Not much unless it's done at a high enough intensity. Then, it adds to fitness -- whether we want to call it "base" or just "fitness."*

*Conceptually, I don't think there is such a thing as "base." It's all just fitness. If you train more, you get more. When you get more, you can train more. A nice virtuous cycle.

But, there is not "this kind" versus "that kind" of fitness. It's all just fitness.

A 40 minute spin session shouldn't be inordinately intense even for Lance Armstrong. Intensity is a relative thing. Too much is not good for anybody.

On the other hand, intensity work commensurate to an athlete's current state of fitness is always valuable. Whenever somebody asks, "When am I ready for some more intensity?" I answer -- Right now! Let's go!*

*Caveat -- this is for cycling. Running is another matter altogether.