Clinically, in semen examination, spermatozoa are categorized into four grades: a, b, c and d according to their motility and activity characteristics. Grade a indicates excellent sperm motility and activity characterized by fast straight forward movement; grade b refers to slow or curved forward movement, grade c refers to non-forward movement such as spinning in place, and grade d refers to completely immobile sperm. Weak spermatozoa can be categorized into three degrees based on the percentage of sperm in these four grades. Mild is when the sum of grade a and b sperm is higher than 30% and lower than 50% or grade a sperm is higher than 10% and lower than 25%; moderate is when the sum of grade a and b sperm is higher than 30% and lower than 50%, with grade a sperm lower than 10%; and severe is when the sum of grade b and c sperm is lower than 30%, with grade a sperm being zero. Patients who are not feeling well need to consult a doctor for examination and early treatment.