There is a fun video from "Flipping Physics" about how foot position (flat feet vs toes pointed forward) affects drag force - and hence the distance you will go at the bottom, horizontal section of a waterslide.
It is a high school level explanation, but I disagree with model he chose and wanted to get some more opinions. In the analysis of the drag force, he focuses on the changing cross-sectional area (of the feet themselves), rather than the change in drag coefficient (for the body as a whole). To my way of thinking, the cross-sectional area (of the body under the water level) would be the constant. The changing foot position would be like changing the nose of a car or changing the bow of a ship.
His model seems to more or less be treating a foot as having a mass of ~ 50 kg and estimating how those disembodied feet behave. I can see that working reasonably well, but it seems an odd perspective for explaining the effect (especially since in the video, the pointed feet are pretty much completely out of the water and all of the drag from the water would be due to the legs and torso).