Movement of the lumbar spine is critical for maintenance of postural recovery following support surface perturbation

Repeated measures design. This study examined recovery of postural equilibrium (centre of pressure (COP) excursion, time to recover balance, and the number of postural adjustments) following unexpected support surface perturbation in healthy participants with and without a rigid lumbar corset to reduce lumbar motion. Lumbar spine movement is thought to aid postural stability, especially when a "hip" (lumbopelvic) strategy is required, such as in response to large and fast perturbations. Delayed onset of lumbar spine movement in association with prolonged postural recovery in chronic low back pain implies reduced spinal motion could underpin balance deficits in this group. However, other explanations such as poor proprioception cannot be excluded, and the relationship between lumbar movement and postural stability remains unclear. We hypothesized restricted lumbar spine movement would impair control of postural recovery following support surface perturbation. Participants regained postural stability following unexpected support surface perturbations in different directions (forward and backward), with different amplitudes (small, medium, and large), with and without restriction of spine motion by a hard lumbar corset. Although the latency of the postural adjustment was unaffected by the corset, the quality of postural recovery was compromised (increased COP range, time taken for postural recovery, and number of postural adjustments) during recovery, especially in response to large perturbation. Restriction of lumbar spine movement adversely affects postural recovery. The results suggest movement of the lumbar spine, although small in amplitude, is critical for efficient recovery of standing balance.