RESUMEN
BACKGROUND: Changes in trunk and hip muscles are believed to be important in subjects with nonspecific chronic low back pain (NSCLBP), but little is known about specific changes, or how they might be affected by core stabilization exercises. The aim of this study was to compare six key muscles before and after these exercises. METHODS: Thirty two NSCLBP patients were assigned randomly into two groups: exercise (n = 17) and control (n = 15). On 5 days per week for 4 weeks, the Exercise group performed 16 core stabilization exercises and the Control group received transcutaneous electrical nerve stimulation and a 'hot-pack'. Surface electromyography (EMG) was used to assess maximum bilateral activity of transversus abdominis (TrA), multifidus (MF) and gluteus maximus (Gmax) muscles. Ultrasound imaging was used to measure the rest and contracted thickness of these muscles. Pain and disability were assessed using a visual analogue scale (VAS) and the Oswestry Disability Index. RESULTS: When left and right-side muscle data were combined, two-way ANOVAs showed a nonsignificant interaction effect for all dependent variables (P > 0.05), significant time effects on resting muscle thickness for TrA (P = 0.01), MF (P = 0.041) and Gmax (P = 0.003), EMG signals of TrA (P = 0.038), pain and disability (P = 0.000). There were a significant group effect on contracted thickness for TrA (P = 0.032) and Gmax (P = 0.026) and disability (P = 0.017). CONCLUSIONS: Core stabilization exercises increased contracted thickness of TrA and Gmax muscles and decreased disability in subjects with NSCLBP.