Objective and quantitative assessment of sperm quality is important for human infertility as well as for animal husbandry. Several techniques, including subjectively scoring sperm based on speed of progression and quantitatively measuring sperm motility parameters, are currently used to assess sperm. Optical tweezers provide a non-invasive way to study sperm motility by measuring sperm swimming forces. The minimum amount of laser power needed to hold the sperm in the trap (or the threshold escape power) is directly proportional to the sperm's swimming force (F = Q * P/c, where F is the swimming force, P is the laser power, c is the speed of light in the medium, and Q is the geometrically determined trapping efficiency parameter).

The purpose of this dissertation is to first develop an objective and quantitative method to analyze sperm motility based on sperm swimming force. A custom system is developed to track, trap, and fluorescently image sperm, measuring sperm swimming speed, swimming force and mitochondrial membrane potential in real-time. This system is then used to study sperm. Specifically, the effects of trap duration and laser trapping power on sperm motility are determined, the relationships between sperm swimming force and swimming speed for various mammalian species are defined, both the effects of cryopreservation and sperm competition in primate species on motility are studied, and finally the relationship between sperm motility (swimming force and swimming speed) and energy production is analyzed.