BACKGROUND: This study aimed to investigate the biomechanical effects of different interventions on astronauts lumbar intervertebral discs in a microgravity environment during spaceflight and in a gravity environment when the astronaut returns.METHODS: A finite element model of the L4L5 lumbar segment was developed with eight loading schemes representing different interventions. The loading schemes included no intervention, wearing a penguin suit, sleeping in a fetal position, wearing a penguin suit combined with sleeping in the fetal position, reclining for 4 or 16 h/d, and maintaining upright posture for 4 or 16 h/d.RESULTS: Without intervention, the microgravity environment led to increased central pore pressure, radial displacement, and water content in the lumbar intervertebral disc. Wearing a penguin suit combined with sleeping in the fetal position can reduce disc pore pressure, axial stress, radial displacement, and water content to 0.156 MPa, 11.50 kPa, 0.538 mm, and 1.390%, respectively. When astronauts return to the gravity environment, staying upright for 4 h can reduce the pore pressure, axial stress, radial displacement, and water content of the intervertebral disc to 0.222 MPa, 10.72 kPa, 0.373 mm, and 0.219%, respectively.CONCLUSION: This study showed that wearing a penguin suit and sleeping in the fetal position both have the potential to protect the lumbar intervertebral disc from the negative effects caused by microgravity. Remaining in the upright posture for 4 h per day may help squeeze out the water in the intervertebral disc safely when astronauts return to the gravity environment.Zhang S, Wang K, Zhu R, Jiang C, Niu W. Penguin suit and fetal position finite element model to prevent low back pain in spaceflight. Aerosp Med Hum Perform. 2021; 92(5):312318.