Researchers in Denmark and The Netherlands have discovered that during exercise, the human brain shifts into a higher gear and uses an "alternative energy" source: it does not feed on glucose but on lactate.
The research was the work of corresponding author Johannes J. Van Lieshout of the University of Amsterdam, and colleagues, and is published in the October 2008 print issue of The FASEB Journal (The journal of the Federation of American Societies for Experimental Biology).
Up to a certain level of exercise, such as walking and light jogging, our muscles and other cells of the body get energy from aerobic respiration, that is glucose is oxidized by oxygen to make ATP molecules that deliver units of energy to cells.
But above a certain level of exercise, as it becomes more strenuous, the muscles shift to another way of making energy, using aerobic respiration, which involves lactate production and does not use oxygen.