Cardinals starter Chris Carpenter explained that he woke up Sunday morning and felt a renewed sense of weakness in his right shoulder and that it persisted as he attempted to play catch later that day.

The lack of strength came two days after the righthander and the organization was buoyant about his pitches to hitters Friday in Kansas City.

He said it would not be wrong to see the similarity between these events -- throw well, but have trouble recovering -- and the ones in spring training that led to his prolonged absence. He has been unable to maintain the strength in the shoulder that he needs to pitch.

"I think we know why," he said. "It's because of the nerve stuff. We need to find out why it's doing it. That's what we don't know. ... It's just not strong enough to throw."