The influence of training on oxygen isotope fractionation in healthy subjects

We determined the oxygen isotope fractionation in expired alveolar gas relative to inspired air (delta(A-I)) in eight young, healthy subjects at rest and at five levels of exercise up to maximal workload both before and after a training period of about 4 weeks which increased maximum oxygen uptake by about 10%. The data for delta(A-I) were used to compute the relative difference (deltaU) between the resistances of 16O18O and 16O2 for oxygen transport from the alveolar space and utilization in the mitochondria. Prior to training, deltaU decreased from 15 per thousand at rest to 5 per thousand at the highest level of exercise and after training from 12 to 5 per thousand. The difference between the results for deltaU before and after training was significant for rest (P < or = 5) but not for exercise conditions. Accordingly, we conclude that for exercise conditions the non-fractionating oxygen transport by blood flow to and the fractionating oxygen transport by diffusion in the muscles have improved by training to more or less the same degree. The decrease in deltaU in rest after training suggests that oxygen transport by diffusion in other tissues also benefits from the effects of training.