for people with shoulder pain while playing, get a flexible shaft + head heavy combo in 3u. If it's too head heavy you won't be able to defend with it, so go as head heavy as you can without feeling like it's too slow. If 3u is so heavy that your shoulder feel strain just from swinging it, then try a 4u.
People who get shoulder pain from badminton have one or combination of the below factors
- wrong technique
- using a racket that's too heavy for their shoulders
- using a racket that is either too headlight, too stiff, or both, and they're trying to compensate by exaggerating their swing
- using a racket that doesn't have sufficient vibration dampening
- using a string that's too hard like BG 80
- using string tension that is too high
- using a string or racket that doesn't have enough repulsion
- don't stretch shoulder muscles properly before and after playing
- have an inflexible shoulder, common for older people, or people who lift weights that have developed shoulder muscles. Stretching is even more essential for these people, they need to slowly widen the range of motion on their shoulder.
- relies too much on shoulder for power, when you should be relying more on your legs, core, forearm, and even the fingers for smashes. Shoulder should be your last resort as a source of power imo.
- This last one probably doesn't apply if you're not a pro or semi-pro, but if you over-train and over-play badminton it could cause shoulder problems, even if you're strong and have good technique
ps. If you're planning to get the most effortless badminton racket, don't forget to get the most effortless strings as well. Get a thin string with a lot of repulsion at the lowest tension you can tolerate, since it will relatively lack control with that setup.