<jats:p>Patient transfer is the primary cause of lower back pain among caregivers because it requires awkward postures and movements such as twisting, lifting, and lowering with heavy external loads such as body weight. To prevent lower back pain, the relationship between lumbar loads and external loads from patient weight should be investigated to explore the hazardous limits of external loads during patient transfer. However, this investigation requires frequent trials and heavier loads than the hazardous limit. Therefore, we have used a computational musculoskeletal simulation for patient handling without the actual measured load data of human subjects. A previous study used a musculoskeletal simulation of sit-to-stand assistance motion; however, this simulation did not consider twisting and lowering patient transfer. Hence, this study aims to investigate the relationship between lumbar loads and external loads during patient transfer, including twisting and lowering. The musculoskeletal simulation for this investigation was implemented using the 3D Static Strength Prediction Program. First, the implemented musculoskeletal simulation was validated by comparison with related research using actual measured motion data and an optical motion capture system. Furthermore, the relationship between lumbar loads (compressive and shear forces of L5/S1) and external loads during patient transfer was investigated using a validated musculoskeletal simulation. According to the results, the compressive and shear forces of L5/S1 during patient transfer exceeded the limits of safety when the external load was more than 40 kgf. These findings will contribute to the prevention of lower back pain due to patient transfer.</jats:p>