Sperm motility is a feature that reflects the ejaculate viability, regarding to the amount of cells in movement into a sample, taking into account that there are always some spermatozoa that do not move at the time of evaluation but however they are alive.

Motility evaluation is usually made visually by an optic microscope or automatically by a device that analyzes series of images taken from the sample and it calculates   motility percentage and also several parameters that define sperm motion.

Visual evaluation consists on the estimation of the percentage of spermatozoa that move and the valuation of the type of movement with 0 (without motion), 1 (motion without advance), 2 and 3 (circular motion making small or wide circles respectively), 4 and 5 (progressive motion with slow or fast velocity respectively).

In order to correctly evaluate the results it is necessary to take into account that the  sperm motility expression depends on sample temperature that must be 37ºC. in can be reached by means of a heating plate where we place a drop from the semen sample and also the slides and the cover glasses. A big drop of semen is placed directly on the heating plate at 37ºC and in a few seconds a little drop from this warmed sample is placed between the slide and the cover glass to be observed in bright field at 200X.  evaluation must be fast before the sample becomes cool, if you we don not count with a heating plate incorporated into the microscope. At least 5 or 6 fields must be evaluated.

Semen samples previously  at 15ºC may need an additional stimulus in order to fully express its real motility. To minimize this percentage of viable but immotile spermatozoa for a lack of stimulus, a solution of caffeine is used (0.4 g caffeine, 2.9 g sodium citrate in 100 ml distilled water). A drop of this solution is mixed in the heating plate with the semen drop before its evaluation. With this technique we can distinguish the samples with a real low motility from the ones a lack of stimulus.