Changes in the external temperature stimulate the cremaster muscle to contract or relax, thereby moving the testes closer to or further from the body cavity. When exposed to cold temperatures, such as swimming in cold water, the cremaster muscle contracts, bringing the testes closer to the body to keep them warm. When temperatures are warm, the cremaster muscle relaxes, moving the testes farther away from the body so excess heat is lost via the increased surface area of the scrotum.