Scientists from Michigan State University have discovered a molecular mechanism that controls the movement of sperm towards the egg. They found that the sperm use glucose as fuel and that at a certain point their metabolism is suddenly activated to a maximum level. A key role in this process is played by the enzyme aldolase, which converts sugar into the energy needed for fertilization. Other enzymes act as regulators that control the flow of this fuel in a carefully orchestrated multistep process. This discovery could lead to the development of a new form of male contraception. Understanding these molecular mechanisms opens new possibilities for the control of human fertility.