Differences in segmental trunk motion during back extension and rotation in gymnasts with a history of low back pain

This study investigated movement onset time and maximal range of motion (ROM) of thoracolumbar, lumbosacral, and hip joints during forward bending, backward bending, lateral bending, and trunk rotation among gymnasts with and without low back pain (LBP). Thirty-three junior gymnasts (9 males, 24 females) were divided into an LBP group (n = 9) with extension-related LBP in the past 3 months and a no-LBP group (n = 24) without LBP for at least 12 months. Eighteen inertial sensors were used to measure three-dimensional joint kinematics at 100 Hz. Onset time and maximal ROM of thoracolumbar, lumbosacral, and hip joints were analysed. In extension and rotation, the LBP group showed no significant differences in onset time between segments, suggesting less clearly differentiated intersegmental onset timing. The no-LBP group demonstrated distinct timing, with thoracolumbar segments initiating movements earlier. The LBP group showed smaller hip extension and thoracolumbar rotation angles and greater lumbosacral rotation than the non-LBP group. These kinematic characteristics were associated with altered segmental movement patterns during back extension and rotation. Earlier thoracolumbar initiation and greater hip and thoracolumbar mobility were observed in gymnasts without LBP, which has implications for movement assessment.