So the upper arm stability, that you see with Harimoto and other pro players is very important. Really what it means is that the shoulder and upper arm is just used to keep the shot consistent by not moving around or getting involved in the technique. It stays still and out in a pretty much fixed position and the shot is generated using the elbow, lower arm and wrist. So as shown in the video this means the shot can be very short and snappy which is how Harimoto manages to have such a fast recovery. I hope this makes sense and let me know if you want some more information on this.
Answer for upper-arm-stability-backhand-loop
