I do exercise to keep thing ticking over. 5km jogs. You hear of people who experience feelings of well-being, even rushes of euphoria, to which they become addicted. Who *are* these people? Sport/exercise to me has always felt like being dragged around a field by a rabid bull. A necessary evil.
@Richard_Littler Research [which I can't reference] suggests ~20% get a positive feeling, ~20% get the opposite, and 60% get neither. Personally I suspect the 20% positive is on the optimistic side!