Ok... First, it's "Chief" (I before E except after C, etc, etc), and "Rhythm"...I think my crew Cheif was inferring that sternal rubs can cause some cardiac issues which I don't really understand how, unless you are doing it so hard that you knock the heart out of rythem...
Secondly - Lets talk commotio cordis. Are you familar with the term? What does it mean? What is involved in "knocking a heart out of rhythm"???