Impact of 8-Week Pilates Program on Lumbar Flexion–Relaxation Dynamics and Functional Outcomes in Women with Chronic Low Back Pain

Objectives: While Pilates exercise is commonly prescribed for chronic low back pain (CLBP), its effect on normalizing the lumbar flexion–relaxation ratio (FRR) remains unclear. This trial examined whether an 8-week Pilates exercise program (PEP) modifies FRR magnitude and side-to-side asymmetry in women with CLBP and explored associations with trunk kinematics, pain, and functional capacity. Methods: In a randomized controlled pre-test–post-test training design, ninety-six women with CLBP (55.8 ± 5.4 y) were allocated to a PEP group (n = 49) or a usual-care control group (n = 47). The PEP included two supervised 60-minute mat sessions per week over eight weeks. Surface electromyography of the right and left erector spinae and trunk flexion range of motion (TFRoM), measured via inertial sensors, were recorded during the standardized flexion–extension task pre- and post-intervention. Pain intensity (Visual Analog Scale) and functional capacity (Low Back Outcome Score, LBOS) were assessed concurrently. Results: Two-way repeated-measures ANOVA revealed no group × time interaction for global FRR (p = 0.454) or TFRoM (p = 0.745). FRR asymmetry increased by 11% in the PEP group (p = 0.033), with no change observed in the controls (p = 0.143). Compared to the controls, the PEP group exhibited a 30% reduction in pain (p = 0.003) and a 13.4% improvement in LBOS (p 0.228). Conclusions: An 8-week Pilates intervention reduces pain and improves functional capacity in women with CLBP but does not restore lumbar extensor relaxation. The observed increase in FRR asymmetry may reflect compensatory or maladaptive redistribution.