Exercise

I just came back from the gym where I did 30 minutes on an exercise bike. I always feel better after doing that. My question is, why don't I develop a positive conditioned reaction to the idea of going to the gym? When I think of other things that make me feel good, I look forward to doing them. But not the gym. When I think about exercising, my first reaction is to wonder whether I can put it off for a day. Yet exercising consistently makes me feel good. So what's the explanation?

The only thing I can think of is that the process of exercising itself is not necessarily enjoyable. I only feel good afterwards. Pavlov's dogs salivated at the prospect of doing something that they enjoyed doing, not at doing something that would make them feel good after finishing it.