In three weeks, Charlie Morton plans to begin throwing bullpen sessions.

His current task: To ensure he has solid mechanics when he gets there.

Morton, who is rehabilitating from Tommy John ligament replacement surgery in June, has progressed to throwing from 120 feet off flat ground. Morton now throws four days a week, the idea being to correct any mechanical imbalances that may have contributed to the ligament damage in the first place before he returns to the mound.

"It really gives you an opportunity to be coached at the same time," Morton said Wednesday at a Pirates voluntary minicamp at their spring training facility. "It gives you a chance to adjust mechanics and adjust mentality, not just throwing to get back to throwing the way you were."

Morton has not thrown anything other than fastballs. Adjusting mechanics on flat ground, he said, removes the various distractions related to throwing a pitch.

"There's no strike zone," Morton said. "There's no radar gun, there's no catcher, there's no one standing in the box. There's no defense behind you. It's the purest form of throwing the baseball."

Morton labors under the watchful eye of special assistant to the general manager Jim Benedict, who instructs Morton to bring his hand higher, earlier in the delivery, so it doesn't drag behind the body. When the hand lags behind the body, it creates extra stress on the ulnar collateral ligament, the ligament that required surgery.

"Your arm is literally behind where it should be, and that's something that [Benedict] and I have been working on, is getting that hand up and out," Morton said.

Film study of throws where Morton's arm stays in sync with his body complements instant feedback from Benedict, who informs Morton when he was on time and when he was late.

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