777 wrote:
Long, continuous runs stimulate growth in the deep capillary beds, train the fast & slow twitch muscles to perform when tired . . .
That's exactly my point. It is that targeted tiredness that is enhanced without consuming calories during the run. If additional sugar is supplied, those initial muscle fibers would be used longer and there would be less of a transition to other muscle fibers. So, essentially, when one refuels during a long run, the stimulus becomes similar to that of two runs adding up to the same distance.
Refueling is important in other, more powerful sports. Maximum recruitment of muscle fibers is necessary in training for those to practice the plays, sprints, jumps, or throws correctly with max power.