A decrease in sperm motility after a month of abstinence is usually considered to be a lack of sperm turnover and dead sperm, and to a lesser extent, it could also be prostatitis, for example.
Sperm is produced in the testicular area of the male and then stored inside the epididymis and vas deferens.
If the general population abstains from sex for a long period of time, it will result in the sperm being stored in the epididymis and vas deferens for a long period of time without being able to metabolize effectively. Then the life span of sperm is limited, the sperm stored in epididymis and vas deferens for a long period of time will undergo aging and dead sperm will occur, and the sperm will show abnormalities such as decreased mobility, increased malformation rate and fragmentation rate.
Prolonged abstinence in young men may induce prostatitis. The prostate gland secretes prostatic fluid to ensure the activity of sperm after ejaculation, and if it is damaged, it will cause a decrease in sperm activity after ejaculation.
There may be other reasons for the decline in sperm activity after a month of abstinence, so it is recommended that you actively seek medical attention under the guidance of a professional physician.