Numerical study on the effect of sitting posture on biomechanical and biochemical signals within the lumbar intervertebral discs

Prolonged sitting is associated with lumbar intervertebral disc (IVD) degeneration and low back pain. However, the differences in biomechanical and biochemical signals within the lumbar IVD under different sitting postures remain poorly understood. The compressive forces on the lumbar IVD were calculated using a full‑body musculoskeletal model under standing, upright sitting, flexed sitting, and extended sitting. These forces were then applied as mechanical boundary conditions to a finite element model based on the multiphasic mixture theory. Water content, fluid pressure, and Von-Mises stress, as well as concentrations and metabolic rates of glucose, oxygen, and lactate within the IVD, were quantitatively analyzed under standing and three sitting postures. The water content and concentrations of glucose and oxygen decreased, while fluid pressure, Von-Mises stress, the metabolic rates of glucose, oxygen and lactate, and lactate concentration increased within the IVD after prolonged sitting compared to standing. These changes were most remarkable under flexed sitting in which fluid pressure and Von-Mises stress increased by 68.6–101.4% and 74.0–95.3%, respectively, whereas oxygen concentration decreased by 1.6–7.0% and lactate concentration increased by 2.9–4.6%. Prolonged sitting, particularly flexed sitting, was associated with posture-related changes in the modeled biomechanical and biochemical environment of the lumbar IVD, including lactate accumulation.