What's wrong with stationary indoor exercise? While those other things may keep you in shape they do not specifically target cycling muscles. Sure it might be a good idea to branch out some to stave off boredom and take a break from cycling. There isn't anything wrong with stationary indoor exercise and if you want to not feel like crap physcially and bad about how much slower you've gotten come march it's a good idea to work some in if your work schedule, lungs or tolerance for misery prevent you from doing much outdoor riding.