Hard to believe maybe, but good balance in the water for all four strokes begins and ends with the hips moving to orient the chest to the best balanced position possible for the body. They are the most critical components of injury prevention, long life in our sport and faster speeds. For example, take baseball players. Technically, yes, but the movement of the hips and strenght of the push of the legs are greater determiners of performane. While bat speed and 2 good eyes looking at the ball help the batter, its their hip movement and accompanying balance that creates the power of the hit, not the arms.
Swimming is the same.
Swimmers can prevent shoulder problems by concentrating on developing a balanced stroke throughout the season. If you have noticed, all practice groups are doing a lot of kicking on their sides with arms down, called head lead, or one hand uo called hand lead. This is because back and freestyle are best balanced on their side with hips rotating the swimmers from one side to the other. This is a hard concept for swimmers to incorporate because swimmers are used to swimming on their stomachs or back. But that position contributes to shoulder injury.