how much physical work soldiers do and explore ways to get food into them in spite of anorexia and other problems.
ROBERT SCHOENE: I heard twice this morning—once from Reed Hoyt and maybe from Al Cymerman—that this initial fluid depletion—diuresis—that occurs at high altitude had some effects on optimizing oxygen consumption at the cellular level. I had not heard that before, and I need to have it explained a little bit more. Reed, do you want to address that?
REED HOYT: The observation at high altitude is that there are improvements in endurance performance that are not explained. In our experience, there is a transition to more fat metabolism. Our suggestion is that changes in the conductance of oxygen down to the cell level may be responsible for these observed changes.
It is not associated with an increase in o2max, because clearly, the number of capillaries and the number of mitochondria are not increasing. In our minds, it is a change in the geometry that facilitates the conduction of oxygen. The change in geometry accompanies diuresis. Clearly, those places where there are no transport pigments between the red cell and the target cell are particularly high resistance points in the conduction of oxygen. So I think that the resistance at those junctures is changing with the changes in fluid distribution. You are familiar with the pathological aspects of anti-diuresis, fluid retention, and altitude illnesses, too, and that is the other side of the coin.
INDER ANAND: One question and a comment. The comment is that the studies that suggest an increase in efficiency came from work on the Quechua Indians.
REED HOYT: Right, you are referring to Hochachka's work.
INDER ANAND: Yes, and those studies were done on subjects whose fluid status was not assessed. So I do not think we can make a deduction from this data regarding efficiency and fluid status.
REED HOYT: Right. The connection with body water is not clear from most studies. It is Hochachka's view, however, that oxygen transport is more tightly coupled. That is, skeletal muscle ATP demand and ATP supply are more tightly linked. Closer coupling means that increases in work rate are accompanied by smaller than expected changes in cell phosphorylation potential, phosphocreatine, and pH, and consequently less stimulation of glycolysis and