Background: Low back pain is common among baseball players and may impair their performance and increase the risk of absence from competition. Abnormalities in the sagittal alignment of the spine and reduced trunk function have been suggested as risk factors, but evidence in collegiate players with skeletal maturity remains limited. This study investigated differences in sagittal alignment of the spine, segmental mobility, trunk flexibility, and isometric trunk muscle strength between collegiate baseball players with and without low back pain.
Methods: This cross-sectional study included collegiate baseball players recruited from our university in July 2024. Players were classified into a low back pain (LBP) group and a control group based on the presence or absence of current low back pain (numeric rating scale ≥ 3). Spinal alignment was assessed in terms of segmental alignment, thoracic kyphosis, lumbar lordosis, and sacral inclination. Spinal mobility was evaluated through segmental motion, total thoracic and lumbar ranges of motion, and changes in sacral inclination during flexion and extension. Additional measures included trunk flexion (using the standing forward bend test), trunk extension (using the prone trunk extension test), and isometric trunk muscle strength (using a handheld dynamometer). Group comparisons were performed using the Mann–Whitney U test. Additionally, logistic regression analysis was conducted to identify independent factors associated with low back pain.
Results: A total of 68 collegiate baseball players were analyzed (LBP: n = 35; Con: n = 33). The LBP group showed a significantly smaller lordosis angle at L1/2 compared with controls (–2.0° [–3.0 to − 1.0] vs. − 3.0° [–5.0 to − 1.0], p = 0.042). For segmental mobility, flexion ROM at L5/S1 was significantly greater in the LBP group (5.0° [2.0–8.0] vs. 3.0° [1.0–5.0], p = 0.030). No significant between-group differences were observed in other sagittal alignment parameters, global spinal mobility, overall trunk flexibility, or isometric trunk muscle strength (all p > 0.05). Logistic regression identified greater kyphotic alignment at L1/2 (OR = 1.263, 95% CI: 1.003–1.592, p = 0.047) and greater flexion ROM at L5/S1 (OR = 1.152, 95% CI: 1.009–1.315, p = 0.036) as independent predictors of low back pain.
Conclusion: The findings indicate that alterations at the thoracolumbar junction (L1/2) and increased flexion mobility at the lumbosacral junction (L5/S1) are independently associated with low back pain in collegiate baseball players. These findings highlight the relevance of evaluating localized sagittal spinal mechanics, particularly at the thoracolumbar and lumbosacral junctions, to better understand low back pain in collegiate baseball players.
Keywords: Baseball; Isometric trunk muscle strength; Low back pain; Segmental mobility; Spinal alignment.