Something you'll see in Olympic swimming that may seem like a redundancy is swimmers wearing two swim caps. But what's the purpose?
As Yahoo! Sports wrote in 2012, one reason seems pretty obvious. The second cap helps make sure the swim goggles stay secure on top of the first cap when the swimmers dive into the pool.
The other reason is about performance. Dave Salo, an assistant coach for the 2012 U.S. Olympic Women's Team as well as a personal coach to several Olympians, said the caps are made of different materials. The first one is usually latex and the second is made of silicone.
The latex cap tends to wrinkle on the head.
"The outer silicone cap better maintains the shape and does not wrinkle as much, thereby causing less drag," Salo told Yahoo!
The Washington Post noted that Michael Phelps and Katie Ledecky are among those who have worn two caps in competition. Not all swimmers use the double-cap method, however.
Why do swimmers slap themselves before a race?
It's mainly to help the warmup process, Tomley writes. It can help increase blood flow.
Why do swimmers splash water on themselves before a race?
There are several reasons for this, Tomley writes, and it depends on the swimmer. Some might do it to decrease the shock of diving into the pool water. Some may be trying to use the water to make sure their swimsuit is tight to their skin. And for some, it may just be part of their pre-race routine.