Originally Posted by
StanSeven
That kind of running will help with cycling but not as much as if you spent the same time and effort on the bike. Indoor cycling is boring but if you want to improve, try some videos to make it interesting. Or take spinning classes or find bike shops where you can do some competitive type indoor training sessions. Of course I'm saying this assuming you want to continue just with cycling. If you just want to build/maintain fitness, running is an excellent activity.
I don't have a lot to go on yet due to the crummy weather here lately, but I started doing spin classes in Dec and on one of the few rides I did in Jan I felt really good, shaved 4 mins off a 42 mile ride I have done numerous times and all with a 10 bpm lower average HR. One ride doesn't mean much but I'm sure I would have been a lot worse off if I had just been sitting on my ass.
I will say I'm not real impressed with spin instructors. There are two that actually ride a road bike and do pretty good workouts but the others are pretty lame. I find that I often ignore them and do my own thing which usually involves a moderately high resistance and holding my HR around my anaerobic threshold for 5 mins or so.