Similar to Gainaxing, where a male character's pectoral muscles jiggle and bounce. However, generally it is used not so much for Fan Service as it is used as a demonstration of "manliness". Another variant is the "Ab Wave", where a character with a well defined six pack will flex their abdominal (stomach muscles) like a wave. Generally, this isn't so much saying "look how strong I am" as it is "aren't I sexy?" Compare Coy Girlish Flirt Pose (a less direct female version).