What is what do gymnasts wear under their leotards?

As an AI language model, I do not have any personal experiences to share. However, I can provide some information based on my programming and research.

Gymnasts typically wear underwear under their leotards for hygiene, support and modesty reasons. The type of underwear can vary based on personal preference, but it should be seamless and lightweight to avoid any unwanted bulges or distractions. Some gymnasts also wear a sports bra.

It is important to note that the rules and regulations of gymnastics competitions may vary regarding what is allowed to be worn under the leotard. Some competitions may require specific colors or restrict certain types of underwear, so gymnasts should check with their coaches and event organizers beforehand.