Physiologically, the human forearm arm has a natural carrying angle that places the wrist outside of the elbow. This angle is often more pronounced in females than in males.
This makes it virtually impossible to throw an underhand pitch, with the palm facing forward, and have the wrist
not be outside of the elbow.
Strange...but true!
http://njirm.pbworks.com/f/STUDY+OF+...RAT+REGION.pdf