SURPRISE, Ariz. -- These days, you can't keep a smile off Kyle Zimmer 's face.

"It feels like I've been given a new life," Zimmer told MLB.com as he walked off the field at the Royals' instructional league camp on Wednesday.

Royals fans know Zimmer's story well: The right-hander was the team's first-round pick in 2012, but his career has been derailed by a seemingly never-ending series of arm and shoulder injuries. Zimmer last pitched in the Minor Leagues in 2017.

But last spring, Royals assistant general manager J.J. Picollo suggested Zimmer try the revolutionary Driveline Baseball training program in Seattle that focuses on weighted baseballs to strengthen muscles and improve mechanics.

Zimmer, 27, knew it was likely his last chance. He was all in, and now he reports he is pain-free throwing a baseball, perhaps for the first time since he was drafted.

"J.J. brought it up, and I was on board immediately," Zimmer said. "We just had to break the cycle and try something new. I kept breaking down every year, and that was through no fault of the Royals. It was just me."

As a procedural move, Zimmer was designated for assignment to remove him from the 40-man roster because, by design, he was going to miss the entire season. He then immediately re-signed with the Royals and arrived in Seattle at the Driveline Baseball facility on May 4. He left there Tuesday and came straight to Arizona.

<p< at="" day="" driveline.="" first="" forget="" his="" never="" will="" zimmer=""> "I couldn't even make it through the first few hours," he said. "I was hurting that bad." </p<>

But before long, Zimmer was enduring the grueling daily regimen, and, to his surprise, progressing.

"It was a long stretch before I felt good," Zimmer said. "A lot of hard work. The core of the program is based around weighted baseball training, but it's kind of all-encompassing: strengthening, weight training, agility. ... It's basically starting over from scratch. I needed that."

Indians right-hander Trevor Bauer is generally recognized as the biggest name to champion Driveline's strategy.

"Trevor was one of the first guys to really have success with it, and that's obvious now," Zimmer said. "But a lot of pro guys are going there now. At least one guy from every team.

"It's not for everyone, because as they say, 'If it's not broke, don't fix it'. But for me, I just needed to jumpstart something. It was one-on-one training, five or six hours a day, every day for six months. You leave dripping sweat every day. It's remapping everything mechanically, just rebuilding from the ground up."

The first tangible breakthrough came in late August, when Zimmer fired a baseball over 100 mph.

"That was with some pull-downs and step-behinds and throwing into a net," Zimmer said, grinning. "But yeah, it felt great. It felt great just to get my body moving like that again. To be that athletic again throwing a baseball, that was the most exciting thing."

And over the last month, Zimmer has returned to throwing off the mound.

"I've been throwing three or four times a week off the mound for about three weeks," Zimmer said. "I'm having no issues at all. It's really crazy, because in the past, if I threw one time off the mound, I'd be blown up for days. Now, it's no soreness at all. No pain. None."

And his present velocity?

"I've been at 93-94 [mph] off the mound and still building," he said. "I have a lot of time until Spring Training. Just to be comfortable again while throwing is pretty exciting. I'm throwing all my pitches, too."

The next step is to finish the instructional league in Surprise, Ariz., next week, then he'll resume his normal maintenance training until Spring Training.

Zimmer said he can look back now and think about how close he came to packing it in.

"I would never quit, because I'm too stubborn," he said, "But every single day for five years it was like, 'How do I keep going? Why?' I just spent so much time down here [in Surprise] alone, trying to recover. Days turned into weeks, weeks into months. I'd be lying if I said I wasn't considering [quitting].

"But I just have to thank the Royals. I don't think any team has given someone so many chances. I'm grateful."

Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB.