There are a few different hitting arm positions that you can use when hitting a forehand.
Regardless of which hitting-arm position you select, that structure — the relationship between your arm and the tennis racket — gets set as you drop the racket down and begin to swing forward.
Your hitting-arm position does not change until after you have made contact with the tennis ball. This is a critically important concept to understand when learning the forehand.
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I think this is a bit of over analysis. I have played on the ITF circuit and I have never once thought in my tennis career about my “Hitting Arm Position”!