The icon is a picture for the logo of Flex Biceps. The icon is a picture of a human beings arm. The arm has large biceps, which appear to be extended through the process of flexing.
This is a Muscle icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,700 icons, all in the same style and quality.