Did Siddartha have a back problem?

in Week 3 Mindfulness of Emotions an online course at:http://www.insightmeditationcenter.org/books-articles/articles/introduction-to-meditation-transcripts/all/1/ Gil Fronsdal says "... the Buddha had a bad back. You wouldn’t believe it with his good posture, but he had a bad back and sometimes he couldn’t give his Dharma talk, so he’d lie down instead and have one of his senior disciples give a talk." Anyone know where he might have got this information from?