So...I'm entering a stretch of time where I know for the next few weeks I won't be able to fit in a 3-4 hour ride at one point during the week. The past two months I've been upping my mileage pretty consistently each week with a long ride on Friday or Saturday and would hate to lose what I've built. I've already done that before, last year after riding my first century. I let the fitness slide and am really trying to reach that distance again. I'm still pissed I let all that work I put in last year go. I'm at about 50 miles now (with moderate climbing) relatively comfortably.

I generally ride another 2-3 times outside of that for 1-1.5 hours, but that might suffer in the next month too.

So what is the best way to maintain as much of the fitness as I can? I realize there is no substitute for time in the saddle but what's the next best thing? If I have an hour or two on the bike, what should I be doing?