PEORIA, Ariz. -- Colin Rea looked noticeably different when he strode into Padres camp this spring. The 25-year-old right-hander had added 20 pounds of muscle, which paid immediate dividends in terms of velocity and stamina.
In short, Rea may have officially made his Major League debut last August. But physically, he made the leap from prospect to big leaguer with his work during the offseason.
"I definitely feel stronger," Rea said. "I feel like overall, I'm using less stress on my arm. I haven't been as sore after the starts as I have been in the past. So I feel like I've incorporated more, using my legs and my core, rather than all arm."
The No. 6 prospect in the Padres' system, Rea is also the most big league-ready of any pitcher on the list. He has spent the spring fighting for a rotation spot -- a battle that is ongoing. But there's little doubt Rea will be given another shot at the big leagues sometime soon.
Already this spring, Rea's fastball has gained a couple ticks in velocity. A pitch that maxed out around 93 mph last season is now routinely hitting 93-94 mph.
"That probably has something to do with being a little fresh, but also a lot to do with the 20 pounds he put on this offseason," said Padres manager Andy Green. "I think you see the guys that work their tails off in the offseason. It starts to reap dividends for them in the future. He's a guy that's constantly working, constantly improving. Don't underestimate what those guys will eventually do."
Pitching coach Darren Balsley loves the way Rea's velocity fits into his four-pitch arsenal. But more than anything else, Balsley praised Rea's mental makeup.
"He doesn't scare away," Balsley said. "He acts like he's been here, which is great. He's just really focused. He knows if he makes his pitch, he's probably going to get an out."
In Balsley's estimation, Rea possesses four pitches that are at, or above, Major League average. But Rea has spent most of the spring focusing on his four-seamer/curveball mix.
Rea made six starts last season and posted a 4.26 ERA with a 1.26 WHIP. If there's anything he learned from his brief big league stint, it's that there's a fine line between success and failure at the highest level. But that doesn't mean Rea's going to shy away from big league hitters.
"You don't want to be too fine, because then you're behind in the count and forced to throw one over the plate," Rea said. "You still want to be aggressive."
Rea was a 12th-round Draft pick of the Padres out of Indiana State University in 2011. He struggled in his first two full seasons, posting an ERA above 4.00 at Class A Fort Wayne and Class A Advanced Lake Elsinore in '12 and '13.
But Rea started finding success with Lake Elsinore in 2014 before posting a 1.95 ERA between Double-A and Triple-A last season.
"He's a late bloomer," Balsley said. "He's come a long way from when we signed him."
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.