Interactive effects of anemia and muscle oxidative capacity on exercise endurance

We used endurance training and acute anemia to assess the interactions among maximal oxygen consumption (V̇O(2max)), muscle oxidative capacity, and exercise endurance in rats. Animals were evaluated under four conditions: untrained and endurance-trained with each group subdivided into anemic (animals with reduced hemoglobin concentrations) and control (animals with unchanged hemoglobin concentrations). Anemia was induced by isovolemic plasma exchange transfusion. Hemoglobin concentration and hematocrit were decreased by 38 and 41%, respectively. Whole body V̇O(2max) was decreased by 18% by anemia regardless of training condition. Anemia significantly reduced endurance by 78% in untrained rats but only 39% in trained animals. Endurance training resulted in a 10% increase in V̇O(2max), a 75% increase in the distance run to exhaustion, and 35, 45, and 58% increases in skeletal muscle pyruvate-malate, α-ketoglutarate, and palmitylcarnitine oxidase activities, respectively. We conclude that endurance is related to the interactive effects of whole body V̇O(2max) and muscle oxidative capacities for the following reasons: 1) anemic untrained and trained animals had similar V̇O(2max) but trained rats had higher muscle oxidative capacities and greater endurance; 2) regardless of training status, the effect of acute anemia was to decrease V̇O(2max) and endurance; and 3) trained anemic rats had lower V̇O(2max) but had greater muscle oxidative capacity and greater endurance than untrained controls.