BackgroundGround reaction forces are biomechanical data, providing information to investigate pathological gait. The vertical component of ground reaction force introduces the upward thrust force within gait progression. Although alterations in the vertical component in patients with spinal disorders were addressed in the literature, still the corresponding effect on spinal disorders is a major issue to scrutiny. In this study, the effects of two different anatomical spinal disorders on the vertical component pattern were investigated. MethodsTwo groups of patients with lumbar spine stenosis and lumbar intervertebral disc degeneration with lesions at L4-L5 and/or L5-S1 levels, were recruited. The vertical component of ground reaction force and spatio-temporal parameters were obtained and analyzed using one-way analysis of variance. FindingsThe results indicated that all spatio-temporal parameters differed significantly (P < 0.05) except step lengths and stride times (P > 0.05). In a similar test, the Fz2 in patients with lumbar stenosis was higher than that of those with disc degeneration (P < 0.05). Besides, the vertical ground reaction force pattern showed lower slopes in stenosis patients. InterpretationThis study showed that the vertical component of ground reaction force alterations and spatio-temporal parameters could be employed as indicators for certain spinal lesions. The results of this study could implement as an adjunct diagnostic method to help clinicians to differentiate between stenosis and disc degeneration patients and plan for their rehabilitation purposes.