Motility
Unlike many other cells, sperm have a definitive life span, in other words at body temperature, they can live for only a given number of hours.
The degree of motility and livability is related to temperature.
Once semen is collected and extended, it is cooled to about 17 to 18 degrees C, this slows down the metabolic activity and motility of the cells and extends their life span. Some extenders contain certain ingredients that inhibits motility as well.
During storage, sperm cells more or less “go to sleep” (anabiosis), they require both time and a warmer temperature in order to “wake up” and regain their motility.