Athletes who are competing strenuously in an endurance event have been know to experience something referred to as the second wind. For example, a runner is participating in a 10 kilometer road race. After thirty or forty minutes they seem to have come to the end of their endurance. Their legs are wobbly and there is a feeling of being out of gas. If the runner persists in their effort they may notice, after ten minutes of agony, a resurrgance of energy.
I will not go into all the theories or explanations for the second-wind phenomena, except to explain on my own terms what is the cause, how it can be overcome, and how it has nothing to do with breathing.

