Disclosure: I am a casual but a very passionate player who is really into badminton. I have never been to a coach, and all my skill is based on self practise by looking at YT videos. As I have dove into the technique part recently, I was a lot into the finger power causing pronation technique part of my arm, that I was solely focusing my swing in that area. Still as expected, for the reason I am about to discuss, was not able to generate that oomph or that downward angle while smashing, I just couldn’t feel or develop that downward thrust just by pronation. So one day I thought why not practise swinging while looking at myself in the mirror by having to replicate the image of pro players swing in my head and voila suddenly I could feel even my 88D OG shaft bending during the end of the swing. I couldn’t believe and practised that swing once more and again I could feel that shaft bend. Now you would think what changed? It was the racket arm’s pectoralis major (chest) getting involved, doing the internal rotation causing the downward thrust, causing even a Yonex stiff shaft to bend ( obviously because the pecs have more power than any muscle of the upper body) In most of the coaching videos present in YT everyone just focuses on the pronation aspect or having bent elbow near the ear etc so much that I never seen one mention or atleast specifically explain the internal rotation part. Also one can never even expect to learn this by looking at pro players slow motion videos as they have tshirts on ( obviously pecs flex). And just like that I always thought it is the arm and in doing that sometimes i would overuse the deltoids to generate that downward thrust. But now atleast for my swing, it has been so clear that you have to use your chest flexion and the finger pronation at the same time. So just after that I tried practising without looking in the mirror and I couldn’t feel the chest flex. But looking into the mirror and practising, I was able to do it. Hence I formed a mental image that a thread which tightens, is present between my hand and the center of my chest( the origin of Pec major), and as I am about to squeeze my fingers for pronation just before hitting shuttle, the thread tightens leading to both pronation and internal rotation of my arm. For the Anatomical part, the Pectoralis major insertion is in the ‘lateral’ lip of the bicipital groove of humerus, which proves my theory. Your comments and criticism is really appreciated as this could really help beginners get the right forehand swing, because for me the importance internal rotation>pronation, which being unknown to many, leads to casual players injuring their shoulders.
Is this different to the kinetic chain? Or just the final part of it? Leg > Hips > "trunk" / abs > Shoulder > Wrist.
Well i don't know re the pec part of what you wrote but The "shoulder rotation" or rotation at the GHJ joint(the main joint of the shoulder), can also be called humerus rotation or upper arm rotation. The head of the humerus meets the shoulder and is considered part of the shoulder that's why they call it shoulder rotation. Cos if the humerus rotates then the head of the humerus must rotate it's just one bone. And so that is activity at the GHJ joint which is a ball and socket joint. And indeed the rotation of the upper arm is possibly even more important than rotation of the forearm (what some might call the "lower arm"). That upper arm rotation is vital. It's not spoken of because usually people do it. But sometimes people focus so much on forearm rotation that they lose their throwing action and don't realise it's a throwing action and they lose the upper arm rotation. They just hear "pronation"(which is a term for forearm internal rotation). Also whatever goes on or doesn't go on, at the chest, flexion isn't the correct word. Flexion is for joints and for joints like the elbow or knee, where there is bending. (I recall a video on anatomy that remarked that the term "flexing biceps" isn't technically correct. Maybe the term doesn't even apply to muscles technically. But colloquially people talk of flexing muscles. Flexion is only a technical term and definitely wouldn't be applied to the chest). You could say you are contracting your chest muscles. One could say tensing them - at the right time. Sometimes badminton players or others in sport don't like the word "tense" for muscles cos the word is associated with muscles having tension / being tensed, when then should be relaxed. Also I have heard an idea once from a coach of fingers driving a fast forearm rotation. And some "theory" about fingers being fast twitch and forearm slow twitch and the fingers can help get it all moving. I don't know that that's anatomically correct but there might be something to it. The pec would be used in horizontal shoulder adduction , / horizontal humerus adduction.. .. pulling the humerus in.. like dumbell flys , target the pecs. It might be that the technique you are using is using the pecs a lot for some reason. But if I just do some overhead techniques in the air, I don't think I see much pec usage. And with overheads I don't hear people complain of a sore pec. Some people get a sore shoulder or if somebody hasn't played for a while then half a buttock maybe the racket side, might get sore. But i've not heard re pec soreness related to overheads which is also a question mark to your theory that pec usage is a big factor. But maybe you are somehow in your version of overhead technique. Also sometimes people get very tense and tense all muscles when they could relax some muscles. The pec is used but I think ti's early on in the swing and just for pulling the arm in.. so it's not much work for it.
