After battling injury problems for much of the last two years, including an elbow issue that required season-ending surgery in August, San Francisco Giants right-hander Matt Cain finally feels like his old self.

Or, rather, his younger self.

"I feel like I'm 18 again," Cain told Henry Schulman of the San Francisco Chronicle on Friday. "I feel as good as I did when I first signed with these guys."

Once considered among the top starters in the National League, Cain has stumbled since 2013, his effectiveness waning amid his struggles to stay on the mound. The 30-year-old fashioned a career-worst 4.18 ERA over 15 starts last season - his fewest since his 2005 debut - while dealing with separate finger, hamstring and elbow problems.

The former first-round pick also had surgery in September to remove bone spurs from his right ankle.

Cain's injury-riddled season was preceded by a similarly disappointing 2013 campaign. After earning three All-Star appearances in the four seasons prior, the right-hander stumbled in 2013, managing a 4.00 ERA while yielding 23 home runs over 184 1/3 innings.

"I underperformed the last couple of years," said Cain, who owns a dismal 85 ERA+ since the beginning of 2013. "I don't want to do that again."

Cain is playing catch five days a week and is scheduled to throw his second bullpen session of the offseason Friday. He expects to be close to having a normal schedule when spring training opens later this month.