Early adaptations in gas exchange, cardiac function and haematology to prolonged exercise training in man

Summary

In order to determine the effect of shortterm training on central adaptations, gas exchange and cardiac function were measured during a prolonged submaximal exercise challenge prior to and following 10–12 consecutive days of exercise. In addition, vascular volumes and selected haematological properties were also examined. The subjects, healthy males between the ages of 19 and 30 years of age, cycled for 2 h per day at approximately 59% of pre-training peak oxygen consumption (VO₂) i.e., maximal oxygen consumption (VO_{2 max}). Following the training,VO_{2 max} (1·min⁻¹) increased (P<0.05) by 4.3% (3.94, 0.11 vs 4.11, 0.11; mean, SE) whereas maximal exercise ventilation (V _E,max) and maximal heart rate (ϕ_c,max) were unchanged. During submaximal exercise,VO₂ was unaltered by the training whereas carbon dioxide production (V _E) and respiratory exchange ratio were all reduced (P<0.05). The altered activity pattern failed to elicit adaptations in either submaximal exercise cardiac output or arteriovenous O₂ difference. ϕ_c was reduced (P<0.05). Plasma volume (PV) as measured by¹²⁵I human serum albumin increased by 365 ml or 11.8%, while red cell volume (RCV) as measured by⁵¹chromium-labelled red blood cells (RBC) was unaltered. The increase in PV was accompanied by reductions (P<0.05) in haematocrit, haemoglobin concentration (g. 100 ml⁻¹), and RBCs (10⁶ mm⁻³). Collectively these changes suggest only minimal adaptations in maximal oxygen transport during the early period of prolonged exercise training. However, as evidenced by the changes during submaximal exercise, both the ventilatory and the cardiodynamic response were altered. Since RCV did not change, it is suggested that the elevated PV accompanying training is instrumental in eliciting the change in cardiac function.