A man’s back pain after ejaculation may refer to back pain after ejaculation, which may be related to lumbar muscle strain, inflammation of the vas deferens and prostate infection. 1. Lumbar muscle strain: Lumbar muscle strain caused by frequent sexual intercourse, prolonged heavy physical labor or excessive exercise can cause a man to experience pain when ejaculating due to pulling the muscles of the lower back. 2. Inflammation of the vas deferens: When a man ejaculates, the sperm needs to be discharged through the vas deferens, which stimulates the inflammation of the vas deferens, causing localized pain, which may radiate to the lower back when the pain is severe. 3. Prostate infection: If a man’s prostate is infected by viruses, bacteria and other pathogens, the prostate gland needs to be congested and swollen during ejaculation, which may cause dysfunction of the periprostatic nervous system, which may lead to low back pain when it involves the nerves distributed in the lower back. If a man has back pain after ejaculation, he should go to the hospital in time to check the cause, so as not to delay the condition.