Kinematics of human spermatozoa incubated under capacitating conditions.

Suspensions of seminal plasma-free human spermatozoa were prepared by swim-up from semen and studied using high magnification videomicrography after incubation under capacitating conditions for 1.5-2 h. Three subpopulations of capacitating spermatozoa showing different patterns of motility could be distinguished visually: forward progressive, transition phase, and hyperactivated motility. The purpose of this study was not to determine the relative proportions of spermatozoa in these three categories but to describe their movement characteristics. Manual track plotting and analysis allowed value derivation for the curvilinear, average path and straight-line velocities (VCL, VAP, and VSL respectively); for the three progression ratios of linearity (LIN = VSL divided by VCL X 100), straightness (STR = VSL divided by VAP X 100), and wobble (WOB = VAP divided by VCL X 100); and also for the amplitude of lateral head displacement (ALH) and the beat/cross frequency (BCF). Algorithms produced from these motion characteristics allowed distinctions to be made between cell motility patterns. Spermatozoa with straight-line velocity (VSL) greater than or equal to 40 microns/s, linearity (LIN) greater than or equal to 60% and amplitude of lateral head displacement (ALH) less than 5 microns were FP or non-hyperactivated. Tracks with curvilinear velocity (VCL) greater than or equal to 100 microns/s, linearity (LIN) less than 60% and amplitude of lateral head displacement (ALH) greater than or equal to 5 microns showed concomitants of hyperactivation. Classical hyperactivated tracks also showed straightness (STR) less than 60% and straight-line velocity (VSL) less than 30 microns/s.