Throwing a javelin just takes technique.
There is a great step to step site on the following link on how to properly do this.
Here it is:
http://www.wikihow.com/Throw-a-Javelin
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To throw a javelin, start by picking it up with your dominant hand holding it towards the back end of the shaft. Take a few steps forward to build momentum, then push off with your back leg and transfer your weight onto your front leg as you extend your arm and release the javelin with a whipping motion. It's important to aim for a slight angle upwards to achieve maximum distance.
recommended: keep thumb within 0 to 2 inches of collarbone
bend your knees
twist your waist
then let it fly
with an explosion from the legs and arm