The down and in shot was my "A-game" my entire life...until April, 2007, when I started suffering from a severe case of elbow tendonitis.
With the elbow problem, I lost most of what little speed I had and began changing my release to help alleviate the pain I was feeling in my elbow. All of a sudden, I was "rev" dominant and couldn't keep the ball left of the headpin when trying to play the down and in shot. I have basically had to "re-learn" how to bowl on a different line due to these changes in my physical game. And my average suffered tremendously with these changes as I wasn't able to practice bowling this "new line" due to the pain in my elbow.
When the pain began to subside in March, 2008, after almost a year of suffering, I was able to practice on this "new" line and have become a better "overall" bolwer. Now that the pain has gone away, I have the ability to play either the down and in shot or move inside with equal proficiency although I still do feel a twinge of pain from time to time in my elbow when playing the down and in shot.
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That which doesn't kill you will only make you stronger, that which doesn't make you stronger is a waste of time!