Contraction
Its function is to raise and lower the testes in order to regulate the temperature of the testes and promote spermatogenesis. Contraction may also occur during arousal which can prevent injury to the testicles during sex.
In a cool environment, the cremaster draws the testis closer to the body and reduces surface area, thereby reducing heat loss, while when it is warmer, the cremaster relaxes, allowing the testis to cool by increasing exposed surface area.
Contraction can also occur during moments of extreme fear, possibly to help avoid injuring the testes while dealing with a fight or flight situation.
Clinically, a reflex arc termed the cremasteric reflex can be demonstrated by lightly stroking the skin of the inner thigh downwards from the hip towards the knee. This causes the cremaster muscle on the same side to rapidly contract, raising that testicle.
The cremaster can also be contracted voluntarily, by contracting the pubococcygeus muscle (using Kegels), or by sucking in the abdomen.
Read more about this topic: Cremaster Muscle