"It's something that started creeping in the last couple outings," Ramirez said Thursday.
The rookie right-hander is on a program with athletic trainer PJ Mainville and strength coach Tim Buss that has helped.
"I've been feeling better this year than I have in the past couple years, so everything I've been doing is starting to help out," Ramirez said. "I want to finish the year strong and build up strength."
Ramirez has given up three earned runs over 28 innings in 33 games with the Cubs, striking out 36. Was he surprised when the Cubs first optioned him to Iowa?
"I appreciate the organization for trying to take care of me," Ramirez said. "I'm the kind of guy who wants to be out there every day and don't want to be babied. That's why I think the stuff I'm doing with PJ and [Buss] is getting me to where I need to be. I'm getting the issue corrected, so I can get back out there strong."
Ramirez was expected to continue his rehab in Mesa, Ariz., at the Cubs' facility rather than travel on the upcoming six-game road trip to Los Angeles and Denver.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.