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Variable kinematics of capacitating human spermatozoa.

Human spermatozoa were prepared by swim-up from semen into in-vitro fertilization (IVF) culture medium, and their movement recorded by videomicrography using NTSC video to give 60 images/s on freeze-frame playback. Trajectories in which spermatozoa appeared to switch from one type of motility pattern to another (from non-hyperactivated to transitional or star-spin hyperactivated), were reconstructed manually and the movement characteristics determined for short consecutive sequences along each track. The spermatozoa were able to switch between all of these motility patterns, apparently at random. These observations illustrated that hyperactivated motility is a reversible state in human spermatozoa, with phase changes from hyperactivated to non-hyperactivated motility patterns along trajectories. It was not necessary for spermatozoa to pass through the transitional hyperactivated motility phase when switching from non-hyperactivated to star-spin hyperactivated motility or vice versa.