Maintaining lumbar spine stability: A study of the specific and combined effects of abdominal activation and lumbosacral orthosis on lumbar intrinsic stiffness

BACKGROUND: Two potential interventions for enhancing lumbar stability are to actively increase abdominal muscle activity, either through the abdominal drawing-in maneuver (ADIM) or bracing, and passively increase lumbar stiffness using a lumbosacral orthosis (LSO). OBJECTIVE: To compare the increase in lumbar stiffness after 2 active interventions (ADIM versus bracing) and 1 passive intervention (LSO), and to evaluate the combined effect of active (abdominal bracing) and passive interventions. METHODS: In this experimental and comparative study, lumbar stiffness, a surrogate measure of lumbar stability, was estimated in 25 healthy individuals during 7 trunk perturbation conditions: (1) control, (2) ADIM, (3) bracing at 5% of right external oblique maximal voluntary activation (5% bracing), (4) bracing at 10% of right external oblique maximal voluntary activation (10% bracing), (5) LSO, (6) LSO plus 5% bracing, and (7) LSO plus 10% bracing. Electromyographic biofeedback of the external oblique was provided on a monitor, while ultrasound was used for the ADIM to ensure a sustained contraction of the transversus abdominis. RESULTS: The ADIM, 5% bracing, and 10% bracing active interventions generated comparable lumbar stiffness. However, considering that bracing can range from 10% to 20%, it may be superior to hollowing, as further estimated with a mixed-effect statistical model. Combining bracing and an LSO resulted in an additive effect on lumbar stiffness. CONCLUSION: Bracing and ADIM produced comparable lumbar stiffness, as they were performed at the same overall abdominal activation levels (5% and 10% maximal voluntary activation). The independent effects of bracing and LSO raises the possibility of combining these interventions in some circumstances.