Abstract

Background: Hamstring Strain Injuries (HSI) and Low Back Pain (LBP) are prevalent musculoskeletal disorders in athletes with high recurrence rates. However, the biomechanical interaction of concurrent HSI and LBP on lower-limb loading under unpredictable conditions remains insufficiently understood. The objective of this study was to compare ground reaction force (GRF) components—vertical, shear, and free moment—between athletes with concurrent hamstring–lumbar injury and healthy controls during an unanticipated side-step cutting maneuver.

Methods: In this cross-sectional comparative study, 40 male athletes (20 with concurrent HSI and non-specific chronic LBP and 20 healthy matched controls) performed unanticipated cutting maneuvers on a force plate at a controlled speed of ~4 m/s. Peak medial-lateral shear force (Fx), vertical impact force (Fz-Impact), active vertical force, and free moment (Tz) were extracted and normalized. Independent t-tests and Hedges’ g effect sizes were calculated.

Findings: The injured group demonstrated significantly greater Fx at heel contact (P=0.001; g=1.53) and vertical impact force (P=0.004; g=0.98) in the involved limb. Significant differences with medium-to-large effect sizes were also observed for active vertical force (P=0.030; g=0.71) and minimum free moment (P=0.038; g=0.68). No significant between-group differences were found for the healthy limb.

Conclusion: Athletes with concurrent HSI and NCLBP exhibit impaired attenuation of shear and vertical forces during unanticipated tasks. The large effect sizes suggest a stiff landing strategy associated with deficient proximal neuromuscular control within the kinetic chain. Rehabilitation programs should emphasize force absorption strategies under neurocognitive demand to reduce re-injury risk.