Ruf is making the move from first base to left field, which means a lot more throwing. He said he felt some soreness in his biceps following throwing drills.
"It's normal," he said. "I was feeling great today and I'm back in there tomorrow."
Ruf, who is competing for a job in the outfield, is 0-for-9 this spring. He grounded out sharply to third baseman Mark Sobolewski in the eighth inning in Wednesday's 12-5 loss to the Twins at Hammond Stadium.
"I felt like I put a good swing on it. Mark just made a good play," Ruf said. "I thought we were better friends than that, but whatever. As long as I'm having good at-bats ... I'm seeing the ball well."