Originally Posted by Chas Tennis
Agree on your sources of 'power'*, the bigger, stronger and slower muscles are the sources of power. Most of that power goes elsewhere but a portion can be transmitted into the arm and racket.
The shoulder transmits more of that power to accelerate the arm and racket effectively if it is tight against the chest. But if it is not tight the transmission is not as good.
I have experimented recently and have begun to study high speed videos of pro players and believe that an important part of the 1hbh is to have the upper arm tight against the chest.
* "Power'. For tennis strokes, I understand and can measure velocities much easier than 'power', which I can't understand well or measure.
Maybe I can explain the "feeling" better. I perform my back swing by turning my core and racquet arm around toward the back. The tight arm against the chest feeling, is not because I'm squashing my arm against my chest, but because I've started uncoiling my core and my arm happens to be in the way and lagging behind...which results in my racquet arm sling-shotting into contact. I don't know all the technical wording, but that is the feeling of what torque feels like to me.