Pronation timed appropriately is extremely important especially for someone who has undergone a reconstruction. Our bodies are hardwired to move certain ways based on physiology, joint orientation, posture, neuromuscular tone, genetics, hyper or hypomobility, etc. etc. Over supination or supination maintained too late in the throwing motion is often catastrophic for throwing athletes. The only absolute in throwing mechanics is that once you start a throw you almost always end up finishing a throw. Excessive supination in the throwing motion will tell the brain that the throw needs to happen earlier which alters upper extremity sequencing, fulcruming, and positions the elbow in a less stable configuration.The most important component for a Tommy John reconstruction is to avoid excessive tensile load or direct valgus stress to the elbow in an unstable position. This can only happen if appropriate lever arm positioning deflects the valgus stress to the elbow and elbows the secondary protective mechanisms to be maximized. Often over supination too late in the throwing motion leads to poor positioning of the glenohumeral joint which limits the elbow’s ability to tolerate stress. I’ve treated hundreds of shoulder and elbow injuries that may or may not have happened because someone told them they needed to be supinated at the exact moment they needed to be pronated.