Trunk dynamics are impaired in ballet dancers with back pain but improve with imagery

Purpose: Trunk control is essential in ballet and may be compromised in dancers with a history low back pain (LBP) by associated changes in motor control. This study aimed to compare trunk mechanical properties between professional ballet dancers with and without a history of LBP. As a secondary aim we assessed whether asking dancers to use motor imagery to respond in a "fluid" manner could change the mechanical properties of the trunk, and whether this was possible for both groups. Methods: Trunk mechanical properties of stiffness and damping were estimated with a linear second order system, from trunk movement in response to perturbations, in professional ballet dancers with (n=22) and without (n=8) a history of LBP. The second order model adequately described trunk movement in response to the perturbations. Trials were performed with and without motor imagery to respond in a "fluid" manner to the perturbation. Results: Dancers with a history of LBP had lower damping than dancers without LBP during the standard condition (P=0.002) but had greater damping during the "fluid" condition (P0.99). Stiffness was not different between dancers with and without a history of LBP (P=0.252) but was less during the "fluid" condition than the standard condition (