There's an anecdote in the book Body by Science that illustrates that our concept of "cardiovascular fitness" may be flawed. That is, it suggests that running may make you a better runner (or spinning may make you a better spinner), but it doesn't improve your CV fitness in a general sense. I know I've seen that running doesn't improve my cycling much and vice versa, which suggest they aren't improving my CV fitness in general.

Anyway, the anecdote is that a company has an annual fitness test involving riding a stationary bike. There's a group of runners in the company who run together every day. There's also an out-of-shape couch potato. The potato is worried about the test, and for the month preceding it, he essentially duplicates the test on the stationary bike.

The couch potato passes the test, and the runners fail it.

Have any of you found that a winter program of, perhaps running, swimming, rowing, and/or spinning can get you ready to jump on the bike in the spring and be near the top of your form?