Flow

The psychologist Csíkszentmihályi coined the term "flow" to describe a state of perfect focus, where skill and challenge are perfectly balanced.  In fact, the interplay of skill and challenge determines what the subject will feel:

Flow occurs where skill level (fitness, for a runner) and challenge are high.  His studies found that folks such as rock climbers, painters, musicians, and other such folk found flow quite often, and consequently described themselves as very happy people.  A fit runner, with perfect fall weather, trails underfoot, and rapidly accruing fitness, may drone on in blog format about experiencing flow during most of his runs recently.  But such ramblings would be insufferably pretentious. 

Our philosophical runner may simply be experiencing the cannabinoids produced in his own brain whenever he gets a few miles into a run.  Are they the same phenomenon?  Or is he just an endogenous-drug-addled addict, pining for an elevated experience?