The Impact of Lower Back Pain on Hip Extension and Lumbosacral Lateral Flexion in Junior Gymnasts during Back-Bending

We sought to compare the spine and lower limb alignment using inertial measurement units (IMUs) in athletes with and without low back pain (LBP). Fifty junior gymnasts were divided into two groups: those with (n = 12) and without LBP (n = 38). IMU sensors were placed throughout the body. Participants were instructed to perform back-bending. The movements of shoulder, thoracolumbar, lumbosacral, hip, and knee joints were assessed. Additionally, differences between thoracolumbar and lumbosacral joints were evaluated. In the sagittal plane, lumbosacral extension was greater in the no-LBP group (37.7° ± 13.6°) than in the LBP group (24.6° ± 20.4°, p < 0.05, d = 0.85). Thoracolumbar extension was similar in the no-LBP (74.1° ± 14.4°) and LBP groups (84.5° ± 20.4°, p > 0.05, d = 0.66). The difference between thoracolumbar and lumbosacral extension was 36.4° ± 22.4° in the no-LBP group and 59.8° ± 34.2° in the LBP group, which was statistically significant (p < 0.05, d = 0.41). Hip extension was greater in the no-LBP group (10.7° ± 7.1°) than the LBP group (5.5° ± 7.6°, p < 0.05, d = 0.73). In the frontal plane, diminished lumbosacral joint lateral flexion was observed in the no-LBP group (5.8° ± 4.6°) compared to the LBP group (11.1° ± 8.3°, p < 0.05, d = 0.45). Junior gymnasts with LBP demonstrated reduced ranges of motion in hip and lumbosacral extension, along with further extension of the thoracolumbar beyond the lumbosacral joints while back-bending. Additionally, lateral flexion was observed at lumbosacral joints.