By age 10 years a general guide is that most children will master the adult forms of running, catching and throwing. The skill patterns may or may not be refined during adolescence and will depend on many things including practice, instruction and time invested in improving movements as they move towards adulthood.
In order to perform a movement as effectively as possible, muscles produce moments of force of the chosen skill in the desired direction. The nervous system tends to figure out the most efficient action based on what it has to work with.
Coaches make the movement more efficient and strength coaches try to augment the skill by adding more muscular tissue to produce more power.
When throwing, athletes tend to move their arm in parallel with the line of the shoulder. It doesn’t matter whether it is a baseball, football, basketball, javelin or hitting a tennis ball, body position effects torque and even untrained 10 year old athletes assume a similar line preferring to bend at the trunk rather than moving the arm above the shoulder.
The good news is if there are specific exercises for throwing they are specific for all throwing motions. Tends to make strength training rather simple. Just Get Strong.
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