Fun fact: did you know that the stress of this type of motion is so great that when done repeatedly in adolescent athletes it can change the structure of their humerus (upper arm bone)? It causes an increase in the humeral retroversion angle in the throwing arm. This is considered a positive adaptation for overhead athletes, allowing more external rotation during cocking phase without soft tissue stretching. 

[ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4622383/

– Dr. Joe Combs, PT, DPT, CSCS