Sam, you might want to try yoga, one or two classes would do to learn the basics then a book or video to try at home during those horrible grim winter days when you just don't want to go out. Its good for when you just have half an hour or so to spare and its a great help with cycling - it stretches the muscles very well and improves balance. And in case you think its a bit wussy, Lance is a big fan!

(oh, and allegedly its very very useful for sex too).