Pain behind the buttocks after lifting heavy objects may be caused by muscle strain, lumbar muscle strain, lumbar disc herniation and other diseases. 1. Muscle strain: Muscle strain may be caused by overstretching of muscle fibers due to heavy lifting and excessive muscle tension. Patients will experience localized muscle soreness, swelling, muscle weakness and other symptoms, manifested as pain behind the buttocks after lifting heavy objects. 2. Lumbar muscle strain: Lumbar muscle strain may be caused by long-term weight bearing, overwork, improper posture and other factors. Patients mainly manifest recurrent lumbar pain, which may radiate to the buttocks and manifest as pain behind the buttocks after lifting heavy objects. 3. Lumbar disc herniation: Lumbar disc herniation may be caused by injury, heredity, lumbar spine developmental abnormality, disc degeneration and other factors. Patients will have lumbar pain, sciatica and other symptoms, and when after lifting heavy objects, the pain in the back of the buttocks worsens. There are many reasons that cause patients to experience pain in the back of the buttocks after lifting heavy objects, and it is recommended that patients go to a regular hospital to find out the cause of the disease.