>>> I didn't see any mention of the muscles that keep the arms in or let the arms out. <<<
Hi Teacherman
This site defines swing mechanics by the forces acting on the bat that generates angular displacement. The muscles that apply THT and pull the lead-arm across the chest would be the same muscles an archer uses in pulling back the bowstring. � There is another site that claims other people�s work as his own by simply renaming the mechanic by the muscles and bones involved. That may be the site for you.