Bikerjoe:
Yes!!! Dust off the fixed gear and log lots of miles on it. Between the turbo and your fixed gear, you can get a lot fitter.
4 weeks completely off the bike sounds like a lot. Everybody is different though. You don't want to lose so much fitness that you have to start all over again. Cross training is ok for the heart, but not at all specific for cycling as far as the legs go.
Also, a 42x18 sounds low if you are a racer. You should be fit enough to handle a 42x16 or 42x15, even if you are a cat 4 rider.
The winter is best spent developing power. Riders who let their fitness slip in the winter often don't progress as racers because they only get back to their old level from last season when the new seasons rolls around.
Let's metaphorically say during the race season, your fitness takes 5 steps forward. During the winter, you slack off and your fitness takes 5 steps backward. Back to zero, and back to your old level of performance next season. Nothing changes.
What if you ended the season 5 steps forward, recovered briefly (1-2 weeks), slipped back 2 steps, then started working on your power. You might be 6-8 steps forward next season. At the end of next season, you recover again, slip back 2 steps to recover and start building power. Now you might be 8-9 steps forward.
You should end every season faster and fitter than the previous one if your goal is to go faster. If not, you are not training correctly (barring injury, etc.)
If you build power each winter, you get stronger and stronger, building on what you finished each season with. If you do it right, you will finish each season with a higher fitness level.
Winter sucks, especially if it's cold and soggy where you live. Seeing nice power gains can help take away the winter blues!!!
Good luck!!!
