It is assumed that mechanical restriction of hamstring tightness disrupts sagittal spine–pelvis–leg alignment and alters the lumbar–pelvic rhythm predisposing to low back pain (LBP) in athletes; however, this association is not clear. A prospective cross-sectional cohort study was conducted to determine the influence of hamstring extensibility (HE) on sagittal pelvic tilt, sagittal spinal curves, and LBP in 94 soccer and basketball players (61 man and 33 woman) with (n = 36) and without recurrent LBP (n = 58). Descriptive analysis displayed significant gender differences for HE, sagittal pelvic tilt, and lumbar curve. Differences were found between the low-HE and high-HE groups in lumbosacral angle in for the maximum trunk forward flexion (LH-MTFP). Low-HE was associated with LH-MTFP, lumbar curve and LBP in male players (p ≤ 0.023). In female players, LH-MTFP and lumbar curve were associated with low-HE (p ≤ 0.020). Low-HE predicted LH-MTFP (p = 0.000; OR = 65.6950) and LBP (p = 0.028; OR = 13.915) in male players. The decision tree analysis showed that 50.8% of the players were classified with restricted LH-MTFP, 77.4% with low-HE among male players. The 100% of male players with recurrent LBP had low-HE. The 65% of female players with low-HE had restricted LH-MTFP. Measurement of HE, lumbar curve, and LH-MTFP are important in making training decisions for to reduce the incidence of recurrent LBP in soccer and basketball players.

Athletes have higher thoracic and lumbar curvature in standing than the reference values of the non-athletic population. The sagittal integral morphotype method (SIM) assessment has not previously been applied to competitive amateur athletes (CAA). The propose of the present study was to determine the SIM of CAA treated at a sports-medicine center and to identify spinal misalignments associated with recurrent low back pain (LBP). An observational analysis was developed to describe the SIM in 94 CAA. The thoracic and lumbar curvatures of the CAA were measured in standing, sitting, and trunk forward flexion. Association analysis (Pearson’s chi-square and Cramér’s V tests) was then performed to identify the SIM misalignments associated with LBP. Effect size was analyzed based on Hedges’ g. The most common thoracic SIMs in CAA were total hyperkyphosis (male = 59.02%; female = 42.42%) and static hyperkyphosis (male = 11.48%; female = 6.06%). Hyperlordotic attitude (female = 30.30%; male = 4.92%), static-functional hyperkyphosis (male = 16.39%; female = 3.03%), and structured hyperlordosis (female = 21.21%; male = 1.64%) were the most common lumbar SIMs. Hyperlordotic attitude, static functional lumbar hyperkyphosis, and structured hyperlordosis were associated with LBP in male and female athletes.