Inhibiting sperm motility for male contraception: will the sperm tail be its "Achilles heel"?

Blocking sperm motility has great appeal as a male contraceptive. A drug that targets sperm motility might have a very rapid onset of action, possibly allowing for administration immediately prior to intercourse and minimizing concerns about compliance. Promising sperm motility targets include transmembrane calcium channels, a unique adenylyl cyclase, and novel flagellar proteins. Future efforts directed towards effectively antagonizing the activities of these or other such targets will be required to completely impair sperm production, function, or both and create a usable male "pill."