I was told Tbombz does a lot of those.
used to do something very similar for wrestling.
im almost positive the guy he saw doing those was a wrestler.
during every wrestling practice for every wrestling team anywwhere you will find the team warming up before training by doing "bridges", among other things.
this video demonstrates the exercise
and heres a clip of the practical application
the exercise in the drawing above would be useful for strengthening the muscles involved