Aerobic Performance: Role of Oxygen Delivery and Utilization, Glycolytic Flux
Oxygen delivery to muscle, its consumption and glycolytic fl ux, all of each affect and restrict aerobic performance, are discussed. Energy supply of intensive exercise till exhaustion lasting 3 to 4 min is provided mainly by oxidative metabolism, simultaneously glycolytic fl ux may be increased considerably. Other conditions being equal, capacity of oxygen delivery determines oxygen partial pressure in myoplasm of exercising/contracting muscle. With <i>P</i>O2 in myoplasm increasing from 0 to 1-2 mm Hg oxygen consumption (<i>V˙ </i>O2) in mitochondria enhances dramatically, with further increase of <i>P</i>O2 its rise slows down. At the ascending part of <i>V˙ </i>O2-<i>P</i>O2 relationship for mitochondria the increase of <i>V˙ </i>O2 is noticeably restricted by oxygen delivery to contracting muscle. When <i>P</i>O2 approaches plateau of the <i>V˙ </i>O2-<i>P</i>O2 relationship, an increase of <i>V˙ </i>O2 is restricted by mitochondria capacity to accumulate oxygen and augmented oxygen delivery will not lead to a signifi cant increase of muscle <i>V˙ </i>O2. On the other hand considerable accumulation of glycolytic metabolites in contracting muscle causes a decrease of contractility which in its turn may restrict aerobic performance. Noteworthy no strict relationship between glycolytic fl ux and <i>P</i>O2 in myoplasm exists. That is why correct evaluation of factors limiting aerobic performance presupposes simultaneous evaluation of both glycolytic fl ux and oxygen consumption in muscle which in its turn depends on oxygen delivery to mitochondria and its utilization.