Sperm activation has been shown to be caused by calcium ionophores in vitro, progesterone[2] released by nearby cumulus cells and binding to ZP3 of the zona pellucida.
The whip-like tail (flagellum) of the sperm is studded with ion channels formed by proteins called CatSper.
The sudden rise in calcium levels causes the flagellum to form deeper bends, propelling the sperm more forcefully through the viscous environment.
This response suggests that hyperactivation serves as method to quickly guide sperm through chemo-attractant gradient.
[4] Before reaching the egg, the sperm are often trapped in epithelial cells in a fallopian tube, meaning they are rendered inert unless they undergo hyperactivation.