Anton van Leeuwenhoek is often credited with designing the earliest of microscopes. With literally a new view of the world, he examined many objects including human sperm described, as you will remember from high school health, as having a "tail, which, when swimming, lashes with a snakelike movement, like eels in water." Turns out he wasn't thinking in all three dimensions.
While indeed, some sperm do have the speed and fortitude of Michael Phelps and his 23 Gold medals, a new study, published in Science Advances utilized high-speed photography and adjustments to the microscope to create three-dimensional images. It shows that van Leeuwenhoek was wrong; the sperm's tail moves only on one side. To compensate for what would result in swimming in circles, the sperm simultaneously rotate resulting in forward motion. But as the title says, a picture is far better at telling the story.