|MadSci Network: Anatomy|
This difference, which is obvious at many a beach party and picnic, might be summed up simply (I'm not a sports physiologist, so this is just a broad-strokes description) by saying that women tend to lead with their elbow and not use their shoulder much when throwing a ball. They sort of "flip" the ball by extending their arm from the elbow. The lack of shoulder rotation greatly reduces the power (and accuracy) of their throw. Most (but not all) men rotate their shoulder and snap their arm forward from the elbow joint late in the throw.
This difference in throwing style is entirely socially determined and is not at all related to anatomy.
How can I say this with such confidence?
Easy: just look at a professional female softball (or baseball) player. They throw with the same style as men, and they probably throw much harder than the average man. So throwing from the shoulder can be learned by anyone.
It probably helps to start learning this technique at a young age. Since most young boys play baseball, throw snowballs, etc., most men learn to throw this way. Until recently girls have not participated as much in these activities, and never learned how to do it. But they definitely can, so your boyfriend is right that you just need to practice.
P.S. Have your boyfriend throw with his non-dominant arm (i.e. his left arm if he's right-handed). His throw will look like "a girl's" too!
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