CLBP) performed crook-lying abdominal drawing-in, dead bug, and bird dog tasks in randomized order. Surface electromyography assessed TrA/IO and RA activation (%MVIC), the TrA/IO-to-RA activation ratio, and relative onset time. Outcomes were analyzed using two-way mixed ANOVA, Bonferroni-adjusted pairwise comparisons, and one-sample t-tests. Results Posture significantly affected TrA/IO activation (p < .001, ηp 2 = .196), RA activation (p < .001, ηp 2 = .490), and the TrA/IO-to-RA ratio (p < .001, ηp 2 = .323), but not relative onset time (p = .188, ηp 2 = .028). No significant posture-by-group interactions (all p ≥ .072, ηp 2 = .008–.044) or group main effects (all p ≥ .647, ηp 2 ≤ .004) were found. Dead bug elicited greater TrA/IO and RA activation and a lower TrA/IO-to-RA ratio than the other postures. The TrA/IO-to-RA activation ratio was significantly greater than 1 in crook lying and bird dog. Conclusion TrA/IO and RA activation and their activation ratio varied across core-stabilization tasks. No statistically significant group main effects or posture-by-group interactions were detected; these findings do not establish equivalence between healthy adults and adults with CLBP.