Sci will admit that the sperm paper she picked for this week really is an excuse to use this image:
But really, sperm swimming is an important questions in terms of fertility. An ovum is only viable for about 24 hours, and a female only produces one per month. Sperm are viable for a little longer than that, but still, timing is rough. And once you get past the timing, you get into sperm getting lost, sperm swimming in circles, sperm getting stuck in the vaginal mucosa, and sperm getting to the egg only to be thwarted by the zona pellucida and corona radiata (the corona radiata is a group of cells surrounding the egg, while the zona pellucida is a tough, thick protein lattice on the outside of the egg, inside the corona radiata. Tough barriers).
So when it comes down to it, it takes more than a straight swimmer to make it to the egg. But what, exactly, does it take?
Force, et al. “Membrane fluidity and lipid content of human spermatozoa selected by swim-up method”. International Journal of Andrology, 2001.