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Bobby Wahl was a highly touted relief prospect who finally made it up to Oakland last year only to have his season cut short by an arm injury that proved difficult to diagnose.

A cortisone shot worked only briefly, and Wahl’s rehab had several setbacks before he was finally diagnosed with thoracic outlet syndrome and had surgery to resolve the problem, which occurs when arteries or nerves are compressed in the area from the neck to the armpit.

Wahl feels better now than he has in years, he said Sunday at Hohokam Stadium. He was in pain for some time, without realizing he had a serious issue. Even just a few days after his Aug. 14 surgery, he felt great.

“The biggest thing is my arm isn’t as heavy in the beginning of my arm path,” Wahl said. “I don’t have to pick it up and throw it like a grenade. Everything is really nice and easy and smooth. And I can wake up now and not wonder ‘Can I throw a baseball today?’ I don’t have to convince myself.”

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Wahl made only seven relief appearances last year before he was sidelined, a frustrating development after making his big-league debut in May and seeing many of his minor-league teammates coming up to Oakland during the summer.

“You finally get where you’ve worked toward your whole life, and you don’t want to say anything about how you’ve been feeling - but you reach that point where you have to,” he said of his injury. “You win together with all these guys in the minor leagues and then start meshing together at the big-league level and not being part of that, being sidelined was tough. But it gave me that perspective, ‘I want to get back to this.’ ”

Wahl arrived at camp early this spring and his work so far has been exceptional, according to pitching coach Scott Emerson, who plants Wahl right back in the group of excellent relievers in the upper reaches of the A’s system.

“I told him these are the best bullpens you’ve thrown since you’ve been in this organization,” Emerson said. “He’s under control, his hand is getting to the spot, he’s in the lane. He said with the surgery he feels relaxed with his arm and he can put it in spots he was having trouble with. I was very encouraged - that definitely adds another guy to the mix.”

Manager Bob Melvin said it looks to him as if Wahl never even had surgery. “Shoot, we were getting him at 93-94 mph per hour in his bullpen,” Melvin said. “That’s tough to do. Obviously, he’s working hard to get back.”