If Kirstie Alley didn't seem at her best last night when she hit the dance floor, it was because injury has been plaguing the actress all week -- but nothing was going to stop her from dancing.

"Kirstie has been practicing so hard that she pulled a muscle," an insider tells me. "It isn't a major injury, but it has taught her how important it is to listen to her body and not push herself too hard."

Earlier in the week, Kirstie admitted via Twitter that she hadn't been taking the best care of herself. "I didn't eat all day. I pulled a muscle and I wasn't as good as I want to be. Sooooo I acted like a bitch."