Interesting talk by Flow author Mihaly Csikszentmihalyi on the state of flow and how this is the state when we are most happy. It is a little dry though, if you start to lose interest skip ahead. In the last three minutes he talks about and uses a great chart that shows you that flow starts when our challenge and skill set are both pushed above average.
This means when we have great skill and are not challenged at all we will often be bored. When we face a challenge and our skills are weak we feel worried.
Then when challenged a little (but still beneath our skill set) we will be relaxed, challenged just below our best skills we will feel in control and challenged to the point of using all our skill we will reach flow (and happiness). When challenged just more than our skills can handle it will create worry, then pushed further the worry becomes anxiety.
This is why as you skills increase the trails you once enjoyed become less interesting or you have to go faster and/or take harder lines to keep that trail as fun as it was with less skill.
He doesn’t mention it but I believe the same thing happens as your fitness increases. As you fitness increases you need to challenge it by going faster and/or further to reach the same level of enjoyment.
Conversely to continue to reach a high level of enjoyment and “flow” or “Zone” state experiences we need to increase our skill set.