I'm a beginner level but I have a favor to ask. Is it still necessary to do pronation on forearm during overhead smash before impact the shuttle when using LJB/panhandle grip/kwun's grip which is not standard classical forehand grip? If my understanding is right, forearm pronation is similar to turn on the car key(turn on by counter clockwise) therefore the thumb is tend to point down and pronation is used in order to make racquet face perpendicular to target direction while hit the bird, moreover, it is making the racquet arm straighten. If we employ some grip that make racquet face perpendicular to target direction we do not need to do pronation, right?
That's not quite the right way to think about it. You need pronation in your smash action, because pronation generates lots of power. If you don't pronate, your smashes will be weak. Therefore, do not choose a grip that prevents pronation (eg. panhandle). The idea of the LJB grip is to make the racket face square on impact following a good stroke with pronation. It is only a slight move towards panhandle.
Well, it could do. Any motion, if performed violently and inaccurately, could cause a strain injury. Remember that you get more power by staying relaxed. Powerful pronation comes from a relaxed, fluid "throwing" swing. Trying to use tense muscles to power the stroke will be ineffective and may cause injury over time.
